Electrochemistry is the study of chemical reactions that produce electrical effects
General Information
bull Charge ndash property of matter
bull There are two kinds of chargendash electron rarr -160 x 10-19 C
ndash proton rarr +160 x 10-19 C
bull 10 Coulomb of charge is equivalent to 625 x 1018 electrons
General Information
bull Currentndashflow of charge
ndashmeasured in amperes (A)
bull 1 Ampndashflow of 10 C of charge per second
past a given point (Cs)
General Information
bull Circuitndasha closed pathway for charge to
travel
ndashmay be a solid or fluid path
Conductors in which only electrons can move
Solution of positive and negative ions that are free to move
Voltaic Cell
bull harnessed chemical reaction which produces an electric current
bull converts chemical potential energy into electrical potential energy
Voltaic Cell
Voltaic Cell
bull Salt bridge (U-tube)ndash connects the two half cellsndash allows ions to be exchanged but prevents
mixing of the solutions
bull This reaction is spontaneousndash oxidation (RA) rarr Zn(s) harr Zn+2
(aq) + 2e-
ndash reduction (OA) rarr Cu2+(aq) + 2e- harr Cu(s)
Voltaic Cell
bull The two metal rods are called electrodes this is where the electrons enter and leave the cellndash The electrode where oxidation occurs is
called the anodendash The electrode where reduction occurs is
called the cathode
Voltaic Cell
bull Anodendash electrons leave the cell from the anodendash positive ions are produced
ndash Zn(s) rarr Zn2+(aq) + 2e-
bull Cathodendash electrons enter the cathodendash solid metal is produced
ndash Cu2+(aq) + 2e- rarr Cu(s)
Voltaic Cell
anode cathode
Voltaic Cell
bull At any time in a given half cell electrical neutrality is maintained by the movement of ions across the salt bridge
bull Negative ions (anions) drift toward the anode
bull Positive ions (cations) drift toward the cathode
The ZnCu Voltaic Cell
Problem
bull Draw a diagram of a copperaluminum voltaic cell Label the anode and cathode and show the direction of electron flow Write the equations for the reactions that occur and predict the cell voltage
Solution
bull Locate the reactions in data bookndash Cu2+
(aq) + 2e- rarr Cu(s) +034
ndash Al3+(aq) + 3e- rarr Al(s) -166
bull For a voltaic cell reverse the lower reaction ( Al is lower on table ndashoxidized)ndash Cu2+
(aq) + 2e- rarr Cu(s) +034
ndash Al(s) rarr Al3+(aq) + 3e- +166
+200
Net ionic reactionCu2+ (aq) + 2e- lt - gt Cu (s)
Al(s) lt - gt Al3+(aq) + 3e-
3 X
2 X
Remember in all redox equations the electrons are removed
3 Cu2+ + 6e- lt - gt 3 Cu(s)
2 Al(s) lt - gt 2Al3+(aq) + 6e-
3 Cu2+ + 2 Al(s) lt - gt 3 Cu(s) + 2Al3+(aq)
ADD
copper aluminum
Cu2+ Al3+
200 V
Voltaic Cellbull the shorthand representation of an
electrochemical cell showing the two half-cells connected by a salt bridge or porous barrier such as
Zn(s)ZnSO4(aq)CuSO4(aq)Cu(s)
anode cathode
Phase boundary
Liquid junction
Remember
bull Redox reactions can be viewed as a competition for electrons Therefore the reaction is always between the strongest oxidizing agent and the strongest reducing agent
Problem
bull A strip of metal X is placed in XNO3 solution It makes an electrochemical cell with Al3+
(aq) half cell It is observed that Al(s) is deposited on the aluminum electrode and the cell voltage is 075 V Calculate the reduction potential of X
Solution
bull Al is reduced Al3+(aq) + 3e- rarr Al(s) -166
bull X is oxidized X(s) rarr X+(aq) + e-
bull Solve for -166 + = +075
= 241 VX is being oxidized reduction potential is ndash 241 V
( ) x 3
Al3+(aq) + 3X(s) rarr Al(s) + 3X+
(aq) 075
WS 15-2
Standard Electrode Potentials
bull A measure of the relative tendency of substances to gain electrons
bull The standard was chosen to be the hydrogen half cell
bull The hydrogen half cell was chosen to be zero This does not mean H+ will not gain electrons
Hydrogen Electrode
bull consists of a platinum electrode covered with a fine powder of platinum around which H2(g) is bubbled Its potential is defined as zero volts
Hydrogen Half-Cell
H2(g) rarr 2 H+(aq) + 2 e-
reversible reaction
Hydrogen Electrode
Non reactive
Standard Electrode Potentials
bull Since the hydrogen half cell has a relative value of 000 V any half cell connected to it will have its standard potential read off of the voltmeter that connects the two half cells
A Voltaic Cell With Zinc and the Standard Hydrogen Electrode
[Zn2+]= [H+] = 1000 M
Standard Electrode Potentials
bull Any half cell that gives up electrons to H+ will have a negative potential since it has less potential to gain electrons than H+
Standard Electrode Potentials
bull Any half cell that takes electrons from H2(g)
has a positive potential since it has a greater potential to gain electrons than H+
Standard Electrode Potentials
bull ExamplesndashCuCu2+ rarr Eo = 034 V 034 V
greater potential than H+H2
ndashAlAl3+ rarr Eo = -166 166 V less potential than H+H2
If the reduction of mercury (I) in a voltaic cell is desired the half reaction is
Which of the following reactions could be used as the anode (oxidation)
WS 15-22
Multiple cells
bull If the cells are connected to the anode then add the potentials
bull If the cells are connected at the cathode then subtract the potentials
Electrolytic cells
bull Electrical energy is converted to chemical energy
bull Non-spontaneous reactions
bull Reaction is still between the strongest OA and RA (OA is not strong enough)
bull Require outside energy source
Electrolytic cells
bull The Eo value for an electrolytic cell is negative
bull The Eo value is the minimum voltage that must be applied to the cell to force it to react
Electrolytic cells
bull In diagramsndashcell with ammeter rarr voltaic
ndashcell with battery rarr electrolytic
anode (+)cathode (-)
ElectroplatingElectrolysis
Electroplating is the process of
ElectroplatingElectrolysis
1) Current = rate of flow of charge
2) I = q t
3) 1 e- = 16 x 10-19 C
4) 1 mol e- = 602 x 1023 e- x 16 x 10-19 C
= 965 x 104 C
current (A) charge (C)
time (s)
Q = 965 x 104 Cmol (Faradayrsquos constant)
ElectroplatingElectrolysis
5) To calculate number of mol of electrons
ne = q Q
ne = q Q
ne = 18000 C 965 x 104 Cmol
ne = 01865 mol of e-
250 A of current runs for 20 hours through a silver nitrate solution Find the mass of silver produced
q = Itq = (250 A) x (7200 s)q = 18 000 C
Ag+(aq) + 1e- rarr Ag(s)
01865mol 01865 mol
m = n x M
m = 01865 mol x 10787 gmol
m = 20 g
Short cut
m = I t M
m = (250 A) (7200 s) (10787 gmol) (965 x 104 Cmol) (1)
m = 20 g
Q V
I rarr current (Amps)
t rarr time (s)
M rarr molar mass (gmol)
Q rarr molar charge (Cmol)
V rarr voltage
m = I t M
100 g = (150 A) t (10787 gmol) (965 x 104 Cmol) (100)
t = 59639589 s = 166 h
Q V
WS 15-33
A person wants to plate an ornament with 100 g of silver The ornament is placed in a salt of silver and a 15 A current is placed through the solution The voltage is 100 How long will the plating process take
Copper plating a key
- +
power
e-
inert anodecathode
Cu2+
NO3-
Molten or Aqueous
Aqueous
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(aq)
ndash Cl- (aq)
ndash H2O(l)
Molten
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(l)
ndash Cl- (l)
bull Calculate the net potentials and write the reactions that occur whenndash NaI(s) is electrolyzed
ndash A solution of NaI(aq) is electrolyzed
NaI(s) is electrolyzed
Na+(l) I-
(l)
Na+(l) + e- rarr Na(s) -271
2I-(l) rarr I2(s) + 2e- -054
2Na+(l) + 2I-
(l) rarr 2Na(s) + I2(s) -325
OA RA
A solution of NaI(aq) is electrolyzed
H2O(l) Na+(aq) I-
(aq)
2H2O(l) + 2e- rarr H2(g)+ 2OH-(aq) -083
2I-(aq) rarr I2(s) + 2e- -
054
2H2O(l) + 2I-(aq) rarr H2(g)+ 2OH-
(aq) + I2(s) -137
OA RA
Electrolysis of Brine
Na+
Cl-
H2O OA
RA
2H2O(l) + 2Cl-(aq) rarr H2(g) + 2OH-(aq) + Cl2(g)
Note
bull The Cl- ion is a stronger reducing agent than H2O during electrolysis of brine even though the table indicates that it is not
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
General Information
bull Charge ndash property of matter
bull There are two kinds of chargendash electron rarr -160 x 10-19 C
ndash proton rarr +160 x 10-19 C
bull 10 Coulomb of charge is equivalent to 625 x 1018 electrons
General Information
bull Currentndashflow of charge
ndashmeasured in amperes (A)
bull 1 Ampndashflow of 10 C of charge per second
past a given point (Cs)
General Information
bull Circuitndasha closed pathway for charge to
travel
ndashmay be a solid or fluid path
Conductors in which only electrons can move
Solution of positive and negative ions that are free to move
Voltaic Cell
bull harnessed chemical reaction which produces an electric current
bull converts chemical potential energy into electrical potential energy
Voltaic Cell
Voltaic Cell
bull Salt bridge (U-tube)ndash connects the two half cellsndash allows ions to be exchanged but prevents
mixing of the solutions
bull This reaction is spontaneousndash oxidation (RA) rarr Zn(s) harr Zn+2
(aq) + 2e-
ndash reduction (OA) rarr Cu2+(aq) + 2e- harr Cu(s)
Voltaic Cell
bull The two metal rods are called electrodes this is where the electrons enter and leave the cellndash The electrode where oxidation occurs is
called the anodendash The electrode where reduction occurs is
called the cathode
Voltaic Cell
bull Anodendash electrons leave the cell from the anodendash positive ions are produced
ndash Zn(s) rarr Zn2+(aq) + 2e-
bull Cathodendash electrons enter the cathodendash solid metal is produced
ndash Cu2+(aq) + 2e- rarr Cu(s)
Voltaic Cell
anode cathode
Voltaic Cell
bull At any time in a given half cell electrical neutrality is maintained by the movement of ions across the salt bridge
bull Negative ions (anions) drift toward the anode
bull Positive ions (cations) drift toward the cathode
The ZnCu Voltaic Cell
Problem
bull Draw a diagram of a copperaluminum voltaic cell Label the anode and cathode and show the direction of electron flow Write the equations for the reactions that occur and predict the cell voltage
Solution
bull Locate the reactions in data bookndash Cu2+
(aq) + 2e- rarr Cu(s) +034
ndash Al3+(aq) + 3e- rarr Al(s) -166
bull For a voltaic cell reverse the lower reaction ( Al is lower on table ndashoxidized)ndash Cu2+
(aq) + 2e- rarr Cu(s) +034
ndash Al(s) rarr Al3+(aq) + 3e- +166
+200
Net ionic reactionCu2+ (aq) + 2e- lt - gt Cu (s)
Al(s) lt - gt Al3+(aq) + 3e-
3 X
2 X
Remember in all redox equations the electrons are removed
3 Cu2+ + 6e- lt - gt 3 Cu(s)
2 Al(s) lt - gt 2Al3+(aq) + 6e-
3 Cu2+ + 2 Al(s) lt - gt 3 Cu(s) + 2Al3+(aq)
ADD
copper aluminum
Cu2+ Al3+
200 V
Voltaic Cellbull the shorthand representation of an
electrochemical cell showing the two half-cells connected by a salt bridge or porous barrier such as
Zn(s)ZnSO4(aq)CuSO4(aq)Cu(s)
anode cathode
Phase boundary
Liquid junction
Remember
bull Redox reactions can be viewed as a competition for electrons Therefore the reaction is always between the strongest oxidizing agent and the strongest reducing agent
Problem
bull A strip of metal X is placed in XNO3 solution It makes an electrochemical cell with Al3+
(aq) half cell It is observed that Al(s) is deposited on the aluminum electrode and the cell voltage is 075 V Calculate the reduction potential of X
Solution
bull Al is reduced Al3+(aq) + 3e- rarr Al(s) -166
bull X is oxidized X(s) rarr X+(aq) + e-
bull Solve for -166 + = +075
= 241 VX is being oxidized reduction potential is ndash 241 V
( ) x 3
Al3+(aq) + 3X(s) rarr Al(s) + 3X+
(aq) 075
WS 15-2
Standard Electrode Potentials
bull A measure of the relative tendency of substances to gain electrons
bull The standard was chosen to be the hydrogen half cell
bull The hydrogen half cell was chosen to be zero This does not mean H+ will not gain electrons
Hydrogen Electrode
bull consists of a platinum electrode covered with a fine powder of platinum around which H2(g) is bubbled Its potential is defined as zero volts
Hydrogen Half-Cell
H2(g) rarr 2 H+(aq) + 2 e-
reversible reaction
Hydrogen Electrode
Non reactive
Standard Electrode Potentials
bull Since the hydrogen half cell has a relative value of 000 V any half cell connected to it will have its standard potential read off of the voltmeter that connects the two half cells
A Voltaic Cell With Zinc and the Standard Hydrogen Electrode
[Zn2+]= [H+] = 1000 M
Standard Electrode Potentials
bull Any half cell that gives up electrons to H+ will have a negative potential since it has less potential to gain electrons than H+
Standard Electrode Potentials
bull Any half cell that takes electrons from H2(g)
has a positive potential since it has a greater potential to gain electrons than H+
Standard Electrode Potentials
bull ExamplesndashCuCu2+ rarr Eo = 034 V 034 V
greater potential than H+H2
ndashAlAl3+ rarr Eo = -166 166 V less potential than H+H2
If the reduction of mercury (I) in a voltaic cell is desired the half reaction is
Which of the following reactions could be used as the anode (oxidation)
WS 15-22
Multiple cells
bull If the cells are connected to the anode then add the potentials
bull If the cells are connected at the cathode then subtract the potentials
Electrolytic cells
bull Electrical energy is converted to chemical energy
bull Non-spontaneous reactions
bull Reaction is still between the strongest OA and RA (OA is not strong enough)
bull Require outside energy source
Electrolytic cells
bull The Eo value for an electrolytic cell is negative
bull The Eo value is the minimum voltage that must be applied to the cell to force it to react
Electrolytic cells
bull In diagramsndashcell with ammeter rarr voltaic
ndashcell with battery rarr electrolytic
anode (+)cathode (-)
ElectroplatingElectrolysis
Electroplating is the process of
ElectroplatingElectrolysis
1) Current = rate of flow of charge
2) I = q t
3) 1 e- = 16 x 10-19 C
4) 1 mol e- = 602 x 1023 e- x 16 x 10-19 C
= 965 x 104 C
current (A) charge (C)
time (s)
Q = 965 x 104 Cmol (Faradayrsquos constant)
ElectroplatingElectrolysis
5) To calculate number of mol of electrons
ne = q Q
ne = q Q
ne = 18000 C 965 x 104 Cmol
ne = 01865 mol of e-
250 A of current runs for 20 hours through a silver nitrate solution Find the mass of silver produced
q = Itq = (250 A) x (7200 s)q = 18 000 C
Ag+(aq) + 1e- rarr Ag(s)
01865mol 01865 mol
m = n x M
m = 01865 mol x 10787 gmol
m = 20 g
Short cut
m = I t M
m = (250 A) (7200 s) (10787 gmol) (965 x 104 Cmol) (1)
m = 20 g
Q V
I rarr current (Amps)
t rarr time (s)
M rarr molar mass (gmol)
Q rarr molar charge (Cmol)
V rarr voltage
m = I t M
100 g = (150 A) t (10787 gmol) (965 x 104 Cmol) (100)
t = 59639589 s = 166 h
Q V
WS 15-33
A person wants to plate an ornament with 100 g of silver The ornament is placed in a salt of silver and a 15 A current is placed through the solution The voltage is 100 How long will the plating process take
Copper plating a key
- +
power
e-
inert anodecathode
Cu2+
NO3-
Molten or Aqueous
Aqueous
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(aq)
ndash Cl- (aq)
ndash H2O(l)
Molten
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(l)
ndash Cl- (l)
bull Calculate the net potentials and write the reactions that occur whenndash NaI(s) is electrolyzed
ndash A solution of NaI(aq) is electrolyzed
NaI(s) is electrolyzed
Na+(l) I-
(l)
Na+(l) + e- rarr Na(s) -271
2I-(l) rarr I2(s) + 2e- -054
2Na+(l) + 2I-
(l) rarr 2Na(s) + I2(s) -325
OA RA
A solution of NaI(aq) is electrolyzed
H2O(l) Na+(aq) I-
(aq)
2H2O(l) + 2e- rarr H2(g)+ 2OH-(aq) -083
2I-(aq) rarr I2(s) + 2e- -
054
2H2O(l) + 2I-(aq) rarr H2(g)+ 2OH-
(aq) + I2(s) -137
OA RA
Electrolysis of Brine
Na+
Cl-
H2O OA
RA
2H2O(l) + 2Cl-(aq) rarr H2(g) + 2OH-(aq) + Cl2(g)
Note
bull The Cl- ion is a stronger reducing agent than H2O during electrolysis of brine even though the table indicates that it is not
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
General Information
bull Currentndashflow of charge
ndashmeasured in amperes (A)
bull 1 Ampndashflow of 10 C of charge per second
past a given point (Cs)
General Information
bull Circuitndasha closed pathway for charge to
travel
ndashmay be a solid or fluid path
Conductors in which only electrons can move
Solution of positive and negative ions that are free to move
Voltaic Cell
bull harnessed chemical reaction which produces an electric current
bull converts chemical potential energy into electrical potential energy
Voltaic Cell
Voltaic Cell
bull Salt bridge (U-tube)ndash connects the two half cellsndash allows ions to be exchanged but prevents
mixing of the solutions
bull This reaction is spontaneousndash oxidation (RA) rarr Zn(s) harr Zn+2
(aq) + 2e-
ndash reduction (OA) rarr Cu2+(aq) + 2e- harr Cu(s)
Voltaic Cell
bull The two metal rods are called electrodes this is where the electrons enter and leave the cellndash The electrode where oxidation occurs is
called the anodendash The electrode where reduction occurs is
called the cathode
Voltaic Cell
bull Anodendash electrons leave the cell from the anodendash positive ions are produced
ndash Zn(s) rarr Zn2+(aq) + 2e-
bull Cathodendash electrons enter the cathodendash solid metal is produced
ndash Cu2+(aq) + 2e- rarr Cu(s)
Voltaic Cell
anode cathode
Voltaic Cell
bull At any time in a given half cell electrical neutrality is maintained by the movement of ions across the salt bridge
bull Negative ions (anions) drift toward the anode
bull Positive ions (cations) drift toward the cathode
The ZnCu Voltaic Cell
Problem
bull Draw a diagram of a copperaluminum voltaic cell Label the anode and cathode and show the direction of electron flow Write the equations for the reactions that occur and predict the cell voltage
Solution
bull Locate the reactions in data bookndash Cu2+
(aq) + 2e- rarr Cu(s) +034
ndash Al3+(aq) + 3e- rarr Al(s) -166
bull For a voltaic cell reverse the lower reaction ( Al is lower on table ndashoxidized)ndash Cu2+
(aq) + 2e- rarr Cu(s) +034
ndash Al(s) rarr Al3+(aq) + 3e- +166
+200
Net ionic reactionCu2+ (aq) + 2e- lt - gt Cu (s)
Al(s) lt - gt Al3+(aq) + 3e-
3 X
2 X
Remember in all redox equations the electrons are removed
3 Cu2+ + 6e- lt - gt 3 Cu(s)
2 Al(s) lt - gt 2Al3+(aq) + 6e-
3 Cu2+ + 2 Al(s) lt - gt 3 Cu(s) + 2Al3+(aq)
ADD
copper aluminum
Cu2+ Al3+
200 V
Voltaic Cellbull the shorthand representation of an
electrochemical cell showing the two half-cells connected by a salt bridge or porous barrier such as
Zn(s)ZnSO4(aq)CuSO4(aq)Cu(s)
anode cathode
Phase boundary
Liquid junction
Remember
bull Redox reactions can be viewed as a competition for electrons Therefore the reaction is always between the strongest oxidizing agent and the strongest reducing agent
Problem
bull A strip of metal X is placed in XNO3 solution It makes an electrochemical cell with Al3+
(aq) half cell It is observed that Al(s) is deposited on the aluminum electrode and the cell voltage is 075 V Calculate the reduction potential of X
Solution
bull Al is reduced Al3+(aq) + 3e- rarr Al(s) -166
bull X is oxidized X(s) rarr X+(aq) + e-
bull Solve for -166 + = +075
= 241 VX is being oxidized reduction potential is ndash 241 V
( ) x 3
Al3+(aq) + 3X(s) rarr Al(s) + 3X+
(aq) 075
WS 15-2
Standard Electrode Potentials
bull A measure of the relative tendency of substances to gain electrons
bull The standard was chosen to be the hydrogen half cell
bull The hydrogen half cell was chosen to be zero This does not mean H+ will not gain electrons
Hydrogen Electrode
bull consists of a platinum electrode covered with a fine powder of platinum around which H2(g) is bubbled Its potential is defined as zero volts
Hydrogen Half-Cell
H2(g) rarr 2 H+(aq) + 2 e-
reversible reaction
Hydrogen Electrode
Non reactive
Standard Electrode Potentials
bull Since the hydrogen half cell has a relative value of 000 V any half cell connected to it will have its standard potential read off of the voltmeter that connects the two half cells
A Voltaic Cell With Zinc and the Standard Hydrogen Electrode
[Zn2+]= [H+] = 1000 M
Standard Electrode Potentials
bull Any half cell that gives up electrons to H+ will have a negative potential since it has less potential to gain electrons than H+
Standard Electrode Potentials
bull Any half cell that takes electrons from H2(g)
has a positive potential since it has a greater potential to gain electrons than H+
Standard Electrode Potentials
bull ExamplesndashCuCu2+ rarr Eo = 034 V 034 V
greater potential than H+H2
ndashAlAl3+ rarr Eo = -166 166 V less potential than H+H2
If the reduction of mercury (I) in a voltaic cell is desired the half reaction is
Which of the following reactions could be used as the anode (oxidation)
WS 15-22
Multiple cells
bull If the cells are connected to the anode then add the potentials
bull If the cells are connected at the cathode then subtract the potentials
Electrolytic cells
bull Electrical energy is converted to chemical energy
bull Non-spontaneous reactions
bull Reaction is still between the strongest OA and RA (OA is not strong enough)
bull Require outside energy source
Electrolytic cells
bull The Eo value for an electrolytic cell is negative
bull The Eo value is the minimum voltage that must be applied to the cell to force it to react
Electrolytic cells
bull In diagramsndashcell with ammeter rarr voltaic
ndashcell with battery rarr electrolytic
anode (+)cathode (-)
ElectroplatingElectrolysis
Electroplating is the process of
ElectroplatingElectrolysis
1) Current = rate of flow of charge
2) I = q t
3) 1 e- = 16 x 10-19 C
4) 1 mol e- = 602 x 1023 e- x 16 x 10-19 C
= 965 x 104 C
current (A) charge (C)
time (s)
Q = 965 x 104 Cmol (Faradayrsquos constant)
ElectroplatingElectrolysis
5) To calculate number of mol of electrons
ne = q Q
ne = q Q
ne = 18000 C 965 x 104 Cmol
ne = 01865 mol of e-
250 A of current runs for 20 hours through a silver nitrate solution Find the mass of silver produced
q = Itq = (250 A) x (7200 s)q = 18 000 C
Ag+(aq) + 1e- rarr Ag(s)
01865mol 01865 mol
m = n x M
m = 01865 mol x 10787 gmol
m = 20 g
Short cut
m = I t M
m = (250 A) (7200 s) (10787 gmol) (965 x 104 Cmol) (1)
m = 20 g
Q V
I rarr current (Amps)
t rarr time (s)
M rarr molar mass (gmol)
Q rarr molar charge (Cmol)
V rarr voltage
m = I t M
100 g = (150 A) t (10787 gmol) (965 x 104 Cmol) (100)
t = 59639589 s = 166 h
Q V
WS 15-33
A person wants to plate an ornament with 100 g of silver The ornament is placed in a salt of silver and a 15 A current is placed through the solution The voltage is 100 How long will the plating process take
Copper plating a key
- +
power
e-
inert anodecathode
Cu2+
NO3-
Molten or Aqueous
Aqueous
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(aq)
ndash Cl- (aq)
ndash H2O(l)
Molten
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(l)
ndash Cl- (l)
bull Calculate the net potentials and write the reactions that occur whenndash NaI(s) is electrolyzed
ndash A solution of NaI(aq) is electrolyzed
NaI(s) is electrolyzed
Na+(l) I-
(l)
Na+(l) + e- rarr Na(s) -271
2I-(l) rarr I2(s) + 2e- -054
2Na+(l) + 2I-
(l) rarr 2Na(s) + I2(s) -325
OA RA
A solution of NaI(aq) is electrolyzed
H2O(l) Na+(aq) I-
(aq)
2H2O(l) + 2e- rarr H2(g)+ 2OH-(aq) -083
2I-(aq) rarr I2(s) + 2e- -
054
2H2O(l) + 2I-(aq) rarr H2(g)+ 2OH-
(aq) + I2(s) -137
OA RA
Electrolysis of Brine
Na+
Cl-
H2O OA
RA
2H2O(l) + 2Cl-(aq) rarr H2(g) + 2OH-(aq) + Cl2(g)
Note
bull The Cl- ion is a stronger reducing agent than H2O during electrolysis of brine even though the table indicates that it is not
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
General Information
bull Circuitndasha closed pathway for charge to
travel
ndashmay be a solid or fluid path
Conductors in which only electrons can move
Solution of positive and negative ions that are free to move
Voltaic Cell
bull harnessed chemical reaction which produces an electric current
bull converts chemical potential energy into electrical potential energy
Voltaic Cell
Voltaic Cell
bull Salt bridge (U-tube)ndash connects the two half cellsndash allows ions to be exchanged but prevents
mixing of the solutions
bull This reaction is spontaneousndash oxidation (RA) rarr Zn(s) harr Zn+2
(aq) + 2e-
ndash reduction (OA) rarr Cu2+(aq) + 2e- harr Cu(s)
Voltaic Cell
bull The two metal rods are called electrodes this is where the electrons enter and leave the cellndash The electrode where oxidation occurs is
called the anodendash The electrode where reduction occurs is
called the cathode
Voltaic Cell
bull Anodendash electrons leave the cell from the anodendash positive ions are produced
ndash Zn(s) rarr Zn2+(aq) + 2e-
bull Cathodendash electrons enter the cathodendash solid metal is produced
ndash Cu2+(aq) + 2e- rarr Cu(s)
Voltaic Cell
anode cathode
Voltaic Cell
bull At any time in a given half cell electrical neutrality is maintained by the movement of ions across the salt bridge
bull Negative ions (anions) drift toward the anode
bull Positive ions (cations) drift toward the cathode
The ZnCu Voltaic Cell
Problem
bull Draw a diagram of a copperaluminum voltaic cell Label the anode and cathode and show the direction of electron flow Write the equations for the reactions that occur and predict the cell voltage
Solution
bull Locate the reactions in data bookndash Cu2+
(aq) + 2e- rarr Cu(s) +034
ndash Al3+(aq) + 3e- rarr Al(s) -166
bull For a voltaic cell reverse the lower reaction ( Al is lower on table ndashoxidized)ndash Cu2+
(aq) + 2e- rarr Cu(s) +034
ndash Al(s) rarr Al3+(aq) + 3e- +166
+200
Net ionic reactionCu2+ (aq) + 2e- lt - gt Cu (s)
Al(s) lt - gt Al3+(aq) + 3e-
3 X
2 X
Remember in all redox equations the electrons are removed
3 Cu2+ + 6e- lt - gt 3 Cu(s)
2 Al(s) lt - gt 2Al3+(aq) + 6e-
3 Cu2+ + 2 Al(s) lt - gt 3 Cu(s) + 2Al3+(aq)
ADD
copper aluminum
Cu2+ Al3+
200 V
Voltaic Cellbull the shorthand representation of an
electrochemical cell showing the two half-cells connected by a salt bridge or porous barrier such as
Zn(s)ZnSO4(aq)CuSO4(aq)Cu(s)
anode cathode
Phase boundary
Liquid junction
Remember
bull Redox reactions can be viewed as a competition for electrons Therefore the reaction is always between the strongest oxidizing agent and the strongest reducing agent
Problem
bull A strip of metal X is placed in XNO3 solution It makes an electrochemical cell with Al3+
(aq) half cell It is observed that Al(s) is deposited on the aluminum electrode and the cell voltage is 075 V Calculate the reduction potential of X
Solution
bull Al is reduced Al3+(aq) + 3e- rarr Al(s) -166
bull X is oxidized X(s) rarr X+(aq) + e-
bull Solve for -166 + = +075
= 241 VX is being oxidized reduction potential is ndash 241 V
( ) x 3
Al3+(aq) + 3X(s) rarr Al(s) + 3X+
(aq) 075
WS 15-2
Standard Electrode Potentials
bull A measure of the relative tendency of substances to gain electrons
bull The standard was chosen to be the hydrogen half cell
bull The hydrogen half cell was chosen to be zero This does not mean H+ will not gain electrons
Hydrogen Electrode
bull consists of a platinum electrode covered with a fine powder of platinum around which H2(g) is bubbled Its potential is defined as zero volts
Hydrogen Half-Cell
H2(g) rarr 2 H+(aq) + 2 e-
reversible reaction
Hydrogen Electrode
Non reactive
Standard Electrode Potentials
bull Since the hydrogen half cell has a relative value of 000 V any half cell connected to it will have its standard potential read off of the voltmeter that connects the two half cells
A Voltaic Cell With Zinc and the Standard Hydrogen Electrode
[Zn2+]= [H+] = 1000 M
Standard Electrode Potentials
bull Any half cell that gives up electrons to H+ will have a negative potential since it has less potential to gain electrons than H+
Standard Electrode Potentials
bull Any half cell that takes electrons from H2(g)
has a positive potential since it has a greater potential to gain electrons than H+
Standard Electrode Potentials
bull ExamplesndashCuCu2+ rarr Eo = 034 V 034 V
greater potential than H+H2
ndashAlAl3+ rarr Eo = -166 166 V less potential than H+H2
If the reduction of mercury (I) in a voltaic cell is desired the half reaction is
Which of the following reactions could be used as the anode (oxidation)
WS 15-22
Multiple cells
bull If the cells are connected to the anode then add the potentials
bull If the cells are connected at the cathode then subtract the potentials
Electrolytic cells
bull Electrical energy is converted to chemical energy
bull Non-spontaneous reactions
bull Reaction is still between the strongest OA and RA (OA is not strong enough)
bull Require outside energy source
Electrolytic cells
bull The Eo value for an electrolytic cell is negative
bull The Eo value is the minimum voltage that must be applied to the cell to force it to react
Electrolytic cells
bull In diagramsndashcell with ammeter rarr voltaic
ndashcell with battery rarr electrolytic
anode (+)cathode (-)
ElectroplatingElectrolysis
Electroplating is the process of
ElectroplatingElectrolysis
1) Current = rate of flow of charge
2) I = q t
3) 1 e- = 16 x 10-19 C
4) 1 mol e- = 602 x 1023 e- x 16 x 10-19 C
= 965 x 104 C
current (A) charge (C)
time (s)
Q = 965 x 104 Cmol (Faradayrsquos constant)
ElectroplatingElectrolysis
5) To calculate number of mol of electrons
ne = q Q
ne = q Q
ne = 18000 C 965 x 104 Cmol
ne = 01865 mol of e-
250 A of current runs for 20 hours through a silver nitrate solution Find the mass of silver produced
q = Itq = (250 A) x (7200 s)q = 18 000 C
Ag+(aq) + 1e- rarr Ag(s)
01865mol 01865 mol
m = n x M
m = 01865 mol x 10787 gmol
m = 20 g
Short cut
m = I t M
m = (250 A) (7200 s) (10787 gmol) (965 x 104 Cmol) (1)
m = 20 g
Q V
I rarr current (Amps)
t rarr time (s)
M rarr molar mass (gmol)
Q rarr molar charge (Cmol)
V rarr voltage
m = I t M
100 g = (150 A) t (10787 gmol) (965 x 104 Cmol) (100)
t = 59639589 s = 166 h
Q V
WS 15-33
A person wants to plate an ornament with 100 g of silver The ornament is placed in a salt of silver and a 15 A current is placed through the solution The voltage is 100 How long will the plating process take
Copper plating a key
- +
power
e-
inert anodecathode
Cu2+
NO3-
Molten or Aqueous
Aqueous
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(aq)
ndash Cl- (aq)
ndash H2O(l)
Molten
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(l)
ndash Cl- (l)
bull Calculate the net potentials and write the reactions that occur whenndash NaI(s) is electrolyzed
ndash A solution of NaI(aq) is electrolyzed
NaI(s) is electrolyzed
Na+(l) I-
(l)
Na+(l) + e- rarr Na(s) -271
2I-(l) rarr I2(s) + 2e- -054
2Na+(l) + 2I-
(l) rarr 2Na(s) + I2(s) -325
OA RA
A solution of NaI(aq) is electrolyzed
H2O(l) Na+(aq) I-
(aq)
2H2O(l) + 2e- rarr H2(g)+ 2OH-(aq) -083
2I-(aq) rarr I2(s) + 2e- -
054
2H2O(l) + 2I-(aq) rarr H2(g)+ 2OH-
(aq) + I2(s) -137
OA RA
Electrolysis of Brine
Na+
Cl-
H2O OA
RA
2H2O(l) + 2Cl-(aq) rarr H2(g) + 2OH-(aq) + Cl2(g)
Note
bull The Cl- ion is a stronger reducing agent than H2O during electrolysis of brine even though the table indicates that it is not
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
Voltaic Cell
bull harnessed chemical reaction which produces an electric current
bull converts chemical potential energy into electrical potential energy
Voltaic Cell
Voltaic Cell
bull Salt bridge (U-tube)ndash connects the two half cellsndash allows ions to be exchanged but prevents
mixing of the solutions
bull This reaction is spontaneousndash oxidation (RA) rarr Zn(s) harr Zn+2
(aq) + 2e-
ndash reduction (OA) rarr Cu2+(aq) + 2e- harr Cu(s)
Voltaic Cell
bull The two metal rods are called electrodes this is where the electrons enter and leave the cellndash The electrode where oxidation occurs is
called the anodendash The electrode where reduction occurs is
called the cathode
Voltaic Cell
bull Anodendash electrons leave the cell from the anodendash positive ions are produced
ndash Zn(s) rarr Zn2+(aq) + 2e-
bull Cathodendash electrons enter the cathodendash solid metal is produced
ndash Cu2+(aq) + 2e- rarr Cu(s)
Voltaic Cell
anode cathode
Voltaic Cell
bull At any time in a given half cell electrical neutrality is maintained by the movement of ions across the salt bridge
bull Negative ions (anions) drift toward the anode
bull Positive ions (cations) drift toward the cathode
The ZnCu Voltaic Cell
Problem
bull Draw a diagram of a copperaluminum voltaic cell Label the anode and cathode and show the direction of electron flow Write the equations for the reactions that occur and predict the cell voltage
Solution
bull Locate the reactions in data bookndash Cu2+
(aq) + 2e- rarr Cu(s) +034
ndash Al3+(aq) + 3e- rarr Al(s) -166
bull For a voltaic cell reverse the lower reaction ( Al is lower on table ndashoxidized)ndash Cu2+
(aq) + 2e- rarr Cu(s) +034
ndash Al(s) rarr Al3+(aq) + 3e- +166
+200
Net ionic reactionCu2+ (aq) + 2e- lt - gt Cu (s)
Al(s) lt - gt Al3+(aq) + 3e-
3 X
2 X
Remember in all redox equations the electrons are removed
3 Cu2+ + 6e- lt - gt 3 Cu(s)
2 Al(s) lt - gt 2Al3+(aq) + 6e-
3 Cu2+ + 2 Al(s) lt - gt 3 Cu(s) + 2Al3+(aq)
ADD
copper aluminum
Cu2+ Al3+
200 V
Voltaic Cellbull the shorthand representation of an
electrochemical cell showing the two half-cells connected by a salt bridge or porous barrier such as
Zn(s)ZnSO4(aq)CuSO4(aq)Cu(s)
anode cathode
Phase boundary
Liquid junction
Remember
bull Redox reactions can be viewed as a competition for electrons Therefore the reaction is always between the strongest oxidizing agent and the strongest reducing agent
Problem
bull A strip of metal X is placed in XNO3 solution It makes an electrochemical cell with Al3+
(aq) half cell It is observed that Al(s) is deposited on the aluminum electrode and the cell voltage is 075 V Calculate the reduction potential of X
Solution
bull Al is reduced Al3+(aq) + 3e- rarr Al(s) -166
bull X is oxidized X(s) rarr X+(aq) + e-
bull Solve for -166 + = +075
= 241 VX is being oxidized reduction potential is ndash 241 V
( ) x 3
Al3+(aq) + 3X(s) rarr Al(s) + 3X+
(aq) 075
WS 15-2
Standard Electrode Potentials
bull A measure of the relative tendency of substances to gain electrons
bull The standard was chosen to be the hydrogen half cell
bull The hydrogen half cell was chosen to be zero This does not mean H+ will not gain electrons
Hydrogen Electrode
bull consists of a platinum electrode covered with a fine powder of platinum around which H2(g) is bubbled Its potential is defined as zero volts
Hydrogen Half-Cell
H2(g) rarr 2 H+(aq) + 2 e-
reversible reaction
Hydrogen Electrode
Non reactive
Standard Electrode Potentials
bull Since the hydrogen half cell has a relative value of 000 V any half cell connected to it will have its standard potential read off of the voltmeter that connects the two half cells
A Voltaic Cell With Zinc and the Standard Hydrogen Electrode
[Zn2+]= [H+] = 1000 M
Standard Electrode Potentials
bull Any half cell that gives up electrons to H+ will have a negative potential since it has less potential to gain electrons than H+
Standard Electrode Potentials
bull Any half cell that takes electrons from H2(g)
has a positive potential since it has a greater potential to gain electrons than H+
Standard Electrode Potentials
bull ExamplesndashCuCu2+ rarr Eo = 034 V 034 V
greater potential than H+H2
ndashAlAl3+ rarr Eo = -166 166 V less potential than H+H2
If the reduction of mercury (I) in a voltaic cell is desired the half reaction is
Which of the following reactions could be used as the anode (oxidation)
WS 15-22
Multiple cells
bull If the cells are connected to the anode then add the potentials
bull If the cells are connected at the cathode then subtract the potentials
Electrolytic cells
bull Electrical energy is converted to chemical energy
bull Non-spontaneous reactions
bull Reaction is still between the strongest OA and RA (OA is not strong enough)
bull Require outside energy source
Electrolytic cells
bull The Eo value for an electrolytic cell is negative
bull The Eo value is the minimum voltage that must be applied to the cell to force it to react
Electrolytic cells
bull In diagramsndashcell with ammeter rarr voltaic
ndashcell with battery rarr electrolytic
anode (+)cathode (-)
ElectroplatingElectrolysis
Electroplating is the process of
ElectroplatingElectrolysis
1) Current = rate of flow of charge
2) I = q t
3) 1 e- = 16 x 10-19 C
4) 1 mol e- = 602 x 1023 e- x 16 x 10-19 C
= 965 x 104 C
current (A) charge (C)
time (s)
Q = 965 x 104 Cmol (Faradayrsquos constant)
ElectroplatingElectrolysis
5) To calculate number of mol of electrons
ne = q Q
ne = q Q
ne = 18000 C 965 x 104 Cmol
ne = 01865 mol of e-
250 A of current runs for 20 hours through a silver nitrate solution Find the mass of silver produced
q = Itq = (250 A) x (7200 s)q = 18 000 C
Ag+(aq) + 1e- rarr Ag(s)
01865mol 01865 mol
m = n x M
m = 01865 mol x 10787 gmol
m = 20 g
Short cut
m = I t M
m = (250 A) (7200 s) (10787 gmol) (965 x 104 Cmol) (1)
m = 20 g
Q V
I rarr current (Amps)
t rarr time (s)
M rarr molar mass (gmol)
Q rarr molar charge (Cmol)
V rarr voltage
m = I t M
100 g = (150 A) t (10787 gmol) (965 x 104 Cmol) (100)
t = 59639589 s = 166 h
Q V
WS 15-33
A person wants to plate an ornament with 100 g of silver The ornament is placed in a salt of silver and a 15 A current is placed through the solution The voltage is 100 How long will the plating process take
Copper plating a key
- +
power
e-
inert anodecathode
Cu2+
NO3-
Molten or Aqueous
Aqueous
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(aq)
ndash Cl- (aq)
ndash H2O(l)
Molten
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(l)
ndash Cl- (l)
bull Calculate the net potentials and write the reactions that occur whenndash NaI(s) is electrolyzed
ndash A solution of NaI(aq) is electrolyzed
NaI(s) is electrolyzed
Na+(l) I-
(l)
Na+(l) + e- rarr Na(s) -271
2I-(l) rarr I2(s) + 2e- -054
2Na+(l) + 2I-
(l) rarr 2Na(s) + I2(s) -325
OA RA
A solution of NaI(aq) is electrolyzed
H2O(l) Na+(aq) I-
(aq)
2H2O(l) + 2e- rarr H2(g)+ 2OH-(aq) -083
2I-(aq) rarr I2(s) + 2e- -
054
2H2O(l) + 2I-(aq) rarr H2(g)+ 2OH-
(aq) + I2(s) -137
OA RA
Electrolysis of Brine
Na+
Cl-
H2O OA
RA
2H2O(l) + 2Cl-(aq) rarr H2(g) + 2OH-(aq) + Cl2(g)
Note
bull The Cl- ion is a stronger reducing agent than H2O during electrolysis of brine even though the table indicates that it is not
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
Voltaic Cell
Voltaic Cell
bull Salt bridge (U-tube)ndash connects the two half cellsndash allows ions to be exchanged but prevents
mixing of the solutions
bull This reaction is spontaneousndash oxidation (RA) rarr Zn(s) harr Zn+2
(aq) + 2e-
ndash reduction (OA) rarr Cu2+(aq) + 2e- harr Cu(s)
Voltaic Cell
bull The two metal rods are called electrodes this is where the electrons enter and leave the cellndash The electrode where oxidation occurs is
called the anodendash The electrode where reduction occurs is
called the cathode
Voltaic Cell
bull Anodendash electrons leave the cell from the anodendash positive ions are produced
ndash Zn(s) rarr Zn2+(aq) + 2e-
bull Cathodendash electrons enter the cathodendash solid metal is produced
ndash Cu2+(aq) + 2e- rarr Cu(s)
Voltaic Cell
anode cathode
Voltaic Cell
bull At any time in a given half cell electrical neutrality is maintained by the movement of ions across the salt bridge
bull Negative ions (anions) drift toward the anode
bull Positive ions (cations) drift toward the cathode
The ZnCu Voltaic Cell
Problem
bull Draw a diagram of a copperaluminum voltaic cell Label the anode and cathode and show the direction of electron flow Write the equations for the reactions that occur and predict the cell voltage
Solution
bull Locate the reactions in data bookndash Cu2+
(aq) + 2e- rarr Cu(s) +034
ndash Al3+(aq) + 3e- rarr Al(s) -166
bull For a voltaic cell reverse the lower reaction ( Al is lower on table ndashoxidized)ndash Cu2+
(aq) + 2e- rarr Cu(s) +034
ndash Al(s) rarr Al3+(aq) + 3e- +166
+200
Net ionic reactionCu2+ (aq) + 2e- lt - gt Cu (s)
Al(s) lt - gt Al3+(aq) + 3e-
3 X
2 X
Remember in all redox equations the electrons are removed
3 Cu2+ + 6e- lt - gt 3 Cu(s)
2 Al(s) lt - gt 2Al3+(aq) + 6e-
3 Cu2+ + 2 Al(s) lt - gt 3 Cu(s) + 2Al3+(aq)
ADD
copper aluminum
Cu2+ Al3+
200 V
Voltaic Cellbull the shorthand representation of an
electrochemical cell showing the two half-cells connected by a salt bridge or porous barrier such as
Zn(s)ZnSO4(aq)CuSO4(aq)Cu(s)
anode cathode
Phase boundary
Liquid junction
Remember
bull Redox reactions can be viewed as a competition for electrons Therefore the reaction is always between the strongest oxidizing agent and the strongest reducing agent
Problem
bull A strip of metal X is placed in XNO3 solution It makes an electrochemical cell with Al3+
(aq) half cell It is observed that Al(s) is deposited on the aluminum electrode and the cell voltage is 075 V Calculate the reduction potential of X
Solution
bull Al is reduced Al3+(aq) + 3e- rarr Al(s) -166
bull X is oxidized X(s) rarr X+(aq) + e-
bull Solve for -166 + = +075
= 241 VX is being oxidized reduction potential is ndash 241 V
( ) x 3
Al3+(aq) + 3X(s) rarr Al(s) + 3X+
(aq) 075
WS 15-2
Standard Electrode Potentials
bull A measure of the relative tendency of substances to gain electrons
bull The standard was chosen to be the hydrogen half cell
bull The hydrogen half cell was chosen to be zero This does not mean H+ will not gain electrons
Hydrogen Electrode
bull consists of a platinum electrode covered with a fine powder of platinum around which H2(g) is bubbled Its potential is defined as zero volts
Hydrogen Half-Cell
H2(g) rarr 2 H+(aq) + 2 e-
reversible reaction
Hydrogen Electrode
Non reactive
Standard Electrode Potentials
bull Since the hydrogen half cell has a relative value of 000 V any half cell connected to it will have its standard potential read off of the voltmeter that connects the two half cells
A Voltaic Cell With Zinc and the Standard Hydrogen Electrode
[Zn2+]= [H+] = 1000 M
Standard Electrode Potentials
bull Any half cell that gives up electrons to H+ will have a negative potential since it has less potential to gain electrons than H+
Standard Electrode Potentials
bull Any half cell that takes electrons from H2(g)
has a positive potential since it has a greater potential to gain electrons than H+
Standard Electrode Potentials
bull ExamplesndashCuCu2+ rarr Eo = 034 V 034 V
greater potential than H+H2
ndashAlAl3+ rarr Eo = -166 166 V less potential than H+H2
If the reduction of mercury (I) in a voltaic cell is desired the half reaction is
Which of the following reactions could be used as the anode (oxidation)
WS 15-22
Multiple cells
bull If the cells are connected to the anode then add the potentials
bull If the cells are connected at the cathode then subtract the potentials
Electrolytic cells
bull Electrical energy is converted to chemical energy
bull Non-spontaneous reactions
bull Reaction is still between the strongest OA and RA (OA is not strong enough)
bull Require outside energy source
Electrolytic cells
bull The Eo value for an electrolytic cell is negative
bull The Eo value is the minimum voltage that must be applied to the cell to force it to react
Electrolytic cells
bull In diagramsndashcell with ammeter rarr voltaic
ndashcell with battery rarr electrolytic
anode (+)cathode (-)
ElectroplatingElectrolysis
Electroplating is the process of
ElectroplatingElectrolysis
1) Current = rate of flow of charge
2) I = q t
3) 1 e- = 16 x 10-19 C
4) 1 mol e- = 602 x 1023 e- x 16 x 10-19 C
= 965 x 104 C
current (A) charge (C)
time (s)
Q = 965 x 104 Cmol (Faradayrsquos constant)
ElectroplatingElectrolysis
5) To calculate number of mol of electrons
ne = q Q
ne = q Q
ne = 18000 C 965 x 104 Cmol
ne = 01865 mol of e-
250 A of current runs for 20 hours through a silver nitrate solution Find the mass of silver produced
q = Itq = (250 A) x (7200 s)q = 18 000 C
Ag+(aq) + 1e- rarr Ag(s)
01865mol 01865 mol
m = n x M
m = 01865 mol x 10787 gmol
m = 20 g
Short cut
m = I t M
m = (250 A) (7200 s) (10787 gmol) (965 x 104 Cmol) (1)
m = 20 g
Q V
I rarr current (Amps)
t rarr time (s)
M rarr molar mass (gmol)
Q rarr molar charge (Cmol)
V rarr voltage
m = I t M
100 g = (150 A) t (10787 gmol) (965 x 104 Cmol) (100)
t = 59639589 s = 166 h
Q V
WS 15-33
A person wants to plate an ornament with 100 g of silver The ornament is placed in a salt of silver and a 15 A current is placed through the solution The voltage is 100 How long will the plating process take
Copper plating a key
- +
power
e-
inert anodecathode
Cu2+
NO3-
Molten or Aqueous
Aqueous
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(aq)
ndash Cl- (aq)
ndash H2O(l)
Molten
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(l)
ndash Cl- (l)
bull Calculate the net potentials and write the reactions that occur whenndash NaI(s) is electrolyzed
ndash A solution of NaI(aq) is electrolyzed
NaI(s) is electrolyzed
Na+(l) I-
(l)
Na+(l) + e- rarr Na(s) -271
2I-(l) rarr I2(s) + 2e- -054
2Na+(l) + 2I-
(l) rarr 2Na(s) + I2(s) -325
OA RA
A solution of NaI(aq) is electrolyzed
H2O(l) Na+(aq) I-
(aq)
2H2O(l) + 2e- rarr H2(g)+ 2OH-(aq) -083
2I-(aq) rarr I2(s) + 2e- -
054
2H2O(l) + 2I-(aq) rarr H2(g)+ 2OH-
(aq) + I2(s) -137
OA RA
Electrolysis of Brine
Na+
Cl-
H2O OA
RA
2H2O(l) + 2Cl-(aq) rarr H2(g) + 2OH-(aq) + Cl2(g)
Note
bull The Cl- ion is a stronger reducing agent than H2O during electrolysis of brine even though the table indicates that it is not
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
Voltaic Cell
bull Salt bridge (U-tube)ndash connects the two half cellsndash allows ions to be exchanged but prevents
mixing of the solutions
bull This reaction is spontaneousndash oxidation (RA) rarr Zn(s) harr Zn+2
(aq) + 2e-
ndash reduction (OA) rarr Cu2+(aq) + 2e- harr Cu(s)
Voltaic Cell
bull The two metal rods are called electrodes this is where the electrons enter and leave the cellndash The electrode where oxidation occurs is
called the anodendash The electrode where reduction occurs is
called the cathode
Voltaic Cell
bull Anodendash electrons leave the cell from the anodendash positive ions are produced
ndash Zn(s) rarr Zn2+(aq) + 2e-
bull Cathodendash electrons enter the cathodendash solid metal is produced
ndash Cu2+(aq) + 2e- rarr Cu(s)
Voltaic Cell
anode cathode
Voltaic Cell
bull At any time in a given half cell electrical neutrality is maintained by the movement of ions across the salt bridge
bull Negative ions (anions) drift toward the anode
bull Positive ions (cations) drift toward the cathode
The ZnCu Voltaic Cell
Problem
bull Draw a diagram of a copperaluminum voltaic cell Label the anode and cathode and show the direction of electron flow Write the equations for the reactions that occur and predict the cell voltage
Solution
bull Locate the reactions in data bookndash Cu2+
(aq) + 2e- rarr Cu(s) +034
ndash Al3+(aq) + 3e- rarr Al(s) -166
bull For a voltaic cell reverse the lower reaction ( Al is lower on table ndashoxidized)ndash Cu2+
(aq) + 2e- rarr Cu(s) +034
ndash Al(s) rarr Al3+(aq) + 3e- +166
+200
Net ionic reactionCu2+ (aq) + 2e- lt - gt Cu (s)
Al(s) lt - gt Al3+(aq) + 3e-
3 X
2 X
Remember in all redox equations the electrons are removed
3 Cu2+ + 6e- lt - gt 3 Cu(s)
2 Al(s) lt - gt 2Al3+(aq) + 6e-
3 Cu2+ + 2 Al(s) lt - gt 3 Cu(s) + 2Al3+(aq)
ADD
copper aluminum
Cu2+ Al3+
200 V
Voltaic Cellbull the shorthand representation of an
electrochemical cell showing the two half-cells connected by a salt bridge or porous barrier such as
Zn(s)ZnSO4(aq)CuSO4(aq)Cu(s)
anode cathode
Phase boundary
Liquid junction
Remember
bull Redox reactions can be viewed as a competition for electrons Therefore the reaction is always between the strongest oxidizing agent and the strongest reducing agent
Problem
bull A strip of metal X is placed in XNO3 solution It makes an electrochemical cell with Al3+
(aq) half cell It is observed that Al(s) is deposited on the aluminum electrode and the cell voltage is 075 V Calculate the reduction potential of X
Solution
bull Al is reduced Al3+(aq) + 3e- rarr Al(s) -166
bull X is oxidized X(s) rarr X+(aq) + e-
bull Solve for -166 + = +075
= 241 VX is being oxidized reduction potential is ndash 241 V
( ) x 3
Al3+(aq) + 3X(s) rarr Al(s) + 3X+
(aq) 075
WS 15-2
Standard Electrode Potentials
bull A measure of the relative tendency of substances to gain electrons
bull The standard was chosen to be the hydrogen half cell
bull The hydrogen half cell was chosen to be zero This does not mean H+ will not gain electrons
Hydrogen Electrode
bull consists of a platinum electrode covered with a fine powder of platinum around which H2(g) is bubbled Its potential is defined as zero volts
Hydrogen Half-Cell
H2(g) rarr 2 H+(aq) + 2 e-
reversible reaction
Hydrogen Electrode
Non reactive
Standard Electrode Potentials
bull Since the hydrogen half cell has a relative value of 000 V any half cell connected to it will have its standard potential read off of the voltmeter that connects the two half cells
A Voltaic Cell With Zinc and the Standard Hydrogen Electrode
[Zn2+]= [H+] = 1000 M
Standard Electrode Potentials
bull Any half cell that gives up electrons to H+ will have a negative potential since it has less potential to gain electrons than H+
Standard Electrode Potentials
bull Any half cell that takes electrons from H2(g)
has a positive potential since it has a greater potential to gain electrons than H+
Standard Electrode Potentials
bull ExamplesndashCuCu2+ rarr Eo = 034 V 034 V
greater potential than H+H2
ndashAlAl3+ rarr Eo = -166 166 V less potential than H+H2
If the reduction of mercury (I) in a voltaic cell is desired the half reaction is
Which of the following reactions could be used as the anode (oxidation)
WS 15-22
Multiple cells
bull If the cells are connected to the anode then add the potentials
bull If the cells are connected at the cathode then subtract the potentials
Electrolytic cells
bull Electrical energy is converted to chemical energy
bull Non-spontaneous reactions
bull Reaction is still between the strongest OA and RA (OA is not strong enough)
bull Require outside energy source
Electrolytic cells
bull The Eo value for an electrolytic cell is negative
bull The Eo value is the minimum voltage that must be applied to the cell to force it to react
Electrolytic cells
bull In diagramsndashcell with ammeter rarr voltaic
ndashcell with battery rarr electrolytic
anode (+)cathode (-)
ElectroplatingElectrolysis
Electroplating is the process of
ElectroplatingElectrolysis
1) Current = rate of flow of charge
2) I = q t
3) 1 e- = 16 x 10-19 C
4) 1 mol e- = 602 x 1023 e- x 16 x 10-19 C
= 965 x 104 C
current (A) charge (C)
time (s)
Q = 965 x 104 Cmol (Faradayrsquos constant)
ElectroplatingElectrolysis
5) To calculate number of mol of electrons
ne = q Q
ne = q Q
ne = 18000 C 965 x 104 Cmol
ne = 01865 mol of e-
250 A of current runs for 20 hours through a silver nitrate solution Find the mass of silver produced
q = Itq = (250 A) x (7200 s)q = 18 000 C
Ag+(aq) + 1e- rarr Ag(s)
01865mol 01865 mol
m = n x M
m = 01865 mol x 10787 gmol
m = 20 g
Short cut
m = I t M
m = (250 A) (7200 s) (10787 gmol) (965 x 104 Cmol) (1)
m = 20 g
Q V
I rarr current (Amps)
t rarr time (s)
M rarr molar mass (gmol)
Q rarr molar charge (Cmol)
V rarr voltage
m = I t M
100 g = (150 A) t (10787 gmol) (965 x 104 Cmol) (100)
t = 59639589 s = 166 h
Q V
WS 15-33
A person wants to plate an ornament with 100 g of silver The ornament is placed in a salt of silver and a 15 A current is placed through the solution The voltage is 100 How long will the plating process take
Copper plating a key
- +
power
e-
inert anodecathode
Cu2+
NO3-
Molten or Aqueous
Aqueous
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(aq)
ndash Cl- (aq)
ndash H2O(l)
Molten
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(l)
ndash Cl- (l)
bull Calculate the net potentials and write the reactions that occur whenndash NaI(s) is electrolyzed
ndash A solution of NaI(aq) is electrolyzed
NaI(s) is electrolyzed
Na+(l) I-
(l)
Na+(l) + e- rarr Na(s) -271
2I-(l) rarr I2(s) + 2e- -054
2Na+(l) + 2I-
(l) rarr 2Na(s) + I2(s) -325
OA RA
A solution of NaI(aq) is electrolyzed
H2O(l) Na+(aq) I-
(aq)
2H2O(l) + 2e- rarr H2(g)+ 2OH-(aq) -083
2I-(aq) rarr I2(s) + 2e- -
054
2H2O(l) + 2I-(aq) rarr H2(g)+ 2OH-
(aq) + I2(s) -137
OA RA
Electrolysis of Brine
Na+
Cl-
H2O OA
RA
2H2O(l) + 2Cl-(aq) rarr H2(g) + 2OH-(aq) + Cl2(g)
Note
bull The Cl- ion is a stronger reducing agent than H2O during electrolysis of brine even though the table indicates that it is not
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
Voltaic Cell
bull The two metal rods are called electrodes this is where the electrons enter and leave the cellndash The electrode where oxidation occurs is
called the anodendash The electrode where reduction occurs is
called the cathode
Voltaic Cell
bull Anodendash electrons leave the cell from the anodendash positive ions are produced
ndash Zn(s) rarr Zn2+(aq) + 2e-
bull Cathodendash electrons enter the cathodendash solid metal is produced
ndash Cu2+(aq) + 2e- rarr Cu(s)
Voltaic Cell
anode cathode
Voltaic Cell
bull At any time in a given half cell electrical neutrality is maintained by the movement of ions across the salt bridge
bull Negative ions (anions) drift toward the anode
bull Positive ions (cations) drift toward the cathode
The ZnCu Voltaic Cell
Problem
bull Draw a diagram of a copperaluminum voltaic cell Label the anode and cathode and show the direction of electron flow Write the equations for the reactions that occur and predict the cell voltage
Solution
bull Locate the reactions in data bookndash Cu2+
(aq) + 2e- rarr Cu(s) +034
ndash Al3+(aq) + 3e- rarr Al(s) -166
bull For a voltaic cell reverse the lower reaction ( Al is lower on table ndashoxidized)ndash Cu2+
(aq) + 2e- rarr Cu(s) +034
ndash Al(s) rarr Al3+(aq) + 3e- +166
+200
Net ionic reactionCu2+ (aq) + 2e- lt - gt Cu (s)
Al(s) lt - gt Al3+(aq) + 3e-
3 X
2 X
Remember in all redox equations the electrons are removed
3 Cu2+ + 6e- lt - gt 3 Cu(s)
2 Al(s) lt - gt 2Al3+(aq) + 6e-
3 Cu2+ + 2 Al(s) lt - gt 3 Cu(s) + 2Al3+(aq)
ADD
copper aluminum
Cu2+ Al3+
200 V
Voltaic Cellbull the shorthand representation of an
electrochemical cell showing the two half-cells connected by a salt bridge or porous barrier such as
Zn(s)ZnSO4(aq)CuSO4(aq)Cu(s)
anode cathode
Phase boundary
Liquid junction
Remember
bull Redox reactions can be viewed as a competition for electrons Therefore the reaction is always between the strongest oxidizing agent and the strongest reducing agent
Problem
bull A strip of metal X is placed in XNO3 solution It makes an electrochemical cell with Al3+
(aq) half cell It is observed that Al(s) is deposited on the aluminum electrode and the cell voltage is 075 V Calculate the reduction potential of X
Solution
bull Al is reduced Al3+(aq) + 3e- rarr Al(s) -166
bull X is oxidized X(s) rarr X+(aq) + e-
bull Solve for -166 + = +075
= 241 VX is being oxidized reduction potential is ndash 241 V
( ) x 3
Al3+(aq) + 3X(s) rarr Al(s) + 3X+
(aq) 075
WS 15-2
Standard Electrode Potentials
bull A measure of the relative tendency of substances to gain electrons
bull The standard was chosen to be the hydrogen half cell
bull The hydrogen half cell was chosen to be zero This does not mean H+ will not gain electrons
Hydrogen Electrode
bull consists of a platinum electrode covered with a fine powder of platinum around which H2(g) is bubbled Its potential is defined as zero volts
Hydrogen Half-Cell
H2(g) rarr 2 H+(aq) + 2 e-
reversible reaction
Hydrogen Electrode
Non reactive
Standard Electrode Potentials
bull Since the hydrogen half cell has a relative value of 000 V any half cell connected to it will have its standard potential read off of the voltmeter that connects the two half cells
A Voltaic Cell With Zinc and the Standard Hydrogen Electrode
[Zn2+]= [H+] = 1000 M
Standard Electrode Potentials
bull Any half cell that gives up electrons to H+ will have a negative potential since it has less potential to gain electrons than H+
Standard Electrode Potentials
bull Any half cell that takes electrons from H2(g)
has a positive potential since it has a greater potential to gain electrons than H+
Standard Electrode Potentials
bull ExamplesndashCuCu2+ rarr Eo = 034 V 034 V
greater potential than H+H2
ndashAlAl3+ rarr Eo = -166 166 V less potential than H+H2
If the reduction of mercury (I) in a voltaic cell is desired the half reaction is
Which of the following reactions could be used as the anode (oxidation)
WS 15-22
Multiple cells
bull If the cells are connected to the anode then add the potentials
bull If the cells are connected at the cathode then subtract the potentials
Electrolytic cells
bull Electrical energy is converted to chemical energy
bull Non-spontaneous reactions
bull Reaction is still between the strongest OA and RA (OA is not strong enough)
bull Require outside energy source
Electrolytic cells
bull The Eo value for an electrolytic cell is negative
bull The Eo value is the minimum voltage that must be applied to the cell to force it to react
Electrolytic cells
bull In diagramsndashcell with ammeter rarr voltaic
ndashcell with battery rarr electrolytic
anode (+)cathode (-)
ElectroplatingElectrolysis
Electroplating is the process of
ElectroplatingElectrolysis
1) Current = rate of flow of charge
2) I = q t
3) 1 e- = 16 x 10-19 C
4) 1 mol e- = 602 x 1023 e- x 16 x 10-19 C
= 965 x 104 C
current (A) charge (C)
time (s)
Q = 965 x 104 Cmol (Faradayrsquos constant)
ElectroplatingElectrolysis
5) To calculate number of mol of electrons
ne = q Q
ne = q Q
ne = 18000 C 965 x 104 Cmol
ne = 01865 mol of e-
250 A of current runs for 20 hours through a silver nitrate solution Find the mass of silver produced
q = Itq = (250 A) x (7200 s)q = 18 000 C
Ag+(aq) + 1e- rarr Ag(s)
01865mol 01865 mol
m = n x M
m = 01865 mol x 10787 gmol
m = 20 g
Short cut
m = I t M
m = (250 A) (7200 s) (10787 gmol) (965 x 104 Cmol) (1)
m = 20 g
Q V
I rarr current (Amps)
t rarr time (s)
M rarr molar mass (gmol)
Q rarr molar charge (Cmol)
V rarr voltage
m = I t M
100 g = (150 A) t (10787 gmol) (965 x 104 Cmol) (100)
t = 59639589 s = 166 h
Q V
WS 15-33
A person wants to plate an ornament with 100 g of silver The ornament is placed in a salt of silver and a 15 A current is placed through the solution The voltage is 100 How long will the plating process take
Copper plating a key
- +
power
e-
inert anodecathode
Cu2+
NO3-
Molten or Aqueous
Aqueous
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(aq)
ndash Cl- (aq)
ndash H2O(l)
Molten
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(l)
ndash Cl- (l)
bull Calculate the net potentials and write the reactions that occur whenndash NaI(s) is electrolyzed
ndash A solution of NaI(aq) is electrolyzed
NaI(s) is electrolyzed
Na+(l) I-
(l)
Na+(l) + e- rarr Na(s) -271
2I-(l) rarr I2(s) + 2e- -054
2Na+(l) + 2I-
(l) rarr 2Na(s) + I2(s) -325
OA RA
A solution of NaI(aq) is electrolyzed
H2O(l) Na+(aq) I-
(aq)
2H2O(l) + 2e- rarr H2(g)+ 2OH-(aq) -083
2I-(aq) rarr I2(s) + 2e- -
054
2H2O(l) + 2I-(aq) rarr H2(g)+ 2OH-
(aq) + I2(s) -137
OA RA
Electrolysis of Brine
Na+
Cl-
H2O OA
RA
2H2O(l) + 2Cl-(aq) rarr H2(g) + 2OH-(aq) + Cl2(g)
Note
bull The Cl- ion is a stronger reducing agent than H2O during electrolysis of brine even though the table indicates that it is not
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
Voltaic Cell
bull Anodendash electrons leave the cell from the anodendash positive ions are produced
ndash Zn(s) rarr Zn2+(aq) + 2e-
bull Cathodendash electrons enter the cathodendash solid metal is produced
ndash Cu2+(aq) + 2e- rarr Cu(s)
Voltaic Cell
anode cathode
Voltaic Cell
bull At any time in a given half cell electrical neutrality is maintained by the movement of ions across the salt bridge
bull Negative ions (anions) drift toward the anode
bull Positive ions (cations) drift toward the cathode
The ZnCu Voltaic Cell
Problem
bull Draw a diagram of a copperaluminum voltaic cell Label the anode and cathode and show the direction of electron flow Write the equations for the reactions that occur and predict the cell voltage
Solution
bull Locate the reactions in data bookndash Cu2+
(aq) + 2e- rarr Cu(s) +034
ndash Al3+(aq) + 3e- rarr Al(s) -166
bull For a voltaic cell reverse the lower reaction ( Al is lower on table ndashoxidized)ndash Cu2+
(aq) + 2e- rarr Cu(s) +034
ndash Al(s) rarr Al3+(aq) + 3e- +166
+200
Net ionic reactionCu2+ (aq) + 2e- lt - gt Cu (s)
Al(s) lt - gt Al3+(aq) + 3e-
3 X
2 X
Remember in all redox equations the electrons are removed
3 Cu2+ + 6e- lt - gt 3 Cu(s)
2 Al(s) lt - gt 2Al3+(aq) + 6e-
3 Cu2+ + 2 Al(s) lt - gt 3 Cu(s) + 2Al3+(aq)
ADD
copper aluminum
Cu2+ Al3+
200 V
Voltaic Cellbull the shorthand representation of an
electrochemical cell showing the two half-cells connected by a salt bridge or porous barrier such as
Zn(s)ZnSO4(aq)CuSO4(aq)Cu(s)
anode cathode
Phase boundary
Liquid junction
Remember
bull Redox reactions can be viewed as a competition for electrons Therefore the reaction is always between the strongest oxidizing agent and the strongest reducing agent
Problem
bull A strip of metal X is placed in XNO3 solution It makes an electrochemical cell with Al3+
(aq) half cell It is observed that Al(s) is deposited on the aluminum electrode and the cell voltage is 075 V Calculate the reduction potential of X
Solution
bull Al is reduced Al3+(aq) + 3e- rarr Al(s) -166
bull X is oxidized X(s) rarr X+(aq) + e-
bull Solve for -166 + = +075
= 241 VX is being oxidized reduction potential is ndash 241 V
( ) x 3
Al3+(aq) + 3X(s) rarr Al(s) + 3X+
(aq) 075
WS 15-2
Standard Electrode Potentials
bull A measure of the relative tendency of substances to gain electrons
bull The standard was chosen to be the hydrogen half cell
bull The hydrogen half cell was chosen to be zero This does not mean H+ will not gain electrons
Hydrogen Electrode
bull consists of a platinum electrode covered with a fine powder of platinum around which H2(g) is bubbled Its potential is defined as zero volts
Hydrogen Half-Cell
H2(g) rarr 2 H+(aq) + 2 e-
reversible reaction
Hydrogen Electrode
Non reactive
Standard Electrode Potentials
bull Since the hydrogen half cell has a relative value of 000 V any half cell connected to it will have its standard potential read off of the voltmeter that connects the two half cells
A Voltaic Cell With Zinc and the Standard Hydrogen Electrode
[Zn2+]= [H+] = 1000 M
Standard Electrode Potentials
bull Any half cell that gives up electrons to H+ will have a negative potential since it has less potential to gain electrons than H+
Standard Electrode Potentials
bull Any half cell that takes electrons from H2(g)
has a positive potential since it has a greater potential to gain electrons than H+
Standard Electrode Potentials
bull ExamplesndashCuCu2+ rarr Eo = 034 V 034 V
greater potential than H+H2
ndashAlAl3+ rarr Eo = -166 166 V less potential than H+H2
If the reduction of mercury (I) in a voltaic cell is desired the half reaction is
Which of the following reactions could be used as the anode (oxidation)
WS 15-22
Multiple cells
bull If the cells are connected to the anode then add the potentials
bull If the cells are connected at the cathode then subtract the potentials
Electrolytic cells
bull Electrical energy is converted to chemical energy
bull Non-spontaneous reactions
bull Reaction is still between the strongest OA and RA (OA is not strong enough)
bull Require outside energy source
Electrolytic cells
bull The Eo value for an electrolytic cell is negative
bull The Eo value is the minimum voltage that must be applied to the cell to force it to react
Electrolytic cells
bull In diagramsndashcell with ammeter rarr voltaic
ndashcell with battery rarr electrolytic
anode (+)cathode (-)
ElectroplatingElectrolysis
Electroplating is the process of
ElectroplatingElectrolysis
1) Current = rate of flow of charge
2) I = q t
3) 1 e- = 16 x 10-19 C
4) 1 mol e- = 602 x 1023 e- x 16 x 10-19 C
= 965 x 104 C
current (A) charge (C)
time (s)
Q = 965 x 104 Cmol (Faradayrsquos constant)
ElectroplatingElectrolysis
5) To calculate number of mol of electrons
ne = q Q
ne = q Q
ne = 18000 C 965 x 104 Cmol
ne = 01865 mol of e-
250 A of current runs for 20 hours through a silver nitrate solution Find the mass of silver produced
q = Itq = (250 A) x (7200 s)q = 18 000 C
Ag+(aq) + 1e- rarr Ag(s)
01865mol 01865 mol
m = n x M
m = 01865 mol x 10787 gmol
m = 20 g
Short cut
m = I t M
m = (250 A) (7200 s) (10787 gmol) (965 x 104 Cmol) (1)
m = 20 g
Q V
I rarr current (Amps)
t rarr time (s)
M rarr molar mass (gmol)
Q rarr molar charge (Cmol)
V rarr voltage
m = I t M
100 g = (150 A) t (10787 gmol) (965 x 104 Cmol) (100)
t = 59639589 s = 166 h
Q V
WS 15-33
A person wants to plate an ornament with 100 g of silver The ornament is placed in a salt of silver and a 15 A current is placed through the solution The voltage is 100 How long will the plating process take
Copper plating a key
- +
power
e-
inert anodecathode
Cu2+
NO3-
Molten or Aqueous
Aqueous
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(aq)
ndash Cl- (aq)
ndash H2O(l)
Molten
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(l)
ndash Cl- (l)
bull Calculate the net potentials and write the reactions that occur whenndash NaI(s) is electrolyzed
ndash A solution of NaI(aq) is electrolyzed
NaI(s) is electrolyzed
Na+(l) I-
(l)
Na+(l) + e- rarr Na(s) -271
2I-(l) rarr I2(s) + 2e- -054
2Na+(l) + 2I-
(l) rarr 2Na(s) + I2(s) -325
OA RA
A solution of NaI(aq) is electrolyzed
H2O(l) Na+(aq) I-
(aq)
2H2O(l) + 2e- rarr H2(g)+ 2OH-(aq) -083
2I-(aq) rarr I2(s) + 2e- -
054
2H2O(l) + 2I-(aq) rarr H2(g)+ 2OH-
(aq) + I2(s) -137
OA RA
Electrolysis of Brine
Na+
Cl-
H2O OA
RA
2H2O(l) + 2Cl-(aq) rarr H2(g) + 2OH-(aq) + Cl2(g)
Note
bull The Cl- ion is a stronger reducing agent than H2O during electrolysis of brine even though the table indicates that it is not
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
Voltaic Cell
anode cathode
Voltaic Cell
bull At any time in a given half cell electrical neutrality is maintained by the movement of ions across the salt bridge
bull Negative ions (anions) drift toward the anode
bull Positive ions (cations) drift toward the cathode
The ZnCu Voltaic Cell
Problem
bull Draw a diagram of a copperaluminum voltaic cell Label the anode and cathode and show the direction of electron flow Write the equations for the reactions that occur and predict the cell voltage
Solution
bull Locate the reactions in data bookndash Cu2+
(aq) + 2e- rarr Cu(s) +034
ndash Al3+(aq) + 3e- rarr Al(s) -166
bull For a voltaic cell reverse the lower reaction ( Al is lower on table ndashoxidized)ndash Cu2+
(aq) + 2e- rarr Cu(s) +034
ndash Al(s) rarr Al3+(aq) + 3e- +166
+200
Net ionic reactionCu2+ (aq) + 2e- lt - gt Cu (s)
Al(s) lt - gt Al3+(aq) + 3e-
3 X
2 X
Remember in all redox equations the electrons are removed
3 Cu2+ + 6e- lt - gt 3 Cu(s)
2 Al(s) lt - gt 2Al3+(aq) + 6e-
3 Cu2+ + 2 Al(s) lt - gt 3 Cu(s) + 2Al3+(aq)
ADD
copper aluminum
Cu2+ Al3+
200 V
Voltaic Cellbull the shorthand representation of an
electrochemical cell showing the two half-cells connected by a salt bridge or porous barrier such as
Zn(s)ZnSO4(aq)CuSO4(aq)Cu(s)
anode cathode
Phase boundary
Liquid junction
Remember
bull Redox reactions can be viewed as a competition for electrons Therefore the reaction is always between the strongest oxidizing agent and the strongest reducing agent
Problem
bull A strip of metal X is placed in XNO3 solution It makes an electrochemical cell with Al3+
(aq) half cell It is observed that Al(s) is deposited on the aluminum electrode and the cell voltage is 075 V Calculate the reduction potential of X
Solution
bull Al is reduced Al3+(aq) + 3e- rarr Al(s) -166
bull X is oxidized X(s) rarr X+(aq) + e-
bull Solve for -166 + = +075
= 241 VX is being oxidized reduction potential is ndash 241 V
( ) x 3
Al3+(aq) + 3X(s) rarr Al(s) + 3X+
(aq) 075
WS 15-2
Standard Electrode Potentials
bull A measure of the relative tendency of substances to gain electrons
bull The standard was chosen to be the hydrogen half cell
bull The hydrogen half cell was chosen to be zero This does not mean H+ will not gain electrons
Hydrogen Electrode
bull consists of a platinum electrode covered with a fine powder of platinum around which H2(g) is bubbled Its potential is defined as zero volts
Hydrogen Half-Cell
H2(g) rarr 2 H+(aq) + 2 e-
reversible reaction
Hydrogen Electrode
Non reactive
Standard Electrode Potentials
bull Since the hydrogen half cell has a relative value of 000 V any half cell connected to it will have its standard potential read off of the voltmeter that connects the two half cells
A Voltaic Cell With Zinc and the Standard Hydrogen Electrode
[Zn2+]= [H+] = 1000 M
Standard Electrode Potentials
bull Any half cell that gives up electrons to H+ will have a negative potential since it has less potential to gain electrons than H+
Standard Electrode Potentials
bull Any half cell that takes electrons from H2(g)
has a positive potential since it has a greater potential to gain electrons than H+
Standard Electrode Potentials
bull ExamplesndashCuCu2+ rarr Eo = 034 V 034 V
greater potential than H+H2
ndashAlAl3+ rarr Eo = -166 166 V less potential than H+H2
If the reduction of mercury (I) in a voltaic cell is desired the half reaction is
Which of the following reactions could be used as the anode (oxidation)
WS 15-22
Multiple cells
bull If the cells are connected to the anode then add the potentials
bull If the cells are connected at the cathode then subtract the potentials
Electrolytic cells
bull Electrical energy is converted to chemical energy
bull Non-spontaneous reactions
bull Reaction is still between the strongest OA and RA (OA is not strong enough)
bull Require outside energy source
Electrolytic cells
bull The Eo value for an electrolytic cell is negative
bull The Eo value is the minimum voltage that must be applied to the cell to force it to react
Electrolytic cells
bull In diagramsndashcell with ammeter rarr voltaic
ndashcell with battery rarr electrolytic
anode (+)cathode (-)
ElectroplatingElectrolysis
Electroplating is the process of
ElectroplatingElectrolysis
1) Current = rate of flow of charge
2) I = q t
3) 1 e- = 16 x 10-19 C
4) 1 mol e- = 602 x 1023 e- x 16 x 10-19 C
= 965 x 104 C
current (A) charge (C)
time (s)
Q = 965 x 104 Cmol (Faradayrsquos constant)
ElectroplatingElectrolysis
5) To calculate number of mol of electrons
ne = q Q
ne = q Q
ne = 18000 C 965 x 104 Cmol
ne = 01865 mol of e-
250 A of current runs for 20 hours through a silver nitrate solution Find the mass of silver produced
q = Itq = (250 A) x (7200 s)q = 18 000 C
Ag+(aq) + 1e- rarr Ag(s)
01865mol 01865 mol
m = n x M
m = 01865 mol x 10787 gmol
m = 20 g
Short cut
m = I t M
m = (250 A) (7200 s) (10787 gmol) (965 x 104 Cmol) (1)
m = 20 g
Q V
I rarr current (Amps)
t rarr time (s)
M rarr molar mass (gmol)
Q rarr molar charge (Cmol)
V rarr voltage
m = I t M
100 g = (150 A) t (10787 gmol) (965 x 104 Cmol) (100)
t = 59639589 s = 166 h
Q V
WS 15-33
A person wants to plate an ornament with 100 g of silver The ornament is placed in a salt of silver and a 15 A current is placed through the solution The voltage is 100 How long will the plating process take
Copper plating a key
- +
power
e-
inert anodecathode
Cu2+
NO3-
Molten or Aqueous
Aqueous
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(aq)
ndash Cl- (aq)
ndash H2O(l)
Molten
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(l)
ndash Cl- (l)
bull Calculate the net potentials and write the reactions that occur whenndash NaI(s) is electrolyzed
ndash A solution of NaI(aq) is electrolyzed
NaI(s) is electrolyzed
Na+(l) I-
(l)
Na+(l) + e- rarr Na(s) -271
2I-(l) rarr I2(s) + 2e- -054
2Na+(l) + 2I-
(l) rarr 2Na(s) + I2(s) -325
OA RA
A solution of NaI(aq) is electrolyzed
H2O(l) Na+(aq) I-
(aq)
2H2O(l) + 2e- rarr H2(g)+ 2OH-(aq) -083
2I-(aq) rarr I2(s) + 2e- -
054
2H2O(l) + 2I-(aq) rarr H2(g)+ 2OH-
(aq) + I2(s) -137
OA RA
Electrolysis of Brine
Na+
Cl-
H2O OA
RA
2H2O(l) + 2Cl-(aq) rarr H2(g) + 2OH-(aq) + Cl2(g)
Note
bull The Cl- ion is a stronger reducing agent than H2O during electrolysis of brine even though the table indicates that it is not
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
Voltaic Cell
bull At any time in a given half cell electrical neutrality is maintained by the movement of ions across the salt bridge
bull Negative ions (anions) drift toward the anode
bull Positive ions (cations) drift toward the cathode
The ZnCu Voltaic Cell
Problem
bull Draw a diagram of a copperaluminum voltaic cell Label the anode and cathode and show the direction of electron flow Write the equations for the reactions that occur and predict the cell voltage
Solution
bull Locate the reactions in data bookndash Cu2+
(aq) + 2e- rarr Cu(s) +034
ndash Al3+(aq) + 3e- rarr Al(s) -166
bull For a voltaic cell reverse the lower reaction ( Al is lower on table ndashoxidized)ndash Cu2+
(aq) + 2e- rarr Cu(s) +034
ndash Al(s) rarr Al3+(aq) + 3e- +166
+200
Net ionic reactionCu2+ (aq) + 2e- lt - gt Cu (s)
Al(s) lt - gt Al3+(aq) + 3e-
3 X
2 X
Remember in all redox equations the electrons are removed
3 Cu2+ + 6e- lt - gt 3 Cu(s)
2 Al(s) lt - gt 2Al3+(aq) + 6e-
3 Cu2+ + 2 Al(s) lt - gt 3 Cu(s) + 2Al3+(aq)
ADD
copper aluminum
Cu2+ Al3+
200 V
Voltaic Cellbull the shorthand representation of an
electrochemical cell showing the two half-cells connected by a salt bridge or porous barrier such as
Zn(s)ZnSO4(aq)CuSO4(aq)Cu(s)
anode cathode
Phase boundary
Liquid junction
Remember
bull Redox reactions can be viewed as a competition for electrons Therefore the reaction is always between the strongest oxidizing agent and the strongest reducing agent
Problem
bull A strip of metal X is placed in XNO3 solution It makes an electrochemical cell with Al3+
(aq) half cell It is observed that Al(s) is deposited on the aluminum electrode and the cell voltage is 075 V Calculate the reduction potential of X
Solution
bull Al is reduced Al3+(aq) + 3e- rarr Al(s) -166
bull X is oxidized X(s) rarr X+(aq) + e-
bull Solve for -166 + = +075
= 241 VX is being oxidized reduction potential is ndash 241 V
( ) x 3
Al3+(aq) + 3X(s) rarr Al(s) + 3X+
(aq) 075
WS 15-2
Standard Electrode Potentials
bull A measure of the relative tendency of substances to gain electrons
bull The standard was chosen to be the hydrogen half cell
bull The hydrogen half cell was chosen to be zero This does not mean H+ will not gain electrons
Hydrogen Electrode
bull consists of a platinum electrode covered with a fine powder of platinum around which H2(g) is bubbled Its potential is defined as zero volts
Hydrogen Half-Cell
H2(g) rarr 2 H+(aq) + 2 e-
reversible reaction
Hydrogen Electrode
Non reactive
Standard Electrode Potentials
bull Since the hydrogen half cell has a relative value of 000 V any half cell connected to it will have its standard potential read off of the voltmeter that connects the two half cells
A Voltaic Cell With Zinc and the Standard Hydrogen Electrode
[Zn2+]= [H+] = 1000 M
Standard Electrode Potentials
bull Any half cell that gives up electrons to H+ will have a negative potential since it has less potential to gain electrons than H+
Standard Electrode Potentials
bull Any half cell that takes electrons from H2(g)
has a positive potential since it has a greater potential to gain electrons than H+
Standard Electrode Potentials
bull ExamplesndashCuCu2+ rarr Eo = 034 V 034 V
greater potential than H+H2
ndashAlAl3+ rarr Eo = -166 166 V less potential than H+H2
If the reduction of mercury (I) in a voltaic cell is desired the half reaction is
Which of the following reactions could be used as the anode (oxidation)
WS 15-22
Multiple cells
bull If the cells are connected to the anode then add the potentials
bull If the cells are connected at the cathode then subtract the potentials
Electrolytic cells
bull Electrical energy is converted to chemical energy
bull Non-spontaneous reactions
bull Reaction is still between the strongest OA and RA (OA is not strong enough)
bull Require outside energy source
Electrolytic cells
bull The Eo value for an electrolytic cell is negative
bull The Eo value is the minimum voltage that must be applied to the cell to force it to react
Electrolytic cells
bull In diagramsndashcell with ammeter rarr voltaic
ndashcell with battery rarr electrolytic
anode (+)cathode (-)
ElectroplatingElectrolysis
Electroplating is the process of
ElectroplatingElectrolysis
1) Current = rate of flow of charge
2) I = q t
3) 1 e- = 16 x 10-19 C
4) 1 mol e- = 602 x 1023 e- x 16 x 10-19 C
= 965 x 104 C
current (A) charge (C)
time (s)
Q = 965 x 104 Cmol (Faradayrsquos constant)
ElectroplatingElectrolysis
5) To calculate number of mol of electrons
ne = q Q
ne = q Q
ne = 18000 C 965 x 104 Cmol
ne = 01865 mol of e-
250 A of current runs for 20 hours through a silver nitrate solution Find the mass of silver produced
q = Itq = (250 A) x (7200 s)q = 18 000 C
Ag+(aq) + 1e- rarr Ag(s)
01865mol 01865 mol
m = n x M
m = 01865 mol x 10787 gmol
m = 20 g
Short cut
m = I t M
m = (250 A) (7200 s) (10787 gmol) (965 x 104 Cmol) (1)
m = 20 g
Q V
I rarr current (Amps)
t rarr time (s)
M rarr molar mass (gmol)
Q rarr molar charge (Cmol)
V rarr voltage
m = I t M
100 g = (150 A) t (10787 gmol) (965 x 104 Cmol) (100)
t = 59639589 s = 166 h
Q V
WS 15-33
A person wants to plate an ornament with 100 g of silver The ornament is placed in a salt of silver and a 15 A current is placed through the solution The voltage is 100 How long will the plating process take
Copper plating a key
- +
power
e-
inert anodecathode
Cu2+
NO3-
Molten or Aqueous
Aqueous
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(aq)
ndash Cl- (aq)
ndash H2O(l)
Molten
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(l)
ndash Cl- (l)
bull Calculate the net potentials and write the reactions that occur whenndash NaI(s) is electrolyzed
ndash A solution of NaI(aq) is electrolyzed
NaI(s) is electrolyzed
Na+(l) I-
(l)
Na+(l) + e- rarr Na(s) -271
2I-(l) rarr I2(s) + 2e- -054
2Na+(l) + 2I-
(l) rarr 2Na(s) + I2(s) -325
OA RA
A solution of NaI(aq) is electrolyzed
H2O(l) Na+(aq) I-
(aq)
2H2O(l) + 2e- rarr H2(g)+ 2OH-(aq) -083
2I-(aq) rarr I2(s) + 2e- -
054
2H2O(l) + 2I-(aq) rarr H2(g)+ 2OH-
(aq) + I2(s) -137
OA RA
Electrolysis of Brine
Na+
Cl-
H2O OA
RA
2H2O(l) + 2Cl-(aq) rarr H2(g) + 2OH-(aq) + Cl2(g)
Note
bull The Cl- ion is a stronger reducing agent than H2O during electrolysis of brine even though the table indicates that it is not
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
The ZnCu Voltaic Cell
Problem
bull Draw a diagram of a copperaluminum voltaic cell Label the anode and cathode and show the direction of electron flow Write the equations for the reactions that occur and predict the cell voltage
Solution
bull Locate the reactions in data bookndash Cu2+
(aq) + 2e- rarr Cu(s) +034
ndash Al3+(aq) + 3e- rarr Al(s) -166
bull For a voltaic cell reverse the lower reaction ( Al is lower on table ndashoxidized)ndash Cu2+
(aq) + 2e- rarr Cu(s) +034
ndash Al(s) rarr Al3+(aq) + 3e- +166
+200
Net ionic reactionCu2+ (aq) + 2e- lt - gt Cu (s)
Al(s) lt - gt Al3+(aq) + 3e-
3 X
2 X
Remember in all redox equations the electrons are removed
3 Cu2+ + 6e- lt - gt 3 Cu(s)
2 Al(s) lt - gt 2Al3+(aq) + 6e-
3 Cu2+ + 2 Al(s) lt - gt 3 Cu(s) + 2Al3+(aq)
ADD
copper aluminum
Cu2+ Al3+
200 V
Voltaic Cellbull the shorthand representation of an
electrochemical cell showing the two half-cells connected by a salt bridge or porous barrier such as
Zn(s)ZnSO4(aq)CuSO4(aq)Cu(s)
anode cathode
Phase boundary
Liquid junction
Remember
bull Redox reactions can be viewed as a competition for electrons Therefore the reaction is always between the strongest oxidizing agent and the strongest reducing agent
Problem
bull A strip of metal X is placed in XNO3 solution It makes an electrochemical cell with Al3+
(aq) half cell It is observed that Al(s) is deposited on the aluminum electrode and the cell voltage is 075 V Calculate the reduction potential of X
Solution
bull Al is reduced Al3+(aq) + 3e- rarr Al(s) -166
bull X is oxidized X(s) rarr X+(aq) + e-
bull Solve for -166 + = +075
= 241 VX is being oxidized reduction potential is ndash 241 V
( ) x 3
Al3+(aq) + 3X(s) rarr Al(s) + 3X+
(aq) 075
WS 15-2
Standard Electrode Potentials
bull A measure of the relative tendency of substances to gain electrons
bull The standard was chosen to be the hydrogen half cell
bull The hydrogen half cell was chosen to be zero This does not mean H+ will not gain electrons
Hydrogen Electrode
bull consists of a platinum electrode covered with a fine powder of platinum around which H2(g) is bubbled Its potential is defined as zero volts
Hydrogen Half-Cell
H2(g) rarr 2 H+(aq) + 2 e-
reversible reaction
Hydrogen Electrode
Non reactive
Standard Electrode Potentials
bull Since the hydrogen half cell has a relative value of 000 V any half cell connected to it will have its standard potential read off of the voltmeter that connects the two half cells
A Voltaic Cell With Zinc and the Standard Hydrogen Electrode
[Zn2+]= [H+] = 1000 M
Standard Electrode Potentials
bull Any half cell that gives up electrons to H+ will have a negative potential since it has less potential to gain electrons than H+
Standard Electrode Potentials
bull Any half cell that takes electrons from H2(g)
has a positive potential since it has a greater potential to gain electrons than H+
Standard Electrode Potentials
bull ExamplesndashCuCu2+ rarr Eo = 034 V 034 V
greater potential than H+H2
ndashAlAl3+ rarr Eo = -166 166 V less potential than H+H2
If the reduction of mercury (I) in a voltaic cell is desired the half reaction is
Which of the following reactions could be used as the anode (oxidation)
WS 15-22
Multiple cells
bull If the cells are connected to the anode then add the potentials
bull If the cells are connected at the cathode then subtract the potentials
Electrolytic cells
bull Electrical energy is converted to chemical energy
bull Non-spontaneous reactions
bull Reaction is still between the strongest OA and RA (OA is not strong enough)
bull Require outside energy source
Electrolytic cells
bull The Eo value for an electrolytic cell is negative
bull The Eo value is the minimum voltage that must be applied to the cell to force it to react
Electrolytic cells
bull In diagramsndashcell with ammeter rarr voltaic
ndashcell with battery rarr electrolytic
anode (+)cathode (-)
ElectroplatingElectrolysis
Electroplating is the process of
ElectroplatingElectrolysis
1) Current = rate of flow of charge
2) I = q t
3) 1 e- = 16 x 10-19 C
4) 1 mol e- = 602 x 1023 e- x 16 x 10-19 C
= 965 x 104 C
current (A) charge (C)
time (s)
Q = 965 x 104 Cmol (Faradayrsquos constant)
ElectroplatingElectrolysis
5) To calculate number of mol of electrons
ne = q Q
ne = q Q
ne = 18000 C 965 x 104 Cmol
ne = 01865 mol of e-
250 A of current runs for 20 hours through a silver nitrate solution Find the mass of silver produced
q = Itq = (250 A) x (7200 s)q = 18 000 C
Ag+(aq) + 1e- rarr Ag(s)
01865mol 01865 mol
m = n x M
m = 01865 mol x 10787 gmol
m = 20 g
Short cut
m = I t M
m = (250 A) (7200 s) (10787 gmol) (965 x 104 Cmol) (1)
m = 20 g
Q V
I rarr current (Amps)
t rarr time (s)
M rarr molar mass (gmol)
Q rarr molar charge (Cmol)
V rarr voltage
m = I t M
100 g = (150 A) t (10787 gmol) (965 x 104 Cmol) (100)
t = 59639589 s = 166 h
Q V
WS 15-33
A person wants to plate an ornament with 100 g of silver The ornament is placed in a salt of silver and a 15 A current is placed through the solution The voltage is 100 How long will the plating process take
Copper plating a key
- +
power
e-
inert anodecathode
Cu2+
NO3-
Molten or Aqueous
Aqueous
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(aq)
ndash Cl- (aq)
ndash H2O(l)
Molten
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(l)
ndash Cl- (l)
bull Calculate the net potentials and write the reactions that occur whenndash NaI(s) is electrolyzed
ndash A solution of NaI(aq) is electrolyzed
NaI(s) is electrolyzed
Na+(l) I-
(l)
Na+(l) + e- rarr Na(s) -271
2I-(l) rarr I2(s) + 2e- -054
2Na+(l) + 2I-
(l) rarr 2Na(s) + I2(s) -325
OA RA
A solution of NaI(aq) is electrolyzed
H2O(l) Na+(aq) I-
(aq)
2H2O(l) + 2e- rarr H2(g)+ 2OH-(aq) -083
2I-(aq) rarr I2(s) + 2e- -
054
2H2O(l) + 2I-(aq) rarr H2(g)+ 2OH-
(aq) + I2(s) -137
OA RA
Electrolysis of Brine
Na+
Cl-
H2O OA
RA
2H2O(l) + 2Cl-(aq) rarr H2(g) + 2OH-(aq) + Cl2(g)
Note
bull The Cl- ion is a stronger reducing agent than H2O during electrolysis of brine even though the table indicates that it is not
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
Problem
bull Draw a diagram of a copperaluminum voltaic cell Label the anode and cathode and show the direction of electron flow Write the equations for the reactions that occur and predict the cell voltage
Solution
bull Locate the reactions in data bookndash Cu2+
(aq) + 2e- rarr Cu(s) +034
ndash Al3+(aq) + 3e- rarr Al(s) -166
bull For a voltaic cell reverse the lower reaction ( Al is lower on table ndashoxidized)ndash Cu2+
(aq) + 2e- rarr Cu(s) +034
ndash Al(s) rarr Al3+(aq) + 3e- +166
+200
Net ionic reactionCu2+ (aq) + 2e- lt - gt Cu (s)
Al(s) lt - gt Al3+(aq) + 3e-
3 X
2 X
Remember in all redox equations the electrons are removed
3 Cu2+ + 6e- lt - gt 3 Cu(s)
2 Al(s) lt - gt 2Al3+(aq) + 6e-
3 Cu2+ + 2 Al(s) lt - gt 3 Cu(s) + 2Al3+(aq)
ADD
copper aluminum
Cu2+ Al3+
200 V
Voltaic Cellbull the shorthand representation of an
electrochemical cell showing the two half-cells connected by a salt bridge or porous barrier such as
Zn(s)ZnSO4(aq)CuSO4(aq)Cu(s)
anode cathode
Phase boundary
Liquid junction
Remember
bull Redox reactions can be viewed as a competition for electrons Therefore the reaction is always between the strongest oxidizing agent and the strongest reducing agent
Problem
bull A strip of metal X is placed in XNO3 solution It makes an electrochemical cell with Al3+
(aq) half cell It is observed that Al(s) is deposited on the aluminum electrode and the cell voltage is 075 V Calculate the reduction potential of X
Solution
bull Al is reduced Al3+(aq) + 3e- rarr Al(s) -166
bull X is oxidized X(s) rarr X+(aq) + e-
bull Solve for -166 + = +075
= 241 VX is being oxidized reduction potential is ndash 241 V
( ) x 3
Al3+(aq) + 3X(s) rarr Al(s) + 3X+
(aq) 075
WS 15-2
Standard Electrode Potentials
bull A measure of the relative tendency of substances to gain electrons
bull The standard was chosen to be the hydrogen half cell
bull The hydrogen half cell was chosen to be zero This does not mean H+ will not gain electrons
Hydrogen Electrode
bull consists of a platinum electrode covered with a fine powder of platinum around which H2(g) is bubbled Its potential is defined as zero volts
Hydrogen Half-Cell
H2(g) rarr 2 H+(aq) + 2 e-
reversible reaction
Hydrogen Electrode
Non reactive
Standard Electrode Potentials
bull Since the hydrogen half cell has a relative value of 000 V any half cell connected to it will have its standard potential read off of the voltmeter that connects the two half cells
A Voltaic Cell With Zinc and the Standard Hydrogen Electrode
[Zn2+]= [H+] = 1000 M
Standard Electrode Potentials
bull Any half cell that gives up electrons to H+ will have a negative potential since it has less potential to gain electrons than H+
Standard Electrode Potentials
bull Any half cell that takes electrons from H2(g)
has a positive potential since it has a greater potential to gain electrons than H+
Standard Electrode Potentials
bull ExamplesndashCuCu2+ rarr Eo = 034 V 034 V
greater potential than H+H2
ndashAlAl3+ rarr Eo = -166 166 V less potential than H+H2
If the reduction of mercury (I) in a voltaic cell is desired the half reaction is
Which of the following reactions could be used as the anode (oxidation)
WS 15-22
Multiple cells
bull If the cells are connected to the anode then add the potentials
bull If the cells are connected at the cathode then subtract the potentials
Electrolytic cells
bull Electrical energy is converted to chemical energy
bull Non-spontaneous reactions
bull Reaction is still between the strongest OA and RA (OA is not strong enough)
bull Require outside energy source
Electrolytic cells
bull The Eo value for an electrolytic cell is negative
bull The Eo value is the minimum voltage that must be applied to the cell to force it to react
Electrolytic cells
bull In diagramsndashcell with ammeter rarr voltaic
ndashcell with battery rarr electrolytic
anode (+)cathode (-)
ElectroplatingElectrolysis
Electroplating is the process of
ElectroplatingElectrolysis
1) Current = rate of flow of charge
2) I = q t
3) 1 e- = 16 x 10-19 C
4) 1 mol e- = 602 x 1023 e- x 16 x 10-19 C
= 965 x 104 C
current (A) charge (C)
time (s)
Q = 965 x 104 Cmol (Faradayrsquos constant)
ElectroplatingElectrolysis
5) To calculate number of mol of electrons
ne = q Q
ne = q Q
ne = 18000 C 965 x 104 Cmol
ne = 01865 mol of e-
250 A of current runs for 20 hours through a silver nitrate solution Find the mass of silver produced
q = Itq = (250 A) x (7200 s)q = 18 000 C
Ag+(aq) + 1e- rarr Ag(s)
01865mol 01865 mol
m = n x M
m = 01865 mol x 10787 gmol
m = 20 g
Short cut
m = I t M
m = (250 A) (7200 s) (10787 gmol) (965 x 104 Cmol) (1)
m = 20 g
Q V
I rarr current (Amps)
t rarr time (s)
M rarr molar mass (gmol)
Q rarr molar charge (Cmol)
V rarr voltage
m = I t M
100 g = (150 A) t (10787 gmol) (965 x 104 Cmol) (100)
t = 59639589 s = 166 h
Q V
WS 15-33
A person wants to plate an ornament with 100 g of silver The ornament is placed in a salt of silver and a 15 A current is placed through the solution The voltage is 100 How long will the plating process take
Copper plating a key
- +
power
e-
inert anodecathode
Cu2+
NO3-
Molten or Aqueous
Aqueous
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(aq)
ndash Cl- (aq)
ndash H2O(l)
Molten
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(l)
ndash Cl- (l)
bull Calculate the net potentials and write the reactions that occur whenndash NaI(s) is electrolyzed
ndash A solution of NaI(aq) is electrolyzed
NaI(s) is electrolyzed
Na+(l) I-
(l)
Na+(l) + e- rarr Na(s) -271
2I-(l) rarr I2(s) + 2e- -054
2Na+(l) + 2I-
(l) rarr 2Na(s) + I2(s) -325
OA RA
A solution of NaI(aq) is electrolyzed
H2O(l) Na+(aq) I-
(aq)
2H2O(l) + 2e- rarr H2(g)+ 2OH-(aq) -083
2I-(aq) rarr I2(s) + 2e- -
054
2H2O(l) + 2I-(aq) rarr H2(g)+ 2OH-
(aq) + I2(s) -137
OA RA
Electrolysis of Brine
Na+
Cl-
H2O OA
RA
2H2O(l) + 2Cl-(aq) rarr H2(g) + 2OH-(aq) + Cl2(g)
Note
bull The Cl- ion is a stronger reducing agent than H2O during electrolysis of brine even though the table indicates that it is not
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
Solution
bull Locate the reactions in data bookndash Cu2+
(aq) + 2e- rarr Cu(s) +034
ndash Al3+(aq) + 3e- rarr Al(s) -166
bull For a voltaic cell reverse the lower reaction ( Al is lower on table ndashoxidized)ndash Cu2+
(aq) + 2e- rarr Cu(s) +034
ndash Al(s) rarr Al3+(aq) + 3e- +166
+200
Net ionic reactionCu2+ (aq) + 2e- lt - gt Cu (s)
Al(s) lt - gt Al3+(aq) + 3e-
3 X
2 X
Remember in all redox equations the electrons are removed
3 Cu2+ + 6e- lt - gt 3 Cu(s)
2 Al(s) lt - gt 2Al3+(aq) + 6e-
3 Cu2+ + 2 Al(s) lt - gt 3 Cu(s) + 2Al3+(aq)
ADD
copper aluminum
Cu2+ Al3+
200 V
Voltaic Cellbull the shorthand representation of an
electrochemical cell showing the two half-cells connected by a salt bridge or porous barrier such as
Zn(s)ZnSO4(aq)CuSO4(aq)Cu(s)
anode cathode
Phase boundary
Liquid junction
Remember
bull Redox reactions can be viewed as a competition for electrons Therefore the reaction is always between the strongest oxidizing agent and the strongest reducing agent
Problem
bull A strip of metal X is placed in XNO3 solution It makes an electrochemical cell with Al3+
(aq) half cell It is observed that Al(s) is deposited on the aluminum electrode and the cell voltage is 075 V Calculate the reduction potential of X
Solution
bull Al is reduced Al3+(aq) + 3e- rarr Al(s) -166
bull X is oxidized X(s) rarr X+(aq) + e-
bull Solve for -166 + = +075
= 241 VX is being oxidized reduction potential is ndash 241 V
( ) x 3
Al3+(aq) + 3X(s) rarr Al(s) + 3X+
(aq) 075
WS 15-2
Standard Electrode Potentials
bull A measure of the relative tendency of substances to gain electrons
bull The standard was chosen to be the hydrogen half cell
bull The hydrogen half cell was chosen to be zero This does not mean H+ will not gain electrons
Hydrogen Electrode
bull consists of a platinum electrode covered with a fine powder of platinum around which H2(g) is bubbled Its potential is defined as zero volts
Hydrogen Half-Cell
H2(g) rarr 2 H+(aq) + 2 e-
reversible reaction
Hydrogen Electrode
Non reactive
Standard Electrode Potentials
bull Since the hydrogen half cell has a relative value of 000 V any half cell connected to it will have its standard potential read off of the voltmeter that connects the two half cells
A Voltaic Cell With Zinc and the Standard Hydrogen Electrode
[Zn2+]= [H+] = 1000 M
Standard Electrode Potentials
bull Any half cell that gives up electrons to H+ will have a negative potential since it has less potential to gain electrons than H+
Standard Electrode Potentials
bull Any half cell that takes electrons from H2(g)
has a positive potential since it has a greater potential to gain electrons than H+
Standard Electrode Potentials
bull ExamplesndashCuCu2+ rarr Eo = 034 V 034 V
greater potential than H+H2
ndashAlAl3+ rarr Eo = -166 166 V less potential than H+H2
If the reduction of mercury (I) in a voltaic cell is desired the half reaction is
Which of the following reactions could be used as the anode (oxidation)
WS 15-22
Multiple cells
bull If the cells are connected to the anode then add the potentials
bull If the cells are connected at the cathode then subtract the potentials
Electrolytic cells
bull Electrical energy is converted to chemical energy
bull Non-spontaneous reactions
bull Reaction is still between the strongest OA and RA (OA is not strong enough)
bull Require outside energy source
Electrolytic cells
bull The Eo value for an electrolytic cell is negative
bull The Eo value is the minimum voltage that must be applied to the cell to force it to react
Electrolytic cells
bull In diagramsndashcell with ammeter rarr voltaic
ndashcell with battery rarr electrolytic
anode (+)cathode (-)
ElectroplatingElectrolysis
Electroplating is the process of
ElectroplatingElectrolysis
1) Current = rate of flow of charge
2) I = q t
3) 1 e- = 16 x 10-19 C
4) 1 mol e- = 602 x 1023 e- x 16 x 10-19 C
= 965 x 104 C
current (A) charge (C)
time (s)
Q = 965 x 104 Cmol (Faradayrsquos constant)
ElectroplatingElectrolysis
5) To calculate number of mol of electrons
ne = q Q
ne = q Q
ne = 18000 C 965 x 104 Cmol
ne = 01865 mol of e-
250 A of current runs for 20 hours through a silver nitrate solution Find the mass of silver produced
q = Itq = (250 A) x (7200 s)q = 18 000 C
Ag+(aq) + 1e- rarr Ag(s)
01865mol 01865 mol
m = n x M
m = 01865 mol x 10787 gmol
m = 20 g
Short cut
m = I t M
m = (250 A) (7200 s) (10787 gmol) (965 x 104 Cmol) (1)
m = 20 g
Q V
I rarr current (Amps)
t rarr time (s)
M rarr molar mass (gmol)
Q rarr molar charge (Cmol)
V rarr voltage
m = I t M
100 g = (150 A) t (10787 gmol) (965 x 104 Cmol) (100)
t = 59639589 s = 166 h
Q V
WS 15-33
A person wants to plate an ornament with 100 g of silver The ornament is placed in a salt of silver and a 15 A current is placed through the solution The voltage is 100 How long will the plating process take
Copper plating a key
- +
power
e-
inert anodecathode
Cu2+
NO3-
Molten or Aqueous
Aqueous
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(aq)
ndash Cl- (aq)
ndash H2O(l)
Molten
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(l)
ndash Cl- (l)
bull Calculate the net potentials and write the reactions that occur whenndash NaI(s) is electrolyzed
ndash A solution of NaI(aq) is electrolyzed
NaI(s) is electrolyzed
Na+(l) I-
(l)
Na+(l) + e- rarr Na(s) -271
2I-(l) rarr I2(s) + 2e- -054
2Na+(l) + 2I-
(l) rarr 2Na(s) + I2(s) -325
OA RA
A solution of NaI(aq) is electrolyzed
H2O(l) Na+(aq) I-
(aq)
2H2O(l) + 2e- rarr H2(g)+ 2OH-(aq) -083
2I-(aq) rarr I2(s) + 2e- -
054
2H2O(l) + 2I-(aq) rarr H2(g)+ 2OH-
(aq) + I2(s) -137
OA RA
Electrolysis of Brine
Na+
Cl-
H2O OA
RA
2H2O(l) + 2Cl-(aq) rarr H2(g) + 2OH-(aq) + Cl2(g)
Note
bull The Cl- ion is a stronger reducing agent than H2O during electrolysis of brine even though the table indicates that it is not
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
Net ionic reactionCu2+ (aq) + 2e- lt - gt Cu (s)
Al(s) lt - gt Al3+(aq) + 3e-
3 X
2 X
Remember in all redox equations the electrons are removed
3 Cu2+ + 6e- lt - gt 3 Cu(s)
2 Al(s) lt - gt 2Al3+(aq) + 6e-
3 Cu2+ + 2 Al(s) lt - gt 3 Cu(s) + 2Al3+(aq)
ADD
copper aluminum
Cu2+ Al3+
200 V
Voltaic Cellbull the shorthand representation of an
electrochemical cell showing the two half-cells connected by a salt bridge or porous barrier such as
Zn(s)ZnSO4(aq)CuSO4(aq)Cu(s)
anode cathode
Phase boundary
Liquid junction
Remember
bull Redox reactions can be viewed as a competition for electrons Therefore the reaction is always between the strongest oxidizing agent and the strongest reducing agent
Problem
bull A strip of metal X is placed in XNO3 solution It makes an electrochemical cell with Al3+
(aq) half cell It is observed that Al(s) is deposited on the aluminum electrode and the cell voltage is 075 V Calculate the reduction potential of X
Solution
bull Al is reduced Al3+(aq) + 3e- rarr Al(s) -166
bull X is oxidized X(s) rarr X+(aq) + e-
bull Solve for -166 + = +075
= 241 VX is being oxidized reduction potential is ndash 241 V
( ) x 3
Al3+(aq) + 3X(s) rarr Al(s) + 3X+
(aq) 075
WS 15-2
Standard Electrode Potentials
bull A measure of the relative tendency of substances to gain electrons
bull The standard was chosen to be the hydrogen half cell
bull The hydrogen half cell was chosen to be zero This does not mean H+ will not gain electrons
Hydrogen Electrode
bull consists of a platinum electrode covered with a fine powder of platinum around which H2(g) is bubbled Its potential is defined as zero volts
Hydrogen Half-Cell
H2(g) rarr 2 H+(aq) + 2 e-
reversible reaction
Hydrogen Electrode
Non reactive
Standard Electrode Potentials
bull Since the hydrogen half cell has a relative value of 000 V any half cell connected to it will have its standard potential read off of the voltmeter that connects the two half cells
A Voltaic Cell With Zinc and the Standard Hydrogen Electrode
[Zn2+]= [H+] = 1000 M
Standard Electrode Potentials
bull Any half cell that gives up electrons to H+ will have a negative potential since it has less potential to gain electrons than H+
Standard Electrode Potentials
bull Any half cell that takes electrons from H2(g)
has a positive potential since it has a greater potential to gain electrons than H+
Standard Electrode Potentials
bull ExamplesndashCuCu2+ rarr Eo = 034 V 034 V
greater potential than H+H2
ndashAlAl3+ rarr Eo = -166 166 V less potential than H+H2
If the reduction of mercury (I) in a voltaic cell is desired the half reaction is
Which of the following reactions could be used as the anode (oxidation)
WS 15-22
Multiple cells
bull If the cells are connected to the anode then add the potentials
bull If the cells are connected at the cathode then subtract the potentials
Electrolytic cells
bull Electrical energy is converted to chemical energy
bull Non-spontaneous reactions
bull Reaction is still between the strongest OA and RA (OA is not strong enough)
bull Require outside energy source
Electrolytic cells
bull The Eo value for an electrolytic cell is negative
bull The Eo value is the minimum voltage that must be applied to the cell to force it to react
Electrolytic cells
bull In diagramsndashcell with ammeter rarr voltaic
ndashcell with battery rarr electrolytic
anode (+)cathode (-)
ElectroplatingElectrolysis
Electroplating is the process of
ElectroplatingElectrolysis
1) Current = rate of flow of charge
2) I = q t
3) 1 e- = 16 x 10-19 C
4) 1 mol e- = 602 x 1023 e- x 16 x 10-19 C
= 965 x 104 C
current (A) charge (C)
time (s)
Q = 965 x 104 Cmol (Faradayrsquos constant)
ElectroplatingElectrolysis
5) To calculate number of mol of electrons
ne = q Q
ne = q Q
ne = 18000 C 965 x 104 Cmol
ne = 01865 mol of e-
250 A of current runs for 20 hours through a silver nitrate solution Find the mass of silver produced
q = Itq = (250 A) x (7200 s)q = 18 000 C
Ag+(aq) + 1e- rarr Ag(s)
01865mol 01865 mol
m = n x M
m = 01865 mol x 10787 gmol
m = 20 g
Short cut
m = I t M
m = (250 A) (7200 s) (10787 gmol) (965 x 104 Cmol) (1)
m = 20 g
Q V
I rarr current (Amps)
t rarr time (s)
M rarr molar mass (gmol)
Q rarr molar charge (Cmol)
V rarr voltage
m = I t M
100 g = (150 A) t (10787 gmol) (965 x 104 Cmol) (100)
t = 59639589 s = 166 h
Q V
WS 15-33
A person wants to plate an ornament with 100 g of silver The ornament is placed in a salt of silver and a 15 A current is placed through the solution The voltage is 100 How long will the plating process take
Copper plating a key
- +
power
e-
inert anodecathode
Cu2+
NO3-
Molten or Aqueous
Aqueous
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(aq)
ndash Cl- (aq)
ndash H2O(l)
Molten
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(l)
ndash Cl- (l)
bull Calculate the net potentials and write the reactions that occur whenndash NaI(s) is electrolyzed
ndash A solution of NaI(aq) is electrolyzed
NaI(s) is electrolyzed
Na+(l) I-
(l)
Na+(l) + e- rarr Na(s) -271
2I-(l) rarr I2(s) + 2e- -054
2Na+(l) + 2I-
(l) rarr 2Na(s) + I2(s) -325
OA RA
A solution of NaI(aq) is electrolyzed
H2O(l) Na+(aq) I-
(aq)
2H2O(l) + 2e- rarr H2(g)+ 2OH-(aq) -083
2I-(aq) rarr I2(s) + 2e- -
054
2H2O(l) + 2I-(aq) rarr H2(g)+ 2OH-
(aq) + I2(s) -137
OA RA
Electrolysis of Brine
Na+
Cl-
H2O OA
RA
2H2O(l) + 2Cl-(aq) rarr H2(g) + 2OH-(aq) + Cl2(g)
Note
bull The Cl- ion is a stronger reducing agent than H2O during electrolysis of brine even though the table indicates that it is not
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
copper aluminum
Cu2+ Al3+
200 V
Voltaic Cellbull the shorthand representation of an
electrochemical cell showing the two half-cells connected by a salt bridge or porous barrier such as
Zn(s)ZnSO4(aq)CuSO4(aq)Cu(s)
anode cathode
Phase boundary
Liquid junction
Remember
bull Redox reactions can be viewed as a competition for electrons Therefore the reaction is always between the strongest oxidizing agent and the strongest reducing agent
Problem
bull A strip of metal X is placed in XNO3 solution It makes an electrochemical cell with Al3+
(aq) half cell It is observed that Al(s) is deposited on the aluminum electrode and the cell voltage is 075 V Calculate the reduction potential of X
Solution
bull Al is reduced Al3+(aq) + 3e- rarr Al(s) -166
bull X is oxidized X(s) rarr X+(aq) + e-
bull Solve for -166 + = +075
= 241 VX is being oxidized reduction potential is ndash 241 V
( ) x 3
Al3+(aq) + 3X(s) rarr Al(s) + 3X+
(aq) 075
WS 15-2
Standard Electrode Potentials
bull A measure of the relative tendency of substances to gain electrons
bull The standard was chosen to be the hydrogen half cell
bull The hydrogen half cell was chosen to be zero This does not mean H+ will not gain electrons
Hydrogen Electrode
bull consists of a platinum electrode covered with a fine powder of platinum around which H2(g) is bubbled Its potential is defined as zero volts
Hydrogen Half-Cell
H2(g) rarr 2 H+(aq) + 2 e-
reversible reaction
Hydrogen Electrode
Non reactive
Standard Electrode Potentials
bull Since the hydrogen half cell has a relative value of 000 V any half cell connected to it will have its standard potential read off of the voltmeter that connects the two half cells
A Voltaic Cell With Zinc and the Standard Hydrogen Electrode
[Zn2+]= [H+] = 1000 M
Standard Electrode Potentials
bull Any half cell that gives up electrons to H+ will have a negative potential since it has less potential to gain electrons than H+
Standard Electrode Potentials
bull Any half cell that takes electrons from H2(g)
has a positive potential since it has a greater potential to gain electrons than H+
Standard Electrode Potentials
bull ExamplesndashCuCu2+ rarr Eo = 034 V 034 V
greater potential than H+H2
ndashAlAl3+ rarr Eo = -166 166 V less potential than H+H2
If the reduction of mercury (I) in a voltaic cell is desired the half reaction is
Which of the following reactions could be used as the anode (oxidation)
WS 15-22
Multiple cells
bull If the cells are connected to the anode then add the potentials
bull If the cells are connected at the cathode then subtract the potentials
Electrolytic cells
bull Electrical energy is converted to chemical energy
bull Non-spontaneous reactions
bull Reaction is still between the strongest OA and RA (OA is not strong enough)
bull Require outside energy source
Electrolytic cells
bull The Eo value for an electrolytic cell is negative
bull The Eo value is the minimum voltage that must be applied to the cell to force it to react
Electrolytic cells
bull In diagramsndashcell with ammeter rarr voltaic
ndashcell with battery rarr electrolytic
anode (+)cathode (-)
ElectroplatingElectrolysis
Electroplating is the process of
ElectroplatingElectrolysis
1) Current = rate of flow of charge
2) I = q t
3) 1 e- = 16 x 10-19 C
4) 1 mol e- = 602 x 1023 e- x 16 x 10-19 C
= 965 x 104 C
current (A) charge (C)
time (s)
Q = 965 x 104 Cmol (Faradayrsquos constant)
ElectroplatingElectrolysis
5) To calculate number of mol of electrons
ne = q Q
ne = q Q
ne = 18000 C 965 x 104 Cmol
ne = 01865 mol of e-
250 A of current runs for 20 hours through a silver nitrate solution Find the mass of silver produced
q = Itq = (250 A) x (7200 s)q = 18 000 C
Ag+(aq) + 1e- rarr Ag(s)
01865mol 01865 mol
m = n x M
m = 01865 mol x 10787 gmol
m = 20 g
Short cut
m = I t M
m = (250 A) (7200 s) (10787 gmol) (965 x 104 Cmol) (1)
m = 20 g
Q V
I rarr current (Amps)
t rarr time (s)
M rarr molar mass (gmol)
Q rarr molar charge (Cmol)
V rarr voltage
m = I t M
100 g = (150 A) t (10787 gmol) (965 x 104 Cmol) (100)
t = 59639589 s = 166 h
Q V
WS 15-33
A person wants to plate an ornament with 100 g of silver The ornament is placed in a salt of silver and a 15 A current is placed through the solution The voltage is 100 How long will the plating process take
Copper plating a key
- +
power
e-
inert anodecathode
Cu2+
NO3-
Molten or Aqueous
Aqueous
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(aq)
ndash Cl- (aq)
ndash H2O(l)
Molten
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(l)
ndash Cl- (l)
bull Calculate the net potentials and write the reactions that occur whenndash NaI(s) is electrolyzed
ndash A solution of NaI(aq) is electrolyzed
NaI(s) is electrolyzed
Na+(l) I-
(l)
Na+(l) + e- rarr Na(s) -271
2I-(l) rarr I2(s) + 2e- -054
2Na+(l) + 2I-
(l) rarr 2Na(s) + I2(s) -325
OA RA
A solution of NaI(aq) is electrolyzed
H2O(l) Na+(aq) I-
(aq)
2H2O(l) + 2e- rarr H2(g)+ 2OH-(aq) -083
2I-(aq) rarr I2(s) + 2e- -
054
2H2O(l) + 2I-(aq) rarr H2(g)+ 2OH-
(aq) + I2(s) -137
OA RA
Electrolysis of Brine
Na+
Cl-
H2O OA
RA
2H2O(l) + 2Cl-(aq) rarr H2(g) + 2OH-(aq) + Cl2(g)
Note
bull The Cl- ion is a stronger reducing agent than H2O during electrolysis of brine even though the table indicates that it is not
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
Voltaic Cellbull the shorthand representation of an
electrochemical cell showing the two half-cells connected by a salt bridge or porous barrier such as
Zn(s)ZnSO4(aq)CuSO4(aq)Cu(s)
anode cathode
Phase boundary
Liquid junction
Remember
bull Redox reactions can be viewed as a competition for electrons Therefore the reaction is always between the strongest oxidizing agent and the strongest reducing agent
Problem
bull A strip of metal X is placed in XNO3 solution It makes an electrochemical cell with Al3+
(aq) half cell It is observed that Al(s) is deposited on the aluminum electrode and the cell voltage is 075 V Calculate the reduction potential of X
Solution
bull Al is reduced Al3+(aq) + 3e- rarr Al(s) -166
bull X is oxidized X(s) rarr X+(aq) + e-
bull Solve for -166 + = +075
= 241 VX is being oxidized reduction potential is ndash 241 V
( ) x 3
Al3+(aq) + 3X(s) rarr Al(s) + 3X+
(aq) 075
WS 15-2
Standard Electrode Potentials
bull A measure of the relative tendency of substances to gain electrons
bull The standard was chosen to be the hydrogen half cell
bull The hydrogen half cell was chosen to be zero This does not mean H+ will not gain electrons
Hydrogen Electrode
bull consists of a platinum electrode covered with a fine powder of platinum around which H2(g) is bubbled Its potential is defined as zero volts
Hydrogen Half-Cell
H2(g) rarr 2 H+(aq) + 2 e-
reversible reaction
Hydrogen Electrode
Non reactive
Standard Electrode Potentials
bull Since the hydrogen half cell has a relative value of 000 V any half cell connected to it will have its standard potential read off of the voltmeter that connects the two half cells
A Voltaic Cell With Zinc and the Standard Hydrogen Electrode
[Zn2+]= [H+] = 1000 M
Standard Electrode Potentials
bull Any half cell that gives up electrons to H+ will have a negative potential since it has less potential to gain electrons than H+
Standard Electrode Potentials
bull Any half cell that takes electrons from H2(g)
has a positive potential since it has a greater potential to gain electrons than H+
Standard Electrode Potentials
bull ExamplesndashCuCu2+ rarr Eo = 034 V 034 V
greater potential than H+H2
ndashAlAl3+ rarr Eo = -166 166 V less potential than H+H2
If the reduction of mercury (I) in a voltaic cell is desired the half reaction is
Which of the following reactions could be used as the anode (oxidation)
WS 15-22
Multiple cells
bull If the cells are connected to the anode then add the potentials
bull If the cells are connected at the cathode then subtract the potentials
Electrolytic cells
bull Electrical energy is converted to chemical energy
bull Non-spontaneous reactions
bull Reaction is still between the strongest OA and RA (OA is not strong enough)
bull Require outside energy source
Electrolytic cells
bull The Eo value for an electrolytic cell is negative
bull The Eo value is the minimum voltage that must be applied to the cell to force it to react
Electrolytic cells
bull In diagramsndashcell with ammeter rarr voltaic
ndashcell with battery rarr electrolytic
anode (+)cathode (-)
ElectroplatingElectrolysis
Electroplating is the process of
ElectroplatingElectrolysis
1) Current = rate of flow of charge
2) I = q t
3) 1 e- = 16 x 10-19 C
4) 1 mol e- = 602 x 1023 e- x 16 x 10-19 C
= 965 x 104 C
current (A) charge (C)
time (s)
Q = 965 x 104 Cmol (Faradayrsquos constant)
ElectroplatingElectrolysis
5) To calculate number of mol of electrons
ne = q Q
ne = q Q
ne = 18000 C 965 x 104 Cmol
ne = 01865 mol of e-
250 A of current runs for 20 hours through a silver nitrate solution Find the mass of silver produced
q = Itq = (250 A) x (7200 s)q = 18 000 C
Ag+(aq) + 1e- rarr Ag(s)
01865mol 01865 mol
m = n x M
m = 01865 mol x 10787 gmol
m = 20 g
Short cut
m = I t M
m = (250 A) (7200 s) (10787 gmol) (965 x 104 Cmol) (1)
m = 20 g
Q V
I rarr current (Amps)
t rarr time (s)
M rarr molar mass (gmol)
Q rarr molar charge (Cmol)
V rarr voltage
m = I t M
100 g = (150 A) t (10787 gmol) (965 x 104 Cmol) (100)
t = 59639589 s = 166 h
Q V
WS 15-33
A person wants to plate an ornament with 100 g of silver The ornament is placed in a salt of silver and a 15 A current is placed through the solution The voltage is 100 How long will the plating process take
Copper plating a key
- +
power
e-
inert anodecathode
Cu2+
NO3-
Molten or Aqueous
Aqueous
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(aq)
ndash Cl- (aq)
ndash H2O(l)
Molten
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(l)
ndash Cl- (l)
bull Calculate the net potentials and write the reactions that occur whenndash NaI(s) is electrolyzed
ndash A solution of NaI(aq) is electrolyzed
NaI(s) is electrolyzed
Na+(l) I-
(l)
Na+(l) + e- rarr Na(s) -271
2I-(l) rarr I2(s) + 2e- -054
2Na+(l) + 2I-
(l) rarr 2Na(s) + I2(s) -325
OA RA
A solution of NaI(aq) is electrolyzed
H2O(l) Na+(aq) I-
(aq)
2H2O(l) + 2e- rarr H2(g)+ 2OH-(aq) -083
2I-(aq) rarr I2(s) + 2e- -
054
2H2O(l) + 2I-(aq) rarr H2(g)+ 2OH-
(aq) + I2(s) -137
OA RA
Electrolysis of Brine
Na+
Cl-
H2O OA
RA
2H2O(l) + 2Cl-(aq) rarr H2(g) + 2OH-(aq) + Cl2(g)
Note
bull The Cl- ion is a stronger reducing agent than H2O during electrolysis of brine even though the table indicates that it is not
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
Remember
bull Redox reactions can be viewed as a competition for electrons Therefore the reaction is always between the strongest oxidizing agent and the strongest reducing agent
Problem
bull A strip of metal X is placed in XNO3 solution It makes an electrochemical cell with Al3+
(aq) half cell It is observed that Al(s) is deposited on the aluminum electrode and the cell voltage is 075 V Calculate the reduction potential of X
Solution
bull Al is reduced Al3+(aq) + 3e- rarr Al(s) -166
bull X is oxidized X(s) rarr X+(aq) + e-
bull Solve for -166 + = +075
= 241 VX is being oxidized reduction potential is ndash 241 V
( ) x 3
Al3+(aq) + 3X(s) rarr Al(s) + 3X+
(aq) 075
WS 15-2
Standard Electrode Potentials
bull A measure of the relative tendency of substances to gain electrons
bull The standard was chosen to be the hydrogen half cell
bull The hydrogen half cell was chosen to be zero This does not mean H+ will not gain electrons
Hydrogen Electrode
bull consists of a platinum electrode covered with a fine powder of platinum around which H2(g) is bubbled Its potential is defined as zero volts
Hydrogen Half-Cell
H2(g) rarr 2 H+(aq) + 2 e-
reversible reaction
Hydrogen Electrode
Non reactive
Standard Electrode Potentials
bull Since the hydrogen half cell has a relative value of 000 V any half cell connected to it will have its standard potential read off of the voltmeter that connects the two half cells
A Voltaic Cell With Zinc and the Standard Hydrogen Electrode
[Zn2+]= [H+] = 1000 M
Standard Electrode Potentials
bull Any half cell that gives up electrons to H+ will have a negative potential since it has less potential to gain electrons than H+
Standard Electrode Potentials
bull Any half cell that takes electrons from H2(g)
has a positive potential since it has a greater potential to gain electrons than H+
Standard Electrode Potentials
bull ExamplesndashCuCu2+ rarr Eo = 034 V 034 V
greater potential than H+H2
ndashAlAl3+ rarr Eo = -166 166 V less potential than H+H2
If the reduction of mercury (I) in a voltaic cell is desired the half reaction is
Which of the following reactions could be used as the anode (oxidation)
WS 15-22
Multiple cells
bull If the cells are connected to the anode then add the potentials
bull If the cells are connected at the cathode then subtract the potentials
Electrolytic cells
bull Electrical energy is converted to chemical energy
bull Non-spontaneous reactions
bull Reaction is still between the strongest OA and RA (OA is not strong enough)
bull Require outside energy source
Electrolytic cells
bull The Eo value for an electrolytic cell is negative
bull The Eo value is the minimum voltage that must be applied to the cell to force it to react
Electrolytic cells
bull In diagramsndashcell with ammeter rarr voltaic
ndashcell with battery rarr electrolytic
anode (+)cathode (-)
ElectroplatingElectrolysis
Electroplating is the process of
ElectroplatingElectrolysis
1) Current = rate of flow of charge
2) I = q t
3) 1 e- = 16 x 10-19 C
4) 1 mol e- = 602 x 1023 e- x 16 x 10-19 C
= 965 x 104 C
current (A) charge (C)
time (s)
Q = 965 x 104 Cmol (Faradayrsquos constant)
ElectroplatingElectrolysis
5) To calculate number of mol of electrons
ne = q Q
ne = q Q
ne = 18000 C 965 x 104 Cmol
ne = 01865 mol of e-
250 A of current runs for 20 hours through a silver nitrate solution Find the mass of silver produced
q = Itq = (250 A) x (7200 s)q = 18 000 C
Ag+(aq) + 1e- rarr Ag(s)
01865mol 01865 mol
m = n x M
m = 01865 mol x 10787 gmol
m = 20 g
Short cut
m = I t M
m = (250 A) (7200 s) (10787 gmol) (965 x 104 Cmol) (1)
m = 20 g
Q V
I rarr current (Amps)
t rarr time (s)
M rarr molar mass (gmol)
Q rarr molar charge (Cmol)
V rarr voltage
m = I t M
100 g = (150 A) t (10787 gmol) (965 x 104 Cmol) (100)
t = 59639589 s = 166 h
Q V
WS 15-33
A person wants to plate an ornament with 100 g of silver The ornament is placed in a salt of silver and a 15 A current is placed through the solution The voltage is 100 How long will the plating process take
Copper plating a key
- +
power
e-
inert anodecathode
Cu2+
NO3-
Molten or Aqueous
Aqueous
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(aq)
ndash Cl- (aq)
ndash H2O(l)
Molten
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(l)
ndash Cl- (l)
bull Calculate the net potentials and write the reactions that occur whenndash NaI(s) is electrolyzed
ndash A solution of NaI(aq) is electrolyzed
NaI(s) is electrolyzed
Na+(l) I-
(l)
Na+(l) + e- rarr Na(s) -271
2I-(l) rarr I2(s) + 2e- -054
2Na+(l) + 2I-
(l) rarr 2Na(s) + I2(s) -325
OA RA
A solution of NaI(aq) is electrolyzed
H2O(l) Na+(aq) I-
(aq)
2H2O(l) + 2e- rarr H2(g)+ 2OH-(aq) -083
2I-(aq) rarr I2(s) + 2e- -
054
2H2O(l) + 2I-(aq) rarr H2(g)+ 2OH-
(aq) + I2(s) -137
OA RA
Electrolysis of Brine
Na+
Cl-
H2O OA
RA
2H2O(l) + 2Cl-(aq) rarr H2(g) + 2OH-(aq) + Cl2(g)
Note
bull The Cl- ion is a stronger reducing agent than H2O during electrolysis of brine even though the table indicates that it is not
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
Problem
bull A strip of metal X is placed in XNO3 solution It makes an electrochemical cell with Al3+
(aq) half cell It is observed that Al(s) is deposited on the aluminum electrode and the cell voltage is 075 V Calculate the reduction potential of X
Solution
bull Al is reduced Al3+(aq) + 3e- rarr Al(s) -166
bull X is oxidized X(s) rarr X+(aq) + e-
bull Solve for -166 + = +075
= 241 VX is being oxidized reduction potential is ndash 241 V
( ) x 3
Al3+(aq) + 3X(s) rarr Al(s) + 3X+
(aq) 075
WS 15-2
Standard Electrode Potentials
bull A measure of the relative tendency of substances to gain electrons
bull The standard was chosen to be the hydrogen half cell
bull The hydrogen half cell was chosen to be zero This does not mean H+ will not gain electrons
Hydrogen Electrode
bull consists of a platinum electrode covered with a fine powder of platinum around which H2(g) is bubbled Its potential is defined as zero volts
Hydrogen Half-Cell
H2(g) rarr 2 H+(aq) + 2 e-
reversible reaction
Hydrogen Electrode
Non reactive
Standard Electrode Potentials
bull Since the hydrogen half cell has a relative value of 000 V any half cell connected to it will have its standard potential read off of the voltmeter that connects the two half cells
A Voltaic Cell With Zinc and the Standard Hydrogen Electrode
[Zn2+]= [H+] = 1000 M
Standard Electrode Potentials
bull Any half cell that gives up electrons to H+ will have a negative potential since it has less potential to gain electrons than H+
Standard Electrode Potentials
bull Any half cell that takes electrons from H2(g)
has a positive potential since it has a greater potential to gain electrons than H+
Standard Electrode Potentials
bull ExamplesndashCuCu2+ rarr Eo = 034 V 034 V
greater potential than H+H2
ndashAlAl3+ rarr Eo = -166 166 V less potential than H+H2
If the reduction of mercury (I) in a voltaic cell is desired the half reaction is
Which of the following reactions could be used as the anode (oxidation)
WS 15-22
Multiple cells
bull If the cells are connected to the anode then add the potentials
bull If the cells are connected at the cathode then subtract the potentials
Electrolytic cells
bull Electrical energy is converted to chemical energy
bull Non-spontaneous reactions
bull Reaction is still between the strongest OA and RA (OA is not strong enough)
bull Require outside energy source
Electrolytic cells
bull The Eo value for an electrolytic cell is negative
bull The Eo value is the minimum voltage that must be applied to the cell to force it to react
Electrolytic cells
bull In diagramsndashcell with ammeter rarr voltaic
ndashcell with battery rarr electrolytic
anode (+)cathode (-)
ElectroplatingElectrolysis
Electroplating is the process of
ElectroplatingElectrolysis
1) Current = rate of flow of charge
2) I = q t
3) 1 e- = 16 x 10-19 C
4) 1 mol e- = 602 x 1023 e- x 16 x 10-19 C
= 965 x 104 C
current (A) charge (C)
time (s)
Q = 965 x 104 Cmol (Faradayrsquos constant)
ElectroplatingElectrolysis
5) To calculate number of mol of electrons
ne = q Q
ne = q Q
ne = 18000 C 965 x 104 Cmol
ne = 01865 mol of e-
250 A of current runs for 20 hours through a silver nitrate solution Find the mass of silver produced
q = Itq = (250 A) x (7200 s)q = 18 000 C
Ag+(aq) + 1e- rarr Ag(s)
01865mol 01865 mol
m = n x M
m = 01865 mol x 10787 gmol
m = 20 g
Short cut
m = I t M
m = (250 A) (7200 s) (10787 gmol) (965 x 104 Cmol) (1)
m = 20 g
Q V
I rarr current (Amps)
t rarr time (s)
M rarr molar mass (gmol)
Q rarr molar charge (Cmol)
V rarr voltage
m = I t M
100 g = (150 A) t (10787 gmol) (965 x 104 Cmol) (100)
t = 59639589 s = 166 h
Q V
WS 15-33
A person wants to plate an ornament with 100 g of silver The ornament is placed in a salt of silver and a 15 A current is placed through the solution The voltage is 100 How long will the plating process take
Copper plating a key
- +
power
e-
inert anodecathode
Cu2+
NO3-
Molten or Aqueous
Aqueous
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(aq)
ndash Cl- (aq)
ndash H2O(l)
Molten
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(l)
ndash Cl- (l)
bull Calculate the net potentials and write the reactions that occur whenndash NaI(s) is electrolyzed
ndash A solution of NaI(aq) is electrolyzed
NaI(s) is electrolyzed
Na+(l) I-
(l)
Na+(l) + e- rarr Na(s) -271
2I-(l) rarr I2(s) + 2e- -054
2Na+(l) + 2I-
(l) rarr 2Na(s) + I2(s) -325
OA RA
A solution of NaI(aq) is electrolyzed
H2O(l) Na+(aq) I-
(aq)
2H2O(l) + 2e- rarr H2(g)+ 2OH-(aq) -083
2I-(aq) rarr I2(s) + 2e- -
054
2H2O(l) + 2I-(aq) rarr H2(g)+ 2OH-
(aq) + I2(s) -137
OA RA
Electrolysis of Brine
Na+
Cl-
H2O OA
RA
2H2O(l) + 2Cl-(aq) rarr H2(g) + 2OH-(aq) + Cl2(g)
Note
bull The Cl- ion is a stronger reducing agent than H2O during electrolysis of brine even though the table indicates that it is not
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
Solution
bull Al is reduced Al3+(aq) + 3e- rarr Al(s) -166
bull X is oxidized X(s) rarr X+(aq) + e-
bull Solve for -166 + = +075
= 241 VX is being oxidized reduction potential is ndash 241 V
( ) x 3
Al3+(aq) + 3X(s) rarr Al(s) + 3X+
(aq) 075
WS 15-2
Standard Electrode Potentials
bull A measure of the relative tendency of substances to gain electrons
bull The standard was chosen to be the hydrogen half cell
bull The hydrogen half cell was chosen to be zero This does not mean H+ will not gain electrons
Hydrogen Electrode
bull consists of a platinum electrode covered with a fine powder of platinum around which H2(g) is bubbled Its potential is defined as zero volts
Hydrogen Half-Cell
H2(g) rarr 2 H+(aq) + 2 e-
reversible reaction
Hydrogen Electrode
Non reactive
Standard Electrode Potentials
bull Since the hydrogen half cell has a relative value of 000 V any half cell connected to it will have its standard potential read off of the voltmeter that connects the two half cells
A Voltaic Cell With Zinc and the Standard Hydrogen Electrode
[Zn2+]= [H+] = 1000 M
Standard Electrode Potentials
bull Any half cell that gives up electrons to H+ will have a negative potential since it has less potential to gain electrons than H+
Standard Electrode Potentials
bull Any half cell that takes electrons from H2(g)
has a positive potential since it has a greater potential to gain electrons than H+
Standard Electrode Potentials
bull ExamplesndashCuCu2+ rarr Eo = 034 V 034 V
greater potential than H+H2
ndashAlAl3+ rarr Eo = -166 166 V less potential than H+H2
If the reduction of mercury (I) in a voltaic cell is desired the half reaction is
Which of the following reactions could be used as the anode (oxidation)
WS 15-22
Multiple cells
bull If the cells are connected to the anode then add the potentials
bull If the cells are connected at the cathode then subtract the potentials
Electrolytic cells
bull Electrical energy is converted to chemical energy
bull Non-spontaneous reactions
bull Reaction is still between the strongest OA and RA (OA is not strong enough)
bull Require outside energy source
Electrolytic cells
bull The Eo value for an electrolytic cell is negative
bull The Eo value is the minimum voltage that must be applied to the cell to force it to react
Electrolytic cells
bull In diagramsndashcell with ammeter rarr voltaic
ndashcell with battery rarr electrolytic
anode (+)cathode (-)
ElectroplatingElectrolysis
Electroplating is the process of
ElectroplatingElectrolysis
1) Current = rate of flow of charge
2) I = q t
3) 1 e- = 16 x 10-19 C
4) 1 mol e- = 602 x 1023 e- x 16 x 10-19 C
= 965 x 104 C
current (A) charge (C)
time (s)
Q = 965 x 104 Cmol (Faradayrsquos constant)
ElectroplatingElectrolysis
5) To calculate number of mol of electrons
ne = q Q
ne = q Q
ne = 18000 C 965 x 104 Cmol
ne = 01865 mol of e-
250 A of current runs for 20 hours through a silver nitrate solution Find the mass of silver produced
q = Itq = (250 A) x (7200 s)q = 18 000 C
Ag+(aq) + 1e- rarr Ag(s)
01865mol 01865 mol
m = n x M
m = 01865 mol x 10787 gmol
m = 20 g
Short cut
m = I t M
m = (250 A) (7200 s) (10787 gmol) (965 x 104 Cmol) (1)
m = 20 g
Q V
I rarr current (Amps)
t rarr time (s)
M rarr molar mass (gmol)
Q rarr molar charge (Cmol)
V rarr voltage
m = I t M
100 g = (150 A) t (10787 gmol) (965 x 104 Cmol) (100)
t = 59639589 s = 166 h
Q V
WS 15-33
A person wants to plate an ornament with 100 g of silver The ornament is placed in a salt of silver and a 15 A current is placed through the solution The voltage is 100 How long will the plating process take
Copper plating a key
- +
power
e-
inert anodecathode
Cu2+
NO3-
Molten or Aqueous
Aqueous
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(aq)
ndash Cl- (aq)
ndash H2O(l)
Molten
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(l)
ndash Cl- (l)
bull Calculate the net potentials and write the reactions that occur whenndash NaI(s) is electrolyzed
ndash A solution of NaI(aq) is electrolyzed
NaI(s) is electrolyzed
Na+(l) I-
(l)
Na+(l) + e- rarr Na(s) -271
2I-(l) rarr I2(s) + 2e- -054
2Na+(l) + 2I-
(l) rarr 2Na(s) + I2(s) -325
OA RA
A solution of NaI(aq) is electrolyzed
H2O(l) Na+(aq) I-
(aq)
2H2O(l) + 2e- rarr H2(g)+ 2OH-(aq) -083
2I-(aq) rarr I2(s) + 2e- -
054
2H2O(l) + 2I-(aq) rarr H2(g)+ 2OH-
(aq) + I2(s) -137
OA RA
Electrolysis of Brine
Na+
Cl-
H2O OA
RA
2H2O(l) + 2Cl-(aq) rarr H2(g) + 2OH-(aq) + Cl2(g)
Note
bull The Cl- ion is a stronger reducing agent than H2O during electrolysis of brine even though the table indicates that it is not
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
Standard Electrode Potentials
bull A measure of the relative tendency of substances to gain electrons
bull The standard was chosen to be the hydrogen half cell
bull The hydrogen half cell was chosen to be zero This does not mean H+ will not gain electrons
Hydrogen Electrode
bull consists of a platinum electrode covered with a fine powder of platinum around which H2(g) is bubbled Its potential is defined as zero volts
Hydrogen Half-Cell
H2(g) rarr 2 H+(aq) + 2 e-
reversible reaction
Hydrogen Electrode
Non reactive
Standard Electrode Potentials
bull Since the hydrogen half cell has a relative value of 000 V any half cell connected to it will have its standard potential read off of the voltmeter that connects the two half cells
A Voltaic Cell With Zinc and the Standard Hydrogen Electrode
[Zn2+]= [H+] = 1000 M
Standard Electrode Potentials
bull Any half cell that gives up electrons to H+ will have a negative potential since it has less potential to gain electrons than H+
Standard Electrode Potentials
bull Any half cell that takes electrons from H2(g)
has a positive potential since it has a greater potential to gain electrons than H+
Standard Electrode Potentials
bull ExamplesndashCuCu2+ rarr Eo = 034 V 034 V
greater potential than H+H2
ndashAlAl3+ rarr Eo = -166 166 V less potential than H+H2
If the reduction of mercury (I) in a voltaic cell is desired the half reaction is
Which of the following reactions could be used as the anode (oxidation)
WS 15-22
Multiple cells
bull If the cells are connected to the anode then add the potentials
bull If the cells are connected at the cathode then subtract the potentials
Electrolytic cells
bull Electrical energy is converted to chemical energy
bull Non-spontaneous reactions
bull Reaction is still between the strongest OA and RA (OA is not strong enough)
bull Require outside energy source
Electrolytic cells
bull The Eo value for an electrolytic cell is negative
bull The Eo value is the minimum voltage that must be applied to the cell to force it to react
Electrolytic cells
bull In diagramsndashcell with ammeter rarr voltaic
ndashcell with battery rarr electrolytic
anode (+)cathode (-)
ElectroplatingElectrolysis
Electroplating is the process of
ElectroplatingElectrolysis
1) Current = rate of flow of charge
2) I = q t
3) 1 e- = 16 x 10-19 C
4) 1 mol e- = 602 x 1023 e- x 16 x 10-19 C
= 965 x 104 C
current (A) charge (C)
time (s)
Q = 965 x 104 Cmol (Faradayrsquos constant)
ElectroplatingElectrolysis
5) To calculate number of mol of electrons
ne = q Q
ne = q Q
ne = 18000 C 965 x 104 Cmol
ne = 01865 mol of e-
250 A of current runs for 20 hours through a silver nitrate solution Find the mass of silver produced
q = Itq = (250 A) x (7200 s)q = 18 000 C
Ag+(aq) + 1e- rarr Ag(s)
01865mol 01865 mol
m = n x M
m = 01865 mol x 10787 gmol
m = 20 g
Short cut
m = I t M
m = (250 A) (7200 s) (10787 gmol) (965 x 104 Cmol) (1)
m = 20 g
Q V
I rarr current (Amps)
t rarr time (s)
M rarr molar mass (gmol)
Q rarr molar charge (Cmol)
V rarr voltage
m = I t M
100 g = (150 A) t (10787 gmol) (965 x 104 Cmol) (100)
t = 59639589 s = 166 h
Q V
WS 15-33
A person wants to plate an ornament with 100 g of silver The ornament is placed in a salt of silver and a 15 A current is placed through the solution The voltage is 100 How long will the plating process take
Copper plating a key
- +
power
e-
inert anodecathode
Cu2+
NO3-
Molten or Aqueous
Aqueous
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(aq)
ndash Cl- (aq)
ndash H2O(l)
Molten
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(l)
ndash Cl- (l)
bull Calculate the net potentials and write the reactions that occur whenndash NaI(s) is electrolyzed
ndash A solution of NaI(aq) is electrolyzed
NaI(s) is electrolyzed
Na+(l) I-
(l)
Na+(l) + e- rarr Na(s) -271
2I-(l) rarr I2(s) + 2e- -054
2Na+(l) + 2I-
(l) rarr 2Na(s) + I2(s) -325
OA RA
A solution of NaI(aq) is electrolyzed
H2O(l) Na+(aq) I-
(aq)
2H2O(l) + 2e- rarr H2(g)+ 2OH-(aq) -083
2I-(aq) rarr I2(s) + 2e- -
054
2H2O(l) + 2I-(aq) rarr H2(g)+ 2OH-
(aq) + I2(s) -137
OA RA
Electrolysis of Brine
Na+
Cl-
H2O OA
RA
2H2O(l) + 2Cl-(aq) rarr H2(g) + 2OH-(aq) + Cl2(g)
Note
bull The Cl- ion is a stronger reducing agent than H2O during electrolysis of brine even though the table indicates that it is not
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
Hydrogen Electrode
bull consists of a platinum electrode covered with a fine powder of platinum around which H2(g) is bubbled Its potential is defined as zero volts
Hydrogen Half-Cell
H2(g) rarr 2 H+(aq) + 2 e-
reversible reaction
Hydrogen Electrode
Non reactive
Standard Electrode Potentials
bull Since the hydrogen half cell has a relative value of 000 V any half cell connected to it will have its standard potential read off of the voltmeter that connects the two half cells
A Voltaic Cell With Zinc and the Standard Hydrogen Electrode
[Zn2+]= [H+] = 1000 M
Standard Electrode Potentials
bull Any half cell that gives up electrons to H+ will have a negative potential since it has less potential to gain electrons than H+
Standard Electrode Potentials
bull Any half cell that takes electrons from H2(g)
has a positive potential since it has a greater potential to gain electrons than H+
Standard Electrode Potentials
bull ExamplesndashCuCu2+ rarr Eo = 034 V 034 V
greater potential than H+H2
ndashAlAl3+ rarr Eo = -166 166 V less potential than H+H2
If the reduction of mercury (I) in a voltaic cell is desired the half reaction is
Which of the following reactions could be used as the anode (oxidation)
WS 15-22
Multiple cells
bull If the cells are connected to the anode then add the potentials
bull If the cells are connected at the cathode then subtract the potentials
Electrolytic cells
bull Electrical energy is converted to chemical energy
bull Non-spontaneous reactions
bull Reaction is still between the strongest OA and RA (OA is not strong enough)
bull Require outside energy source
Electrolytic cells
bull The Eo value for an electrolytic cell is negative
bull The Eo value is the minimum voltage that must be applied to the cell to force it to react
Electrolytic cells
bull In diagramsndashcell with ammeter rarr voltaic
ndashcell with battery rarr electrolytic
anode (+)cathode (-)
ElectroplatingElectrolysis
Electroplating is the process of
ElectroplatingElectrolysis
1) Current = rate of flow of charge
2) I = q t
3) 1 e- = 16 x 10-19 C
4) 1 mol e- = 602 x 1023 e- x 16 x 10-19 C
= 965 x 104 C
current (A) charge (C)
time (s)
Q = 965 x 104 Cmol (Faradayrsquos constant)
ElectroplatingElectrolysis
5) To calculate number of mol of electrons
ne = q Q
ne = q Q
ne = 18000 C 965 x 104 Cmol
ne = 01865 mol of e-
250 A of current runs for 20 hours through a silver nitrate solution Find the mass of silver produced
q = Itq = (250 A) x (7200 s)q = 18 000 C
Ag+(aq) + 1e- rarr Ag(s)
01865mol 01865 mol
m = n x M
m = 01865 mol x 10787 gmol
m = 20 g
Short cut
m = I t M
m = (250 A) (7200 s) (10787 gmol) (965 x 104 Cmol) (1)
m = 20 g
Q V
I rarr current (Amps)
t rarr time (s)
M rarr molar mass (gmol)
Q rarr molar charge (Cmol)
V rarr voltage
m = I t M
100 g = (150 A) t (10787 gmol) (965 x 104 Cmol) (100)
t = 59639589 s = 166 h
Q V
WS 15-33
A person wants to plate an ornament with 100 g of silver The ornament is placed in a salt of silver and a 15 A current is placed through the solution The voltage is 100 How long will the plating process take
Copper plating a key
- +
power
e-
inert anodecathode
Cu2+
NO3-
Molten or Aqueous
Aqueous
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(aq)
ndash Cl- (aq)
ndash H2O(l)
Molten
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(l)
ndash Cl- (l)
bull Calculate the net potentials and write the reactions that occur whenndash NaI(s) is electrolyzed
ndash A solution of NaI(aq) is electrolyzed
NaI(s) is electrolyzed
Na+(l) I-
(l)
Na+(l) + e- rarr Na(s) -271
2I-(l) rarr I2(s) + 2e- -054
2Na+(l) + 2I-
(l) rarr 2Na(s) + I2(s) -325
OA RA
A solution of NaI(aq) is electrolyzed
H2O(l) Na+(aq) I-
(aq)
2H2O(l) + 2e- rarr H2(g)+ 2OH-(aq) -083
2I-(aq) rarr I2(s) + 2e- -
054
2H2O(l) + 2I-(aq) rarr H2(g)+ 2OH-
(aq) + I2(s) -137
OA RA
Electrolysis of Brine
Na+
Cl-
H2O OA
RA
2H2O(l) + 2Cl-(aq) rarr H2(g) + 2OH-(aq) + Cl2(g)
Note
bull The Cl- ion is a stronger reducing agent than H2O during electrolysis of brine even though the table indicates that it is not
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
Hydrogen Electrode
Non reactive
Standard Electrode Potentials
bull Since the hydrogen half cell has a relative value of 000 V any half cell connected to it will have its standard potential read off of the voltmeter that connects the two half cells
A Voltaic Cell With Zinc and the Standard Hydrogen Electrode
[Zn2+]= [H+] = 1000 M
Standard Electrode Potentials
bull Any half cell that gives up electrons to H+ will have a negative potential since it has less potential to gain electrons than H+
Standard Electrode Potentials
bull Any half cell that takes electrons from H2(g)
has a positive potential since it has a greater potential to gain electrons than H+
Standard Electrode Potentials
bull ExamplesndashCuCu2+ rarr Eo = 034 V 034 V
greater potential than H+H2
ndashAlAl3+ rarr Eo = -166 166 V less potential than H+H2
If the reduction of mercury (I) in a voltaic cell is desired the half reaction is
Which of the following reactions could be used as the anode (oxidation)
WS 15-22
Multiple cells
bull If the cells are connected to the anode then add the potentials
bull If the cells are connected at the cathode then subtract the potentials
Electrolytic cells
bull Electrical energy is converted to chemical energy
bull Non-spontaneous reactions
bull Reaction is still between the strongest OA and RA (OA is not strong enough)
bull Require outside energy source
Electrolytic cells
bull The Eo value for an electrolytic cell is negative
bull The Eo value is the minimum voltage that must be applied to the cell to force it to react
Electrolytic cells
bull In diagramsndashcell with ammeter rarr voltaic
ndashcell with battery rarr electrolytic
anode (+)cathode (-)
ElectroplatingElectrolysis
Electroplating is the process of
ElectroplatingElectrolysis
1) Current = rate of flow of charge
2) I = q t
3) 1 e- = 16 x 10-19 C
4) 1 mol e- = 602 x 1023 e- x 16 x 10-19 C
= 965 x 104 C
current (A) charge (C)
time (s)
Q = 965 x 104 Cmol (Faradayrsquos constant)
ElectroplatingElectrolysis
5) To calculate number of mol of electrons
ne = q Q
ne = q Q
ne = 18000 C 965 x 104 Cmol
ne = 01865 mol of e-
250 A of current runs for 20 hours through a silver nitrate solution Find the mass of silver produced
q = Itq = (250 A) x (7200 s)q = 18 000 C
Ag+(aq) + 1e- rarr Ag(s)
01865mol 01865 mol
m = n x M
m = 01865 mol x 10787 gmol
m = 20 g
Short cut
m = I t M
m = (250 A) (7200 s) (10787 gmol) (965 x 104 Cmol) (1)
m = 20 g
Q V
I rarr current (Amps)
t rarr time (s)
M rarr molar mass (gmol)
Q rarr molar charge (Cmol)
V rarr voltage
m = I t M
100 g = (150 A) t (10787 gmol) (965 x 104 Cmol) (100)
t = 59639589 s = 166 h
Q V
WS 15-33
A person wants to plate an ornament with 100 g of silver The ornament is placed in a salt of silver and a 15 A current is placed through the solution The voltage is 100 How long will the plating process take
Copper plating a key
- +
power
e-
inert anodecathode
Cu2+
NO3-
Molten or Aqueous
Aqueous
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(aq)
ndash Cl- (aq)
ndash H2O(l)
Molten
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(l)
ndash Cl- (l)
bull Calculate the net potentials and write the reactions that occur whenndash NaI(s) is electrolyzed
ndash A solution of NaI(aq) is electrolyzed
NaI(s) is electrolyzed
Na+(l) I-
(l)
Na+(l) + e- rarr Na(s) -271
2I-(l) rarr I2(s) + 2e- -054
2Na+(l) + 2I-
(l) rarr 2Na(s) + I2(s) -325
OA RA
A solution of NaI(aq) is electrolyzed
H2O(l) Na+(aq) I-
(aq)
2H2O(l) + 2e- rarr H2(g)+ 2OH-(aq) -083
2I-(aq) rarr I2(s) + 2e- -
054
2H2O(l) + 2I-(aq) rarr H2(g)+ 2OH-
(aq) + I2(s) -137
OA RA
Electrolysis of Brine
Na+
Cl-
H2O OA
RA
2H2O(l) + 2Cl-(aq) rarr H2(g) + 2OH-(aq) + Cl2(g)
Note
bull The Cl- ion is a stronger reducing agent than H2O during electrolysis of brine even though the table indicates that it is not
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
Standard Electrode Potentials
bull Since the hydrogen half cell has a relative value of 000 V any half cell connected to it will have its standard potential read off of the voltmeter that connects the two half cells
A Voltaic Cell With Zinc and the Standard Hydrogen Electrode
[Zn2+]= [H+] = 1000 M
Standard Electrode Potentials
bull Any half cell that gives up electrons to H+ will have a negative potential since it has less potential to gain electrons than H+
Standard Electrode Potentials
bull Any half cell that takes electrons from H2(g)
has a positive potential since it has a greater potential to gain electrons than H+
Standard Electrode Potentials
bull ExamplesndashCuCu2+ rarr Eo = 034 V 034 V
greater potential than H+H2
ndashAlAl3+ rarr Eo = -166 166 V less potential than H+H2
If the reduction of mercury (I) in a voltaic cell is desired the half reaction is
Which of the following reactions could be used as the anode (oxidation)
WS 15-22
Multiple cells
bull If the cells are connected to the anode then add the potentials
bull If the cells are connected at the cathode then subtract the potentials
Electrolytic cells
bull Electrical energy is converted to chemical energy
bull Non-spontaneous reactions
bull Reaction is still between the strongest OA and RA (OA is not strong enough)
bull Require outside energy source
Electrolytic cells
bull The Eo value for an electrolytic cell is negative
bull The Eo value is the minimum voltage that must be applied to the cell to force it to react
Electrolytic cells
bull In diagramsndashcell with ammeter rarr voltaic
ndashcell with battery rarr electrolytic
anode (+)cathode (-)
ElectroplatingElectrolysis
Electroplating is the process of
ElectroplatingElectrolysis
1) Current = rate of flow of charge
2) I = q t
3) 1 e- = 16 x 10-19 C
4) 1 mol e- = 602 x 1023 e- x 16 x 10-19 C
= 965 x 104 C
current (A) charge (C)
time (s)
Q = 965 x 104 Cmol (Faradayrsquos constant)
ElectroplatingElectrolysis
5) To calculate number of mol of electrons
ne = q Q
ne = q Q
ne = 18000 C 965 x 104 Cmol
ne = 01865 mol of e-
250 A of current runs for 20 hours through a silver nitrate solution Find the mass of silver produced
q = Itq = (250 A) x (7200 s)q = 18 000 C
Ag+(aq) + 1e- rarr Ag(s)
01865mol 01865 mol
m = n x M
m = 01865 mol x 10787 gmol
m = 20 g
Short cut
m = I t M
m = (250 A) (7200 s) (10787 gmol) (965 x 104 Cmol) (1)
m = 20 g
Q V
I rarr current (Amps)
t rarr time (s)
M rarr molar mass (gmol)
Q rarr molar charge (Cmol)
V rarr voltage
m = I t M
100 g = (150 A) t (10787 gmol) (965 x 104 Cmol) (100)
t = 59639589 s = 166 h
Q V
WS 15-33
A person wants to plate an ornament with 100 g of silver The ornament is placed in a salt of silver and a 15 A current is placed through the solution The voltage is 100 How long will the plating process take
Copper plating a key
- +
power
e-
inert anodecathode
Cu2+
NO3-
Molten or Aqueous
Aqueous
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(aq)
ndash Cl- (aq)
ndash H2O(l)
Molten
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(l)
ndash Cl- (l)
bull Calculate the net potentials and write the reactions that occur whenndash NaI(s) is electrolyzed
ndash A solution of NaI(aq) is electrolyzed
NaI(s) is electrolyzed
Na+(l) I-
(l)
Na+(l) + e- rarr Na(s) -271
2I-(l) rarr I2(s) + 2e- -054
2Na+(l) + 2I-
(l) rarr 2Na(s) + I2(s) -325
OA RA
A solution of NaI(aq) is electrolyzed
H2O(l) Na+(aq) I-
(aq)
2H2O(l) + 2e- rarr H2(g)+ 2OH-(aq) -083
2I-(aq) rarr I2(s) + 2e- -
054
2H2O(l) + 2I-(aq) rarr H2(g)+ 2OH-
(aq) + I2(s) -137
OA RA
Electrolysis of Brine
Na+
Cl-
H2O OA
RA
2H2O(l) + 2Cl-(aq) rarr H2(g) + 2OH-(aq) + Cl2(g)
Note
bull The Cl- ion is a stronger reducing agent than H2O during electrolysis of brine even though the table indicates that it is not
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
A Voltaic Cell With Zinc and the Standard Hydrogen Electrode
[Zn2+]= [H+] = 1000 M
Standard Electrode Potentials
bull Any half cell that gives up electrons to H+ will have a negative potential since it has less potential to gain electrons than H+
Standard Electrode Potentials
bull Any half cell that takes electrons from H2(g)
has a positive potential since it has a greater potential to gain electrons than H+
Standard Electrode Potentials
bull ExamplesndashCuCu2+ rarr Eo = 034 V 034 V
greater potential than H+H2
ndashAlAl3+ rarr Eo = -166 166 V less potential than H+H2
If the reduction of mercury (I) in a voltaic cell is desired the half reaction is
Which of the following reactions could be used as the anode (oxidation)
WS 15-22
Multiple cells
bull If the cells are connected to the anode then add the potentials
bull If the cells are connected at the cathode then subtract the potentials
Electrolytic cells
bull Electrical energy is converted to chemical energy
bull Non-spontaneous reactions
bull Reaction is still between the strongest OA and RA (OA is not strong enough)
bull Require outside energy source
Electrolytic cells
bull The Eo value for an electrolytic cell is negative
bull The Eo value is the minimum voltage that must be applied to the cell to force it to react
Electrolytic cells
bull In diagramsndashcell with ammeter rarr voltaic
ndashcell with battery rarr electrolytic
anode (+)cathode (-)
ElectroplatingElectrolysis
Electroplating is the process of
ElectroplatingElectrolysis
1) Current = rate of flow of charge
2) I = q t
3) 1 e- = 16 x 10-19 C
4) 1 mol e- = 602 x 1023 e- x 16 x 10-19 C
= 965 x 104 C
current (A) charge (C)
time (s)
Q = 965 x 104 Cmol (Faradayrsquos constant)
ElectroplatingElectrolysis
5) To calculate number of mol of electrons
ne = q Q
ne = q Q
ne = 18000 C 965 x 104 Cmol
ne = 01865 mol of e-
250 A of current runs for 20 hours through a silver nitrate solution Find the mass of silver produced
q = Itq = (250 A) x (7200 s)q = 18 000 C
Ag+(aq) + 1e- rarr Ag(s)
01865mol 01865 mol
m = n x M
m = 01865 mol x 10787 gmol
m = 20 g
Short cut
m = I t M
m = (250 A) (7200 s) (10787 gmol) (965 x 104 Cmol) (1)
m = 20 g
Q V
I rarr current (Amps)
t rarr time (s)
M rarr molar mass (gmol)
Q rarr molar charge (Cmol)
V rarr voltage
m = I t M
100 g = (150 A) t (10787 gmol) (965 x 104 Cmol) (100)
t = 59639589 s = 166 h
Q V
WS 15-33
A person wants to plate an ornament with 100 g of silver The ornament is placed in a salt of silver and a 15 A current is placed through the solution The voltage is 100 How long will the plating process take
Copper plating a key
- +
power
e-
inert anodecathode
Cu2+
NO3-
Molten or Aqueous
Aqueous
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(aq)
ndash Cl- (aq)
ndash H2O(l)
Molten
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(l)
ndash Cl- (l)
bull Calculate the net potentials and write the reactions that occur whenndash NaI(s) is electrolyzed
ndash A solution of NaI(aq) is electrolyzed
NaI(s) is electrolyzed
Na+(l) I-
(l)
Na+(l) + e- rarr Na(s) -271
2I-(l) rarr I2(s) + 2e- -054
2Na+(l) + 2I-
(l) rarr 2Na(s) + I2(s) -325
OA RA
A solution of NaI(aq) is electrolyzed
H2O(l) Na+(aq) I-
(aq)
2H2O(l) + 2e- rarr H2(g)+ 2OH-(aq) -083
2I-(aq) rarr I2(s) + 2e- -
054
2H2O(l) + 2I-(aq) rarr H2(g)+ 2OH-
(aq) + I2(s) -137
OA RA
Electrolysis of Brine
Na+
Cl-
H2O OA
RA
2H2O(l) + 2Cl-(aq) rarr H2(g) + 2OH-(aq) + Cl2(g)
Note
bull The Cl- ion is a stronger reducing agent than H2O during electrolysis of brine even though the table indicates that it is not
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
Standard Electrode Potentials
bull Any half cell that gives up electrons to H+ will have a negative potential since it has less potential to gain electrons than H+
Standard Electrode Potentials
bull Any half cell that takes electrons from H2(g)
has a positive potential since it has a greater potential to gain electrons than H+
Standard Electrode Potentials
bull ExamplesndashCuCu2+ rarr Eo = 034 V 034 V
greater potential than H+H2
ndashAlAl3+ rarr Eo = -166 166 V less potential than H+H2
If the reduction of mercury (I) in a voltaic cell is desired the half reaction is
Which of the following reactions could be used as the anode (oxidation)
WS 15-22
Multiple cells
bull If the cells are connected to the anode then add the potentials
bull If the cells are connected at the cathode then subtract the potentials
Electrolytic cells
bull Electrical energy is converted to chemical energy
bull Non-spontaneous reactions
bull Reaction is still between the strongest OA and RA (OA is not strong enough)
bull Require outside energy source
Electrolytic cells
bull The Eo value for an electrolytic cell is negative
bull The Eo value is the minimum voltage that must be applied to the cell to force it to react
Electrolytic cells
bull In diagramsndashcell with ammeter rarr voltaic
ndashcell with battery rarr electrolytic
anode (+)cathode (-)
ElectroplatingElectrolysis
Electroplating is the process of
ElectroplatingElectrolysis
1) Current = rate of flow of charge
2) I = q t
3) 1 e- = 16 x 10-19 C
4) 1 mol e- = 602 x 1023 e- x 16 x 10-19 C
= 965 x 104 C
current (A) charge (C)
time (s)
Q = 965 x 104 Cmol (Faradayrsquos constant)
ElectroplatingElectrolysis
5) To calculate number of mol of electrons
ne = q Q
ne = q Q
ne = 18000 C 965 x 104 Cmol
ne = 01865 mol of e-
250 A of current runs for 20 hours through a silver nitrate solution Find the mass of silver produced
q = Itq = (250 A) x (7200 s)q = 18 000 C
Ag+(aq) + 1e- rarr Ag(s)
01865mol 01865 mol
m = n x M
m = 01865 mol x 10787 gmol
m = 20 g
Short cut
m = I t M
m = (250 A) (7200 s) (10787 gmol) (965 x 104 Cmol) (1)
m = 20 g
Q V
I rarr current (Amps)
t rarr time (s)
M rarr molar mass (gmol)
Q rarr molar charge (Cmol)
V rarr voltage
m = I t M
100 g = (150 A) t (10787 gmol) (965 x 104 Cmol) (100)
t = 59639589 s = 166 h
Q V
WS 15-33
A person wants to plate an ornament with 100 g of silver The ornament is placed in a salt of silver and a 15 A current is placed through the solution The voltage is 100 How long will the plating process take
Copper plating a key
- +
power
e-
inert anodecathode
Cu2+
NO3-
Molten or Aqueous
Aqueous
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(aq)
ndash Cl- (aq)
ndash H2O(l)
Molten
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(l)
ndash Cl- (l)
bull Calculate the net potentials and write the reactions that occur whenndash NaI(s) is electrolyzed
ndash A solution of NaI(aq) is electrolyzed
NaI(s) is electrolyzed
Na+(l) I-
(l)
Na+(l) + e- rarr Na(s) -271
2I-(l) rarr I2(s) + 2e- -054
2Na+(l) + 2I-
(l) rarr 2Na(s) + I2(s) -325
OA RA
A solution of NaI(aq) is electrolyzed
H2O(l) Na+(aq) I-
(aq)
2H2O(l) + 2e- rarr H2(g)+ 2OH-(aq) -083
2I-(aq) rarr I2(s) + 2e- -
054
2H2O(l) + 2I-(aq) rarr H2(g)+ 2OH-
(aq) + I2(s) -137
OA RA
Electrolysis of Brine
Na+
Cl-
H2O OA
RA
2H2O(l) + 2Cl-(aq) rarr H2(g) + 2OH-(aq) + Cl2(g)
Note
bull The Cl- ion is a stronger reducing agent than H2O during electrolysis of brine even though the table indicates that it is not
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
Standard Electrode Potentials
bull Any half cell that takes electrons from H2(g)
has a positive potential since it has a greater potential to gain electrons than H+
Standard Electrode Potentials
bull ExamplesndashCuCu2+ rarr Eo = 034 V 034 V
greater potential than H+H2
ndashAlAl3+ rarr Eo = -166 166 V less potential than H+H2
If the reduction of mercury (I) in a voltaic cell is desired the half reaction is
Which of the following reactions could be used as the anode (oxidation)
WS 15-22
Multiple cells
bull If the cells are connected to the anode then add the potentials
bull If the cells are connected at the cathode then subtract the potentials
Electrolytic cells
bull Electrical energy is converted to chemical energy
bull Non-spontaneous reactions
bull Reaction is still between the strongest OA and RA (OA is not strong enough)
bull Require outside energy source
Electrolytic cells
bull The Eo value for an electrolytic cell is negative
bull The Eo value is the minimum voltage that must be applied to the cell to force it to react
Electrolytic cells
bull In diagramsndashcell with ammeter rarr voltaic
ndashcell with battery rarr electrolytic
anode (+)cathode (-)
ElectroplatingElectrolysis
Electroplating is the process of
ElectroplatingElectrolysis
1) Current = rate of flow of charge
2) I = q t
3) 1 e- = 16 x 10-19 C
4) 1 mol e- = 602 x 1023 e- x 16 x 10-19 C
= 965 x 104 C
current (A) charge (C)
time (s)
Q = 965 x 104 Cmol (Faradayrsquos constant)
ElectroplatingElectrolysis
5) To calculate number of mol of electrons
ne = q Q
ne = q Q
ne = 18000 C 965 x 104 Cmol
ne = 01865 mol of e-
250 A of current runs for 20 hours through a silver nitrate solution Find the mass of silver produced
q = Itq = (250 A) x (7200 s)q = 18 000 C
Ag+(aq) + 1e- rarr Ag(s)
01865mol 01865 mol
m = n x M
m = 01865 mol x 10787 gmol
m = 20 g
Short cut
m = I t M
m = (250 A) (7200 s) (10787 gmol) (965 x 104 Cmol) (1)
m = 20 g
Q V
I rarr current (Amps)
t rarr time (s)
M rarr molar mass (gmol)
Q rarr molar charge (Cmol)
V rarr voltage
m = I t M
100 g = (150 A) t (10787 gmol) (965 x 104 Cmol) (100)
t = 59639589 s = 166 h
Q V
WS 15-33
A person wants to plate an ornament with 100 g of silver The ornament is placed in a salt of silver and a 15 A current is placed through the solution The voltage is 100 How long will the plating process take
Copper plating a key
- +
power
e-
inert anodecathode
Cu2+
NO3-
Molten or Aqueous
Aqueous
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(aq)
ndash Cl- (aq)
ndash H2O(l)
Molten
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(l)
ndash Cl- (l)
bull Calculate the net potentials and write the reactions that occur whenndash NaI(s) is electrolyzed
ndash A solution of NaI(aq) is electrolyzed
NaI(s) is electrolyzed
Na+(l) I-
(l)
Na+(l) + e- rarr Na(s) -271
2I-(l) rarr I2(s) + 2e- -054
2Na+(l) + 2I-
(l) rarr 2Na(s) + I2(s) -325
OA RA
A solution of NaI(aq) is electrolyzed
H2O(l) Na+(aq) I-
(aq)
2H2O(l) + 2e- rarr H2(g)+ 2OH-(aq) -083
2I-(aq) rarr I2(s) + 2e- -
054
2H2O(l) + 2I-(aq) rarr H2(g)+ 2OH-
(aq) + I2(s) -137
OA RA
Electrolysis of Brine
Na+
Cl-
H2O OA
RA
2H2O(l) + 2Cl-(aq) rarr H2(g) + 2OH-(aq) + Cl2(g)
Note
bull The Cl- ion is a stronger reducing agent than H2O during electrolysis of brine even though the table indicates that it is not
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
Standard Electrode Potentials
bull ExamplesndashCuCu2+ rarr Eo = 034 V 034 V
greater potential than H+H2
ndashAlAl3+ rarr Eo = -166 166 V less potential than H+H2
If the reduction of mercury (I) in a voltaic cell is desired the half reaction is
Which of the following reactions could be used as the anode (oxidation)
WS 15-22
Multiple cells
bull If the cells are connected to the anode then add the potentials
bull If the cells are connected at the cathode then subtract the potentials
Electrolytic cells
bull Electrical energy is converted to chemical energy
bull Non-spontaneous reactions
bull Reaction is still between the strongest OA and RA (OA is not strong enough)
bull Require outside energy source
Electrolytic cells
bull The Eo value for an electrolytic cell is negative
bull The Eo value is the minimum voltage that must be applied to the cell to force it to react
Electrolytic cells
bull In diagramsndashcell with ammeter rarr voltaic
ndashcell with battery rarr electrolytic
anode (+)cathode (-)
ElectroplatingElectrolysis
Electroplating is the process of
ElectroplatingElectrolysis
1) Current = rate of flow of charge
2) I = q t
3) 1 e- = 16 x 10-19 C
4) 1 mol e- = 602 x 1023 e- x 16 x 10-19 C
= 965 x 104 C
current (A) charge (C)
time (s)
Q = 965 x 104 Cmol (Faradayrsquos constant)
ElectroplatingElectrolysis
5) To calculate number of mol of electrons
ne = q Q
ne = q Q
ne = 18000 C 965 x 104 Cmol
ne = 01865 mol of e-
250 A of current runs for 20 hours through a silver nitrate solution Find the mass of silver produced
q = Itq = (250 A) x (7200 s)q = 18 000 C
Ag+(aq) + 1e- rarr Ag(s)
01865mol 01865 mol
m = n x M
m = 01865 mol x 10787 gmol
m = 20 g
Short cut
m = I t M
m = (250 A) (7200 s) (10787 gmol) (965 x 104 Cmol) (1)
m = 20 g
Q V
I rarr current (Amps)
t rarr time (s)
M rarr molar mass (gmol)
Q rarr molar charge (Cmol)
V rarr voltage
m = I t M
100 g = (150 A) t (10787 gmol) (965 x 104 Cmol) (100)
t = 59639589 s = 166 h
Q V
WS 15-33
A person wants to plate an ornament with 100 g of silver The ornament is placed in a salt of silver and a 15 A current is placed through the solution The voltage is 100 How long will the plating process take
Copper plating a key
- +
power
e-
inert anodecathode
Cu2+
NO3-
Molten or Aqueous
Aqueous
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(aq)
ndash Cl- (aq)
ndash H2O(l)
Molten
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(l)
ndash Cl- (l)
bull Calculate the net potentials and write the reactions that occur whenndash NaI(s) is electrolyzed
ndash A solution of NaI(aq) is electrolyzed
NaI(s) is electrolyzed
Na+(l) I-
(l)
Na+(l) + e- rarr Na(s) -271
2I-(l) rarr I2(s) + 2e- -054
2Na+(l) + 2I-
(l) rarr 2Na(s) + I2(s) -325
OA RA
A solution of NaI(aq) is electrolyzed
H2O(l) Na+(aq) I-
(aq)
2H2O(l) + 2e- rarr H2(g)+ 2OH-(aq) -083
2I-(aq) rarr I2(s) + 2e- -
054
2H2O(l) + 2I-(aq) rarr H2(g)+ 2OH-
(aq) + I2(s) -137
OA RA
Electrolysis of Brine
Na+
Cl-
H2O OA
RA
2H2O(l) + 2Cl-(aq) rarr H2(g) + 2OH-(aq) + Cl2(g)
Note
bull The Cl- ion is a stronger reducing agent than H2O during electrolysis of brine even though the table indicates that it is not
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
If the reduction of mercury (I) in a voltaic cell is desired the half reaction is
Which of the following reactions could be used as the anode (oxidation)
WS 15-22
Multiple cells
bull If the cells are connected to the anode then add the potentials
bull If the cells are connected at the cathode then subtract the potentials
Electrolytic cells
bull Electrical energy is converted to chemical energy
bull Non-spontaneous reactions
bull Reaction is still between the strongest OA and RA (OA is not strong enough)
bull Require outside energy source
Electrolytic cells
bull The Eo value for an electrolytic cell is negative
bull The Eo value is the minimum voltage that must be applied to the cell to force it to react
Electrolytic cells
bull In diagramsndashcell with ammeter rarr voltaic
ndashcell with battery rarr electrolytic
anode (+)cathode (-)
ElectroplatingElectrolysis
Electroplating is the process of
ElectroplatingElectrolysis
1) Current = rate of flow of charge
2) I = q t
3) 1 e- = 16 x 10-19 C
4) 1 mol e- = 602 x 1023 e- x 16 x 10-19 C
= 965 x 104 C
current (A) charge (C)
time (s)
Q = 965 x 104 Cmol (Faradayrsquos constant)
ElectroplatingElectrolysis
5) To calculate number of mol of electrons
ne = q Q
ne = q Q
ne = 18000 C 965 x 104 Cmol
ne = 01865 mol of e-
250 A of current runs for 20 hours through a silver nitrate solution Find the mass of silver produced
q = Itq = (250 A) x (7200 s)q = 18 000 C
Ag+(aq) + 1e- rarr Ag(s)
01865mol 01865 mol
m = n x M
m = 01865 mol x 10787 gmol
m = 20 g
Short cut
m = I t M
m = (250 A) (7200 s) (10787 gmol) (965 x 104 Cmol) (1)
m = 20 g
Q V
I rarr current (Amps)
t rarr time (s)
M rarr molar mass (gmol)
Q rarr molar charge (Cmol)
V rarr voltage
m = I t M
100 g = (150 A) t (10787 gmol) (965 x 104 Cmol) (100)
t = 59639589 s = 166 h
Q V
WS 15-33
A person wants to plate an ornament with 100 g of silver The ornament is placed in a salt of silver and a 15 A current is placed through the solution The voltage is 100 How long will the plating process take
Copper plating a key
- +
power
e-
inert anodecathode
Cu2+
NO3-
Molten or Aqueous
Aqueous
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(aq)
ndash Cl- (aq)
ndash H2O(l)
Molten
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(l)
ndash Cl- (l)
bull Calculate the net potentials and write the reactions that occur whenndash NaI(s) is electrolyzed
ndash A solution of NaI(aq) is electrolyzed
NaI(s) is electrolyzed
Na+(l) I-
(l)
Na+(l) + e- rarr Na(s) -271
2I-(l) rarr I2(s) + 2e- -054
2Na+(l) + 2I-
(l) rarr 2Na(s) + I2(s) -325
OA RA
A solution of NaI(aq) is electrolyzed
H2O(l) Na+(aq) I-
(aq)
2H2O(l) + 2e- rarr H2(g)+ 2OH-(aq) -083
2I-(aq) rarr I2(s) + 2e- -
054
2H2O(l) + 2I-(aq) rarr H2(g)+ 2OH-
(aq) + I2(s) -137
OA RA
Electrolysis of Brine
Na+
Cl-
H2O OA
RA
2H2O(l) + 2Cl-(aq) rarr H2(g) + 2OH-(aq) + Cl2(g)
Note
bull The Cl- ion is a stronger reducing agent than H2O during electrolysis of brine even though the table indicates that it is not
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
Multiple cells
bull If the cells are connected to the anode then add the potentials
bull If the cells are connected at the cathode then subtract the potentials
Electrolytic cells
bull Electrical energy is converted to chemical energy
bull Non-spontaneous reactions
bull Reaction is still between the strongest OA and RA (OA is not strong enough)
bull Require outside energy source
Electrolytic cells
bull The Eo value for an electrolytic cell is negative
bull The Eo value is the minimum voltage that must be applied to the cell to force it to react
Electrolytic cells
bull In diagramsndashcell with ammeter rarr voltaic
ndashcell with battery rarr electrolytic
anode (+)cathode (-)
ElectroplatingElectrolysis
Electroplating is the process of
ElectroplatingElectrolysis
1) Current = rate of flow of charge
2) I = q t
3) 1 e- = 16 x 10-19 C
4) 1 mol e- = 602 x 1023 e- x 16 x 10-19 C
= 965 x 104 C
current (A) charge (C)
time (s)
Q = 965 x 104 Cmol (Faradayrsquos constant)
ElectroplatingElectrolysis
5) To calculate number of mol of electrons
ne = q Q
ne = q Q
ne = 18000 C 965 x 104 Cmol
ne = 01865 mol of e-
250 A of current runs for 20 hours through a silver nitrate solution Find the mass of silver produced
q = Itq = (250 A) x (7200 s)q = 18 000 C
Ag+(aq) + 1e- rarr Ag(s)
01865mol 01865 mol
m = n x M
m = 01865 mol x 10787 gmol
m = 20 g
Short cut
m = I t M
m = (250 A) (7200 s) (10787 gmol) (965 x 104 Cmol) (1)
m = 20 g
Q V
I rarr current (Amps)
t rarr time (s)
M rarr molar mass (gmol)
Q rarr molar charge (Cmol)
V rarr voltage
m = I t M
100 g = (150 A) t (10787 gmol) (965 x 104 Cmol) (100)
t = 59639589 s = 166 h
Q V
WS 15-33
A person wants to plate an ornament with 100 g of silver The ornament is placed in a salt of silver and a 15 A current is placed through the solution The voltage is 100 How long will the plating process take
Copper plating a key
- +
power
e-
inert anodecathode
Cu2+
NO3-
Molten or Aqueous
Aqueous
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(aq)
ndash Cl- (aq)
ndash H2O(l)
Molten
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(l)
ndash Cl- (l)
bull Calculate the net potentials and write the reactions that occur whenndash NaI(s) is electrolyzed
ndash A solution of NaI(aq) is electrolyzed
NaI(s) is electrolyzed
Na+(l) I-
(l)
Na+(l) + e- rarr Na(s) -271
2I-(l) rarr I2(s) + 2e- -054
2Na+(l) + 2I-
(l) rarr 2Na(s) + I2(s) -325
OA RA
A solution of NaI(aq) is electrolyzed
H2O(l) Na+(aq) I-
(aq)
2H2O(l) + 2e- rarr H2(g)+ 2OH-(aq) -083
2I-(aq) rarr I2(s) + 2e- -
054
2H2O(l) + 2I-(aq) rarr H2(g)+ 2OH-
(aq) + I2(s) -137
OA RA
Electrolysis of Brine
Na+
Cl-
H2O OA
RA
2H2O(l) + 2Cl-(aq) rarr H2(g) + 2OH-(aq) + Cl2(g)
Note
bull The Cl- ion is a stronger reducing agent than H2O during electrolysis of brine even though the table indicates that it is not
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
Electrolytic cells
bull Electrical energy is converted to chemical energy
bull Non-spontaneous reactions
bull Reaction is still between the strongest OA and RA (OA is not strong enough)
bull Require outside energy source
Electrolytic cells
bull The Eo value for an electrolytic cell is negative
bull The Eo value is the minimum voltage that must be applied to the cell to force it to react
Electrolytic cells
bull In diagramsndashcell with ammeter rarr voltaic
ndashcell with battery rarr electrolytic
anode (+)cathode (-)
ElectroplatingElectrolysis
Electroplating is the process of
ElectroplatingElectrolysis
1) Current = rate of flow of charge
2) I = q t
3) 1 e- = 16 x 10-19 C
4) 1 mol e- = 602 x 1023 e- x 16 x 10-19 C
= 965 x 104 C
current (A) charge (C)
time (s)
Q = 965 x 104 Cmol (Faradayrsquos constant)
ElectroplatingElectrolysis
5) To calculate number of mol of electrons
ne = q Q
ne = q Q
ne = 18000 C 965 x 104 Cmol
ne = 01865 mol of e-
250 A of current runs for 20 hours through a silver nitrate solution Find the mass of silver produced
q = Itq = (250 A) x (7200 s)q = 18 000 C
Ag+(aq) + 1e- rarr Ag(s)
01865mol 01865 mol
m = n x M
m = 01865 mol x 10787 gmol
m = 20 g
Short cut
m = I t M
m = (250 A) (7200 s) (10787 gmol) (965 x 104 Cmol) (1)
m = 20 g
Q V
I rarr current (Amps)
t rarr time (s)
M rarr molar mass (gmol)
Q rarr molar charge (Cmol)
V rarr voltage
m = I t M
100 g = (150 A) t (10787 gmol) (965 x 104 Cmol) (100)
t = 59639589 s = 166 h
Q V
WS 15-33
A person wants to plate an ornament with 100 g of silver The ornament is placed in a salt of silver and a 15 A current is placed through the solution The voltage is 100 How long will the plating process take
Copper plating a key
- +
power
e-
inert anodecathode
Cu2+
NO3-
Molten or Aqueous
Aqueous
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(aq)
ndash Cl- (aq)
ndash H2O(l)
Molten
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(l)
ndash Cl- (l)
bull Calculate the net potentials and write the reactions that occur whenndash NaI(s) is electrolyzed
ndash A solution of NaI(aq) is electrolyzed
NaI(s) is electrolyzed
Na+(l) I-
(l)
Na+(l) + e- rarr Na(s) -271
2I-(l) rarr I2(s) + 2e- -054
2Na+(l) + 2I-
(l) rarr 2Na(s) + I2(s) -325
OA RA
A solution of NaI(aq) is electrolyzed
H2O(l) Na+(aq) I-
(aq)
2H2O(l) + 2e- rarr H2(g)+ 2OH-(aq) -083
2I-(aq) rarr I2(s) + 2e- -
054
2H2O(l) + 2I-(aq) rarr H2(g)+ 2OH-
(aq) + I2(s) -137
OA RA
Electrolysis of Brine
Na+
Cl-
H2O OA
RA
2H2O(l) + 2Cl-(aq) rarr H2(g) + 2OH-(aq) + Cl2(g)
Note
bull The Cl- ion is a stronger reducing agent than H2O during electrolysis of brine even though the table indicates that it is not
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
Electrolytic cells
bull The Eo value for an electrolytic cell is negative
bull The Eo value is the minimum voltage that must be applied to the cell to force it to react
Electrolytic cells
bull In diagramsndashcell with ammeter rarr voltaic
ndashcell with battery rarr electrolytic
anode (+)cathode (-)
ElectroplatingElectrolysis
Electroplating is the process of
ElectroplatingElectrolysis
1) Current = rate of flow of charge
2) I = q t
3) 1 e- = 16 x 10-19 C
4) 1 mol e- = 602 x 1023 e- x 16 x 10-19 C
= 965 x 104 C
current (A) charge (C)
time (s)
Q = 965 x 104 Cmol (Faradayrsquos constant)
ElectroplatingElectrolysis
5) To calculate number of mol of electrons
ne = q Q
ne = q Q
ne = 18000 C 965 x 104 Cmol
ne = 01865 mol of e-
250 A of current runs for 20 hours through a silver nitrate solution Find the mass of silver produced
q = Itq = (250 A) x (7200 s)q = 18 000 C
Ag+(aq) + 1e- rarr Ag(s)
01865mol 01865 mol
m = n x M
m = 01865 mol x 10787 gmol
m = 20 g
Short cut
m = I t M
m = (250 A) (7200 s) (10787 gmol) (965 x 104 Cmol) (1)
m = 20 g
Q V
I rarr current (Amps)
t rarr time (s)
M rarr molar mass (gmol)
Q rarr molar charge (Cmol)
V rarr voltage
m = I t M
100 g = (150 A) t (10787 gmol) (965 x 104 Cmol) (100)
t = 59639589 s = 166 h
Q V
WS 15-33
A person wants to plate an ornament with 100 g of silver The ornament is placed in a salt of silver and a 15 A current is placed through the solution The voltage is 100 How long will the plating process take
Copper plating a key
- +
power
e-
inert anodecathode
Cu2+
NO3-
Molten or Aqueous
Aqueous
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(aq)
ndash Cl- (aq)
ndash H2O(l)
Molten
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(l)
ndash Cl- (l)
bull Calculate the net potentials and write the reactions that occur whenndash NaI(s) is electrolyzed
ndash A solution of NaI(aq) is electrolyzed
NaI(s) is electrolyzed
Na+(l) I-
(l)
Na+(l) + e- rarr Na(s) -271
2I-(l) rarr I2(s) + 2e- -054
2Na+(l) + 2I-
(l) rarr 2Na(s) + I2(s) -325
OA RA
A solution of NaI(aq) is electrolyzed
H2O(l) Na+(aq) I-
(aq)
2H2O(l) + 2e- rarr H2(g)+ 2OH-(aq) -083
2I-(aq) rarr I2(s) + 2e- -
054
2H2O(l) + 2I-(aq) rarr H2(g)+ 2OH-
(aq) + I2(s) -137
OA RA
Electrolysis of Brine
Na+
Cl-
H2O OA
RA
2H2O(l) + 2Cl-(aq) rarr H2(g) + 2OH-(aq) + Cl2(g)
Note
bull The Cl- ion is a stronger reducing agent than H2O during electrolysis of brine even though the table indicates that it is not
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
Electrolytic cells
bull In diagramsndashcell with ammeter rarr voltaic
ndashcell with battery rarr electrolytic
anode (+)cathode (-)
ElectroplatingElectrolysis
Electroplating is the process of
ElectroplatingElectrolysis
1) Current = rate of flow of charge
2) I = q t
3) 1 e- = 16 x 10-19 C
4) 1 mol e- = 602 x 1023 e- x 16 x 10-19 C
= 965 x 104 C
current (A) charge (C)
time (s)
Q = 965 x 104 Cmol (Faradayrsquos constant)
ElectroplatingElectrolysis
5) To calculate number of mol of electrons
ne = q Q
ne = q Q
ne = 18000 C 965 x 104 Cmol
ne = 01865 mol of e-
250 A of current runs for 20 hours through a silver nitrate solution Find the mass of silver produced
q = Itq = (250 A) x (7200 s)q = 18 000 C
Ag+(aq) + 1e- rarr Ag(s)
01865mol 01865 mol
m = n x M
m = 01865 mol x 10787 gmol
m = 20 g
Short cut
m = I t M
m = (250 A) (7200 s) (10787 gmol) (965 x 104 Cmol) (1)
m = 20 g
Q V
I rarr current (Amps)
t rarr time (s)
M rarr molar mass (gmol)
Q rarr molar charge (Cmol)
V rarr voltage
m = I t M
100 g = (150 A) t (10787 gmol) (965 x 104 Cmol) (100)
t = 59639589 s = 166 h
Q V
WS 15-33
A person wants to plate an ornament with 100 g of silver The ornament is placed in a salt of silver and a 15 A current is placed through the solution The voltage is 100 How long will the plating process take
Copper plating a key
- +
power
e-
inert anodecathode
Cu2+
NO3-
Molten or Aqueous
Aqueous
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(aq)
ndash Cl- (aq)
ndash H2O(l)
Molten
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(l)
ndash Cl- (l)
bull Calculate the net potentials and write the reactions that occur whenndash NaI(s) is electrolyzed
ndash A solution of NaI(aq) is electrolyzed
NaI(s) is electrolyzed
Na+(l) I-
(l)
Na+(l) + e- rarr Na(s) -271
2I-(l) rarr I2(s) + 2e- -054
2Na+(l) + 2I-
(l) rarr 2Na(s) + I2(s) -325
OA RA
A solution of NaI(aq) is electrolyzed
H2O(l) Na+(aq) I-
(aq)
2H2O(l) + 2e- rarr H2(g)+ 2OH-(aq) -083
2I-(aq) rarr I2(s) + 2e- -
054
2H2O(l) + 2I-(aq) rarr H2(g)+ 2OH-
(aq) + I2(s) -137
OA RA
Electrolysis of Brine
Na+
Cl-
H2O OA
RA
2H2O(l) + 2Cl-(aq) rarr H2(g) + 2OH-(aq) + Cl2(g)
Note
bull The Cl- ion is a stronger reducing agent than H2O during electrolysis of brine even though the table indicates that it is not
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
ElectroplatingElectrolysis
Electroplating is the process of
ElectroplatingElectrolysis
1) Current = rate of flow of charge
2) I = q t
3) 1 e- = 16 x 10-19 C
4) 1 mol e- = 602 x 1023 e- x 16 x 10-19 C
= 965 x 104 C
current (A) charge (C)
time (s)
Q = 965 x 104 Cmol (Faradayrsquos constant)
ElectroplatingElectrolysis
5) To calculate number of mol of electrons
ne = q Q
ne = q Q
ne = 18000 C 965 x 104 Cmol
ne = 01865 mol of e-
250 A of current runs for 20 hours through a silver nitrate solution Find the mass of silver produced
q = Itq = (250 A) x (7200 s)q = 18 000 C
Ag+(aq) + 1e- rarr Ag(s)
01865mol 01865 mol
m = n x M
m = 01865 mol x 10787 gmol
m = 20 g
Short cut
m = I t M
m = (250 A) (7200 s) (10787 gmol) (965 x 104 Cmol) (1)
m = 20 g
Q V
I rarr current (Amps)
t rarr time (s)
M rarr molar mass (gmol)
Q rarr molar charge (Cmol)
V rarr voltage
m = I t M
100 g = (150 A) t (10787 gmol) (965 x 104 Cmol) (100)
t = 59639589 s = 166 h
Q V
WS 15-33
A person wants to plate an ornament with 100 g of silver The ornament is placed in a salt of silver and a 15 A current is placed through the solution The voltage is 100 How long will the plating process take
Copper plating a key
- +
power
e-
inert anodecathode
Cu2+
NO3-
Molten or Aqueous
Aqueous
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(aq)
ndash Cl- (aq)
ndash H2O(l)
Molten
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(l)
ndash Cl- (l)
bull Calculate the net potentials and write the reactions that occur whenndash NaI(s) is electrolyzed
ndash A solution of NaI(aq) is electrolyzed
NaI(s) is electrolyzed
Na+(l) I-
(l)
Na+(l) + e- rarr Na(s) -271
2I-(l) rarr I2(s) + 2e- -054
2Na+(l) + 2I-
(l) rarr 2Na(s) + I2(s) -325
OA RA
A solution of NaI(aq) is electrolyzed
H2O(l) Na+(aq) I-
(aq)
2H2O(l) + 2e- rarr H2(g)+ 2OH-(aq) -083
2I-(aq) rarr I2(s) + 2e- -
054
2H2O(l) + 2I-(aq) rarr H2(g)+ 2OH-
(aq) + I2(s) -137
OA RA
Electrolysis of Brine
Na+
Cl-
H2O OA
RA
2H2O(l) + 2Cl-(aq) rarr H2(g) + 2OH-(aq) + Cl2(g)
Note
bull The Cl- ion is a stronger reducing agent than H2O during electrolysis of brine even though the table indicates that it is not
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
ElectroplatingElectrolysis
1) Current = rate of flow of charge
2) I = q t
3) 1 e- = 16 x 10-19 C
4) 1 mol e- = 602 x 1023 e- x 16 x 10-19 C
= 965 x 104 C
current (A) charge (C)
time (s)
Q = 965 x 104 Cmol (Faradayrsquos constant)
ElectroplatingElectrolysis
5) To calculate number of mol of electrons
ne = q Q
ne = q Q
ne = 18000 C 965 x 104 Cmol
ne = 01865 mol of e-
250 A of current runs for 20 hours through a silver nitrate solution Find the mass of silver produced
q = Itq = (250 A) x (7200 s)q = 18 000 C
Ag+(aq) + 1e- rarr Ag(s)
01865mol 01865 mol
m = n x M
m = 01865 mol x 10787 gmol
m = 20 g
Short cut
m = I t M
m = (250 A) (7200 s) (10787 gmol) (965 x 104 Cmol) (1)
m = 20 g
Q V
I rarr current (Amps)
t rarr time (s)
M rarr molar mass (gmol)
Q rarr molar charge (Cmol)
V rarr voltage
m = I t M
100 g = (150 A) t (10787 gmol) (965 x 104 Cmol) (100)
t = 59639589 s = 166 h
Q V
WS 15-33
A person wants to plate an ornament with 100 g of silver The ornament is placed in a salt of silver and a 15 A current is placed through the solution The voltage is 100 How long will the plating process take
Copper plating a key
- +
power
e-
inert anodecathode
Cu2+
NO3-
Molten or Aqueous
Aqueous
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(aq)
ndash Cl- (aq)
ndash H2O(l)
Molten
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(l)
ndash Cl- (l)
bull Calculate the net potentials and write the reactions that occur whenndash NaI(s) is electrolyzed
ndash A solution of NaI(aq) is electrolyzed
NaI(s) is electrolyzed
Na+(l) I-
(l)
Na+(l) + e- rarr Na(s) -271
2I-(l) rarr I2(s) + 2e- -054
2Na+(l) + 2I-
(l) rarr 2Na(s) + I2(s) -325
OA RA
A solution of NaI(aq) is electrolyzed
H2O(l) Na+(aq) I-
(aq)
2H2O(l) + 2e- rarr H2(g)+ 2OH-(aq) -083
2I-(aq) rarr I2(s) + 2e- -
054
2H2O(l) + 2I-(aq) rarr H2(g)+ 2OH-
(aq) + I2(s) -137
OA RA
Electrolysis of Brine
Na+
Cl-
H2O OA
RA
2H2O(l) + 2Cl-(aq) rarr H2(g) + 2OH-(aq) + Cl2(g)
Note
bull The Cl- ion is a stronger reducing agent than H2O during electrolysis of brine even though the table indicates that it is not
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
ElectroplatingElectrolysis
5) To calculate number of mol of electrons
ne = q Q
ne = q Q
ne = 18000 C 965 x 104 Cmol
ne = 01865 mol of e-
250 A of current runs for 20 hours through a silver nitrate solution Find the mass of silver produced
q = Itq = (250 A) x (7200 s)q = 18 000 C
Ag+(aq) + 1e- rarr Ag(s)
01865mol 01865 mol
m = n x M
m = 01865 mol x 10787 gmol
m = 20 g
Short cut
m = I t M
m = (250 A) (7200 s) (10787 gmol) (965 x 104 Cmol) (1)
m = 20 g
Q V
I rarr current (Amps)
t rarr time (s)
M rarr molar mass (gmol)
Q rarr molar charge (Cmol)
V rarr voltage
m = I t M
100 g = (150 A) t (10787 gmol) (965 x 104 Cmol) (100)
t = 59639589 s = 166 h
Q V
WS 15-33
A person wants to plate an ornament with 100 g of silver The ornament is placed in a salt of silver and a 15 A current is placed through the solution The voltage is 100 How long will the plating process take
Copper plating a key
- +
power
e-
inert anodecathode
Cu2+
NO3-
Molten or Aqueous
Aqueous
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(aq)
ndash Cl- (aq)
ndash H2O(l)
Molten
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(l)
ndash Cl- (l)
bull Calculate the net potentials and write the reactions that occur whenndash NaI(s) is electrolyzed
ndash A solution of NaI(aq) is electrolyzed
NaI(s) is electrolyzed
Na+(l) I-
(l)
Na+(l) + e- rarr Na(s) -271
2I-(l) rarr I2(s) + 2e- -054
2Na+(l) + 2I-
(l) rarr 2Na(s) + I2(s) -325
OA RA
A solution of NaI(aq) is electrolyzed
H2O(l) Na+(aq) I-
(aq)
2H2O(l) + 2e- rarr H2(g)+ 2OH-(aq) -083
2I-(aq) rarr I2(s) + 2e- -
054
2H2O(l) + 2I-(aq) rarr H2(g)+ 2OH-
(aq) + I2(s) -137
OA RA
Electrolysis of Brine
Na+
Cl-
H2O OA
RA
2H2O(l) + 2Cl-(aq) rarr H2(g) + 2OH-(aq) + Cl2(g)
Note
bull The Cl- ion is a stronger reducing agent than H2O during electrolysis of brine even though the table indicates that it is not
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
ne = q Q
ne = 18000 C 965 x 104 Cmol
ne = 01865 mol of e-
250 A of current runs for 20 hours through a silver nitrate solution Find the mass of silver produced
q = Itq = (250 A) x (7200 s)q = 18 000 C
Ag+(aq) + 1e- rarr Ag(s)
01865mol 01865 mol
m = n x M
m = 01865 mol x 10787 gmol
m = 20 g
Short cut
m = I t M
m = (250 A) (7200 s) (10787 gmol) (965 x 104 Cmol) (1)
m = 20 g
Q V
I rarr current (Amps)
t rarr time (s)
M rarr molar mass (gmol)
Q rarr molar charge (Cmol)
V rarr voltage
m = I t M
100 g = (150 A) t (10787 gmol) (965 x 104 Cmol) (100)
t = 59639589 s = 166 h
Q V
WS 15-33
A person wants to plate an ornament with 100 g of silver The ornament is placed in a salt of silver and a 15 A current is placed through the solution The voltage is 100 How long will the plating process take
Copper plating a key
- +
power
e-
inert anodecathode
Cu2+
NO3-
Molten or Aqueous
Aqueous
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(aq)
ndash Cl- (aq)
ndash H2O(l)
Molten
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(l)
ndash Cl- (l)
bull Calculate the net potentials and write the reactions that occur whenndash NaI(s) is electrolyzed
ndash A solution of NaI(aq) is electrolyzed
NaI(s) is electrolyzed
Na+(l) I-
(l)
Na+(l) + e- rarr Na(s) -271
2I-(l) rarr I2(s) + 2e- -054
2Na+(l) + 2I-
(l) rarr 2Na(s) + I2(s) -325
OA RA
A solution of NaI(aq) is electrolyzed
H2O(l) Na+(aq) I-
(aq)
2H2O(l) + 2e- rarr H2(g)+ 2OH-(aq) -083
2I-(aq) rarr I2(s) + 2e- -
054
2H2O(l) + 2I-(aq) rarr H2(g)+ 2OH-
(aq) + I2(s) -137
OA RA
Electrolysis of Brine
Na+
Cl-
H2O OA
RA
2H2O(l) + 2Cl-(aq) rarr H2(g) + 2OH-(aq) + Cl2(g)
Note
bull The Cl- ion is a stronger reducing agent than H2O during electrolysis of brine even though the table indicates that it is not
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
Short cut
m = I t M
m = (250 A) (7200 s) (10787 gmol) (965 x 104 Cmol) (1)
m = 20 g
Q V
I rarr current (Amps)
t rarr time (s)
M rarr molar mass (gmol)
Q rarr molar charge (Cmol)
V rarr voltage
m = I t M
100 g = (150 A) t (10787 gmol) (965 x 104 Cmol) (100)
t = 59639589 s = 166 h
Q V
WS 15-33
A person wants to plate an ornament with 100 g of silver The ornament is placed in a salt of silver and a 15 A current is placed through the solution The voltage is 100 How long will the plating process take
Copper plating a key
- +
power
e-
inert anodecathode
Cu2+
NO3-
Molten or Aqueous
Aqueous
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(aq)
ndash Cl- (aq)
ndash H2O(l)
Molten
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(l)
ndash Cl- (l)
bull Calculate the net potentials and write the reactions that occur whenndash NaI(s) is electrolyzed
ndash A solution of NaI(aq) is electrolyzed
NaI(s) is electrolyzed
Na+(l) I-
(l)
Na+(l) + e- rarr Na(s) -271
2I-(l) rarr I2(s) + 2e- -054
2Na+(l) + 2I-
(l) rarr 2Na(s) + I2(s) -325
OA RA
A solution of NaI(aq) is electrolyzed
H2O(l) Na+(aq) I-
(aq)
2H2O(l) + 2e- rarr H2(g)+ 2OH-(aq) -083
2I-(aq) rarr I2(s) + 2e- -
054
2H2O(l) + 2I-(aq) rarr H2(g)+ 2OH-
(aq) + I2(s) -137
OA RA
Electrolysis of Brine
Na+
Cl-
H2O OA
RA
2H2O(l) + 2Cl-(aq) rarr H2(g) + 2OH-(aq) + Cl2(g)
Note
bull The Cl- ion is a stronger reducing agent than H2O during electrolysis of brine even though the table indicates that it is not
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
m = I t M
100 g = (150 A) t (10787 gmol) (965 x 104 Cmol) (100)
t = 59639589 s = 166 h
Q V
WS 15-33
A person wants to plate an ornament with 100 g of silver The ornament is placed in a salt of silver and a 15 A current is placed through the solution The voltage is 100 How long will the plating process take
Copper plating a key
- +
power
e-
inert anodecathode
Cu2+
NO3-
Molten or Aqueous
Aqueous
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(aq)
ndash Cl- (aq)
ndash H2O(l)
Molten
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(l)
ndash Cl- (l)
bull Calculate the net potentials and write the reactions that occur whenndash NaI(s) is electrolyzed
ndash A solution of NaI(aq) is electrolyzed
NaI(s) is electrolyzed
Na+(l) I-
(l)
Na+(l) + e- rarr Na(s) -271
2I-(l) rarr I2(s) + 2e- -054
2Na+(l) + 2I-
(l) rarr 2Na(s) + I2(s) -325
OA RA
A solution of NaI(aq) is electrolyzed
H2O(l) Na+(aq) I-
(aq)
2H2O(l) + 2e- rarr H2(g)+ 2OH-(aq) -083
2I-(aq) rarr I2(s) + 2e- -
054
2H2O(l) + 2I-(aq) rarr H2(g)+ 2OH-
(aq) + I2(s) -137
OA RA
Electrolysis of Brine
Na+
Cl-
H2O OA
RA
2H2O(l) + 2Cl-(aq) rarr H2(g) + 2OH-(aq) + Cl2(g)
Note
bull The Cl- ion is a stronger reducing agent than H2O during electrolysis of brine even though the table indicates that it is not
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
Copper plating a key
- +
power
e-
inert anodecathode
Cu2+
NO3-
Molten or Aqueous
Aqueous
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(aq)
ndash Cl- (aq)
ndash H2O(l)
Molten
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(l)
ndash Cl- (l)
bull Calculate the net potentials and write the reactions that occur whenndash NaI(s) is electrolyzed
ndash A solution of NaI(aq) is electrolyzed
NaI(s) is electrolyzed
Na+(l) I-
(l)
Na+(l) + e- rarr Na(s) -271
2I-(l) rarr I2(s) + 2e- -054
2Na+(l) + 2I-
(l) rarr 2Na(s) + I2(s) -325
OA RA
A solution of NaI(aq) is electrolyzed
H2O(l) Na+(aq) I-
(aq)
2H2O(l) + 2e- rarr H2(g)+ 2OH-(aq) -083
2I-(aq) rarr I2(s) + 2e- -
054
2H2O(l) + 2I-(aq) rarr H2(g)+ 2OH-
(aq) + I2(s) -137
OA RA
Electrolysis of Brine
Na+
Cl-
H2O OA
RA
2H2O(l) + 2Cl-(aq) rarr H2(g) + 2OH-(aq) + Cl2(g)
Note
bull The Cl- ion is a stronger reducing agent than H2O during electrolysis of brine even though the table indicates that it is not
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
Molten or Aqueous
Aqueous
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(aq)
ndash Cl- (aq)
ndash H2O(l)
Molten
bull NaCl rarr Na+ + Cl-
bull Species present
ndash Na+(l)
ndash Cl- (l)
bull Calculate the net potentials and write the reactions that occur whenndash NaI(s) is electrolyzed
ndash A solution of NaI(aq) is electrolyzed
NaI(s) is electrolyzed
Na+(l) I-
(l)
Na+(l) + e- rarr Na(s) -271
2I-(l) rarr I2(s) + 2e- -054
2Na+(l) + 2I-
(l) rarr 2Na(s) + I2(s) -325
OA RA
A solution of NaI(aq) is electrolyzed
H2O(l) Na+(aq) I-
(aq)
2H2O(l) + 2e- rarr H2(g)+ 2OH-(aq) -083
2I-(aq) rarr I2(s) + 2e- -
054
2H2O(l) + 2I-(aq) rarr H2(g)+ 2OH-
(aq) + I2(s) -137
OA RA
Electrolysis of Brine
Na+
Cl-
H2O OA
RA
2H2O(l) + 2Cl-(aq) rarr H2(g) + 2OH-(aq) + Cl2(g)
Note
bull The Cl- ion is a stronger reducing agent than H2O during electrolysis of brine even though the table indicates that it is not
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
bull Calculate the net potentials and write the reactions that occur whenndash NaI(s) is electrolyzed
ndash A solution of NaI(aq) is electrolyzed
NaI(s) is electrolyzed
Na+(l) I-
(l)
Na+(l) + e- rarr Na(s) -271
2I-(l) rarr I2(s) + 2e- -054
2Na+(l) + 2I-
(l) rarr 2Na(s) + I2(s) -325
OA RA
A solution of NaI(aq) is electrolyzed
H2O(l) Na+(aq) I-
(aq)
2H2O(l) + 2e- rarr H2(g)+ 2OH-(aq) -083
2I-(aq) rarr I2(s) + 2e- -
054
2H2O(l) + 2I-(aq) rarr H2(g)+ 2OH-
(aq) + I2(s) -137
OA RA
Electrolysis of Brine
Na+
Cl-
H2O OA
RA
2H2O(l) + 2Cl-(aq) rarr H2(g) + 2OH-(aq) + Cl2(g)
Note
bull The Cl- ion is a stronger reducing agent than H2O during electrolysis of brine even though the table indicates that it is not
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
NaI(s) is electrolyzed
Na+(l) I-
(l)
Na+(l) + e- rarr Na(s) -271
2I-(l) rarr I2(s) + 2e- -054
2Na+(l) + 2I-
(l) rarr 2Na(s) + I2(s) -325
OA RA
A solution of NaI(aq) is electrolyzed
H2O(l) Na+(aq) I-
(aq)
2H2O(l) + 2e- rarr H2(g)+ 2OH-(aq) -083
2I-(aq) rarr I2(s) + 2e- -
054
2H2O(l) + 2I-(aq) rarr H2(g)+ 2OH-
(aq) + I2(s) -137
OA RA
Electrolysis of Brine
Na+
Cl-
H2O OA
RA
2H2O(l) + 2Cl-(aq) rarr H2(g) + 2OH-(aq) + Cl2(g)
Note
bull The Cl- ion is a stronger reducing agent than H2O during electrolysis of brine even though the table indicates that it is not
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
A solution of NaI(aq) is electrolyzed
H2O(l) Na+(aq) I-
(aq)
2H2O(l) + 2e- rarr H2(g)+ 2OH-(aq) -083
2I-(aq) rarr I2(s) + 2e- -
054
2H2O(l) + 2I-(aq) rarr H2(g)+ 2OH-
(aq) + I2(s) -137
OA RA
Electrolysis of Brine
Na+
Cl-
H2O OA
RA
2H2O(l) + 2Cl-(aq) rarr H2(g) + 2OH-(aq) + Cl2(g)
Note
bull The Cl- ion is a stronger reducing agent than H2O during electrolysis of brine even though the table indicates that it is not
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
Electrolysis of Brine
Na+
Cl-
H2O OA
RA
2H2O(l) + 2Cl-(aq) rarr H2(g) + 2OH-(aq) + Cl2(g)
Note
bull The Cl- ion is a stronger reducing agent than H2O during electrolysis of brine even though the table indicates that it is not
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
Note
bull The Cl- ion is a stronger reducing agent than H2O during electrolysis of brine even though the table indicates that it is not
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
Electrolysis of molten NaCl
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
Changing Concentration
bull A change in concentration around the cathode or anode will change the value of Eo for half cells
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
Cu(s) rarr Cu2+(aq) + 2e-
bull An increase in concentration of copper ions will cause a shift to the left making less products
bull Increase in concentration around anode causes a decrease in Eo
Cu(s)
Cu2+
Anode
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
Cu2+(aq) + 2e- rarr Cu(s)
bull An increase in concentration of copper ions will cause a shift to the right making more products
bull Increase in concentration around cathode causes a increase in Eo
Cu(s)
Cu2+
Cathode
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
bull Since E(Fe2+Fe) lt E(O2H2O) iron can be oxidized by oxygen
bull Cathodendash O2(g) + 4 H+
(aq) + 4 e- 2 H2O(l)
bull Anode ndash Fe(s) Fe2+
(aq) + 2 e-
bull Fe2+ initially formed ndash further oxidized to Fe3+ which forms rust
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
Rusting (Corrosion) of Iron
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
Preventing the Corrosion of Iron
bull Corrosion can be prevented by coating the iron with paint or another metal
bull Galvanized iron - Fe is coated with Znbull Zn protects the iron (Zn - anode and Fe -
the cathode)
Zn2+(aq) +2e- Zn(s) E(Zn2+Zn) = -076 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
Preventing the Corrosion of Iron
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
Preventing the Corrosion of Iron
To protect underground pipelines a sacrificial anode is added
The water pipe - turned into the cathode and an active metal is used as the sacrificial anode
Mg is used as the sacrificial anode
Mg2+(aq) +2e- Mg(s) E(Mg2+Mg) = -237 V
Fe2+(aq) + 2e- Fe(s) E(Fe2+Fe) = -044 V
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
Corrosion Prevention
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
Living Battery
bull The eel generates electric charge in a battery of biological electrochemical cells each cell providing about 015 V and an overall potential difference of ~ 700 V Note that the eels head is the cathode(+) and its tail the anode(-) The cells extend over the length of the eel
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
Types of Batteries
Batteriesndash device that converts chemical energy into electricity
Primary Cellsndash non-reversible electrochemical cellndash non-rechargeable cell
Secondary Cellsndash reversible electrochemical cellndash rechargeable cell
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
Types of Batteries
Primary Cells
dry cell amp alkaline cell 15 vcell
mercury cell 134 vcell
fuel cell 123vcell
Secondary Cells
lead-acid (automobile battery) 2 vcell
NiCad 125 vcell
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
Lead-Acid Battery
bull A 12 V car battery - 6 cathodeanode pairs each producing 2 V
Cathode PbO2 on a metal grid in sulfuric acid
PbO2(s) + SO42-
(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(l)
Anode Pb
Pb(s) + SO42-
(aq) PbSO4(s) + 2e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
A Picture of a Car Battery
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
An Alkaline Battery
bull Anode Zn cap
Zn(s) Zn2+(aq) + 2e-
bull Cathode MnO2 NH4Cl and carbon paste
2 NH4+
(aq) + 2 MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)
bull Graphite rod in the center - inert cathode
bull Alkaline battery NH4Cl is replaced with KOH
bull Anode Zn powder mixed in a gel
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
ldquoDryrdquo Cell
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
The Alkaline Battery
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
ldquoNewrdquo Super Iron Battery
BaFeO4 + 32 Zn rarr 12 Fe2O3 + 12 ZnO + BaZnO2
Environmentally friendlier than MnO2 containing batteries
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-
Fuel Cells
bull Direct production of electricity from fuels occurs in a fuel cell
bull H2- O2 fuel cell was the primary source of electricity on Apollo moon flights
bull Cathode reduction of oxygen
2 H2O(l) + O2(g) + 4 e- 4 OH-(aq)
bull Anode
2 H2(g) + 4 OH-(aq) 4 H2O(l) + 4 e-