Balance Redox Rxns:
Fe(OH)3 +
[Cr(OH)4]-1
Fe(OH)2 + CrO4-2
AP CHM HW•Read: Chapter 18
Review the Multiple-Choice
Section of the Midterm.
Electro-chemistry
Metallic Conduction
•The flow of electrons through a metal
Ionic Conduction•The movement of ions (electrolytes) through a solution
•Electrolytic Conduct.
Electrode•The surface or point in which oxidation or reduction takes place
Anode•The electrode where oxidation
takes place
•An Ox (-)
Cathode•The electrode where reduction
takes place
•Red Cat (+)
Voltaic or Galvanic Cell
Electrochemical Cell in which:
a spontaneous oxidation-reduction reaction produces electrical energy
Half-Cell•A cell where only
oxidation or only reduction takes
place
•An electrochemical cell must have two
half-cells connected by a salt
bridge
•A half-cell will not work by itself
•Both half-cells are required
Salt Bridge
1) Allows electrical contact between the two half-cells
2) Prevents mixing of the two half-cell solutions
3) Allows ions to flow maintaining
electrical neutrality
Determining the Redox Rxn & Voltage of an
Electrochemical Cell
Identify all molecules & ions
(reactants) that exist in the
electrolytic cell
1) Determine all possible half-reactions that
could occur in the system
2 ) Look up each half-rxn from
the Std. Redox Tables
3) Record each half-rxn & its
standard voltage
4) Save the oxidation half-rxn that has the highest voltage
5) Save the reduction half-rxn that has the highest voltage
6) Balance the electrons
between the two half-rxns
7) Add the two half-rxns to
obtain the full electrochemical
reaction
7) Add the voltage of each half-rxn to
obtain the std. voltage required
Determine Eo
Zn(s) + 2 Ag+1(aq)
2 Ag(s) + Zn+2(aq)
AP CHM HW•Read: Chapter 18
•Problems: 7 & 15a
•Page: 526
REDOX Shorthand•Zn|Zn+2||Ag+1|Ag ox
red
•Zn||Zn|Zn+2||Ag+1|Ag||Pt an ox red cat
Drill: Determine Shorthand Rxn & voltage when Cu+1 is reacts with solid
potassium
Voltaic Cell Problems
Determine all when a cell with a Cu electrode in CuCl2(aq) is connected
to a cell with a Zn
electrode in ZnBr2(aq)
Determine all when a cell with a Fe electrode in FeCl3(aq) is connected
to a cell with a Mn
electrode in MnCl2(aq)
Determine all when a cell with a Mg electrode in MgCl2(aq) is connected
to a cell with a Au
electrode in AuCl3(aq)
Drill: What is the best
reducing agent on the chart?
Electrolysis•Using electricity to force an, oh fooey, non-spontaneous
electrochemical rxn
Electrolytic Cell
•Chemical cell where electrolysis is being performed
How to determine the Redox Rxn &
voltage of an Electrolytic Cell
Identify all molecules & ions
(reactants) that exist in the
electrolytic cell
1) Determine all possible half-reactions that
could occur in the system
2 ) Look up each half-rxn from
the Std. Redox Tables
3) Record each half-rxn & its
standard voltage
4) Save the oxidation half-rxn that has the highest voltage
5) Save the reduction half-rxn that has the highest voltage
6) Balance the electrons
between the two half-rxns
7) Add the two half-rxns to
obtain the full electrochemical
reaction
7) Add the voltage of each half-rxn to
obtain the std. voltage required
• Determine the rxn that takes place when 1.5 V is passed through two
Pt electrodes in a solution containing
MgI2(aq) & ZnCl2(aq)
AP CHM HW•Read: Chapter 18
•Problems: 23
•Page: 527
• Determine the rxn that takes place when
2.5 V is passed through two Pt electrode in a
solution of NaCl(aq)
Determine the rxn that takes place when
electricity is passed through two Pt
electrode in molten
NaCl
Drill: Determine the rxn that takes place when
electricity is passed through two Pt
electrodes in ZnCl2(aq)
A car battery has lead & lead(IV)oxide electrodes in
an acidified aqueous lead(II)sulfate solution.
Using the book, determine the voltage that can be
produced.
Relating Equations
Go = Ho - TSo
Go = -RTlnKeq
Go = -nFEo
Determine rxn, Eo, Go, & Keq for a
voltaic cell with half-cells containing Ni(s)
in NiCl2(aq) & Sn(s)
in SnCl2(aq).
Nernst Equation
E = Eo - (RT/nF)lnQ
for non-standard conditions
• Determine the voltage of a cell with a silver
electrode in 1.0 M AgNO3 & an iron
electrode in 0.10 M
FeCl2 at 27oC
• Determine the voltage of a cell with a silver
electrode in 1.0 M AgNO3 & a zinc
electrode in 0.010 M
ZnCl2 at 27oC
• Drill: Determine the rxns that take place when 9.65 mA is passed for 2.5 Hrs through two Pt electrodes in a solution containing
MnBr2(aq) & CuF2(aq)
• Determine the voltage of a cell with a copper
electrode in 0.10 M CuI & a zinc electrode
in 1.0 M ZnCl2 at 27oC
• Determine the voltage of a cell with a silver electrode in 0.10 M
AgNO3 & a zinc electrode in 1.0 M
ZnCl2 at 27oC
AP CHM HW•Read: Chapter 18
•Problems: 41
•Page: 528
The test on electrochemistry
will be on ____day.
Electroplating & Electro-purifying
Electrolysis• During electrolysis, oxidation
& degradation would occur at the anode while reduction & electroplating would occur at the cathode
Current Formula• Current = charge/unit time
• Amps = coul/sec
• Amount (mass, volume, moles, etc) can be
determined from the charge
Calculate the mass of copper plated onto the cathode when a 9.65
mAmp current is applied to a solution of CuSO4
for 5.0 minutes.
Calculate the years required to plate 216 kg
of silver onto the cathode when a 96.5
mAmp current is applied to a solution of AgNO3
Drill: Calculate the current required to purify 510 kg of
aluminum oxide in 5.0 hours
Current, Mass, Time Formula:
nFm = MWIt
Check HW
Test Tuesday
Balance the Rxn
KMnO4 + HCl
MnO2 + KClO2
Calculate the time required to electroplate 19.7 mg of gold onto a
plate by passing 965 mA current through a
solution of Au(NO3)3
• Determine the voltage of a cell with a silver
electrode in 5.0 M AgNO3 & an zinc
electrode in 0.25 M
ZnCl2 at 27oC
Determine the rxn that takes place when 1.0 V is passed through
two Pt electrodes in a soln containing NaI(aq)
& CoCl2(aq).
Calculate the time required to gold plate a 2.0 mm
layer onto a plate(SA = 750 cm2) by passing 965 mA current through a
solution of AuCl3
(DAu = 20 g/cm3)
Calculate the time required to purify a 204 kg of ore that is 60.0 % Al2O3 by
applying a 965 kA current through molten ore sample:
Calculate the time required to purify a 32 kg of ore that
is 75.0 % Fe2O3 by applying a 9.65 kA current through molten ore sample:
A voltaic cell with a silver electrode in 0.10 M Ag+ & a zinc electrode in 1.0 M Zn+2
at 27oC is allowed to react for 5.0 mins at 9.65 A.
Calculate: Eo, E, Go, & mass increase of the cathode.
A voltaic cell with a gold electrode in 0.0010 M Au+3 &
a zinc electrode in 10.0 M Zn+2 at 27oC is allowed to react for 5.0 hrs at 9.65 A.
Calculate: Eo, E, Go, & mass increase of the cathode.