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Redox Reactions and Electrochemistry
Redox Reactions and Electrochemistry
Redox Reactions and Electrochemistry Redox Reactions (19.1) Galvanic Cells (19.2) Standard Reduction Potentials (19.3) Thermodynamics of Redox Reactions (19.4) The Effect of Concentration on Cell Emf
(19.5) Batteries (19.6) Corrosion (19.7) Electrolysis (19.8) Electrometallurgy (19.9)
General Chemistry I – Concepts Representations of matter (1.3-1.4) Formula calculations and stoichiometry (3.6-
3.9) All concepts related to redox reactions
(assigning oxidation numbers, assigning oxidation versus reduction, balancing electrons between oxidation and reduction half-reactions and oxidizing and reducing agents), molar concentration, dilutions, and solution stoichiometry (4.5-4.6)
19.1 Redox Reactions
Review: How do we assign oxidation numbers?
Figure 4.10, p 113
19.1 Redox Reactions
Review: How do we assign oxidation numbers?
Review: What is oxidation? Review: What is reduction? Review: What is an oxidizing agent? Review: What is a reducing agent? Review: What is a redox reaction? Consider the example of zinc and acid…
19.1 Redox Reactions
Balancing more complicated redox reactions:◦ Acidic solution◦ Basic solution
Half reactions and overall reactions:◦ Mass balanced◦ Charge balanced
19.1 Redox Reactions
Practice:What is the balanced (net) redox reaction for the reaction of aqueous nitrate ion with copper to form copper(II) and nitric oxide in acidic solution?- What is the oxidizing agent?- What is the reducing agent?- How many electrons are transferred?- What does this look like?
19.1 Redox Reactions
Practice:What is the balanced (net) redox reaction for the reaction of aqueous permanganate with lead to form lead(II) and manganese dioxide in basic solution?- What is the oxidizing agent?- What is the reducing agent?- How many electrons are transferred?- What does this look like?
19.2 Galvanic Cells
Review: Reaction of zinc with acid:◦ This reaction is
spontaneous.◦ What would this
look like?
Figure 4.12, p 115
19.2 Galvanic Cells
Review: Reaction of zinc with acid:◦ This reaction is
spontaneous◦ What would this
look like?◦ What is
happening with the electrons?
Figure 4.14, p 117
19.2 Galvanic Cells
Review: Reaction of zinc with copper(II):◦ This reaction is
spontaneous◦ What would this
look like?◦ What is
happening with the electrons?
Figure 4.13, p 116
19.2 Galvanic Cells
Review: Reaction of zinc with copper(II):◦ This reaction is
spontaneous.◦ What would this
look like?◦ What is
happening with the electrons?
Figure 4.14, p 117
19.2 Galvanic Cells
Review: Reaction of zinc with copper(II):◦ What would the
half reactions look like?
Figure 4.13, p 116
19.2 Galvanic Cells
The reaction of zinc with copper(II):◦ What is happening with the electrons?
How can we measure this transfer of electrons (measure the number of electrons or the potential of these electrons)?
To insert a meter (or a device to use the energy), need to separate the half-reactions
19.2 Galvanic Cells
Figure 19.1, p 665
What is a “cathode”?What is an “anode”?
What is a salt bridge? What does it do?
19.2 Galvanic Cells
What is a galvanic or voltaic cell? What is the measured potential? What is this called?
Figure 19.2, p 667
19.2 Galvanic Cells
What is “cell diagram” or “cell notation”? What is the cell diagram for this cell?
Practice:What is the cell diagram for:1. Aqueous lead ions reacting with zinc2. Aqueous copper ions reacting with lead3. Zinc metal reacting with acid
19.2 Galvanic Cells
Practice:What is the cell diagram for zinc metal reacting with acid
Figure 19.3, p 667
19.3 Standard Reduction PotentialsReview: All of these redox reactions are spontaneous: Zinc with aqueous
copper ions (standard cell potential of 1.10 V)
Lead with aqueous copper ions
Zinc with aqueous lead ions
Zinc with aqueous hydrogen ions
Figure 4.14, p 117
19.3 Standard Reduction Potentials
Zinc with aqueous copper ions (standard cell potential of 1.10 V)
Lead with aqueous copper ions Zinc with aqueous lead ions Zinc with aqueous hydrogen ions Can we measure a standard half-
reaction potential? What if we compare to a standard half-
reaction potential that is zero?
19.3 Standard Reduction Potentials
What if we compare to a standard half-reaction potential that is zero?
Zinc with aqueous hydrogen ions◦ Standard reduction potential (Eo
red) of:
◦ What is the standard oxidation potential (Eo
ox) of:
+ o22H aq 2e H g 0.0 V by definitionredE
+ o2H g 2H aq 2e ?oxE
19.3 Standard Reduction Potentials
What if we compare to a standard half-reaction potential that is zero?
What is the standard cell potential of zinc reacting with aqueous hydrogen ions
Figure 19.4, p 668
19.3 Standard Reduction Potentials
What if we compare to a standard half-reaction potential that is zero?
What is the standard reduction potential of zinc?
Figure 19.4, p 668
19.3 Standard Reduction Potentials
What if we compare to a standard half-reaction potential that is zero?
What is the standard cell potential of copper reacting with aqueous hydrogen ions
Figure 19.4, p 668
19.3 Standard Reduction Potentials
What if we compare to a standard half-reaction potential that is zero?
What is the standard reduction potential of copper?
Figure 19.4, p 668
19.3 Standard Reduction Potentials
What if we compare to a standard half-reaction potential that is zero?
What is the standard cell potential of copper reacting with aqueous zinc ions?
Figure 19.1, p 665
Table19.1, p 670
19.3 Standard Reduction Potentials
What does standard reduction potential (Eo
red) tell us? What are the rules for calculating
standard cell potential (Eo)?◦ Reversing the reaction◦ Intensive or extensive
What does standard cell potential (Eo) tell us?
19.3 Standard Reduction Potentials
Practice:What is the standard cell potential for the reactions of:
Lead with aqueous copper ions Zinc with aqueous lead ions
Will tin reduce iodine?Will silver reduce iodine?What is a stronger oxidizing agent, Au3+ or Ag+?What is a stronger reducing agent, Al or Mg?
19.4 Thermodynamics of Redox Reactions
Review: All of these redox reactions are spontaneous:
Therefore, Eo and free energy (ΔG) should be related.
2+ 2+ o
2+ 2+ o
2+ 2+ o
2+ 2+ o2
Zn s Cu aq Zn aq Cu s 1.10 V
Pb s Cu aq Pb aq Cu s 0.47 V
Zn s Pb aq Zn aq Pb s 0.61 V
Zn s 2H aq Zn aq H g 0.76 V
E
E
E
E
19.4 Thermodynamics of Redox Reactions
Figure 19.5, p 674
19.4 Thermodynamics of Redox Reactions
Review: All of these redox reactions are spontaneous:
What is the standard free energy change (ΔGo) for each of these reactions:
2+ 2+ o
2+ 2+ o
2+ 2+ o
2+ 2+ o2
Zn s Cu aq Zn aq Cu s 1.10 V
Pb s Cu aq Pb aq Cu s 0.47 V
Zn s Pb aq Zn aq Pb s 0.61 V
Zn s 2H aq Zn aq H g 0.76 V
E
E
E
E
19.4 Thermodynamics of Redox Reactions
Figure 19.5, p 674
19.4 Thermodynamics of Redox Reactions
Review: All of these redox reactions are spontaneous:
What is the equilibrium constant for each of these reactions:
2+ 2+ o
2+ 2+ o
2+ 2+ o
2+ 2+ o2
Zn s Cu aq Zn aq Cu s 1.10 V
Pb s Cu aq Pb aq Cu s 0.47 V
Zn s Pb aq Zn aq Pb s 0.61 V
Zn s 2H aq Zn aq H g 0.76 V
E
E
E
E
19.5 The Effect of Concentration on Cell Emf
Review: All of these redox reactions are spontaneous:
What if these are not under standard conditions?
2+ 2+ o
2+ 2+ o
2+ 2+ o
2+ 2+ o2
Zn s Cu aq Zn aq Cu s 1.10 V
Pb s Cu aq Pb aq Cu s 0.47 V
Zn s Pb aq Zn aq Pb s 0.61 V
Zn s 2H aq Zn aq H g 0.76 V
E
E
E
E
19.5 The Effect of Concentration on Cell Emf
What will happen to the cell potential if the reactant concentration is less than 1 M (and the product concentration is 1 M)?
What will happen to the cell potential if the product concentration is less than 1 M (and the reactant concentration is 1 M)?
19.5 The Effect of Concentration on Cell Emf
Practice:What are the cell potentials for these reactions (at 25oC)? Zn(s) | Zn2+ (0.75 M) ǁ Cu2+ (0.0015 M) | Cu(s) Zn(s) | Zn2+ (0.0015 M) ǁ Cu2+ (0.75 M) | Cu(s) Pb(s) | Pb2+ (0.75 M) ǁ Cu2+ (0.0015 M) | Cu(s) Pb(s) | Pb2+ (0.0015 M) ǁ Cu2+ (0.75 M) | Cu(s)
Are these reactions spontaneous (at 25oC)?
19.5 The Effect of Concentration on Cell Emf
How does a pH electrode work?
What is a concentration cell?◦ What are the oxidation
and reduction half reactions◦ What is Eo
Figure 19.6, p 679
19.5 The Effect of Concentration on Cell Emf
Practice:What is the cell potential for this reaction (at 25oC)?Pb(s) | Pb2+ (0.75 M) ǁ Pb2+ (0.0015 M) | Pb(s)
Is this reaction spontaneous (at 25oC)?
19.6 Batteries
Review: What is a spontaneous redox reaction (or galvanic cell) in terms of:◦ Cell potential◦ Gibbs free energy◦ Equilibrium constant
How would this be useful in designing a stand-alone source of electricity?
What is a battery?
19.6 Batteries
What is a battery? What are different types of batteries?◦ The Dry Cell Battery
Figure 19.7, p 680
19.6 Batteries
What is a battery? What are different types of batteries?◦ The Mercury Battery
Figure 19.8, p 681
19.6 Batteries
What is a battery? What are different types of batteries?◦ The Lead Storage Battery
Figure 19.9, p 681
19.6 Batteries
What makes the Lead Storage Battery different?
Figure 19.9, p 681
19.6 Batteries
What makes the Lithium-Ion Battery different?
Figure 19.10, p 683
19.6 Batteries
What are fuel cells? What is one example of a fuel cell?
Figure 19.11, p 684
19.7 Corrosion
Review: What is the spontaneous redox reaction (or galvanic cell) for many metals in the presence of water or hydrogen ions?
19.7 Corrosion
Review: What is the spontaneous redox reaction (or galvanic cell) for many metals in the presence of water or hydrogen ions?
19.7 Corrosion
Review: What is the spontaneous redox reaction (or galvanic cell) for iron in the presence of hydrogen ions?
19.7 Corrosion
Figure 19.13, p 686
19.7 Corrosion
Review: What is the spontaneous redox reaction (or galvanic cell) for iron in the presence of hydrogen ions?
What does this mean for the protection of iron surfaces?◦ Tin-plated◦ Galvanized◦ Stainless steel
What is a sacrificial electrode?
19.7 Corrosion
Figure 19.15, p 687
19.8 Electrolysis
Review: What indicates a redox reaction that is not spontaneous?
Can a redox reaction that isn’t spontaneous be made spontaneous?
What is electrolysis? What are some specific examples of
electrolysis (keeping in mind the reaction at the anode and cathode)?
19.8 Electrolysis
Figure 19.16, p 688
19.8 Electrolysis
Figure 19.18, p 689
19.8 Electrolysis
What would happen if these processes were combined?◦ Electrolysis of salt water (seawater)?
Can we determine how much of a substance is reduced or oxidized?
19.8 Electrolysis
Can we determine how much of a substance is reduced or oxidized?
Figure 19.19, p 691
19.8 Electrolysis
Practice:What mass of zinc can be plated onto an iron nail (with a mass of 1.565 g) when 355 mA is used for 25 minutes in aqueous zinc chloride?
What is the density of the galvanized nail?
Figure 19.19, p 691
19.9 Electrometallurgy
Review: What is spontaneous – the reduction of aluminum ions to aluminum metal or the oxidation of aluminum metal to aluminum ions?
How do we refine or prepare aluminum?
Can we use the same principles to refine other metals?
What about purification?
19.9 Electrometallurgy
Can we use the same principles to refine other metals?
What about purification?
Figure 19.21, p 693
