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