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 halfreactions

19.2 Galvanic Cells What is an anode? What is a cathode? What is a salt bridge? What does it do? Figure 19.1, p 665

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 zinc 2. Aqueous copper ions reacting with lead 3. 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 Potentials Review: 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 halfreaction potential? What if we compare to a standard halfreaction potential that is zero?

19.3 Standard Reduction Potentials What if we compare to a standard halfreaction potential that is zero? Zinc with aqueous hydrogen ions Standard reduction potential (E o red) of: 2H aq 2e H g 0.0 V by definition + o 2 E red What is the standard oxidation potential (E o ox) of: + o H2 g 2H aq 2e E ox?

19.3 Standard Reduction Potentials What if we compare to a standard halfreaction 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 halfreaction 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 halfreaction 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 halfreaction 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 halfreaction 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 (E o red) tell us? What are the rules for calculating standard cell potential (E o )? Reversing the reaction Intensive or extensive What does standard cell potential (E o ) 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, Au 3+ 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: 2+ 2+ Zn s Cu aq Zn aq Cu s o E 1.10 V 2+ 2+ Pb s Cu aq Pb aq Cu s o E 0.47 V 2+ 2+ Zn s Pb aq Zn aq Pb s o E 0.61 V 2+ 2+ Zn s 2H aq Zn aq H g o E 0.76 V Therefore, E o and free energy (ΔG) should be related. 2

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 (ΔG o ) for each of these reactions: 2+ 2+ o Zn s Cu aq Zn aq Cu s 1.10 V E 2+ 2+ o Pb s Cu aq Pb aq Cu s 0.47 V E 2+ 2+ o Zn s Pb aq Zn aq Pb s 0.61 V E Zn s 2H aq Zn aq H g E 0.76 V 2+ 2+ o 2

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 Zn s Cu aq Zn aq Cu s 1.10 V E 2+ 2+ o Pb s Cu aq Pb aq Cu s 0.47 V E 2+ 2+ o Zn s Pb aq Zn aq Pb s 0.61 V E Zn s 2H aq Zn aq H g E 0.76 V 2+ 2+ o 2

19.5 The Effect of Concentration on Cell Emf Review: All of these redox reactions are spontaneous: 2+ 2+ Zn s Cu aq Zn aq Cu s o E 1.10 V 2+ 2+ Pb s Cu aq Pb aq Cu s o E 0.47 V 2+ 2+ Zn s Pb aq Zn aq Pb s o E 0.61 V 2+ 2+ Zn s 2H aq Zn aq H g o E 0.76 V What if these are not under standard conditions? 2

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 25 o C)? Zn(s) Zn 2+ (0.75 M) ǁ Cu 2+ (0.0015 M) Cu(s) Zn(s) Zn 2+ (0.0015 M) ǁ Cu 2+ (0.75 M) Cu(s) Pb(s) Pb 2+ (0.75 M) ǁ Cu 2+ (0.0015 M) Cu(s) Pb(s) Pb 2+ (0.0015 M) ǁ Cu 2+ (0.75 M) Cu(s) Are these reactions spontaneous (at 25 o C)?

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 E o Figure 19.6, p 679

19.5 The Effect of Concentration on Cell Emf Practice: What is the cell potential for this reaction (at 25 o C)? Pb(s) Pb 2+ (0.75 M) ǁ Pb 2+ (0.0015 M) Pb(s) Is this reaction spontaneous (at 25 o C)?

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