1. Chapter 18 Electrochemistry

2. Chapter 18 Table of Contents Copyright © Cengage Learning. All rights reserved 2 18.1Balancing Oxidation–Reduction Equations 18.2 Galvanic Cells 18.3 Standard Reduction Potentials 18.4Cell Potential, Electrical Work, and Free Energy 18.5Dependence of Cell Potential on Concentration 18.6Batteries 18.7Corrosion 18.8Electrolysis 18.9Commercial Eletrolytic Processes

3. Chapter 18 Table of Contents Introduction car, calculator, digital watch, radio... corrosion, industrial preparation (Al, Cl 2...) analytical chemistry: pH meter, pollutants, diseases… electrochemistry: the study of the interchange of chemical & electrical energy.

4. Section 18.1 Balancing Oxidation–Reduction Equations Return to TOC Copyright © Cengage Learning. All rights reserved 4 Review of Terms Oxidation – reduction (redox) reaction – involves a transfer of electrons from the reducing agent to the oxidizing agent Oxidation – loss of electrons Reduction – gain of electrons Reducing agent – electron donor Oxidizing agent – electron acceptor

5. Section 18.1 Balancing Oxidation–Reduction Equations Return to TOC Copyright © Cengage Learning. All rights reserved 5 Half–Reactions The overall reaction is split into two half – reactions, one involving oxidation and one reduction. 8H + + MnO 4 – + 5Fe 2+ → Mn 2+ + 5Fe 3+ + 4H 2 O Reduction: 8H + + MnO 4 – + 5e – → Mn 2+ + 4H 2 O Oxidation: 5Fe 2+ → 5Fe 3+ + 5e –

6. Section 18.1 Balancing Oxidation–Reduction Equations Return to TOC Copyright © Cengage Learning. All rights reserved 6 The Half–Reaction Method for Balancing Equations for Oxidation– Reduction Reactions Occurring in Acidic Solution

7. Section 18.1 Balancing Oxidation–Reduction Equations Return to TOC Copyright © Cengage Learning. All rights reserved 7 The Half–Reaction Method for Balancing Equations for Oxidation– Reduction Reactions Occurring in Basic Solution

8. Section 18.2 Atomic MassesGalvanic Cells Return to TOC Copyright © Cengage Learning. All rights reserved 8 Galvanic Cell Device in which chemical energy is changed to electrical energy. Uses a spontaneous redox reaction to produce a current that can be used to do work.

9. Section 18.2 Atomic MassesGalvanic Cells Return to TOC 1)oxidation-reduction (redox) reaction rxn: half-reactions:

10. Section 18.2 Atomic MassesGalvanic Cells Return to TOC 2)When the oxidizing agent & reducing agent are physically separated, e transfer through an external wire.  generates electricity.generates electricity 3)salt bridge: connect two solns 4)electrodes; where the redox rxn occur anode: oxidation occur cathode: reduction occur

11. Section 18.2 Atomic MassesGalvanic Cells Return to TOC 5 ) Cell potential ( ) a)The voltage difference between the electrodes.  electromotive force (emf) b)can be measured by voltmeter. c)emf of a cell depends on The nature of the electrodes [ions] Temp.

12. Section 18.3 The MoleStandard Reduction Potentials Return to TOC 1)It is impossible to measure ε cell of a half-rxn directly,  need a reference rxn  SHE standard hydrogen electrode:

13. Section 18.3 The MoleStandard Reduction Potentials Return to TOC 2) Standard reduction potential Table 18.1

14. Section 18.3 The MoleStandard Reduction Potentials Return to TOC

15. Section 18.3 The MoleStandard Reduction Potentials Return to TOC 3)

16. Section 18.3 The MoleStandard Reduction Potentials Return to TOC

17. Section 18.3 The MoleStandard Reduction Potentials Return to TOC 4). rxn

18. Section 18.3 The MoleStandard Reduction Potentials Return to TOC Copyright © Cengage Learning. All rights reserved 18 Concept Check Order the following from strongest to weakest oxidizing agent and justify. Of those you cannot order, explain why. FeNaF - Na + Cl 2

19. Section 18.3 The MoleStandard Reduction Potentials Return to TOC Copyright © Cengage Learning. All rights reserved 19 Line Notation Used to describe electrochemical cells. Anode components are listed on the left. Cathode components are listed on the right. Separated by double vertical lines. The concentration of aqueous solutions should be specified in the notation when known. Example: Mg(s)|Mg 2+ (aq)||Al 3+ (aq)|Al(s)  Mg → Mg 2+ + 2e – (anode)  Al 3+ + 3e – → Al(cathode)

20. Section 18.3 The MoleStandard Reduction Potentials Return to TOC Copyright © Cengage Learning. All rights reserved 20 Concept Check Sketch a cell using the following solutions and electrodes. Include:  The potential of the cell  The direction of electron flow  Labels on the anode and the cathode a)Ag electrode in 1.0 M Ag + (aq) and Cu electrode in 1.0 M Cu 2+ (aq)

21. Section 18.3 The MoleStandard Reduction Potentials Return to TOC Copyright © Cengage Learning. All rights reserved 21 Concept Check Sketch a cell using the following solutions and electrodes. Include:  The potential of the cell  The direction of electron flow  Labels on the anode and the cathode b)Zn electrode in 1.0 M Zn 2+ (aq) and Cu electrode in 1.0 M Cu 2+ (aq)

22. Section 18.3 The MoleStandard Reduction Potentials Return to TOC Copyright © Cengage Learning. All rights reserved 22 Concept Check Consider the cell from part b. What would happen to the potential if you increase the [Cu 2+ ]? Explain. The cell potential should increase.

23. Section 18.4 Cell Potential, Electrical Work, and Free Energy Return to TOC Copyright © Cengage Learning. All rights reserved 23 Work Work is never the maximum possible if any current is flowing. In any real, spontaneous process some energy is always wasted – the actual work realized is always less than the calculated maximum.

24. Section 18.4 Cell Potential, Electrical Work, and Free Energy Return to TOC

25. Section 18.4 Cell Potential, Electrical Work, and Free Energy Return to TOC (ex) 18.5 P812

26. Section 18.4 Cell Potential, Electrical Work, and Free Energy Return to TOC (ex) 18.6 Predict whether 1M HNO 3 will dissolve gold metal to form 1M Au 3+ ?

27. Section 18.5 Dependence of Cell Potential on Concentration Return to TOC 1)[C] & ε cell standard conditions: [C]=1M what if [C]≠1M? (ex) 18.7 a)[Al 3+ ]=2.0M, [Mn 2+ ]=1.0M ε cell <0.48V b)[Al 3+ ]=1.0M, [Mn 2+ ]=3.0M ε cell >0.48V

28. Section 18.5 Dependence of Cell Potential on Concentration Return to TOC 2)The Nernst eqn

29. Section 18.5 Dependence of Cell Potential on Concentration Return to TOC 3) Concentration Cells Determine a) e flow direction? b) anode? cathode? c) ε=? at 25 ℃

30. Section 18.5 Dependence of Cell Potential on Concentration Return to TOC 4) Ion-Selective Electrodes: pH meter

31. Section 18.5 Dependence of Cell Potential on Concentration Return to TOC 5) at equilibrium: ΔG=0, ε cell =0, Q=K ex:18.10at p818

32. Section 18.5 Dependence of Cell Potential on Concentration Return to TOC (ex) Calculate K sp for AgCl at 25 ℃ ε=0.58V soln:

33. Section 18.5 Dependence of Cell Potential on Concentration Return to TOC Copyright © Cengage Learning. All rights reserved 33 Concept Check Explain the difference between E and E °. When is E equal to zero? W hen the cell is in equilibrium ("dead" battery). When is E ° equal to zero? E  is equal to zero for a concentration cell.

34. Section 18.6 Batteries Return to TOC Copyright © Cengage Learning. All rights reserved 34 One of the Six Cells in a 12–V Lead Storage Battery

35. Section 18.6 Batteries Return to TOC Copyright © Cengage Learning. All rights reserved 35 A Common Dry Cell Battery

36. Section 18.6 Batteries Return to TOC Copyright © Cengage Learning. All rights reserved 36 A Mercury Battery

37. Section 18.6 Batteries Return to TOC Copyright © Cengage Learning. All rights reserved 37 Schematic of the Hydrogen-Oxygen Fuel Cell

38. Section 18.7 Corrosion Return to TOC Copyright © Cengage Learning. All rights reserved 38 Process of returning metals to their natural state – the ores from which they were originally obtained. Involves oxidation of the metal.

39. Section 18.7 Corrosion Return to TOC 1)(ex) 2) Table 18.1 : : metals & O 2 3)Al & Al 2 O 3 [Al 2 (OH) 6 ] protect layer 4)Compare of Au, O 2, Cu, Ag.

40. Section 18.7 Corrosion Return to TOC 5)Corrosion

41. Section 18.7 Corrosion Return to TOC 6)Moisture (H2O) act as a “salt bridge” Salt (NaCl)  corroision ∵ [ ] & conductivity ‚complex ion

42. Section 18.7 Corrosion Return to TOC 7)Prevention Corrosion paint or metal plating Sn: cans oxide Cr: bumpers for automobiles coating Zn: sacrificial coating ‚alloying: Stainless steel: (Cr, Ni, Fe) form oxide coatings & change

43. Section 18.7 Corrosion Return to TOC ƒcathodic protection fuel tanks & pipelines (Mg… need to be replaced)  any metal that is more easily oxidized than Fe ( is more  )  force metal become a cathode. (reduction)

44. Section 18.8 Electrolysis Return to TOC Copyright © Cengage Learning. All rights reserved 44 Forcing a current through a cell to produce a chemical change for which the cell potential is negative.

45. Section 18.8 Electrolysis Return to TOC 1)galvanic cellelectrolytic cell chemical E  electrical E electrical E  chemical E ‚Fig 18.19(a)Fig 18.19(b) ƒredox rxn: spontaneousnonspontaneous

46. Section 18.8 Electrolysis Return to TOC 2)Stoichiometry (ex) determine the mass of Cu that is plated out? I = 10 amp (c/s) for t = 30 mins charge (c) = amp × sec = 10 × 30 × 60 (c) ‚c  mol of e = 96485 : 1 ƒmol of e  mol of Cu = 2 : 1 „.„.

47. Section 18.8 Electrolysis Return to TOC 3)Electrolysis of H 2 O ..

48. Section 18.8 Electrolysis Return to TOC ‚in pure water: [H + ] = [OH - ] = 10 -7 M from for electrolysis of H 2 O

49. Section 18.8 Electrolysis Return to TOC 4)Electrolysis of mixtures of ions ..

50. Section 18.8 Electrolysis Return to TOC ‚Electrolysis of NaCl (aq) : Na +, Cl -, H 2 O

51. Section 18.8 Electrolysis Return to TOC Copyright © Cengage Learning. All rights reserved 51 Concept Check Consider a solution containing 0.10 M of each of the following: Pb 2+, Cu 2+, Sn 2+, Ni 2+, and Zn 2+. Predict the order in which the metals plate out as the voltage is turned up from zero. Cu 2+, Pb 2+, Sn 2+, Ni 2+, Zn 2+ Do the metals form on the cathode or the anode? Explain.

52. Section 18.9 Commercial Electrolytic Processes Return to TOC Copyright © Cengage Learning. All rights reserved 52 Production of aluminum Purification of metals Metal plating Electrolysis of sodium chloride Production of chlorine and sodium hydroxide

53. Section 18.9 Commercial Electrolytic Processes Return to TOC Copyright © Cengage Learning. All rights reserved 53 Producing Aluminum by the Hall-Heroult Process

54. Section 18.9 Commercial Electrolytic Processes Return to TOC Copyright © Cengage Learning. All rights reserved 54 Electroplating a Spoon

55. Section 18.9 Commercial Electrolytic Processes Return to TOC Copyright © Cengage Learning. All rights reserved 55 The Downs Cell for the Electrolysis of Molten Sodium Chloride

56. Section 18.9 Commercial Electrolytic Processes Return to TOC Copyright © Cengage Learning. All rights reserved 56 The Mercury Cell for Production of Chlorine and Sodium Hydroxide