1. 1741

2. 1742

3. When a piece of zinc metal is placed in an aqueous CuSO 4 solution: 1743

4. When a piece of zinc metal is placed in an aqueous CuSO 4 solution: Zinc atoms enter the solution as Zn 2+ ions. 1744

5. When a piece of zinc metal is placed in an aqueous CuSO 4 solution: Zinc atoms enter the solution as Zn 2+ ions. Cu 2+ ions convert to Cu atoms which deposit on the Zn metal. 1745

6. When a piece of zinc metal is placed in an aqueous CuSO 4 solution: Zinc atoms enter the solution as Zn 2+ ions. Cu 2+ ions convert to Cu atoms which deposit on the Zn metal. oxidation: Zn (s) Zn 2+ (aq) + 2 e - 1746

7. When a piece of zinc metal is placed in an aqueous CuSO 4 solution: Zinc atoms enter the solution as Zn 2+ ions. Cu 2+ ions convert to Cu atoms which deposit on the Zn metal. oxidation: Zn (s) Zn 2+ (aq) + 2 e - reduction: Cu 2+ (aq) + 2 e - Cu (s) 1747

8. When a piece of zinc metal is placed in an aqueous CuSO 4 solution: Zinc atoms enter the solution as Zn 2+ ions. Cu 2+ ions convert to Cu atoms which deposit on the Zn metal. oxidation: Zn (s) Zn 2+ (aq) + 2 e - reduction: Cu 2+ (aq) + 2 e - Cu (s) Overall: Cu 2+ (aq) + Zn (s) Zn 2+ (aq) + Cu (s) 1748

9. When a piece of zinc metal is placed in an aqueous CuSO 4 solution: Zinc atoms enter the solution as Zn 2+ ions. Cu 2+ ions convert to Cu atoms which deposit on the Zn metal. oxidation: Zn (s) Zn 2+ (aq) + 2 e - reduction: Cu 2+ (aq) + 2 e - Cu (s) Overall: Cu 2+ (aq) + Zn (s) Zn 2+ (aq) + Cu (s) When a piece of copper metal is placed in an aqueous ZnSO 4 solution: nothing happens. 1749

10. When a piece of zinc metal is placed in an aqueous CuSO 4 solution: Zinc atoms enter the solution as Zn 2+ ions. Cu 2+ ions convert to Cu atoms which deposit on the Zn metal. oxidation: Zn (s) Zn 2+ (aq) + 2 e - reduction: Cu 2+ (aq) + 2 e - Cu (s) Overall: Cu 2+ (aq) + Zn (s) Zn 2+ (aq) + Cu (s) When a piece of copper metal is placed in an aqueous ZnSO 4 solution: nothing happens. One conclusion: zinc has a greater tendency to be oxidized than copper. 1750

11. 1751

12. It is possible, by a suitable arrangement, to make the electrons flow along an external circuit. This is carried out in a galvanic cell. 1752

13. It is possible, by a suitable arrangement, to make the electrons flow along an external circuit. This is carried out in a galvanic cell. A galvanic cell operates on the principle that the oxidation of Zn to Zn 2+ and the reduction of Cu 2+ to Cu can be made to take place separately (and simultaneously) with electron transfer taking place through a connecting wire between the two electrodes. 1753

14. For the reaction Cu 2+ (aq) + Zn (s) Zn 2+ (aq) + Cu (s) 1754

15. For the reaction Cu 2+ (aq) + Zn (s) Zn 2+ (aq) + Cu (s) the two half-cell reactions are just the oxidation and reduction steps: 1755

16. For the reaction Cu 2+ (aq) + Zn (s) Zn 2+ (aq) + Cu (s) the two half-cell reactions are just the oxidation and reduction steps: oxidation: Zn (s) Zn 2+ (aq) + 2 e - 1756

17. For the reaction Cu 2+ (aq) + Zn (s) Zn 2+ (aq) + Cu (s) the two half-cell reactions are just the oxidation and reduction steps: oxidation: Zn (s) Zn 2+ (aq) + 2 e - reduction: Cu 2+ (aq) + 2 e - Cu (s) 1757

18. For the reaction Cu 2+ (aq) + Zn (s) Zn 2+ (aq) + Cu (s) the two half-cell reactions are just the oxidation and reduction steps: oxidation: Zn (s) Zn 2+ (aq) + 2 e - reduction: Cu 2+ (aq) + 2 e - Cu (s) Note: It is essential to separate the two solutions, otherwise the Cu 2+ ions will react directly with the zinc electrode, and there would be no electron flow through the external wire. 1758

19. In order to complete the electrical circuit, the two solutions must be connected by a connecting medium. 1759

20. In order to complete the electrical circuit, the two solutions must be connected by a connecting medium. This is accomplished by using a salt bridge – which contains an inert electrolyte such as KCl. 1760

21. In order to complete the electrical circuit, the two solutions must be connected by a connecting medium. This is accomplished by using a salt bridge – which contains an inert electrolyte such as KCl. The electrolyte is usually present dissolved in a gel (such as agar-agar). 1761

22. In order to complete the electrical circuit, the two solutions must be connected by a connecting medium. This is accomplished by using a salt bridge – which contains an inert electrolyte such as KCl. The electrolyte is usually present dissolved in a gel (such as agar-agar). During the reaction, electrons flow externally from the anode (the Zn electrode) to the cathode (the Cu electrode). 1762

23. 1763

24. The fact that electrons flow from one electrode to the other means that there must be a voltage difference (also called a potential difference) between the electrodes. 1764

25. The fact that electrons flow from one electrode to the other means that there must be a voltage difference (also called a potential difference) between the electrodes. This difference, called the electromotive force, or emf, can be measured by placing a voltmeter in the external circuit between the two electrodes. 1765

26. The fact that electrons flow from one electrode to the other means that there must be a voltage difference (also called a potential difference) between the electrodes. This difference, called the electromotive force, or emf, can be measured by placing a voltmeter in the external circuit between the two electrodes. If electrons flow from the anode to the cathode, then the anode must be labeled negative with respect to the cathode, which is labeled positive. 1766

27. The fact that electrons flow from one electrode to the other means that there must be a voltage difference (also called a potential difference) between the electrodes. This difference, called the electromotive force, or emf, can be measured by placing a voltmeter in the external circuit between the two electrodes. If electrons flow from the anode to the cathode, then the anode must be labeled negative with respect to the cathode, which is labeled positive. In solution, negative ions move towards the anode, which means the region close to the anode must be positively charged (the Zn 2+ are formed there). 1767

28. Notation for Electrochemical Cells 1768

29. Notation for Electrochemical Cells Zn(s)| Zn 2+ (aq) 1769

30. Notation for Electrochemical Cells Zn(s)| Zn 2+ (aq) vertical line means a phase boundary 1770

31. Notation for Electrochemical Cells Zn(s)| Zn 2+ (aq) vertical line means a phase boundary Sometimes concentrations will be indicated, e.g. Zn(s)| Zn 2+ (1 M) 1771

32. Notation for Electrochemical Cells Zn(s)| Zn 2+ (aq) vertical line means a phase boundary Sometimes concentrations will be indicated, e.g. Zn(s)| Zn 2+ (1 M) Often ordered in the form: reactant|product 1772

33. Notation for Electrochemical Cells Zn(s)| Zn 2+ (aq) vertical line means a phase boundary Sometimes concentrations will be indicated, e.g. Zn(s)| Zn 2+ (1 M) Often ordered in the form: reactant|product For example, Zn(s)| Zn 2+ (aq) would indicate 1773

34. Notation for Electrochemical Cells Zn(s)| Zn 2+ (aq) vertical line means a phase boundary Sometimes concentrations will be indicated, e.g. Zn(s)| Zn 2+ (1 M) Often ordered in the form: reactant|product For example, Zn(s)| Zn 2+ (aq) would indicate Zn Zn 2+ (aq) 1774

35. For H + (aq)|H 2 (g)|Pt(s) 1775

36. For H + (aq)|H 2 (g)|Pt(s) The Pt is employed as an inert metal electrode. 1776

37. For H + (aq)|H 2 (g)|Pt(s) The Pt is employed as an inert metal electrode. So the reaction is 2 H + (aq) H 2(g) 1777

38. For H + (aq)|H 2 (g)|Pt(s) The Pt is employed as an inert metal electrode. So the reaction is 2 H + (aq) H 2(g) (The Pt is not involved in the chemistry.) 1778

39. For H + (aq)|H 2 (g)|Pt(s) The Pt is employed as an inert metal electrode. So the reaction is 2 H + (aq) H 2(g) (The Pt is not involved in the chemistry.) Carbon is also often used as an inert electrode. 1779

40. For H + (aq)|H 2 (g)|Pt(s) The Pt is employed as an inert metal electrode. So the reaction is 2 H + (aq) H 2(g) (The Pt is not involved in the chemistry.) Carbon is also often used as an inert electrode. For Pt(s)|H 2 (g)|H + (aq), the reaction is H 2(g) 2 H + (aq) 1780

41. For H + (aq)|H 2 (g)|Pt(s) The Pt is employed as an inert metal electrode. So the reaction is 2 H + (aq) H 2(g) (The Pt is not involved in the chemistry.) Carbon is also often used as an inert electrode. For Pt(s)|H 2 (g)|H + (aq), the reaction is H 2(g) 2 H + (aq) An electrode consisting of a platinum wire dipping into a solution of iron (II) and iron (III) is denoted by 1781

42. For H + (aq)|H 2 (g)|Pt(s) The Pt is employed as an inert metal electrode. So the reaction is 2 H + (aq) H 2(g) (The Pt is not involved in the chemistry.) Carbon is also often used as an inert electrode. For Pt(s)|H 2 (g)|H + (aq), the reaction is H 2(g) 2 H + (aq) An electrode consisting of a platinum wire dipping into a solution of iron (II) and iron (III) is denoted by Fe 2+ (aq), Fe 3+ (aq)|Pt(s) 1782

43. For H + (aq)|H 2 (g)|Pt(s) The Pt is employed as an inert metal electrode. So the reaction is 2 H + (aq) H 2(g) (The Pt is not involved in the chemistry.) Carbon is also often used as an inert electrode. For Pt(s)|H 2 (g)|H + (aq), the reaction is H 2(g) 2 H + (aq) An electrode consisting of a platinum wire dipping into a solution of iron (II) and iron (III) is denoted by Fe 2+ (aq), Fe 3+ (aq)|Pt(s) There is no phase boundary between the Fe 2+ and Fe 3+ solutions. 1783

44. A comma is used to separate half-cell components that are in the same phase. 1784

45. A cell is represented as: Zn(s)| Zn 2+ (aq)||Cu 2+ (aq)|Cu(s) 1785

46. A cell is represented as: Zn(s)| Zn 2+ (aq)||Cu 2+ (aq)|Cu(s) The || represents a salt bridge. 1786

47. A cell is represented as: Zn(s)| Zn 2+ (aq)||Cu 2+ (aq)|Cu(s) The || represents a salt bridge. It also indicates the divide between the two half cells. 1787

48. A cell is represented as: Zn(s)| Zn 2+ (aq)||Cu 2+ (aq)|Cu(s) The || represents a salt bridge. It also indicates the divide between the two half cells. Often ordered so that it is in the form: anode compartment|| cathode compartment 1788

49. A cell is represented as: Zn(s)| Zn 2+ (aq)||Cu 2+ (aq)|Cu(s) The || represents a salt bridge. It also indicates the divide between the two half cells. Often ordered so that it is in the form: anode compartment|| cathode compartment The contents of the salt bridge are usually omitted – they are not part of the chemistry of the cell. 1789

50. Example: Write the balanced reactions occurring at the anode and cathode for the cell: C|I - (aq)|I 2 (s)||MnO 4 - (aq), H + (aq), Mn 2+ (aq)|C 1790

51. Example: Write the balanced reactions occurring at the anode and cathode for the cell: C|I - (aq)|I 2 (s)||MnO 4 - (aq), H + (aq), Mn 2+ (aq)|C anode 2 I - (aq) I 2(s) + 2e - 1791

52. Example: Write the balanced reactions occurring at the anode and cathode for the cell: C|I - (aq)|I 2 (s)||MnO 4 - (aq), H + (aq), Mn 2+ (aq)|C anode 2 I - (aq) I 2(s) + 2e - cathode MnO 4 - (aq) + 8H + (aq) + 5e - Mn 2+ (aq) + 4H 2 O 1792

53. Example: Write the balanced reactions occurring at the anode and cathode for the cell: C|I - (aq)|I 2 (s)||MnO 4 - (aq), H + (aq), Mn 2+ (aq)|C anode 2 I - (aq) I 2(s) + 2e - cathode MnO 4 - (aq) + 8H + (aq) + 5e - Mn 2+ (aq) + 4H 2 O Note that the C serves as an inert electrode, and is not involved in the chemistry. 1793

54. 1794

55. Example: The following chemistry is made to occur in an electrochemical cell: 1795

56. Example: The following chemistry is made to occur in an electrochemical cell: 14H + (aq) + Cr 2 O 7 2- (aq) + 6e - 2 Cr 3+ (aq) + 7H 2 O 1796

57. Example: The following chemistry is made to occur in an electrochemical cell: 14H + (aq) + Cr 2 O 7 2- (aq) + 6e - 2 Cr 3+ (aq) + 7H 2 O Fe 2+ (aq) Fe 3+ (aq) + e - 1797

58. Example: The following chemistry is made to occur in an electrochemical cell: 14H + (aq) + Cr 2 O 7 2- (aq) + 6e - 2 Cr 3+ (aq) + 7H 2 O Fe 2+ (aq) Fe 3+ (aq) + e - Write the cell notation that describe this cell. 1798

59. Example: The following chemistry is made to occur in an electrochemical cell: 14H + (aq) + Cr 2 O 7 2- (aq) + 6e - 2 Cr 3+ (aq) + 7H 2 O Fe 2+ (aq) Fe 3+ (aq) + e - Write the cell notation that describe this cell. It is a solution reaction, so use an inert electrode such as C or Pt. 1799

60. Example: The following chemistry is made to occur in an electrochemical cell: 14H + (aq) + Cr 2 O 7 2- (aq) + 6e - 2 Cr 3+ (aq) + 7H 2 O Fe 2+ (aq) Fe 3+ (aq) + e - Write the cell notation that describe this cell. It is a solution reaction, so use an inert electrode such as C or Pt. C|Fe 2+ (aq),Fe 3+ (aq)||Cr 2 O 7 2- (aq), H + (aq), Cr 3+ (aq)|C 1800