Chapter 2 Solutions — Electrochemistry

Exercises

1. 1.
   Arrange the following metals in the order in which they displace each other from the solution of their salts. Al, Cu, Fe, Mg and Zn.
2. 2.
   Given the standard electrode potentials, K⁺/K = -2.93 V, Ag⁺/Ag = 0.80 V, Hg²⁺/Hg = 0.79 V, Mg²⁺/Mg = -2.37 V, Cr³⁺/Cr = -0.74 V. Arrange these metals in their increasing order of reducing power.
3. 3.
   Depict the galvanic cell in which the reaction Zn(s) + 2Ag+(aq) -> Zn₂+(aq) + 2Ag(s) takes place. Further show:

   • (i) Which of the electrode is negatively charged?
   • (ii) The carriers of the current in the cell.
   • (iii) Individual reaction at each electrode.
4. 4.
   Calculate the standard cell potentials of galvanic cell in which the following reactions take place:

   • (i) 2Cr(s) + 3Cd₂+(aq) -> 2Cr₃+(aq) + 3Cd
   • (ii) Fe₂+(aq) + Ag+(aq) -> Fe₃+(aq) + Ag(s). Calculate the DrG° and equilibrium constant of the reactions.
5. 5.
   Write the Nernst equation and emf of the following cells at 298 K:

   • (i) Mg(s)|Mg₂+(0.001M)||Cu₂+(0.0001 M)|Cu(s)
   • (ii) Fe(s)|Fe₂+(0.001M)||H+(1M)|H₂(g)(1bar)|Pt(s)
   • (iii) Sn(s)|Sn₂+(0.050 M)||H+(0.020 M)|H₂(g)(1 bar)|Pt(s)
   • (iv) Pt(s)|Br-(0.010 M)|Br₂(l)||H+(0.030 M)|H₂(g)(1 bar)|Pt(s).
6. 6.
   In the button cells widely used in watches and other devices the following reaction takes place: Zn(s) + Ag₂O(s) + H₂O(l) -> Zn₂+(aq) + 2Ag(s) + 2OH-(aq). Determine DrG° and E° for the reaction.
7. 7.
   Define conductivity and molar conductivity for the solution of an electrolyte. Discuss their variation with concentration.
8. 8.
   The conductivity of 0.20 M solution of KCl at 298 K is 0.0248 S cm-1. Calculate its molar conductivity.
9. 9.
   The resistance of a conductivity cell containing 0.001M KCl solution at 298 K is 1500 Ohm. What is the cell constant if conductivity of 0.001M KCl solution at 298 K is 0.146 × 10-3 S cm-1.
10. 10.
    The conductivity of sodium chloride at 298 K has been determined at different concentrations: Concentration/M: 0.001, 0.010, 0.020, 0.050, 0.100; 10² × k / S m-1: 1.237, 11.85, 23.15, 55.53, 106.74. Calculate Lm for all concentrations and draw a plot between Lm and c⁰.5. Find the value of Lm°.
11. 11.
    Conductivity of 0.00241 M acetic acid is 7.896 × 10-5 S cm-1. Calculate its molar conductivity. If Lm° for acetic acid is 390.5 S cm₂ mol-1, what is its dissociation constant?
12. 12.
    How much charge is required for the following reductions:

    • (i) 1 mol of Al³⁺ to Al?
    • (ii) 1 mol of Cu²⁺ to Cu?
    • (iii) 1 mol of MnO₄⁻ to Mn₂+?
13. 13.
    How much electricity in terms of Faraday is required to produce

    • (i) 20.0 g of Ca from molten CaCl₂?
    • (ii) 40.0 g of Al from molten Al₂O₃?
14. 14.
    How much electricity is required in coulomb for the oxidation of

    • (i) 1 mol of H₂O to O₂?
    • (ii) 1 mol of FeO to Fe₂O₃?
15. 15.
    A solution of Ni(NO₃)₂ is electrolysed between platinum electrodes using a current of 5 amperes for 20 minutes. What mass of Ni is deposited at the cathode?
16. 16.
    Three electrolytic cells A, B, C containing solutions of ZnSO₄, AgNO₃ and CuSO₄, respectively are connected in series. A steady current of 1.5 amperes was passed through them until 1.45 g of silver deposited at the cathode of cell B. How long did the current flow? What mass of copper and zinc were deposited?
17. 17.
    Using the standard electrode potentials given in Table 2.1, predict if the reaction between the following is feasible:

    • (i) Fe₃+(aq) and I-(aq)
    • (ii) Ag+(aq) and Cu(s)
    • (iii) Fe₃+(aq) and Br-(aq)
    • (iv) Ag(s) and Fe₃+(aq)
    • (v) Br₂(aq) and Fe₂+(aq).
18. 18.
    Predict the products of electrolysis in each of the following:

    • (i) An aqueous solution of AgNO₃ with silver electrodes.
    • (ii) An aqueous solution of AgNO₃ with platinum electrodes.
    • (iii) A dilute solution of H₂SO₄ with platinum electrodes.
    • (iv) An aqueous solution of CuCl₂ with platinum electrodes.