Electrochemistry

The following problems are taken from T. L. Brown, H. E. Lemay, B. E. Bursten, & J. R. Burdge, Chemistry: The Central Science, Ninth Edition, Chapter 20.

24) Calculate the standard emf for each of the following reactions:

       (a) H₂(g) + F₂(g) 2H⁺(aq) + 2F ^-(aq)

       (b) Cu(s) + Ba²⁺(aq) Cu²⁺(aq) + Ba(s)

       (c) 3Fe²⁺(aq) Fe(s) + 2Fe³⁺(aq)

       (d) Hg₂²⁺(aq) + 2Cu⁺(aq) 2Hg(l) + 2Cu²⁺(aq)

26) Given the following half-reactions and associated standard reduction potentials:

      AuBr₄^-(aq) + 3e^- Au(s) + 4Br^-(aq)                    E°_red = -0.858 V

      Eu³⁺(aq) + e^- Eu²⁺(aq)                                       E°_red = -0.43 V
             
      IO^-(aq) + H₂O(l) + 2e^- I^-(aq) + 2OH^-(aq)          E°_red = +0.49 V

      Sn²⁺(aq) + 2e^- Sn(s)                                            E°_red = -0.14 V

      (a) Write the cell reaction for the combination of these half-cell reactions that leads to the largest positive cell emf, and calculate the value.

      (b) Write the cell reaction for the combination of half-cell reactions that leads to the smallest positive cell emf, and calculate that value.

44) For each of the following reactions, write a balanced equation, calculate the emf, and calculate ΔG° at 298 K.    

      (a) Aqueous iodide ion is oxidized to I₂(s) by Hg₂²⁺(aq).      

      (b) In acidic solution, copper(I) ion is oxidized to copper(II) ion by nitrate ion.

      (c) In basic solution, Cr(OH)₃(s) is oxidized to CrO₄^2-(aq) by ClO^-(aq).

56) A voltaic cell is constructed that is based on the following reaction:

      Sn²⁺(aq) + Pb(s) Sn(s) + Pb²⁺(aq)  

      (a) If the concentration of Sn²⁺ in the cathode compartment is 1.00 M and the cell generates an emf of +0.22 V, what is the concentration of Pb²⁺ in the anode compartment?

      (b) If the anode compartment contains [SO₄^2-] = 1.00 M in equilibrium with PbSO4(s), what is the K_sp of PbSO4?

80) Metallic magnesium can be made by the electrolysis of molten MgCl₂.

      (a) What mass of Mg is formed by passing a current of 5.25 A through molten MgCl₂ for 2.50 days?

      (b) How many minutes are needed to plate out 10.00 g Mg from molten MgCl₂ using 3.50 A current?

94) A voltaic cell is constructed that uses the following half-cell reactions:

      Cu⁺(aq) + e^- Cu(s)

      I₂(s) + 2e^- 2I ^-(aq)

      The cell is operated at 298 K with [Cu⁺] = 2.5 M and [I ^-] = 3.5 M.

      (a) Determine E for the cell at these concentrations.    

      (b) Which electrode is the anode of the cell?

      (c) Is the answer to part (b) the same as it would be if the cell were operated under standard conditions?

      (d) If [Cu⁺] were equal to 1.4 M, at what concentration of I ^- would the cell have zero potential?