Oxidation-Reduction

34) The reason for each of the choices below is the same. The more readily a substance is oxidized (the more negative the E°_red or the more positive the E°_ox ) the stronger the reducing agent.

      (a) Fe²⁺(aq) + 2e^- Fe(s)              E°_red = -0.440 V

           Mg²⁺(aq) + 2e^- Mg(s)           E°_red = -2.37 V

           Mg(s) is the better reducing agent.

      (b) Ca²⁺(aq) + 2e^- Ca(s)              E°_red = -2.87 V

           Al³⁺(aq) + 3e^- Al(s)                 E°_red = -1.66 V

           Ca(s) is the better reducing agent.

      (c) 2H⁺(aq) + 2e^- H₂(g)                               E°_red = 0.000 V

           S(s) + 2H⁺(aq) + 2e^- H₂S(g)                  E°_red = +0.141 V

           H₂(g) is the better reducing agent.

      (d) HSO₄^- (aq) + 3H⁺ + 2e^- H₂SO₃(aq) + H₂O(l)                             E°_red = +0.17 V

           2CO₂(g) + 2H⁺(aq) + 2e^- H₂C₂O₄(aq)                                         E°_red = -0.49 V

           H₂C₂O₄(aq) is the better reducing agent.