Question

From each of the following pairs of substances, use data in Appendix \(\mathrm{E}\) to choose the one that is the stronger oxidizing agent: (a) \(\mathrm{Cl}_{2}(g)\) or \(\mathrm{Br}_{2}(l)\) (b) \(\mathrm{Zn}^{2+}(a q)\) or \(\mathrm{Cd}^{2+}(a q)\) (c) \(\mathrm{BrO}_{3}^{-}(a q)\) or \(\mathrm{IO}_{3}^{-}(a q)\) (d) \(\mathrm{H}_{2} \mathrm{O}_{2}(a q)\) or \(\mathrm{O}_{3}(g)\)

Short answer

(a) \(Cl_{2}(g)\) is the stronger oxidizing agent. (b) \(Cd^{2+}(aq)\) is the stronger oxidizing agent. (c) \(BrO_{3}^-(aq)\) is the stronger oxidizing agent. (d) \(O_{3}(g)\) is the stronger oxidizing agent.

Step-by-step solution

Look up the reduction potential values for each substance

Search for the substances in Appendix E. Appendix E should have a table showing the standard reduction potentials for various substances.

Compare the standard reduction potentials for each pair

Determine the stronger oxidizing agent by comparing each reduction potential value. The substance with the more positive (higher) reduction potential is the stronger oxidizing agent. (a) For \(Cl_{2}(g)\) and \(Br_{2}(l)\): \(Cl_{2}(g) + 2e^- \rightarrow 2Cl^-(aq)\), \(E^\circ = +1.36\, V\) \(Br_{2}(l) + 2e^- \rightarrow 2Br^-(aq)\), \(E^\circ = +1.07\, V\) \(Cl_{2}(g)\) has a more positive reduction potential, so it is the stronger oxidizing agent. (b) For \(Zn^{2+}(aq)\) and \(Cd^{2+}(aq)\): \(Zn^{2+}(aq) + 2e^- \rightarrow Zn(s)\), \(E^\circ = -0.76\, V\) \(Cd^{2+}(aq) + 2e^- \rightarrow Cd(s)\), \(E^\circ = -0.40\, V\) \(Cd^{2+}(aq)\) has a more positive reduction potential, so it is the stronger oxidizing agent. (c) For \(BrO_{3}^-(aq)\) and \(IO_{3}^-(aq)\): \(BrO_{3}^-(aq) + 6H^+(aq) + 6e^- \rightarrow Br^-(aq) + 3H_2O(l)\), \(E^\circ = +1.49\, V\) \(IO_{3}^-(aq) + 6H^+(aq) + 6e^- \rightarrow I^-(aq) + 3H_2O(l)\), \(E^\circ = +1.21\, V\) \(BrO_{3}^-(aq)\) has a more positive reduction potential, so it is the stronger oxidizing agent. (d) For \(H_{2}O_{2}(aq)\) and \(O_{3}(g)\): \(H_{2}O_{2}(aq) + 2H^+(aq) + 2e^- \rightarrow 2H_2O(l)\), \(E^\circ = +1.77\, V\) \(O_{3}(g) + 2H^+(aq) + 2e^- \rightarrow O_{2}(g) + H_2O(l)\), \(E^\circ = +2.07\, V\) \(O_{3}(g)\) has a more positive reduction potential, so it is the stronger oxidizing agent.