Question

Which species in each pair is the stronger reducing agent? (a) \(\mathrm{Cl}^{-}\) or \(\mathrm{Br}^{-}\) (b) Cu or Ni (c) \(\mathrm{Hg}_{2}^{2+}\) or \(\mathrm{NO}(g)\)

Short answer

Question: Determine the stronger reducing agent in each of the following pairs: (a) \(\mathrm{Cl}^{-}\) and \(\mathrm{Br}^{-}\), (b) Cu and Ni, (c) \(\mathrm{Hg}_{2}^{2+}\) and \(\mathrm{NO}(g)\). Answer: (a) \(\mathrm{Br}^{-}\), (b) Ni, (c) \(\mathrm{Hg}_{2}^{2+}\).

Step-by-step solution

Refer to Standard Reduction Potentials Table

Find a table with standard reduction potentials for the species mentioned in the exercise. You can usually find a table in chemistry textbooks or online.

Compare Standard Reduction Potentials for (a) \(\mathrm{Cl}^{-}\) and \(\mathrm{Br}^{-}\)

Look for the standard reduction potentials of \(\mathrm{Cl}^{-}\) and \(\mathrm{Br}^{-}\). The standard reduction potentials are as follows: \(\mathrm{Cl}_{2}(g) + 2e^{-} \rightarrow 2\mathrm{Cl}^{-}\), E° = +1.36 V \(\mathrm{Br}_{2}(l) + 2e^{-} \rightarrow 2\mathrm{Br}^{-}\), E° = +1.07 V

Determine Stronger Reducing Agent for (a)

Since the standard reduction potential of \(\mathrm{Br}^{-}\) (+1.07 V) is less positive than that of \(\mathrm{Cl}^{-}\) (+1.36 V), \(\mathrm{Br}^{-}\) is the stronger reducing agent in the pair.

Compare Standard Reduction Potentials for (b) Cu and Ni

Look for the standard reduction potentials of Cu and Ni. The standard reduction potentials are as follows: \(\mathrm{Cu}^{2+}(aq) + 2e^{-} \rightarrow \mathrm{Cu}(s)\), E° = +0.34 V \(\mathrm{Ni}^{2+}(aq) + 2e^{-} \rightarrow \mathrm{Ni}(s)\), E° = -0.26 V

Determine Stronger Reducing Agent for (b)

Since the standard reduction potential of Ni (-0.26 V) is more negative than that of Cu (+0.34 V), Ni is the stronger reducing agent in the pair.

Compare Standard Reduction Potentials for (c) \(\mathrm{Hg}_{2}^{2+}\) and \(\mathrm{NO}(g)\)

Look for the standard reduction potentials of \(\mathrm{Hg}_{2}^{2+}\) and \(\mathrm{NO}(g)\). The standard reduction potentials are as follows: \(\mathrm{Hg}_{2}^{2+}(aq) + 2e^{-} \rightarrow 2\mathrm{Hg}(l)\), E° = +0.85 V \(\mathrm{NO}_{3}^{-}(aq) + 4\mathrm{H}^{+}(aq) + 3e^{-} \rightarrow \mathrm{NO}(g) + 2\mathrm{H}_{2}\mathrm{O}(l)\), E° = +0.96 V

Determine Stronger Reducing Agent for (c)

Since the standard reduction potential of \(\mathrm{Hg}_{2}^{2+}\) (+0.85 V) is less positive than that of \(\mathrm{NO}(g)\) (+0.96 V), \(\mathrm{Hg}_{2}^{2+}\) is the stronger reducing agent in the pair. To summarize: (a) \(\mathrm{Br}^{-}\) is the stronger reducing agent. (b) Ni is the stronger reducing agent. (c) \(\mathrm{Hg}_{2}^{2+}\) is the stronger reducing agent.