Question 20.6: Determining the Relative Strengths of Oxidizing and Reducing...
Determining the Relative Strengths of Oxidizing and Reducing Agents
a. Order the following oxidizing agents by increasing strength under standard-state conditions: \mathrm{Cl}_{2}(g), \mathrm{H}_{2} \mathrm{O}_{2}(a q), \mathrm{Fe}^{3+}(a q).
b. Order the following reducing agents by increasing strength under standard-state conditions: \mathrm{H}_{2}(g), \mathrm{Al}(s), \mathrm{Cu}(s).
PROBLEM STRATEGY
a. Read down the table of electrode potentials, picking out the reduction half-reactions in which the species of interest occur as reactants. The order from top to bottom in which these species occur in the table is the order of increasing oxidizing power.
b. Read down the table of electrode potentials, picking out the reduction halfreactions in which the species of interest occur as products. The order from bottom to top in which these species occur in the table is the order of increasing reducing strength.
a. The half-reactions and corresponding electrode potentials are as follows:
\begin{array}{ll} \mathrm{Fe}^{3+}(a q)+\mathrm{e}^{-} \longrightarrow \mathrm{Fe}^{2+}(a q) & 0.77 \mathrm{~V} \\ \mathrm{Cl}_{2}(g)+2 \mathrm{e}^{-} \longrightarrow 2 \mathrm{Cl}^{-}(a q) & 1.36 \mathrm{~V} \\ \mathrm{H}_{2} \mathrm{O}_{2}(a q)+2 \mathrm{H}^{+}(a q)+2 \mathrm{e}^{-} \longrightarrow 2 \mathrm{H}_{2} \mathrm{O}(l) & 1.78 \mathrm{~V} \end{array}
The order by increasing oxidizing strength is \mathrm{Fe}^{3+}(a q), \mathrm{Cl}_{\mathbf{2}}(\mathrm{g}), \mathrm{H}_{\mathbf{2}} \mathrm{O}_{\mathbf{2}}(\mathrm{aq}).
b. The half-reactions and corresponding electrode potentials are
\begin{array}{lr} \mathrm{Al}^{3+}(a q)+3 \mathrm{e}^{-} \longrightarrow \mathrm{Al}(s) & -1.66 \mathrm{~V} \\ 2 \mathrm{H}^{+}(a q)+2 \mathrm{e}^{-} \longrightarrow \mathrm{H}_{2}(g) & 0.00 \mathrm{~V} \\ \mathrm{Cu}^{2+}(a q)+2 \mathrm{e}^{-} \longrightarrow \mathrm{Cu}(s) & 0.34 \mathrm{~V} \end{array}
The order by increasing reducing strength is \mathbf{C u}(s), \mathbf{H}_{2}(g), \mathrm{Al}(s).