6.1 Exercises

Section 6.1 Exercises

1. For each of the following balanced half-reactions, determine whether an oxidation or reduction is occurring.

   (a) $\text{Fe}^{3+}\;+\;3\text{e}^{-}\;{\longrightarrow}\;\text{Fe}$

   (b) $\text{Cr}\;{\longrightarrow}\;\text{Cr}^{3+}\;+\;3\text{e}^{-}$

   (c) $\text{MnO}_4^{\;\;2-}\;{\longrightarrow}\;\text{MnO}_4^{\;\;-}\;+\;\text{e}^{-}$

   (d) $\text{Li}^{+}\;+\;\text{e}^{-}\;{\longrightarrow}\;\text{Li}$

2. Given the following pairs of balanced half-reactions, determine the balanced reaction for each pair of half-reactions in an acidic solution.

   (a) $\text{Ca}\;{\longrightarrow}\;\text{Ca}^{2+}\;+\;2\text{e}^{-},\;\text{F}_2\;+\;2\text{e}^{-}\;{\longrightarrow}\;2\text{F}^{-}$

   (b) $\text{Li}\;{\longrightarrow}\;\text{Li}^{+}\;+\;\text{e}^{-},\;\text{Cl}_2\;+\;2\text{e}^{-}\;{\longrightarrow}\;2\text{Cl}^{-}$

   (c) $\text{Fe}\;{\longrightarrow}\;\text{Fe}^{3+}\;+\;3\text{e}^{-},\;\text{Br}_2\;+\;2\text{e}^{-}\;{\longrightarrow}\;2\text{Br}^{-}$

   (d) $\text{Ag}\;{\longrightarrow}\;\text{Ag}^{+}\;+\;\text{e}^{-},\;\text{MnO}_4^{\;\;-}\;+\;4\text{H}^{+}\;+\;3\text{e}^{-}\;{\longrightarrow}\;\text{MnO}_2\;+\;2\text{H}_2\text{O}$

3. Identify the species that undergoes oxidation, the species that undergoes reduction, the oxidizing agent, and the reducing agent in each of the reactions.

   (a) $\text{H}_2\text{O}_2\;+\;\text{Sn}^{2+}\;{\longrightarrow}\;\text{H}_2\text{O}\;+\;\text{Sn}^{4+}$

   (b) $\text{PbO}_2\;+\;\text{Hg}\;{\longrightarrow}\;\text{Hg}_2^{\;\;2+}\;+\;\text{Pb}^{2+}$

   (c) $\text{Al}\;+\;\text{Cr}_2\text{O}_7^{\;\;2-}\;{\longrightarrow}\;\text{Al}^{3+}\;+\;\text{Cr}^{3+}$

4. Identify the species that was oxidized, the species that was reduced, the oxidizing agent, and the reducing agent in each of the reactions.

   (a) $\text{SO}_3^{\;\;2-}(aq)\;+\;\text{Cu(OH)}_2(s)\;{\longrightarrow}\;\text{SO}_4^{\;\;2-}(aq)\;+\;\text{Cu(OH)}(s)$

   (b) $\text{O}_2(g)\;+\;\text{Mn(OH)}_2(s)\;{\longrightarrow}\;\text{MnO}_2(s)$

   (c) $\text{NO}_3^{\;\;-}(aq)\;+\;\text{H}_2(g)\;{\longrightarrow}\;\text{NO}(g)$

   (d) $\text{Al}(s)\;+\;\text{CrO}_4^{\;\;2-}(aq)\;{\longrightarrow}\;\text{Al(OH)}_3(s)\;+\;\text{Cr(OH)}_4^{\;\;-}(aq)$

5. Why is it not possible for hydrogen ion (H⁺) to appear in either of the half-reactions or the overall equation when balancing oxidation-reduction reactions in basic solution?