Question 5.5: Representing an Oxidation–Reduction Reaction Through Half-Eq......
Representing an Oxidation–Reduction Reaction Through Half-Equations and an Overall Equation
Write equations for the oxidation and reduction processes that occur and the overall equation for the reaction of iron with hydrochloric acid solution to produce H_{2}(g) and Fe^{2+}. The reaction is shown in Figure 5-14.
Analyze
The reactants are and and the products are H_{2}(g) and FeCl_{2}(aq), a soluble ionic compound. In the reaction, the oxidation state of iron changes from 0 in Fe to +2 in FeCl_{2}, and the oxidation state of hydrogen changes from +1 in HCl to 0 in H_{2}. Thus, iron is oxidized and hydrogen is reduced.
Solve
The balanced chemical equations are as follows.
\begin{array}{r c} \begin{matrix} Oxidation: \\ Reduction: \\ Overall: \end{matrix} \end{array}\begin{array}{r c} \begin{matrix} & Fe(s) & \longrightarrow & Fe^{2+}(aq) & + & 2 e^{- } \\ 2 H^{+}(aq) & +2 e^{- } & \longrightarrow & H_{2}(g) \\ \hline Fe(s) & + 2 H^{+}(aq) & \longrightarrow & Fe^{2+}(aq) & + & H_{2}(g)\end{matrix} \end{array}
Assess
This example illustrates that iron dissolves in acid solution. Iron is a major component of steel and the reaction in this example contributes to the corrosion of steel that is exposed to air and moisture. For example, H^{+} ions from acid rain cause Fe atoms in steel to become oxidized to Fe^{2+} ions. The oxidation of iron creates small pits in the steel surface and leads to corrosion.