Question

The first stage in corrosion of iron upon exposure to air is oxidation to \(\mathrm{Fe}^{2+}\). (a) Write a balanced chemical equation to show the reaction of iron with oxygen and protons from acid rain. (b) Would you expect the same sort of reaction to occur with a silver surface? Explain.

Short answer

The balanced chemical equation for the oxidation of iron upon exposure to air and protons from acid rain is \(4\mathrm{Fe}(s) + 4\mathrm{H}^+(aq) + \mathrm{O}_2(g) \rightarrow 4\mathrm{Fe}^{2+}(aq) + 2\mathrm{H}_2\mathrm{O}(l)\). The same reaction is unlikely to occur with a silver surface, as silver has low reactivity due to its completely filled d-orbital. However, silver can still undergo other chemical reactions when exposed to air, such as tarnishing by forming silver sulfide.

Step-by-step solution

Writing the balanced equation for iron oxidation

The oxidation of iron occurs when iron reacts with oxygen in the presence of protons from acid rain, forming iron (II) ions (Fe²⁺). To write the balanced chemical equation, we need to make sure that both the number of atoms and charge are conserved on both sides. The balanced equation for this process is: \[ 4\mathrm{Fe}(s) + 4\mathrm{H}^+(aq) + \mathrm{O}_2(g) \rightarrow 4\mathrm{Fe}^{2+}(aq) + 2\mathrm{H}_2\mathrm{O}(l) \]

Determine if the same reaction occurs with silver

Silver, being less reactive than iron, does not oxidize upon exposure to air as easily as iron does. Silver exhibits a very low reactivity due to the presence of a completely filled d-orbital in its atomic structure. The same sort of reaction is unlikely to occur with a silver surface. However, certain compounds like hydrogen sulfide, present in the atmosphere, can tarnish the silver surface by forming silver sulfide. Thus, silver can undergo a different chemical reaction when exposed to air, but not the same reaction as iron.

Conclusion

In conclusion, we have written the balanced chemical equation for the oxidation of iron upon exposure to air and protons from acid rain as \(4\mathrm{Fe}(s) + 4\mathrm{H}^+(aq) + \mathrm{O}_2(g) \rightarrow 4\mathrm{Fe}^{2+}(aq) + 2\mathrm{H}_2\mathrm{O}(l)\). We also determined that the same kind of reaction is unlikely to occur with a silver surface due to its low reactivity, but it can still undergo other chemical reactions when exposed to air.