Zinc is attached to a ship's steel propeller to prevent the steel from rusting. Write balanced equations for the corro-sion reactions that occur (a) in the presence of Zn and (b) in the absence of Zn.

Verified step by step guidance

1. insert step 1> Identify the role of zinc in preventing corrosion. Zinc acts as a sacrificial anode, meaning it will oxidize preferentially over the steel, protecting it from rusting.
2. insert step 2> Write the oxidation half-reaction for zinc. The reaction is: Zn(s) \rightarrow Zn^{2+}(aq) + 2e^{-}.
3. insert step 3> Write the reduction half-reaction for oxygen in the presence of water, which is common in marine environments: O_2(g) + 4H^+(aq) + 4e^- \rightarrow 2H_2O(l).
4. insert step 4> Combine the half-reactions to form the overall balanced equation for the corrosion process in the presence of zinc: 2Zn(s) + O_2(g) + 4H^+(aq) \rightarrow 2Zn^{2+}(aq) + 2H_2O(l).
5. insert step 5> For the absence of zinc, write the oxidation half-reaction for iron: Fe(s) \rightarrow Fe^{2+}(aq) + 2e^-. Combine this with the reduction half-reaction for oxygen to form the overall balanced equation: 2Fe(s) + O_2(g) + 4H^+(aq) \rightarrow 2Fe^{2+}(aq) + 2H_2O(l).

Key Concepts

Corrosion

Corrosion is the process by which metals deteriorate due to chemical reactions with their environment, often involving oxidation. In the case of steel, it typically reacts with oxygen and moisture, leading to rust formation, which is primarily iron oxide. Understanding corrosion is essential for predicting how materials will behave in different conditions and for developing methods to prevent it.

Galvanic Protection

Galvanic protection is a method used to prevent corrosion by using a more reactive metal, such as zinc, to sacrifice itself in place of the metal being protected. When zinc is attached to steel, it acts as a sacrificial anode, corroding preferentially and thus protecting the steel from rusting. This principle is crucial in applications like ship propellers, where exposure to seawater accelerates corrosion.

Balanced Chemical Equations

Balanced chemical equations represent the reactants and products of a chemical reaction with equal numbers of each type of atom on both sides. This is important for understanding the stoichiometry of reactions, predicting the amounts of substances consumed or produced, and ensuring the conservation of mass. In the context of corrosion reactions, writing balanced equations helps illustrate the specific changes occurring in the presence or absence of protective measures like zinc.