Question

Identify the correct statement regarding corrosion of iron rod left exposed to atmosphere.

• A. The reaction occurring at the cathodic area is: \[ \text{O}_2(g) + 2\text{H}_2\text{O}(l) + 4e^- \rightarrow 4\text{OH}^- \]
• B. The reaction occurring at the cathodic area is: \[ \text{O}_2(g) + 4\text{H}^+(aq) + 4e^- \rightarrow 2\text{H}_2\text{O}(l); E^\circ = +1.23 V \]
• C. Reaction occurring at anodic area is: \[ 2\text{Fe}(s) \rightarrow 2\text{Fe}^{2+}(aq) + 4e^- \]
• D. The overall reaction occurring during the corrosion process is: \[ 2\text{Fe}(s) + 3\text{O}_2(g) + 6\text{H}_2\text{O}(l) \rightarrow 2\text{Fe}^{3+}(aq) + 3\text{OH}^-(aq); E^\circ = -1.23 V \]

Hint:

When studying corrosion, remember that the anodic reaction involves oxidation (loss of electrons), while the cathodic reaction involves reduction (gain of electrons).

Answer 1

The Correct Option is B

Corrosion of iron is a redox reaction that occurs in two half-reactions: an anodic reaction (oxidation) and a cathodic reaction (reduction). 1. Anodic reaction (oxidation): Iron atoms lose electrons (oxidation) and are converted into \( \text{Fe}^{2+} \) ions. This reaction occurs at the anodic area of the iron rod: \[ \text{Fe}(s) \rightarrow \text{Fe}^{2+}(aq) + 2e^- \] 2. Cathodic reaction (reduction): Oxygen from the air reacts with water and electrons to form hydroxide ions (\( \text{OH}^- \)) at the cathodic area: \[ \text{O}_2(g) + 2\text{H}_2\text{O}(l) + 4e^- \rightarrow 4\text{OH}^- \] This reaction represents the reduction half-reaction at the cathode. 3. Overall reaction: The overall corrosion reaction involves the iron reacting with oxygen and water to form iron(III) hydroxide, which can eventually lead to rust: \[ 4\text{Fe}(s) + 3\text{O}_2(g) + 6\text{H}_2\text{O}(l) \rightarrow 4\text{Fe(OH)}_3(s) \] This corrosion process occurs in the presence of oxygen and water, and the reaction at the cathode is correctly represented in option (B). Thus, the correct statement is (B).