Question

Iron (III) catalyses the reaction between iodide and persulphate ions, in which
A. \(\text{Fe}^{3+}\) oxidises the iodide ion
B. \(\text{Fe}^{3+}\) oxidises the persulphate ion
C. \(\text{Fe}^{2+}\) reduces the iodide ion
D. \(\text{Fe}^{2+}\) reduces the persulphate ion
Choose the most appropriate answer from the options given below:

• A. B and C only
• B. B only
• C. A only
• D. A and D only

Answer 1

The Correct Option is D

To elucidate the catalytic role of Iron (III) in the reaction between iodide and persulphate ions, we will examine the functions of Iron (III) \((\text{Fe}^{3+})\) and Iron (II) \((\text{Fe}^{2+})\):

• Iron (III)'s catalytic activity is demonstrated through the following redox reactions:
• Iron (III) \([\text{Fe}^{3+}]\): As an oxidizing agent, Iron (III) oxidizes iodide ions \((\text{I}^-)\) to iodine \((\text{I}_2)\), simultaneously reducing itself to Iron (II) \((\text{Fe}^{2+})\).
• The corresponding reaction is: \(\text{I}^- + \text{Fe}^{3+} \rightarrow \text{I}_2 + \text{Fe}^{2+}\)
• Iron (II) \([\text{Fe}^{2+}]\): The reduced form, Iron (II), acts as a reducing agent. It reduces persulphate ions \((\text{S}_2\text{O}_8^{2-})\), becoming re-oxidized to Iron (III).
• The corresponding reaction is: \(\text{Fe}^{2+} + \text{S}_2\text{O}_8^{2-} \rightarrow \text{Fe}^{3+} + 2\text{SO}_4^{2-}\)

In this cycle, Iron (III) catalyzes the iodide-persulphate reaction by cycling between its oxidized and reduced states:

1. Iron (III) \(\text{Fe}^{3+}\) oxidizes iodide ions \((\text{I}^-)\) (Option A).
2. Iron (II) \(\text{Fe}^{2+}\) reduces persulphate ions (Option D).

Consequently, options "A and D only" are the most fitting, as Iron (III) initiates the oxidation of iodide ions, followed by the reduction of persulphate ions by the resulting Iron (II).