SO₃²⁻(aq) + H₂O(l) → SO₄²⁻(aq) + 2H⁺(aq) + 2e⁻ Which of the following ions could be used to oxidise sulfite ions to sulfate ions? A Cr³⁺(aq) B Al²⁺(aq) C Fe³⁺(aq) D Sn²⁺(aq) - Scottish Highers Chemistry - Question 18 - 2018

To determine which ions can oxidize sulfite ions ( ext{SO}_3^{2-}) to sulfate ions ( ext{SO}_4^{2-}), we need to consider the oxidation states of the ions listed.

1. Cr³⁺(aq): Chromium can be an oxidizing agent, but typically in higher oxidation states (e.g., Cr⁶⁺). Cr³⁺ is less likely to oxidize sulfite in this context.

2. Al²⁺(aq): Aluminum is usually a reducing agent and does not typically act as an oxidizer for sulfite ions.

3. Fe³⁺(aq): Iron(III) ion is a known oxidizing agent and can effectively oxidize sulfite to sulfate. This means it can indeed facilitate the necessary oxidation reaction.

4. Sn²⁺(aq): Tin(II) is generally a reducing agent and is not suitable for this oxidation.

Based on the analysis, the correct answer is C) Fe³⁺(aq).