JEE Main 2023 · 24 January · evening · Single correct · +4 / −1
In which of the following reactions the hydrogen peroxide acts as a reducing agent?
- (a) Mn²⁺ + H₂O₂ → Mn⁴⁺ + 2OH -
- (b) HOCl + H₂O₂ → H₃O + + Cl - + O₂
- (c) PbS + 4H₂O₂ → PbSO₄ + 4H₂O
- (d) 2Fe²⁺ + H₂O₂ → 2Fe³⁺ + 2OH -
Answer and solution
Answer (b) HOCl + H₂O₂ → H₃O + + Cl - + O₂
Solution
Chemistry ma’am · 3 steps
Watch where the peroxide oxygen goes: if it leaves as O₂, H₂O₂ is the reducing agent.
- Oxygen in peroxide. In H₂O₂ each oxygen is at -1. It can go down to -2 (in H₂O or OH⁻) or up to 0 (in O₂).
- Two possible roles. If oxygen goes to -2, H₂O₂ is reduced, so it acts as an oxidising agent. If it goes to 0 and O₂ is released, H₂O₂ is oxidised, so it acts as a reducing agent.
Option Other species Peroxide O ends up in Role of H₂O₂ (a) Mn: +2 → +4, oxidised OH⁻, O at -2 oxidising agent (b) Cl: +1 → -1, reduced O₂, O at 0 reducing agent (c) S: -2 → +6, oxidised H₂O, O at -2 oxidising agent (d) Fe: +2 → +3, oxidised OH⁻, O at -2 oxidising agent - So. Only in (b) does H₂O₂ give up electrons: chlorine in HOCl is reduced from +1 to -1, and the peroxide oxygen is oxidised to O₂. The answer is (b).
The idea to keep. H₂O₂ works both ways because its oxygen sits at -1. Oxygen gas among the products means peroxide was the reducing agent; water or OH⁻ means it was the oxidising agent.
Answer from the NTA final answer key. Solution by PrepWiser.