JEE Main 2023 · 31 January · morning · Single correct · +4 / −1
H₂ O₂ acts as a reducing agent in :
- (a) Mn²⁺+2 H₂ O₂ → MnO₂+2 H₂ O
- (b) 2 Fe²⁺+2 H⁺+H₂ O₂ → 2 Fe³⁺+2 H₂ O
- (c) Na₂ S+4 H₂ O₂ → Na₂ SO₄+4 H₂ O
- (d) 2 NaOCl+H₂ O₂ → 2 NaCl+H₂ O+O₂
Answer and solution
Answer (d) 2 NaOCl+H₂ O₂ → 2 NaCl+H₂ O+O₂
Solution
Chemistry ma’am · 3 steps
Follow the oxygen of H₂O₂: if it ends up as O₂, peroxide has been oxidised and is the reducer.
- Two possible fates. Oxygen in H₂O₂ is at -1, halfway between -2 and 0. Going to H₂O (-2) means it is reduced, so it is an oxidising agent. Going to O₂ (0) means it is oxidised, so it is a reducing agent.
Option What the other species does What peroxide oxygen does Role of H₂O₂ (a) Mn²⁺ (+2) to MnO₂ (+4), oxidised -1 to -2 in H₂O oxidising agent (b) Fe²⁺ to Fe³⁺, oxidised -1 to -2 in H₂O oxidising agent (c) S from -2 in Na₂S to +6 in Na₂SO₄, oxidised -1 to -2 oxidising agent (d) Cl from +1 in NaOCl to -1 in NaCl, reduced -1 to 0 in O₂ reducing agent - Check (d). Each Cl gains 2 electrons, so 2 Cl gain 4 electrons in total. The two O atoms of one H₂O₂ lose 1 electron each to form O₂, and the equation is balanced with 2 NaOCl to 1 H₂O₂.
- So. Only in (d) does H₂O₂ release O₂ while reducing hypochlorite to chloride, so it acts as a reducing agent there.
The idea to keep. H₂O₂ can go either way. If O₂ gas is released, it is a reducing agent. If only water forms, it is an oxidising agent. Look at the products first.
Answer from the NTA final answer key. Solution by PrepWiser.