JEE Main 2022 · 26 July · evening · Single correct · +4 / −1

The products obtained from a reaction of hydrogen peroxide and acidified potassium permanganate are :

  1. (a) Mn⁴⁺, H₂ O only
  2. (b) Mn²⁺, H₂ O only
  3. (c) Mn⁴⁺, H₂ O, O₂ only
  4. (d) Mn²⁺, H₂ O, O₂ only
Answer and solution

Answer (d) Mn²⁺, H₂ O, O₂ only

Solution

Chemistry ma’am · 4 steps

Permanganate is the stronger oxidant here, so H₂O₂ gets oxidised and gives off oxygen gas.

  1. Who gets reduced. In acid, MnO₄⁻ takes 5 electrons and Mn drops from +7 to +2. So the manganese product is Mn²⁺, the nearly colourless ion. Mn⁴⁺ (as MnO₂) forms only in neutral or weakly basic solution.
  2. Who gets oxidised. Against an oxidant this strong, H₂O₂ acts as a reducing agent. Its oxygen goes from -1 to 0, so each H₂O₂ loses 2 electrons and releases O₂ gas.

    2MnO₄⁻ + 5H₂O₂ + 6H⁺ → 2Mn²⁺ + 5O₂ + 8H₂O

  3. Check the balance. Electrons match: 2 × 5 = 10 gained and 5 × 2 = 10 lost. Charge matches too: -2 + 6 = +4 on the left and 2 × (+2) = +4 on the right.
  4. So. The products are Mn²⁺, H₂O and O₂, which is option (d).

The idea to keep. H₂O₂ can act both ways. Against a strong oxidant like KMnO₄ it is the reducing agent, and it always gives off O₂. Acidic MnO₄⁻ always goes to Mn²⁺.

Answer from the NTA final answer key. Solution by PrepWiser.

Study Redox Reactions

Asked about 90 times in JEE Main since 2020. This question is from 2022.