Question

Give the relationship between the equivalent mass and molar mass of KMnO₄ (molar mass = 158 g mol⁻¹) in neutral medium.

Answer 1

1. In neutral medium, KMnO₄ acts as a moderate oxidising agent and the permanganate ion \[\ce{(MnO^−_4)}\] is reduced to manganese dioxide (MnO₂).
2. The reduction involves 3 electrons per \[\ce{MnO^-_4}\] ion.
3. Therefore, the equivalent mass of KMnO₄ in a neutral medium is one-third of its molar mass.
4. Since molar mass = 158 g/mol, equivalent mass = 158 ÷ 3 ≈ 52.7 g/equiv.
5. This happens because 1 mole of KMnO₄ gains 3 moles of electrons during the reduction to MnO₂.