Question

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

Answer 1

1. In an acidic medium, the equivalent mass of KMnO₄ is the molar mass divided by 5.
2. This is because one mole of KMnO₄ gains 5 moles of electrons to reduce \[\ce{MnO^-_4}\] to Mn²⁺.
3. Therefore, equivalent mass = molar mass/n, where n = number of electrons involved = 5.
4. Given molar mass of KMnO₄ = 158 g/mol, equivalent mass = 158 ÷ 5 = 31.6 g/equiv.
5. The large standard reduction potential (1.51 V) makes KMnO₄ a strong oxidizing agent in an acidic medium.