Question

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

Answer 1

1. In an alkaline medium, KMnO₄ is reduced from Mn in the +7 oxidation state to MnO₂, where Mn is in the +4 state.
2. The reduction involves 3 electrons per \[\ce{MnO^-_4}\] ion.
3. Therefore, equivalent mass = molar mass/number of electrons = 158 g/mol ÷ 3 = 52.7 g/equivalent.
4. This happens because KMnO₄ gains 3 electrons to form MnO₂ in an alkaline solution.
5. Thus, the equivalent mass of KMnO₄ in an alkaline medium is one-third of its molar mass.