Question

Give a reason for the following:

The pink coloured KMnO₄ solution turns colourless when reacted with Mohr’s salt (Fe²⁺) in acidic medium.

Answer 1

When KMnO₄ solution is mixed with Mohr’s salt in an acidic medium, the pink color goes away. This is because KMnO₄ is a strong oxidizing agent and gets reduced in acidic media. Mohr’s salt, which is FeSO₄ (NH₄)₂SO₄.6H₂O, has Fe²⁺ in it, which is a reducing agent. \[\ce{MnO^-_4}\] (pink) is changed into Mn²⁺ (colorless) in the acidic medium, and Fe²⁺ is changed into Fe³⁺.

\[\ce{MnO^-_4 + 5Fe^{2+} + 8H+ -> Mn^{2+} + 5Fe^{3+} + 4H2O}\]

As \[\ce{MnO^-_4}\] is consumed, the pink colour disappears making the solution colourless.