Question

Why is KMnO₄ capable of exhibiting oxidising properties in neutral, alkaline as well as in acidic solutions?

Answer 1

1. In an acidic solution, KMnO₄ acts as a strong oxidising agent as \[\ce{MnO^-_4}\] ions get reduced to Mn²⁺. The reaction involves 5 electrons per \[\ce{MnO^-_4}\]and has a high standard reduction potential (E° = 1.51 V), making it very effective to oxidise other substances.
2. In neutral and alkaline media, \[\ce{MnO^-_4}\] ions are reduced to MnO₂ (manganese dioxide). The reaction involves 3 electrons per \[\ce{MnO^-_4}\] ion with moderate oxidation strength.
3. The oxidising property is due to the ability of KMnO₄ to accept electrons (get reduced) by changing the oxidation states of manganese from +7 in \[\ce{MnO^-_4}\] to lower states (+4 in MnO₂ or +2 in Mn²⁺), depending on the medium.
4. Thus, the versatility in the change of oxidation states under different pH conditions allows KMnO₄ to act as an oxidising agent in acidic, neutral, and alkaline solutions.
5. In alkaline medium, formation of intermediate manganate \[\ce{(MnO^{2-}_4)}\] also facilitates its oxidising ability.