Question

Describe with an example the oxidising actions of the permanganate ion in acidic media. What acids are actually used for?

Answer 1

In an acidic medium, the permanganate ion (MnO⁴⁻) acts as a strong oxidising agent. It gets reduced from Mn⁷⁺ to Mn²⁺, and in the process, it oxidises other substances.

The reduction half-reaction of the permanganate ion in an acidic medium is:

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

Example:

When potassium permanganate is added to an acidified ferrous sulphate solution, the ferrous ion (Fe²⁺) is oxidised to ferric ion (Fe3+), and the permanganate ion is reduced to (Mn²⁺).

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

Dilute sulphuric acid (H₂SO₄) is used to provide the acidic medium.

It does not interfere with the redox reaction.

Hydrochloric acid (HCl) is not used, as it gets oxidised to chlorine gas.

Nitric acid (HNO₃) is also not suitable, as it is itself a strong oxidising agent.

Thus, KMnO₄ acts as a strong oxidising agent in an acidic medium and oxidises Fe²⁺ to Fe³⁺ using dilute sulphuric acid.