Question

Which of the statements are incorrect about potassium permanganate?

• A. Potassium permanganate is a powerful oxidizing agent
• B. Potassium permanganate is a violet-black crystalline solid
• C. Potassium permanganate is stable in acidic medium
• D. Potassium permanganate can oxidize sulphites to sulphates

Answer 1

The correct option is C Potassium permanganate is stable in acidic medium

Manganese exists in its highest stable oxidation state of +7 in potassium permanganate. Hence potassium permanganate is a very powerful oxidizing agent. Like chromium(VI) compounds, the color in this d0 ion is derived from charge transfer electron transitions. Potassium permanganate is a violet-black solid, which dissolves in water to give a deep purple solution.
In acidic solution, manganate ion is reduced to the colourless $M{n}^{2+}$ ion. This medium brings out the maximum ability to oxidize because of the sheer number of electrons acquired.
$\left[Mn{O}_4{]}^{-}\right(aq)+8H^{+}(aq)+5e^{-}\to M{n}^{2+}(aq)+4H_{2}O(l)$
What about the reaction of potassium permanganate with a mild reducing agent like sulphite? The half reactions are:
$\left[Mn{O}_4{]}^{-}\right(aq)+e^{-}\to [Mn{O}_4{]}^{2-}\left(aq\right)$
$S{O}_3^{2-}\left(aq\right)+2O{H}^{-}\to S{O}_4^{2-}\left(aq\right)+H_{2}O\left(l\right)+2e^{-}$
So only option c is inappropriate.