Question

Which of the following options about the oxidising property of $KMn{O}_4$ in acidic medium is incorrect?

• A. $H_{2}S$ can be oxidised to S
• B. $S{O}_3^{2-}$ can be oxidised to $S{O}_4^{2-}$
• C. $I^{-}$ can be oxidised to $I_2$
• D. None of the above

Answer 1

The correct option is D None of the above

$KMn{O}_4$ is an oxidising agent. The following reactions take place in acidic medium:

1) Hydrogen sulphide is oxidised, sulphur being precipitated.
$5S^{2-}+2Mn{O}_4^{-}+16H^{+}\to 5S+2M{n}^{2+}+8H_{2}O$

2) Sulphurous acid or sulphite is oxidised to a sulphate or sulphuric acid.
$2Mn{O}_4^{-}+5S{O}_3^{2-}+6H^{+}\to 2M{n}^{2+}+5S{O}_4^{2-}+3H_{2}O$

3) Iodine is liberated from potassium iodide.
$10I^{-}+2Mn{O}_4^{-}+16H^{+}\to 5I_2+8H_{2}O+2M{n}^{2+}$