Question

When $KMn{O}_4$ solution is added to oxalic acid solution, the decolourisation is slow in the beginning but becomes instantaneous after some time because:

• A. $C{O}_2$ is formed as the product
• B. Reaction is exothermic
• C. $M{n}^{2+}$ acts as an autocatalyst.
• D. $Mn{O}_4^{-}$ catalyses the reaction

Answer 1

The correct option is C $M{n}^{2+}$ acts as an autocatalyst.

On adding $KMn{O}_4$ solution to oxalic acid solution, the following reaction takes place.

$5C_2{O}_4^{2-}+2Mn{O}_4^{-}+16H^{+}\to 2M{n}^{2+}+8H_{2}O+10C{O}_2$

When $KMn{O}_4$ reacts with oxalic acid, the formation of $M{n}^{2+}$ takes place, which acts as an auto-catalyst. This implies that $M{n}^{2+}$ increases the rate of the reaction and the reaction proceeds fast.

Initially, when $KMn{O}_4$ is getting converted to $M{n}^{2+}$, the decolourisation is slow, but after the formation of $M{n}^{2+}$, the decolourisation process becomes instantaneous.

So, option $\left(D\right)$ is the correct answer.