When `KMnO_(4)` solution is added to oxalic acid solution , the decolourisation is slow in the beginning but becomes instantaneous after some time because

Options

A. `CO_2` is formed as the product.
B. Reaction is exothermic.
C. `MnO_4^(-)` catalyses the reaction.
D. `Mn^(2+)` acts as auto-catalyst.

Answer

D

Explanation

When `KMnO_4` solution is added to oxalic acid solution, the decolourisation is slow in the beginning but becomes instantaneous after sometime because `Mn^(2+)` acts as an auto-catalyst. Reduction half-reaction:
` [MnO_(4)^(-), +8H^(+) +5e^(-) rarrMn^(2+) + 4H_2O]xx2`
Oxidation half-reaction:
`[C_2O_(4)^(2-) rarr 2CO_2 +2e^(-)]xx5 `
Overall equation:
`2MnO_(4)^(-) +16H^(+) + 5C_2O_(4)^(2-) rarr2Mn^(2+) +10CO_2+8H_2O`
End point of this reaction : Colourless to light pink.