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  • When {KMnO}_{4} solution is added to the oxalic acid solution, the decolourisation is slow in the beginning but becomes instantaneous after some time because (i){CO}_{2} is formed as the product. (ii) The reaction is exothermic.

When \text {KMnO}_{4} solution is added to the oxalic acid solution, the decolourisation is slow in the beginning but becomes instantaneous after some time because

(i) \text {CO}_{2} is formed as the product.

(ii) The reaction is exothermic.

(iii) \text {MnO}_{4}^{-} catalyses the reaction.

(iv) \text {Mn}^{2+} acts as an autocatalyst.

Answers (1)

The answer is option (iv). Acidified \text {KMnO}_{4} oxidises Oxalate ion to \text {CO}_{2} on addition and \text {Mn}^{2+} acts as an auto catalyst. This is why decolourisation is slow in the beginning but becomes instantaneous after some time.

Reduction half \text {MnO}_{4}^{-}+\text {8H}^{+}+\text {5e}^{-}\rightarrow \text {Mn}^{2+}+\text {H}_{2}\text {O}]\times 2

Oxidation half \text {C}_{2}\text {O}_{4}^{2-}\rightarrow \text {2CO}_{2}+\text {2e}^{-}]\times 5

Overall equation \text {2MnO}_{4}^{-}+\text {16H}^{+}+\text {5C}_{2}\text {O}_{4}^{2-}\rightarrow \text {2Mn}^{2+}+\text {10CO}_{2}+\text {8H}_{2}\text {O}

The end point of this reaction is colourless to light pink.

Posted by

infoexpert23

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