Question

Which is an example of autocatalysis:
A.Hydrolysis of methyl acetate
B.Decomposition of TNG
C.Oxidation of Oxalic acid by $KMn{O_4}$
D.All of the above

Answer 1

An autocatalysis is a chemical reaction in which one of the reaction products catalyze the same or a coupled reaction.

Complete step by step answer:
We know that Catalysts are the chemical substances capable of increasing the rate of a reaction without undergoing any permanent chemical change.Catalysts are Foreign substances but some time product formed can act as catalyst and the process is known as autocatalysis.
Consider the titration of Potassium permanganate by Oxalic acid.
Potassium permanganate is a strong oxidizing agent. In acidic solution the oxidizing ability of $KMn{O_4}$ can be represented by the following equation:
$Mn{O_4}^ - + 8{H^ + } + 5{e^ - }$ $\rightarrow$ $M{n^{2 + }} + 4{H_2}O$
Solution containing MnO4- is purple in color and the solution containing $M{n^{2 + }}$ is colorless. In this titration $KMn{O_4}$ acts as a Self-indicator. Permanganate solution is decolorized when added to a solution of reducing agent.
Oxalic acid contains oxalate ions. Permanganate in Acidic solution oxidize the oxalate ions in oxalic acid. Thus $M{n^{2 + }}$ ions are getting formed. This $M{n^{2 + }}$ catalyzes the further reaction. When potassium permanganate undergoes a reaction with acidic oxalate ions, the rate of the reaction is initially slow. But due to the formation of $M{n^{2 + }}$ ions the rate slowly increases.
Another example for Autocatalysis is the Hydrolysis of methyl acetate.
$C{H_3}COOC{H_3} + {H_2}O$ $\rightarrow$ $C{H_3}COOH + C{H_3}OH$

In this reaction acetic acid catalyzes the further reaction.
Decomposition of TNG is also an autocatalysis reaction. The gases formed in this reaction act as auto-catalysts. TNG is decomposed and evolves into nitrous yellow Vapour.

Hence, the correct answer is option (D) i.e All of the above.

Note: There are some catalysts which increase the rate of a reaction is called a positive catalyst. The catalyst which decreases the rate of a reaction is called negative catalyst. Activity of a catalyst can be enhanced by a particular substance known as promoter. Activity of a catalyst can be diminished by a particular substance known as poison.