Question

Protons accelerate the hydrolysis of the ester. This is an example:
A. A promoter
B. A heterogeneous catalyst
C. An acid-base catalyst
D. An auto catalyst

Answer 1

Hint: Catalyst is a substance that increases the speed of a reaction and does not get consumed in the process. This process is called catalysis. When one of the products of a reaction acts as a catalyst it is known as autocatalysis.

Complete Step by Step Answer:
A reaction usually happens at a much faster rate after the addition of a catalyst. The catalyst continues as it was in terms of the chemical composition and mass when the reaction gets completed. The amount of the catalyst at the end of the reaction was found to be the same as the amount taken at the beginning of the reaction. So, it does not get consumed during the reaction.

Its physical state such as size, colour, etc., may change. Hydrolysis means the breaking down of a compound due to its reaction with water. Hydrolysis of an ester yields carboxylic acid and alcohol. Carboxylic acid works as a catalyst for the reaction.

Let us take the example of hydrolysis of ethyl acetate.
Acetic acid and ethanol are formed as a product.

The reaction happens as follows:
$CH_{3}COOC_{2}H_{5}+H_{2}O\overset{H^{+}}\rightleftharpoons CH_{3}COOH+C_{2}H_{5}OH$
Here acetic acid which is a reactant acts as a catalyst by accepting a proton.
Protons make the hydrolysis of the ester faster.
When one of the products of a reaction acts as a catalyst it is known as autocatalysis. The catalyst is known as an autocatalyst.
Here protons act as an autocatalyst.
Acid-base catalysis is the adding of an acid or a base to a chemical reaction to accelerate the reaction with zero depletion of the acid or base.
According to Bronsted–Lowry acid-base theory, an acid is a proton contributor and the base is the proton gainer.
In this reaction, acetic acid accepts the proton. So, it is acid-base catalysis.
Protons are also acid-base catalysts.

So, options C and D are correct.

Note: In certain reactions, one of the products works as a catalyst. Initially, the reaction is slow however as soon as the products are formed the reaction rate increases. This process is auto-catalysis.