Question

(a) Esters are sweet-smelling substances and are used in making perfumes. Describe an activity for the preparation of an ester with the help of a well labelled diagram. Write an equation for the chemical reaction involved in the formation of the ester. Also write the names of all the substances involved in the process of esterification.
(b) State any two uses of esters.

Answer 1

(a) Esters are sweet-smelling substances which are used to make perfumes. The process in which a carboxylic acid reacts with an alcohol to form an ester is called esterification.
An ester is formed when ethanol (alcohol) reacts with ethanoic acid, on heating, in the presence of a few drops of concentrated sulphuric acid. The name of the ester formed is ethyl ethanoate.

Let's prepare an ester.
(i) In a test tube, take 1 ml of ethanoic acid and add some ethanol to it along with a few drops of concentrated sulphuric acid.
(ii) Warm the test tube in a beaker, containing hot water, for 5 minutes.
(iii) Take about 50 ml of water in another beaker and pour the contents of the test tube into it. When you smell it, a sweet fragrance is obtained indicating the formation of an ester.

The diagrammatic representation of the above process is as follows:


The chemical equation involved in the formation of ester is as follows:

${\mathrm{CH}}_3\mathrm{COOH}+{\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}\stackrel{\mathrm{Conc}.{\mathrm{H}}_2{\mathrm{SO}}_4}{\to }{\mathrm{CH}}_3{\mathrm{COOC}}_2{\mathrm{H}}_5+{\mathrm{H}}_2\mathrm{O}$

(b) Uses of esters:
(i) Esters are used in making artificial perfumes because of their sweet fragrance.
(ii) Esters are used as flavouring agents in ice-creams, sweets and cold drinks.