Question

Mohan heated ethanol with a compound ‘X’ in the presence of a few drops of conc. H₂SO₄ and observed a sweet smelling compound ‘Y’ is formed. When ‘Y’ is treated with sodium hydroxide it gives back ethanol and a compound ‘Z’.

1. Identify ‘X’, ‘Y’ and ‘X’.
2. Write the role of conc. H₂SO₄ in the reaction.
3. Write the chemical equations involved and name the reactions.

Answer 1

i. Ethanol reacts with a compound ‘X’ to give a sweet-smelling compound ‘Y’. This indicates ‘Y’ is an ester.

Esters are formed by reacting alcohol with carboxylic acid. Thus, ‘X’ is Ethanoic acid (CH₃COOH) and ‘Y’ is Ethyl ethanoate (CH₃COOC₂H₅).

Reaction of an ester with NaOH (alkali) is called Saponification. It gives back ethanol and the sodium salt of the acid. So, ‘Z’ is Sodium acetate (CH₃COONa).

ii. In the esterification reaction, concentrated sulphuric acid functions as a catalyst to accelerate the reaction and as a dehydrating agent to eliminate the water produced, so altering the balance to favour the products.

iii. Esterification Reaction:

\[\ce{CH3COOH + C2H5OH ->[Conc{.} H2SO4] CH3COOC2H5 + H2O}\]

Saponification Reaction:

\[\ce{CH3COOC2H5 + NaOH -> CH3COONa + C2H5OH}\]