An organic compound 'A' is widely used as a preservative in pickles and has a molecular formula C₂H₄O₂. This compound reacts with ethanol to form a sweet smelling compound 'B'.
(i) Identify the compound 'A'.
(ii) Write the chemical equation for its reaction with ethanol to form compound 'B'.
(iii) How can we get compound 'A' back from 'B'?
(iv) Name the process and write corresponding chemical equation.
(v) Which gas is produced when compound 'A' reacts with washing soda? Write the chemical equation.

(i) An organic compound A widely used as a preservative in a pickle with the molecular formula, C₂H₄O₂ must be an ethanoic acid (${\mathrm{CH}}_3\mathrm{COOH}$).

(ii) When ethanoic acid(A) reacts with ethanol it produces sweet-smelling compound i.e. an ester.
${\mathrm{CH}}_3\mathrm{COOH}+{\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{OH}\to {\mathrm{CH}}_3{\mathrm{COOCH}}_2{\mathrm{CH}}_3+{\mathrm{H}}_2\mathrm{O}$
Hence, the compound B will be ethyl ethanoate.

(iii) We can get ethanoic acid from ethyl ethanoate by hydrolysis in either acidic or basic medium.
$$\begin{gathered} {\mathrm{CH}}_3{\mathrm{COOCH}}_2{\mathrm{CH}}_3+{\mathrm{H}}_2\mathrm{O}\stackrel{{\mathrm{H}}^{+}}{\to }{\mathrm{CH}}_3\mathrm{COOH}+{\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{OH} \\ {\mathrm{CH}}_3{\mathrm{COOC}}_2{\mathrm{H}}_5+\mathrm{NaOH}\to {\mathrm{CH}}_3\mathrm{COONa}+{\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH} \end{gathered}$$

(iv) The hydrolysis of ester in the presence of base is generally known as saponification.
${\mathrm{CH}}_3{\mathrm{COOC}}_2{\mathrm{H}}_5+\mathrm{NaOH}\to {\mathrm{CH}}_3\mathrm{COONa}+{\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}$

(v) When compound A is treated with washing soda brisk effervescence of carbon dioxide is observed.
$2{\mathrm{CH}}_3\mathrm{COOH}+{\mathrm{Na}}_2{\mathrm{CO}}_3\to 2{\mathrm{CH}}_3\mathrm{COONa}+{\mathrm{CO}}_2+{\mathrm{H}}_2\mathrm{O}$