Question

An organic compound 'A' produces a gas with brisk effervescence when sodium bicarbonate is added to it. The compound 'A' contains the same number of carbons as in ethane. The compound 'A' reacts with ethanol to form a sweet smelling compound 'C' in presence of conc. H₂SO₄ acid. Then the name of compound A and the gas evolved is:

• A. Ethanoic acid ; CO₂
• B. Methanoic acid ; CO₂
• C. Ethanoic acid ; H₂
• D. Methanoic acid ; H₂

Answer 1

The correct option is A

Ethanoic acid ; CO₂

The explanation for the correct option:

(A) Information available from the given statement:

• Compound A contains 2 Carbon $\left(\mathrm{C}\right)$atoms as it is given that compound A has as many carbon atoms as in ethane $\left({\mathrm{C}}_2{\mathrm{H}}_6\right)$.
• It can be predicted that A is acid as brisk effervescence is produced on reaction with a base i.e.; Sodium bicarbonate $\left({\mathrm{NaHCO}}_3\right)$ as shown below.
• $\underset{(\mathrm{Ethanoic}\mathrm{acid})}{{\mathrm{CH}}_3\mathrm{COOH}}\left(\mathrm{aq}\right)+\underset{(\mathrm{Sodium}\mathrm{bicarbonate})}{{\mathrm{NaHCO}}_3\left(\mathrm{s}\right)}\to \underset{(\mathrm{Sodium}\mathrm{acetate})}{{\mathrm{CH}}_3\mathrm{COONa}}\left(\mathrm{aq}\right)+\underset{(\mathrm{Carbon}\mathrm{dioxide})}{{\mathrm{CO}}_2\left(\mathrm{g}\right)}+\underset{\left(\mathrm{Water}\right)}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}$
• Sweet-smelling compound C is formed and this is a distinguishing feature of esters. An ester is formed when an acid and alcohol react. As it is given that A reacts with Ethanol (${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}$, alcohol), this also indicates that A could be an acid.
• So by knowing that A is an acid with 2 carbon atoms, we can predict that A is Ethanoic acid.

Esterification: The process of formation of esters by treating alcohol with an acid in the presence of concentrated Sulphuric acid $\left({\mathrm{H}}_2{\mathrm{SO}}_4\right)$.

• $\underset{(\mathrm{Ethanoic}\mathrm{acid})}{{\mathrm{CH}}_3\mathrm{COOH}\left(\mathrm{aq}\right)}+\underset{\left(\mathrm{Ethanol}\right)}{{\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}\left(\mathrm{aq}\right)}\stackrel{\mathrm{conc}.{\mathrm{H}}_2{\mathrm{SO}}_4}{\rightleftharpoons }\underset{(\mathrm{Ethyl}\mathrm{acetate})}{{\mathrm{CH}}_3{\mathrm{COOC}}_2{\mathrm{H}}_5\left(\mathrm{aq}\right)}+\underset{\left(\mathrm{Water}\right)}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}$

The explanation for the incorrect options:

(B) Methanoic acid is HCOOH and it contains only one carbon atom whereas it is given that compound A has 2 carbon atoms.

(C) Compound A is ethanoic acid but the gas evolved by brisk effervescence is Carbon dioxide $\left({\mathrm{CO}}_2\right)$ and not Hydrogen $\left({\mathrm{H}}_2\right)$

(D) Compound A is not Methanoic acid as it contains only one carbon atom and the gas evolved by brisk effervescence is Carbon dioxide $\left({\mathrm{CO}}_2\right)$ and not Hydrogen $\left({\mathrm{H}}_2\right)$

Hence, option (A) is correct.