Question

Hina dipped a glass rod in $\text{conc. HCl}$ and observed faint fumes. These fumes became dense when she dipped the same glass rod in ${\text{NH}}_3$ gas. The possible reason for Hina's observation is:

• A. the sublimation of ${\text{NH}}_4\text{Cl}$ which is formed when $\text{HCl}$ reacts with ${\text{NH}}_3$.
• B. the condensation of ${\text{NH}}_4\text{Cl}$ which is formed when $\text{HCl}$ reacts with ${\text{NH}}_3$.
• C. the sublimation of ${\text{NH}}_4\text{OH}$ which is formed when $\text{HCl}$ reacts with ${\text{NH}}_3$.
• D. the evaporation of ${\text{NH}}_4\text{OH}$ which is formed when $\text{HCl}$ reacts with ${\text{NH}}_3$.

Answer 1

The correct option is A the sublimation of ${\text{NH}}_4\text{Cl}$ which is formed when $\text{HCl}$ reacts with ${\text{NH}}_3$.

When a glass rod is dipped in $\text{conc. HCl}$, the faint fumes are observed. This is due to the reaction of $\text{HCl}$ with moisture in the air.

A solid ammonium chloride is formed when this rod is dipped in ${\text{NH}}_3$ gas. The reaction involved is as follows:

${\text{NH}}_3\text{(g)}+\text{HCl (g)}\to {\text{NH}}_4\text{Cl (s)}$

This solid ammonium chloride undergoes sublimation and gets converted to ammonium chloride gas which gives dense fume.