Question

Name two gases which produce dense white fumes with rod dipped in ammonia solution.

Answer 1

Hydrochloric acid (HCl) and Chlorine (Cl₂) gas produce dense white fumes with rod dipped in ammonia solution.

Reaction with Hydrochloric acid:

When a rod dipped in ammonia is brought near Hydrochloric acid, dense white fumes or smog of Ammonium chloride are produced.

• $$\begin{gathered} {\mathrm{NH}}_3\left(\mathrm{aq}\right)+\mathrm{HCl}\left(\mathrm{g}\right)\to {\mathrm{NH}}_4\mathrm{Cl}\left(\mathrm{s}\right) \\ \left(\mathrm{Ammonia}\right)(\mathrm{Hydrochloric}\mathrm{acid})(\mathrm{Ammonium}\mathrm{chloride}) \\ (\mathrm{white}\mathrm{fumes}) \end{gathered}$$

Reaction with Chlorine gas:

• $$\begin{gathered} 8{\mathrm{NH}}_3\left(\mathrm{aq}\right)+3{\mathrm{Cl}}_2\left(\mathrm{g}\right)\to {\mathrm{N}}_2\left(\mathrm{g}\right)+6{\mathrm{NH}}_4\mathrm{Cl}\left(\mathrm{s}\right) \\ \left(\mathrm{Ammonia}\right)\left(\mathrm{Chlorine}\right)\left(\mathrm{Nitrogen}\right)(\mathrm{Ammonium}\mathrm{chloride}) \\ (\mathrm{white}\mathrm{fumes}) \end{gathered}$$

This reaction occurs in two steps.

1. In the first step, Hydrochloric acid (HCl) is formed by the reaction of ammonia with chlorine gas.
2. This Hydrochloric acid reacts again with ammonia to form white fumes of ammonium chloride.

Hence, this reaction needs excess of ammonia.