Question

Give reason for the following :

Ammonia is unionised in the gaseous state but in the aqueous solution is a weak electrolyte.

Answer 1

• Ammonia is a covalent compound, therefore, it is unionized in the gaseous state.

Whereas in the aqueous solution,

Ammonia with water :

Ammonia reacts with water to form Ammonium hydroxide, then dissociates to form ammonium and hydroxide ions.

${\mathrm{NH}}_3\left(\mathrm{g}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\rightleftharpoons {\mathrm{NH}}_4\mathrm{OH}\left(\mathrm{aq}\right)\rightleftharpoons {\mathrm{NH}}_4^{+}\left(\mathrm{aq}\right)+{\mathrm{OH}}^{-}\left(\mathrm{aq}\right)$

• Here, ${\mathrm{NH}}_4\mathrm{OH}$ dissociates partially to give free ions.
• Hence, ${\mathrm{NH}}_4\mathrm{OH}$ is a weak electrolyte.