Question

When a test tube containing ${\mathrm{NH}}_4\mathrm{Cl}$salt is strongly heated, the solid completely disappears. Explain.

Answer 1

Heating of Ammonium chloride:

• When the Ammonium chloride $\left({\mathrm{NH}}_4\mathrm{Cl}\right)$ is strongly heated in a test tube, it undergoes sublimation to give Hydrochloric gas $\left(\mathrm{HCl}\right)$ and Ammonia gas $\left({\mathrm{NH}}_3\right).$
• Sublimation is the process of changing a solid into the gaseous state without converting into the liquid state.
• The solid directly changes to gas and there is no residue left behind.

$\underset{(\mathrm{Ammonium}\mathrm{chloride})}{{\mathrm{NH}}_4\mathrm{Cl}\left(\mathrm{s}\right)}\to \underset{(\mathrm{Ammonia}\mathrm{gas})}{{\mathrm{NH}}_3\left(\mathrm{g}\right)\uparrow }+\underset{(\mathrm{Hydrogen}\mathrm{chloride}\mathrm{gas})}{\mathrm{HCl}\left(\mathrm{g}\right)\uparrow }$.

Therefore, when a test tube containing ${\mathrm{NH}}_4\mathrm{Cl}$salt is strongly heated, the solid completely disappears.