Question

Give a reason for the following.

Hydrogen chloride gas cannot be dried over quick lime.

Answer 1

• Hydrogen chloride gas:

1. The chemical formula of Hydrogen chloride gas is $\mathrm{HCl}$.
2. It is acidic in nature.

• Quick lime:

1. Calcium oxide$\left(\mathrm{CaO}\right)$ is commonly known as quick lime.
2. It is basic in nature.

Reason Hydrogen chloride gas cannot be dried over quick lime:

Hydrogen chloride is acidic in nature whereas quick lime is basic in nature. If we use calcium oxide or quick lime for drying, then both quick lime and Hydrogen chloride gas will react with each other to form water and calcium chloride salt. Hence, it cannot be used for drying $HCl$ gas.

The reaction between Hydrogen chloride gas and quick lime: $\mathrm{CaO}\left(\mathrm{s}\right)+2\mathrm{HCl}\left(\mathrm{aq}\right)\to {\mathrm{CaCl}}_2\left(\mathrm{aq}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$.

Hydrogen chloride is acidic in nature whereas quick lime is basic in nature. If we use calcium oxide or quick lime for drying, then both quick lime and Hydrogen chloride gas will react with each other to form a salt. Hence, it is not used for drying $\mathrm{HCl}$ gas.