Question

Choose the correct answer from the options given below:

(ii) Hydrogen chloride gas being highly soluble in water, is dried by:

• A. Anhydrous Calcium chloride
• B. Phosphorus Pentoxide
• C. Quick lime
• D. Concentrated Sulphuric acid

Answer 1

The correct option is D

Concentrated Sulphuric acid

An explanation for the correct option (d): Concentrated Sulphuric acid

• The drying of Hydrogen chloride gas after laboratory preparation is necessary as the gas contains moisture in it.
• For drying of the formed gas, the moistened gas is passed through Sulphuric acid in concentrated form which is a good absorber of moisture.
• And in this way, dry Hydrogen Chloride is obtained.
• Therefore, concentrated Sulphuric acid is used to dry Hydrogen chloride gas.

An explanation for incorrect option (a): Anhydrous Calcium chloride

• Anhydrous Calcium chloride is a salt. It is not a drying agent.

An explanation for incorrect option (b): Phosphorus Pentoxide

• Phosphorus Pentoxide is not used to dry Hydrogen chloride gas because it undergoes a reaction with HCl.
• The reaction is shown below.

$$\begin{gathered} 2{\mathrm{P}}_2{\mathrm{O}}_5\left(s\right)+3\mathrm{HCl}\left(g\right)\to {\mathrm{POCl}}_3\left(l\right)+3{\mathrm{HPO}}_3\left(l\right) \\ PhosphorousHydrogenPhosphorylMetaphosphoric \\ pentoxidechloridechlorideacid\sqrt[]{} \end{gathered}$$

An explanation for incorrect option (c): Quick lime

• Quick lime is not used to dry Hydrogen chloride gas because it is a base that undergoes a reaction with HCl to form the salt.
• The reaction is shown below.

$$\begin{gathered} \mathrm{CaO}\left(aq\right)+\mathrm{HCl}g)\to {\mathrm{CaCl}}_2(aq)+{\mathrm{H}}_2\mathrm{O}(\mathrm{l}) \\ \mathrm{Calcium}\mathrm{Hydrogen}\mathrm{Calcium} \\ \mathrm{oxide}\mathrm{chloride}\mathrm{chloride} \end{gathered}$$

Therefore, Hydrogen chloride is dried by Concentrated Sulphuric acid. Therefore, the correct answer is option (d).