The following questions pertain to the laboratory preparation of hydrogen chloride gas:
(i) Write the equation for it’s preparation mentioning the condition required.
(ii) Name the drying agent used in the above preparation and give a reason for the choice.
(iii) State a safety precaution taken during the preparation of hydrochloric acid.

(i) The equation for the laboratory preparation of hydrogen chloride gas :

NaCl + H₂SO₄ {\overset{ < 200^oC}{\longrightarrow}} NaHSO₄ + HCl

(ii) Concentrated sulphuric acid is used as the drying agent used in the above preparation.

Reason – Drying agent used for drying should only remove the moisture and not react with it, hence, conc. sulphuric acid is used as the drying agent.

(iii) The precautions taken are:

1. The reaction mixture is initially heated very slowly to control the evolution of HCl gas.
2. The lower end of the thistle funnel should dip below the acid in the flask otherwise the HCl gas obtained will escape out from the thistle funnel.