For the preparation of hydrochloric acid in the laboratory:

(i) Hydrogen chloride gas is sufficiently soluble, so, it is absorbed more quickly than it is being generated in the flask. This causes back-suction due to partial vacuum created in the tube. Hence, direct absorption of hydrogen chloride gas in water is not feasible.

(ii) A special funnel arrangement is done in which an inverted funnel, connected to the hydrogen chloride gas supply is placed in the beaker in such a way that it just touches the water taken in the trough. This arrangement minimizes back suction.