Question

For the preparation of hydrochloric acid in the laboratory.
(i) Why is direct absorption of hydrogen chloride gas in water not feasible?
(ii) What arrangement is done to dissolve hydrogen chloride gas in water?

Answer 1

Hydrogen chloride is a covalently bonded molecule which generally exists as a gas. When added in water it ionizes forming a proton and chloride ion. You must recall the preparation of hydrogen chloride in the laboratory in order to answer this question.

Complete step by step answer:
(i) Direct absorption of hydrogen chloride gas in water is not feasible as direct absorption leads to the back suction of water. It is caused when the rate of absorption exceeds the rate of production of the hydrogen chloride gas. Thus, a low pressure is created in the flask causing the water to be pulled into the reaction flask.
(ii) Hydrogen chloride gas is produced in the laboratory by treating sodium chloride with sulphuric acid in a reaction vessel. The hydrogen chloride produced is put into another vessel containing sulphuric acid which dries the gas. The dry hydrogen chloride gas is then made to go to the vessel containing water through an extra empty vessel which accommodates for the back suction of water during the absorption of the dry hydrogen chloride gas. The pipe that leads the dry gas into the vessel containing water is attached to an inverted funnel which provides an enhanced surface area for absorption and minimizes back suction of water.

Note:
Most of the hydrogen chloride produced industrially is for the production of hydrochloric acid. At large scale, hydrogen chloride is produced by directly combining hydrogen gas and chlorine gas. The reaction is highly exothermic and a great amount of heat is produced. The gas produced is then absorbed into water forming pure hydrochloric acid.