Question

Draw a labelled diagram for the laboratory preparation of hydrogen chloride gas and answer the following.

1. Name the acid used. Why is this particular acid preferred to other acids?
2. Give the balanced equation for the reaction.
3. Name the drying agent used in drying hydrogen chloride gas.
4. Phosphorous pentoxide and calcium oxide are good drying agents, but they cannot be used to dry hydrogen chloride gas. Why?
5. Why is the direct absorption of \[\ce{HCl}\] gas in water not feasible?
6. What arrangement is done to dissolve \[\ce{HCl}\] gas in the water?

Answer 1

The labelled diagram for laboratory preparation of hydrogen chloride is: 

a. Concentrated \[\ce{H2SO4}\]. Hydrogen chloride gas, when dissolved in water, forms hydrochloric acid. The gas is highly soluble in water and thus cannot be passed through water with the help of a delivery tube because it leads to back suction, i.e., water may move back into the hot flask through the delivery tube. The delivery tube is connected to a funnel, as shown, and gas is dissolved in water. This prevents the back suction of water.

b. The balanced equation for the reaction:

\[\ce{NaCl + H2SO4 ->[<200°C]NaHSO4 + HCl ^}\]

c. The drying agent used in drying hydrogen chloride gas is conc. Sulphuric acid.

d. Phosphorous pentoxide and calcium oxide are good drying agents, but they cannot be used to dry hydrogen chloride gas because they react with hydrogen chloride.

\[\ce{2P2O5 + 3HCl -> POCl3 + 3HPO3}\]

\[\ce{CaO + 2HCl -> CaCl2 + H2O}\]

e. Hydrogen chloride gas is highly soluble in water. Therefore, it is not collected over water.

f. The funnel arrangement is done to dissolve \[\ce{HCl}\] gas in water.