Hydrogen Chloride

Hydrogen chloride was prepared by Glauber in 1648, by heating common salt with concentrated sulfuric acid. Davy, in 1810, showed that it is a compound of hydrogen and chlorine.

a. Preparation : In the laboratory, hydrogen chloride is prepared by heating sodium chloride (common salt) with concentrated sulfuric acid.

HCl gas can be dried by passing it through concentrated sulfuric acid.

a. Physical properties of HCl (the book letters this sub-heading "a." again — a duplicate of the preparation heading's letter, reproduced as printed)

i. Hydrogen chloride is a colourless and pungent smelling gas.

ii. It can be easily liquified to a colourless liquid (b.p. 189 K), which freezes to a white crystalline solid (m.p. 159 K).

iii. It is highly soluble in water.

Chemical properties :

i. Acidic property : Hydrogen chloride is highly soluble in water and ionises as follows:

The aqueous solution of HCl gas is called hydrochloric acid. The high value of the dissociation constant ($K_a$) indicates that it is a strong acid in water.

ii. Reaction with $\mathrm{NH_3}$ : Hydrochloric acid reacts with ammonia and gives white fumes of ammonium chloride.

$\mathrm{NH_3 + HCl \longrightarrow NH_4Cl}$ …