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Hydrochloric Acid, Its Preparation and Properties

 

Preparation of Hydrochloric Acid

Hydrochloric acid (HCl) can be produced in any of the following ways:

(a). By heating sodium chloride (NaCl) with concentrated H2SO4.

The gas (HCl) produced is dried by passing it into conc. H2SO4

H2SO4(aq) + NaCl(s) → NaHSO4(s), + HCl(g)

The above reaction will also occur in the cold state - Laboratory preparation.

Application of heat produces large quantity of the gas - industrial preparation.

A solution of the gas is obtained by dissolving it in water.

(b). Another method for producing hydrochloric acid is by direct combination of chlorine and hydrogen.

Properties of Hydrochloric Acid

Hydrochloric acid shows the following properties:

(1). It has a choking, irritating smell.

(2). It is an acid gas which turns moist blue litmus paper red.

(3). It is very soluble in water, hence it is used in the fountain experiment.

(4). Hydrogen chloride gas is evolved if a concentrated solution of HCl is heated. At higher temperatures, the solubility of the gas decreases, and vice versa.

(5). Hydrochloric acid is not used to acidify an oxidizing agent such as KMnO4 during titration because chlorine is liberated from the HCl by the oxidizing agent.

Test for Chlorides

(a). Chlorides produce white precipitate when silver nitrate, acidified with dilute HNO3 is added to their solutions.

The white precipitate is silver chloride, AgCl which dissolves in aqueous ammonia.

Ag+(aq) + Cl-(aq) → AgCl(s)

Note:

The reason for acidifying the AgNO3 solution with dilute HNO3 is to prevent other salts from precipitating along.

Hence, the precipitate, AgCl is not soluble in dilute HNO3 but soluble in aqueous ammonia.

(b). If the chloride is hydrogen chloride gas, a white dense fume is produced with ammonia. The fume is ammonium chloride.

NH3(g), + HCl(g) → NH4Cl(s)

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