Hydrochloric Acid

Hydrochloric Acid

HCl  36.46

DEFINITION

Concentrated hydrochloric acid contains not less than 35.0 per cent m/m and not more than 39.0 per cent m/m of HCl.

CHARACTERS

A clear, colorless, fuming liquid, miscible with water.  It has a relative density of about 1.18.

IDENTIFICATION

 A. Dilute with water R. The solution is strongly acid, pH<4 & Green or blue in Congo red paper R indicator.

 B. It gives the reactions of chlorides.

 C. It complies with the limits of the assay.

TESTS

Appearance of solution

To 2 ml add 8 ml of water R. The solution is clear and colorless.

Free chlorine

To 15 ml add 100 ml of carbon dioxide-free water R, 1 ml of a 100 g/l solution of potassium iodide R and 0.5 ml of iodide-free starch solution R. Allow to stand in the dark for 2 min. Any blue color disappears on the addition of 0.2 ml of 0.01 M sodium thiosulphate (4 ppm).

Sulphates

To 6.4 ml add 10 mg of sodium hydrogen carbonate R and evaporate to dryness on a water-bath. Dissolve the residue in 15 ml of distilled water R. The solution complies with the limit test for sulphates (20 ppm).

Heavy metals

Dissolve the residue obtained in the test for residue on evaporation in 1 ml of dilute hydrochloric acid R and dilute to 25 ml with water R. Dilute 5 ml of this solution to 20 ml with water R. 12 ml of the solution complies with limit test A for heavy metals (2 ppm). Prepare the standard using lead standard solution (2 ppm Pb) R.

Residue on evaporation

Evaporate 100.0 g to dryness on a water-bath and dry at 100 °C to 105 °C. The residue weighs not more than 10 mg (0.01 per cent).

ASSAY

Weigh accurately a ground-glass-stoppered flask containing 30 ml of water R.  Introduce 1.5 ml of the acid and weigh again. Titrate with 1 M sodium hydroxide, using methyl red solution R as indicator.

1 ml of 1 M sodium hydroxide is equivalent to 36.46 mg of HCl.

STORAGE

Store in a stoppered container made of glass or another inert material, at a temperature below 30 °C.