Hydrogen Chloride (HCl)

Hydrogen Chloride:

(1) HCl gas is obtained by a direct combination of H₂ and Cl₂ in the presence of diffused sunlight.

(2) HCl gas is prepared in the laboratory by the action of conc. H₂SO₄ and NaCl.

(3) HCl gas is dried by conc. H₂SO₄ and not by CaO or P₂O₅ because it reacts with them.

(4) Hydrogen Chloride gas is collected by upward displacement of air, as it is heavier than air and highly soluble in water.

(5) Hydrogen Chloride gas is colorless, pungent smell, and sour taste, density of 18.25, and is highly soluble in water- demonstrated by the Fountain experiment, acidic in nature.

(6) HCl gas reacts with NH₃ gas to form solid NH₄Cl.

(7) When HCl gas is passed through water until no more gas is absorbed, hydrochloric acid is formed which contains about 36% HCl by weight. Thus, an aqueous solution of HCl gas is HCl acid and completely ionized.

(8) An aqueous solution of Hydrogen Chloride containing 22.2% HCl by mass is azeotropic i.e., constant boiling mixture.

(9) HCl is a strong monobasic acid. Its acidic properties are exhibited by reactions with metals, oxides, hydroxides, carbonates, sulfites, and sulfides.

(10) With AgNO₃, white ppt. of AgCl is formed which is soluble in NH₄OH to form complex [Ag(NH₃)₂]Cl.

(11) With lead nitrate, white ppt. of PbCl₂ is formed which is soluble in hot water.

(12) Aqua regia is a mixture of one part by volume of conc. HNO₃ and three parts by volume of conc. HCl. It can dissolve noble metals like Pt and Au.

(13) Conc. HCl shows reducing properties as it is oxidized by strong oxidizing agents like MnO₂, PbO₂, Pb₃O₄, CaCl₂, KMnO₄, K₂Cr₂O₇, etc. with the formation of metal chlorides, water, and greenish-yellow chlorine gas.

(14) Hydrochloric acid is used in the manufacture of drugs, dyes, paints, glucose, etc., in the tanning industry, in the steel industry, and as a reagent.