Hydrochloric acid(HCL)

Hydrochloric acid:

Laboratory preparation:

It is prepared by the action of sodium chloride and concentrated sulphuric acid.

NaCl + H₂SO₄ → NaHSO₄ + HCl

NaHSO₄ + NaCl → Na₂SO₄ + HCl

Dry hydrochloric acid is obtained by passing the gas through conc. sulphuric acid

Properties:

Hydrogen chloride is a colourless, pungent smelling gas, easily liquefied to a colourless liquid (boiling point 189K) and frozen into a white crystalline solid (melting point 159K). It is extremely soluble in water.

HCl (g) + H₂O (l) → H₃O⁺ + Cl^-

Chemical properties:

Like all acids it liberates hydrogen gas from metals and carbon dioxide from carbonate and bicarbonate salts.

Zn + 2HCl → ZnCl₂ + H₂

Mg + 2HCl → MgCl₂ + H₂

Na₂CO₃ + 2HCl → 2NaCl + CO₂ + H₂

CaCO₃ + 2HCl → CaCl₂ + CO₂ + H₂

NaHCO₃ + 2HCl → 2NaCl + CO₂ + H₂O

It liberates sulphur dioxide from sodium sulphate

Na₂SO₄ + 2HCl → 2NaCl + H₂O + SO₂

When three parts of concentrated hydrochloric acid and one part of concentrated nitric acid are mixed, Aquaregia (Royal water) is obtained. This is used for dissolving gold, platinum etc...

Au + 4H⁺ + NO₃^- + 4 Cl^-  → AuCl₄^- + NO + 2H₂O

Pt + 8H⁺ + 4NO₃^- + 6Cl^- → [PtCl₆]²- + 4NO₂ + 4H₂O

Uses of hydrochloric acid:

·           Hydrochloric acid is used for the manufacture of chlorine, ammonium chloride, glucose from corn starch etc.,

·           It is used in the extraction of glue from bone and also for purification of bone black