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
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-
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
· 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