Hydrogen Chloride Chemistry PDF

Study of Compounds – Hydrogen Chloride Hydrogen Chloride Molecular formula: HCl Molecular mass: 36.5 amu Bond: Covalent Lewis structure Orbital diagram General Preparation of HCl gas i. By synthesis Moist hydrogen gas combines with chlorine in the p...

Study of Compounds – Hydrogen Chloride Hydrogen Chloride Molecular formula: HCl Molecular mass: 36.5 amu Bond: Covalent Lewis structure Orbital diagram General Preparation of HCl gas i. By synthesis Moist hydrogen gas combines with chlorine in the presence of diffused sunlight. ii. By heating metallic chloride with conc. sulphuric acid Laboratory Preparation of Hydrogen Chloride Hydrogen chloride gas is prepared by heating a metallic chloride (NaCl) with conc. sulphuric acid (H 2SO4). Reactions: Collection  Hydrogen chloride gas is collected by the upward displacement of air as it is 1.28 times heavier than air.  It is not collected over water because it is highly soluble in water. Physical Properties  Colourless, pungent, choking odour, slight sour taste.  It is 1.28 times heavier than water and highly soluble in water.  Liquefies at temperature of about 10°C at 40 atmospheric pressure.  Boiling point is −83°C, and freezing point is −113°C. Chemical Properties of HCl 1. Combustibility: The gas is neither combustible nor a supporter of combustion. 2. Thermal dissociation: On heating above 500°C, it dissociates into hydrogen and chlorine. 3. With metals: Metals which come before hydrogen in the electrochemical series form chlorides with the liberation of hydrogen. Zn + 2HCl  ZnCl2 + H2 (g) 4. Reaction with ammonia: It combines with ammonia to form dense white fumes of ammonium chloride. NH3 (g) + HCl (g)  NH4Cl Hydrochloric Acid Hydrochloric acid is prepared by dissolving hydrogen chloride gas in water using a special funnel arrangement because direct absorption of HCl gas in water using a delivery tube causes back suction. Properties of Hydrochloric Acid Physical Properties  Colourless, slightly pungent with sharp sour taste.  Corrosive in nature and causes blisters on the skin.  Density is 1.2 gm/cc with boiling point of 110°C. Chemical Properties  Monobasic in nature HCl dissociates in aqueous solution to produce one hydrogen ion [H+] per molecule of the acid. HCl + H2O  H3O+ + Cl−  Acidic nature The presence of hydrogen ion [H+] in HCl imparts acidic properties to an aqueous solution of hydrochloric acid.  Action on metals Ca + 2HCl  CaCl2 + H2 Mg + 2HCl  MgCl2 + H2  Action on oxides and hydroxides MgO + 2HCl  MgCl2 + H2O Ca (OH)2 + 2HCl  CaCl2 + H2O  With salts of weaker acids Na2CO3 + 2HCl  2NaCl + H2O + CO2 NaHCO3 + HCl  NaCl + H2O + CO2 Na2SO3 + 2HCl  2NaCl + H2O + SO2 NaHSO3 + HCl  NaCl + H2O + SO2 Na2S + 2HCl  2NaCl + H2S  Action on thiosulphates Na2SO3 + 2HCl  2NaCl + H2O + SO2 + S  Reaction with nitrates AgNO3 + HCl  AgCl + HNO3 Oxidation of Hydrochloric Acid MnO2 + 4HCl MnCl2 + 2H2O + Cl2 K2Cr2O7 + 14HCl 2KCl + 2CrCl3 + 7H2O + 3Cl2 2KMnO4 + 16HCl 2KCl + 2MnCl2 + 8H2O + 5Cl2 Pb3O4 + 8HCl 3 PbCl2 + 4H2O + Cl2 Formation of Aqua Regia Aqua regia is a mixture of one part of conc. nitric acid and three parts of conc. hydrochloric acid. HNO3 + 3HCl  NOCl + 2H2O + 2[Cl] The nascent chlorine released reacts with noble metals such as gold and platinum to give their soluble chlorides. Au + 3[Cl]  AuCl3 Pt + 4[Cl]  PtCl4 Uses of Hydrochloric Acid a. In the manufacture of dyes, drugs, paints and silver chloride. b. For purifying bone black, because HCl dissolves the calcium phosphate present in bones. c. To remove rust from iron sheets.