Chlorine

Occurrence

Common salt, NaCl is the major source of chlorine. It is also present in sea water and as rock salt.

Preparation of Chlorine

a. By heating manganese dioxide with concentrated hydrochloric acid.

MnO₂ + 4HCl → MnCl₂ + Cl₂ + 2H₂O

However, a mixture of common salt and concentrated H₂SO₄ is used in place of HCl (Weldon’s Process).

4NaCl + MnO₂ + 4H₂SO₄ → MnCl₂ + 4NaHSO₄ + 2H₂O + Cl₂

b. By the action of HCl on potassium permanganate.

2KMnO₄ + 16HCl → 2KCl + 2MnCl₂ + 8H₂O + 5Cl₂

Oxo acid	Name
H3PO2	Hypophosphorus acid
H3PO3	Phosphorus acid
H4P2O6	Hypophosphoric acid
H3PO4	Orthophosphoric acid
H4P2O7	Pyrophosphoric acid
HPO3	Metaphosphoric acid

Manufacture of chlorine

a. Deacon’s process:
By oxidation of hydrogen chloride gas by atmospheric oxygen in the presence of CuCl₂(catalyst) at 723 K.

4HCl + O₂  2Cl₂ + 2H₂O

b. Electrolytic process:
Chlorine is obtained by the electrolysis of brine (concentrated NaCl solution). Chlorine is liberated at anode. It is also obtained as a by–product in many chemical industries.

2NaCl + 2H₂O ↔ 2NaOH + Cl₂ + H₂

Physical properties of chlorine

It is yellowish green gas, collected by upward displacement of (it is heavier than) air, poisonous in nature, soluble in water. It’s aqueous solution is known as chlorine water. Boiling point is 239K.

Chemical properties of chlorine

• Chlorine reacts with a number of metals and non-metals to form chlorides.

2Al + 3Cl₂ → 2AlCl₃

P₄ + 6Cl₂ → 4PCl₃

2Na + Cl₂ → 2NaCl

S₈ + 4Cl₂ → 4S₂Cl₂

2Fe + 3Cl₂ → 2FeCl₃

• It has great affinity for hydrogen,

H₂ + Cl₂ → 2HCl

H₂S + Cl₂ → 2HCl + S

C₁₀H₁₆ + 8Cl₂ → 16HCl + 10C

• Action of water

Cl₂ + H₂O → HOCl + HCl

HOCL → HCl + [O] (Nascent Oxygen)

• The bleaching action of chlorine is due to oxidation and is permanent.

Cl₂ + H₂O → 2HCl + [O]

Coloured matter + [O] → colourless matter

With dry slaked lime it gives bleaching powder.

2Ca(OH)₂ + 2Cl₂ → Ca(OCl)₂ + CaCl₂ + 2H₂O

The composition of bleaching powder is Ca(OCl)₂.CaCl₂.Ca(OH)₂.2H₂O.

• It oxidises ferrous to ferric and sulphite to sulphate. Chlorine oxidises sulphur dioxide to sulphur trioxide and iodine to iodate. In the presence of water they form sulphuric acid and iodic acid respectively.

2FeSO₄ + H₂SO₄ + Cl₂ → Fe₂(SO₄)₃ + 2HCl

Na₂SO₃ + Cl₂ + H₂O → Na₂SO₄ + 2HCl

SO₂ + 2H₂O + Cl₂ → H₂SO₄ + 2HCl

I₂ + 6H₂O + 5Cl₂ → 2HIO₃ + 10HCl

• With cold and dilute alkalies chlorine produces a mixture of chloride and hypochlorite but with hot and concentrated alkalies it gives chloride and chlorate.

• Chlorine reacts with hydrocarbons and gives substitution products with saturated hydrocarbons and addition products with unsaturated hydrocarbons. For example,

CH₄ + Cl₂ CH₃Cl + HCl

C₂H₄ + Cl₂  C₂H₄Cl₂

Uses of chlorine

Ø Chlorine is used for bleaching wood pulp (required for the manufacture of paper and rayon), bleaching cotton and textiles.

Ø It is used in the extraction of gold and platinum.

Ø It is used in the manufacture of dyes, drugs and organic compounds such as CCl₄, CHCl₃, DDT, refrigerants, etc.

Ø It is used in sterilising drinking water.

Ø Chlorine is used in preparation of poisonous gases such as phosgene (COCl₂), tear gas (CCl₃NO₂), mustard gas (ClCH₂CH₂SCH₂CH₂Cl).