ü Chlorine (Cl2):

Ø Preparation: It can be prepared by any one of the following methods:

·       By heating manganese dioxide with concentrated hydrochloric acid.

MnO2 + 4HCl → MnCl2 + Cl2 + 2H2O

Conc. HCl can be replaced by a mixture of common salt and concentrated H2SO4

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

·       By the action of HCl on potassium permanganate.

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

Ø  Manufacture of Chlorine:

·        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

·      Electrolytic Process: Chlorine is obtained by the electrolysis of brine solution (concentrated NaCl solution). During electrolysis chlorine is liberated at the anode.



 

Ø  Properties: 

·       It is a greenish yellow gas with pungent and suffocating odour.

·       It is soluble in water.

·       It 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

·      With excess ammonia, chlorine gives nitrogen and ammonium chloride whereas with excess chlorine, nitrogen trichloride (explosive) is formed.

8NH3 + 3Cl2 → 6NH4Cl + N2

(excess)

NH3 + 3Cl2 → NCl3 + 3HCl                                             

                    (excess)

·  With cold and dilute alkalies chlorine produces a mixture of chloride and hypochlorite.

2NaOH + Cl2 → NaCl + NaOCl + H2O         

(cold and dilute)

With hot and concentrated alkalies it gives chloride and chlorate.

6 NaOH + 3Cl2 → 5NaCl + NaClO3 + 3H2O

(hot and conc.)

·       With dry slaked lime it gives bleaching powder-+.

2Ca(OH)2 + 2Cl2 → CaOCl2 + CaCl2 + 2H2O

·   Chlorine reacts with hydrocarbons and gives substitution products with saturated hydrocarbons and addition products with unsaturated hydrocarbons.

CH4 + Cl2 ⎯⎯UV⎯→ CH3Cl + HCl

Methane      Methyl chloride

 

·      Chlorine water on standing loses its yellow colour due to the formation of HCl and HOCl. Hypochlorous acid (HOCl) so formed is unstable and dissociates to give nascent oxygen which is responsible for oxidising and bleaching properties of chlorine.

·       It oxidises ferrous to ferric, sulphite to sulphate, sulphur dioxide to sulphuric acid and iodine to iodic acid.

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

Na2SO3 + Cl2 + H2O → Na2SO4 + 2HCl

SO2 + 2H2O + Cl2 → H2SO4 + 2HCl

I2 + 6H2O + 5Cl2 → 2HIO3 + 10HCl

·       It is a powerful bleaching agent. Bleaching action is due to oxidation. 

      Cl2 + H2O → 2HCl + [O]

Coloured substance + [O] → Colourless substance

It bleaches vegetable or organic matter in the presence of moisture. Its bleaching action is permanent.

 

Ø  Uses of Cl2: It is used

·       For bleaching wood pulp, bleaching cotton and textiles

·       In the extraction of gold and platinum

·       In the manufacture of dyes, drugs and organic compounds such as CCl4, CHCl3, DDT, refrigerants, etc.

·       In sterilising drinking water

·  Preparation of poisonous gases such as Phosgene (COCl2), Tear gas (CCl3NO2), Mustard gas (ClCH2CH2SCH2CH2Cl).