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Chlorine - Preparation, Physical and Chemical Properties, Manufacture, Structure, Uses | Study Material, Lecturing Notes, Assignment, Reference, Wiki description explanation, brief detail |

Chapter: 12th Chemistry : p-Block Elements-II

Chlorine

Chlorine is highly reactive hence it doesn’t occur free in nature. It is usually distributed as various metal chlorides.


Chlorine is highly reactive hence it doesn’t occur free in nature. It is usually distributed as various metal chlorides. The most important chloride is sodium chloride which occurs in sea water.


Preparation:

Chlorine is prepared by the action of conc. sulphuric acid on chlorides in presence of manganese dioxide.

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

It can also be prepared by oxidising hydrochloric acid using various oxidising agents such as manganese dioxide, lead dioxide, potassium permanganate or dichromate.

PbO2 + 4HCl → PbCl2 + 2H2O + Cl2

MnO2 + 4HCl → MnCl2 + 2H2O + Cl2

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

K2Cr2O7 + 14HCl → 2KCl + 2CrCl3 + 7H2O + 3Cl2

When bleaching powder is treated with mineral acids chlorine is liberated

CaOCl2 + 2HCl → CaCl2 + H2O + Cl2

CaOCl2 + H2SO4 → CaSO4 + H2O + Cl2


Manufacture of chlorine:

Chlorine is manufactured by the electrolysis of brine in electrolytic process or by oxidation of HCl by air in Deacon’s process.

Electrolytic process: When a solution of brine (NaCl) is electrolysed, Na+ and Cl ions are formed. Na+ ion reacts with OH- ions of water and forms sodium hydroxide. Hydrogen and chlorine are liberated as gases.


Deacon’s process: In this process a mixture of air and hydrochloric acid is passed up a chamber containing a number of shelves, pumice stones soaked in cuprous chloride are placed. Hot gases at about 723 K are passed through a jacket that surrounds the chamber.


The chlorine obtained by this method is dilute and is employed for the manufacture of bleaching powder. The catalysed reaction is given below,

2Cu2Cl2 + O2 → 2Cu2OCl2 Cuprous oxy chloride

Cu2OCl2 + 2HCl → 2CuCl2 Cupric chloride + H2O

2CuCl2 → Cu2Cl2 Cuprous chl + Cl2


Physical properties:

Chlorine is a greenish yellow gas with a pungent irritating odour. It produces headache when inhaled even in small quantities whereas inhalation of large quantities could be fatal. It is 2.5 times heavier than air.

Chlorine is soluble in water and its solution is referred as chlorine water. It deposits greenish yellow crystals of chlorine hydrate (Cl2.8H2O). It can be converted into liquid (Boiling point – 34.6° C) and yellow crystalline solid (Melting point -102° C)


Chemical properties:

Action with metals and non-metals: It reacts with metals and non metals to give the corresponding chlorides.

2Na + Cl2 → 2NaCl

2Fe + 3Cl2 → 2FeCl3

2Al + 3Cl2 → 2AlCl3

Cu + Cl2 → CuCl2

H2 + Cl2 2HCl ; H = 44kCal

2B + 3Cl2 → 2BCl3

2S + Cl2 → S2Cl2 disulphur dichloride

P4 + 6Cl2 → 4PCl3

2As + 3Cl2 → 2AsCl3

2Sb + 3Cl2 → 2SbCl3

Affinity for hydrogen : When burnt with turpentine it forms carbon and hydrochloric acid.

C10H16 + 8Cl2 → 10C + 16HCl

It forms dioxygen when reacting with water in presence of sunlight. When chlorine in water is exposed to sunlight it loses its colour and smell as the chlorine is converted into hydrochloric acid.

2Cl2 + 2H2O → O2 + 4HCl

Chlorine reacts with ammonia to give ammonium chloride and other products as shown below:

With excess ammonia,

2NH3 + 3Cl2 N2 + 6HCl

6HCl + 6 NH3 6 NH4Cl

overall reaction

8NH3 + 3Cl2 → N2 + 6 NH4Cl

With excess chlorine,

NH3 + 3Cl2 NCl3 + 3HCl

3HCl + 3NH3 3NH4Cl

overall reaction

4NH3 + 3Cl2 NCl3 + 3NH4Cl

Chlorine oxidises hydrogen sulphide to sulphur and liberates bromine and iodine from iodides and bromides. However, it doesn't oxidise fluorides

H2S + Cl2 2HCl + S

Cl2 + 2KBr 2KCl + Br2

Cl2 + 2KI 2KCl + I2

Reaction with alkali: Chlorine reacts with cold dilute alkali to give chloride and hypochlorite while with hot concentrated alkali chlorides and chlorates are formed.

Cl2 + H2O HCl + HOCl

HCl + NaOH NaCl + H2O

HOCl + NaOH NaOCl + H2O

overall reaction


Cl2 + 2NaOH NaOCl sodium hypo chlorite + NaCl + H2O

( Cl2 + H2O HCl + HOCl) × 3

( HCl + NaOH NaCl + H2O) × 3

( HOCl + NaOH NaOCl + H2O) × 3

3NaOCl NaClO3 + 2NaCl

overall reaction

3Cl2 + 6NaOH NaClO3 + 5NaCl + 3H2O

Oxidising and bleaching action: Chlorine is a strong oxidising and bleaching agent because of the nascent oxygen.

H2O + Cl2 HCl + HOCl Hypo chlorous acid

HOCl HCl + (O)

Colouring matter + Nascent oxygen → Colourless oxidation product

The bleaching of chlorine is permanent. It oxidises ferrous salts to ferric, sulphites to sulphates and hydrogen sulphide to sulphur.

2FeCl2 + Cl2 → 2FeCl3

Cl2 + H2O →HCl + HOCl

2FeSO4 + H2SO4 + HOCl →Fe2 (SO4 )3 + HCl + H2O

overall reaction

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

Cl2 + H2O →HCl + HOCl

Na2SO3 + HOCl →Na2SO4 + HCl

overall reaction

Na2SO3 + H2O + Cl2 →Na2SO4 + 2HCl

Cl2 + H2S →2HCl + S

Preparation of bleaching powder: Bleaching powder is produced by passing chlorine gas through dry slaked lime (calcium hydroxide).

Ca(OH)2 + Cl2 → CaOCl2 + H2O

Displacement redox reactions: Chlorine displaces bromine from bromides and iodine from iodide salts.

Cl2 + 2KBr → 2KCl + Br2

Cl2 + 2KI →2KCl + I2

Formation of addition compounds: Chlorine forms addition products with sulphur dioxide, carbon monoixde and ethylene. It forms substituted products with alkanes/arenes.

SO2 + Cl2 → SO2Cl2Sulphuryl chloride

CO + Cl2 → COCl2Carbonyl chloride

C 2 H4 + Cl2 → C2H4Cl2ethylene dichloride

CH4 + Cl2 →CH3Cl + HCl

C6H6 + Cl2 FeCl3→C6H5Cl + HCl



Uses of chlorine:

·           It is used in

·           Purification of drinking water

·           Bleaching of cotton textiles, paper and rayon

·           Extraction of gold and platinum

 

Tags : Preparation, Physical and Chemical Properties, Manufacture, Structure, Uses Preparation, Physical and Chemical Properties, Manufacture, Structure, Uses
Study Material, Lecturing Notes, Assignment, Reference, Wiki description explanation, brief detail


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