CHLORINE (PREPARATION, PROPERTIES AND USES)

CHLORINE

Chlorine is the most important element of all halogens. It was discovered by Scheede in 1774 when he heated some concentrated hydrochloric acid with manganese (IV) oxide. The gas was named Chlorine in 1810 by Davy from the Greek word ‘Chloros’ meaning greenish yellow.

Laboratory Preparation of Chlorine

Chlorine is generally prepared in the laboratory by the oxidation of concentrated hydrochloric acid (HCl). The two common oxidising agents that can be used are manganese (IV) oxide (MnO₂) and potassium tetraoxomanganate (VII) acid (KMnO₄).

Industrial Preparation of Chlorine

Chlorine is prepared or manufactured industrially by the electrolysis of:

·        Brine

·         Chlorides of molten sodium, magnesium and calcium. The chlorine is then liquefied and stored under pressure in steel cylinders.

Physical Properties of Chlorine

a. Chlorine is a greenish-yellow gas with choking, unpleasant, irritating smell

b. It is denser than air

c. It is moderately soluble in water

d. It is easily liquefied under pressure

e. Chlorine is a poisonous gas. If inhaled to a very small extent, it can damage the mucous lining of the lungs.

Chemical Properties of Chlorine

Chlorine combines directly with most other elements to form chlorides. It reacts directly with metals and non-metals to form metallic and non-metallic chlorides.

a. Reactions with metals: metals react readily with chlorine especially when heated to form their chlorides. Example;

   2Na_(s) + Cl₂ → 2NaCl_(s)

   Mg_(s) + Cl_2(g)  → MgCl₂

b. Reaction with non-metals: with the exception of oxygen, carbon, nitrogen and noble gases, all other non-metals burn in chlorine to produce the corresponding chlorides. Examples include burning of phosphorous in chlorine to produce a mixture of phosphorous (V) chloride and phosphorous (III) chloride.

  2P + 3Cl₂ → 2PCl₃

  2P + 5Cl₂ → 2PCl₅

c. Chlorine as an oxidizing agent: chlorine readily removes hydrogen from its compound to form hydrogen chloride. Chlorine behaves as an oxidizing agent by removing hydrogen from compounds like ammonia, hydrogen sulphide, hydrocarbons, iron (II) chloride and trioxosulphate ((IV) ion.

d. Reaction with alkalis: chlorine forms a pale yellow solution of sodium oxochlorate (I) when passed into a cold sodium hydroxide solution.

NaOH_(aq) + Cl_2(g) → NaCl_(aq) + NaClO_(aq) + H₂O_(l)

e. As a bleaching agent: chlorine is a common bleaching agent. It bleaches most dyes and inks in the presence of water

  HOCl_(aq) + HCl_(aq) → [O] Dye + [O] → (Dye + O)

Uses of Chlorine

a. Chlorine is used as a bleaching agent for cotton, linen and wood- pulp.

b. It is used in the sterilization of water for domestic and industrial use

c. Chlorine is used in the manufacture of important organic solvents such as trichloromethane (CHCl₃), trichloroethene (C₂HCl₃) and trichloro ethanal (CCl₃. CHO).

d. It is used in the manufacture of plastic, poly(chloroethene) known as PVC and synthetic rubber

e. It is used in the manufacture of hydrochloric acid and domestic antiseptic such as acidified sodium oxochlorate (1) solution.