Chemistry Preparation of Chlorine

Topics Covered :

● Preparation of Chlorine
● Manufacture of Chlorine
● Properties of Chlorine
● Uses of Chlorine

Chlorine :

`=>` Chlorine was discovered in `1774` by Scheele by the action of `color{red}(HCl)` on `color{red}(MnO_2)`.

`=>` In `1810` Davy established its elementary nature and suggested the name chlorine on account of its colour (Greek, chloros = greenish yellow).

Preparation :

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

(i) By heating manganese dioxide with concentrated hydrochloric acid.

`color{red}(MnO_2 +4HCl → MnCl_2 +Cl_2 +2H_2O)`

However, a mixture of common salt and concentrated `color{red}(H_2SO_4)` is used in place of `color{red}(HCl)`.

(ii) By the action of `color{red}(HCl)` on potassium permanganate.

`color{red}(2KMnO_4 +16 HCl → 2KCl +2MnCl_2 +8H_2O +5Cl_2)`

Manufacture of chlorine :

(i) `color{green}("Deacon’s Process ")` : By oxidation of hydrogen chloride gas by atmospheric oxygen in the presence of `color{red}(CuCl_2)` (catalyst) at `723 K`.

`color{red}(4HCl+O_2 overset (CuCl_2)→ 2Cl_2+2H_2O)`

(ii) `color{green}("Electrolytic Process" )` : Chlorine is obtained by the electrolysis of brine (concentrated `color{red}(NaCl)` solution).

● Chlorine is liberated at anode.

● It is also obtained as a by–product in many chemical industries.

Properties :

`=>` It is a greenish yellow gas with pungent and suffocating odour.

`=>` It is about `2-5` times heavier than air.

`=>` It can be liquefied easily into greenish yellow liquid which boils at `239 K`.

`=>` It is soluble in water.

`=>` Chlorine reacts with a number of metals and non-metals to form chlorides.

`color{red}(2Al +3Cl_2 → 2AlCl_3 ; \ \ \ \ \ \ \ \ P_4 +6Cl_2 → 4PCl_3)`

`color{red}(2Na + Cl_2 → 2NaCl ; \ \ \ \ \ \ \ \ \ S_8+4Cl_2 → 4S_2Cl_2)`

`=>` It has great affinity for hydrogen. It reacts with compounds containing hydrogen to form `color{red}(HCl)`.

`color{red}(H_2+Cl_2 → 2HCl)`

`color{red}(H_2S + Cl_2 → 2HCl + S)`

`color{red}(C_(10) H_(16) +8Cl_2 → 16 HCl +10 C)`

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

`color{red}(undersettext{(excess)} (8NH_3) +3Cl_2 → 6NH_4Cl +N_2 ; \ \ \ \ \ \ NH_3 + undersettext{(excess)}(3Cl_2) → NCl_3+3HCl)`

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

`color{red}(undersettext{(cold and dilute)} (2NaOH) +3Cl_2 → 5NaCl +NaOCl+H_2O)`

`color{red}(undersettext{(hot and conc.)}(6 Na OH) +3Cl_2 → 5NaCl +NaClO_3+3H_2O)`

`=>` With dry slaked lime it gives bleaching powder.

`color{red}(2Ca (OH)_2+2Cl_2 → Ca (OCl)_2 + CaCl_2+2H_2O)`

● The composition of bleaching powder is `color{red}(Ca(OCl)_2.CaCl_2.Ca(OH)_2 . 2H_2O).`

`=>` Chlorine reacts with hydrocarbons and gives substitution products with saturated hydrocarbons and addition products with unsaturated hydrocarbons. For example,

`color{red}(undersettext(Methane) (CH_4) +Cl_2 overset(UV)→ undersettext{Methyl chloride}(CH_3Cl) +HCl)`

`color{red}(undersettext(Ethane)(C_2H_4) +Cl_2 oversettext(Room temp.)→ undersettext(1,2-Dichloroethane) (C_2H_4Cl_2))`

`=>` Chlorine water on standing loses its yellow colour due to the formation of `color{red}(HCl)` and `color{red}(HOCl)`.

● Hypochlorous acid `color{red}(HOCl)` so formed, gives nascent oxygen which is responsible for oxidising and bleaching properties of chlorine.

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

`color{red}(2FeSO_4 +H_2SO_4 + Cl_2 → Fe_2 (SO_4)_3+2HCl)`

`color{red}(Na_2SO_3 +Cl_2 +H_2O → Na_2SO_4 +2HCl)`

`color{red}(SO_2+2H_2O +Cl_2 → H_2SO_4 +2HCl)`

`color{red}(I_2+6H_2O +5Cl_2 → 2HIO_3+10HCl)`

(ii) It is a powerful bleaching agent; bleaching action is due to oxidation.

`color{red}(Cl_2+H_2O → 2HCl)`

Coloured substance `color{red}(+ O →)` Colourless substance It bleaches vegetable or organic matter in the presence of moisture. Bleaching effect of chlorine is permanent.
Q 3070691516

Write the balanced chemical equation for the reaction of `Cl_2` with hot and concentrated `NaOH`. Is this reaction a disproportionation
reaction? Justify.


`3Cl_2 + 6NaOH → 5NaCl + NaClO_3 + 3H_2O` Yes, chlorine from zero oxidation state is changed to –1 and +5 oxidation states.

Uses :

`color{green}("It is used ")` :

● For bleaching wood pulp (required for the manufacture of paper and rayon), bleaching cotton and textiles

● In the extraction of gold and platinum

● In the manufacture of dyes, drugs and organic compounds such as `color{red}(C Cl_4, CHCl_3)`, DDT, refrigerants, etc.

● In sterilising drinking water and

● Preparation of poisonous gases such as phosgene `color{red}(COCl_2)`, tear gas `color{red}(C Cl_3NO_2)`, mustard gas `color{red}(ClCH_2CH_2SCH_2CH_2Cl)`