Chemistry PREPARATION, PROPERTIES AND USES OF COMPOUNDS OF HALOGEN
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PREPARATION, PROPERTIES AND USES OF COMPOUNDS OF HALOGEN

Fluorine (`F_2`) :

Modern method of Isolation :

In this method `F_2` is prepared by the electrolysis of fused fluoride, (`KHF_2`) potassium hydrogen fluoride. The electrolytic cells are made of `Cu`, `Ni` or monel metal. Reaction in the electrolytic cell : See fig.

(i) `text(Uses :)` It is used in the preparation of fluorine compound such as.

(a) Freon: Freon - 12 i.e. `CF_2Cl_2` as used in refrigeration and air conditioning in place of `NH_3` and

(b) Teflon : `(- F_2C - CF_2)_n`. It is a new plastic.


Chlorine (`Cl_2`) :

`text(Preparation :)`

(a) By the electrolysis of brine (Aq. solution of `NaCl`) in nelson cell. This is the cheapest method

`NaCl ⇋ Na^(+) + Cl^(-)`

`H_2O ⇋ H^(+) + OH^(-)`

At Cathode : `H^(+) + e^(-) -> H`

`H + H -> H_2`

At anode : `Cl^(-) -> Cl + e^(-)`

`Cl + Cl -> Cl_2`

(b) `text(Decon's Process :)`

`4HCl + O_2 -> 2H_2O + 2Cl_2 uparrow`

Chlorine gas thus obtained contains `N_2` and `O_2` and is used for the manufacture of bleaching powder by hansenclever's process

(c) `text(Lab Method :)` `MnO_2 + 4HCl -> MnCl_2 + Cl_2 + 2H_2O`

`text(Properties :)`

Bleaching :

`Cl_2 + H_2O -> 2HCl + [O]`

Coloured matter `+ [O] ->` Colourless matter.

`text(Uses :)`

(a) As a Germicide and disinfectant.

(b) Domestic antiseptic solution (`NaOCl`)

(c) In manufacture of bleaching powder, D.D.T etc.

(d) In warfare gases such as phosgene `CaOCl_2`, tear gas `(C Cl_3NO_2)` and mustard gas `(ClC_2H_4 - S - C_2H_4Cl)`

Bromide (`Br_2`) :

`text(Preparation :)`

Bittern : Mother liquar contains about `0.25%` of bromine or `MgBr_2` and is known as bittern. Bittern is treated with Chlorine gas.

`MgBr_2 + Cl_2 -> MgCl_2 + Br_2`.

`text(Uses :)`

It is used in preparation of ethyl bromide which is used in the manufactre of tetraethyllead (TEL) as an important anti-knock compound in the petroleum industry.

`C_2H_6 + Br_2 -> C_2H_5Br + HBr`

`4C_2H_5Br + 4Na - Pb -> (C_2H_5)_4 Pb + 4NaBr + 2Pb`

Iodine (`I_2`) :

(i) `I_2` is the rarest of all the halogens. Its main source is kelp (varee).

(ii) `text(Properties :)`

(a) It is only sparingly soluble in water but readily soluble in `Na` or `K` iodide due to formation of triiodide.

`KI + I_2 -> KI_3`

However, this solution behaves as a simple mixture of `KI` and free `I_2`.

`text(Note :)` Tincture of Iodine contains `2` ounce `I_2, 1/4` ounce `KI` and `1` pinch of rectified spirit.

(b) `text(Iodoform Reaction :)`

`2C_2H_5OH + 6KOH + 4I_2 -> HCOOK + CHI_3 + 5KI + H_2O`

Iodoform or Haloform reaction show by following- See fig.

When `R = H`, `CH_3, C_2H_5`, .

`R` = Benzyl and its derivatives

`R` = Every 2-Alcohol (not secondary)

`R` = `C_2H_5OH` (only Ethyl Alcohol in Primary)

`R` = No. tertiary Alcohol.

Potassium Chlorate (`KClO_3`) :

(i) On heating with conc. `HCl`, `KClO_3` gives a mixture of chlorine and chlorine dioxide known as exchlorine.

`2KClO_3 + 4HCl -> 2KCl + 2ClO_2 + Cl_2 + 2H_2O`

(ii) `text(Uses :)` In manufacturing of matches, fire works and photographic flash powders.
 
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