Write preparation of dichlorine (`Cl_2`).

Explanation

(A) General Methods : By heating manganese dioxide with concentrated hydrochloric acid.
`MnO_2 + 4HCl to MnCl_2 + Cl_2 + 2H_2O`
However, a mixture of common salt and concentrated `H_2SO_4` is used in place of HCl
`4NaCl + MnO_2 + 4H_2SO_4 to MnCl_2 + 4NaHSO_4 + 2H_2O + Cl_2`
By the action of HCl on potassium permanganate.
`2KMnO_4 + 16HCl 2KCl + 2MnCl_2 + 8H2_O + 5Cl_2`
(B) Manufacture of dichlorine :
(i) Deacon.s process: By oxidation of hydrogen chloride gas by atmospheric oxygen in the presence of `CuCl_2` (catalyst) at 723 K.
`4HCl + O_2 CuCl_2 gt 2Cl_2 + 2H_2O`
(ii) Electrolytic process : Chlorine is obtained by the electrolysis of brine (concentrated NaCl solution). Chlorine is liberated at anode. It is also obtained as a by product in many chemical industries.
Anode : `2Cl_(aq) to Cl_2(g) + 2e^(-)`
Chlorine was discovered in 1774 by Scheele by action of HCl on `MnO_2`. In 1810, Davy established its elementary nature and suggested the name chlorine on account of its colour (Greek, Chloros = Greenish Yellow).