Preparation of Sodium by Down's cell

In down's cell sodium is prepared by electrolysis of molten (fused) sodium chloride some Cacl2 is added to low the melting point of Nacl from 801 c to 600 c.The cell consists of n iron vessel. A large block of graphite acts as an anode. Above the anode there is an iron dome for the collection of chlorine.

The cathode is made of iron or copper. It is separated from anode by iron gauze screen. When electric current passes through molten Nacl, following reactions take place.

                                                Nacl------>  Na+ + cl-

                                                Na+ + e- -------> Na ( at cathode)

                                                2cl- -----------> Cl2 + 2e- (at anode)

The sodium collects over cathode and chlorine collects over anode. They are taken out from different holes. This process has following advantages.

(1) The metallic fog is not produced. 

(2) Liquid sodium is collected at 600c.

(3) It gives 99.9% pure sodium.

(4) Material of the cell is not attacked by the products formed during electrolysis.