What do you know about Castner-Kellner process? Write the principle involved in it.

Explanation

Castner- Kellner process is a commerical method used for the preparation of sodium hydroxide.
In this process sodium hydroxide is prepared by the electrolysis of sodium chloride in Castner- Kellner cell.
Brine solution is electrolysed using a mercury cathode and a carbon anode.
Sodium metal is formed at cathode and it combine with mercury to form sodium amalgam. Chlorine gas is evolved at anode.
The amalgum is treated with water to form sodium hydroxide.
Cell reactions:
`2NaCl to 2Na^(+) +2Cl^-`
`2Na^+ + 2e^(-) overset(Hg) to 2Na`- amalgam
`2Cl^(-) to Cl_2 +2e^(-)`
2Na- amalgam `+2 H_2O to 2NaOH +2Hg +H_2`
This process is also called as mercury cathode process.