Preparation of Caustic soda
- It is commercially prepared by electrolysis of sodium chloride in Castner-Kellner cell.
- Brine solution is first electrolyzed.
- Mercury is made the cathode.
- Carbon is made the anode.
- Sodium metal gets discharged at cathode.
- This discharged sodium combines with mercury and forms sodium amalgam.
- Chlorinegas is evolved at the anode.
- The amalgam then reacts with water and produces sodium hydroxide and hydrogen gas.
2Na-amalgam + 2H2O --> 2NaOH+ 2Hg +H2