s-Block Elements

In which of the following processes, fused sodium hydroxide is electrolysed at a temperature of 330 C for extraction of sodium?

1. Castner's process
2. Downs process
3. Cyanide process
4. Both (2) and (3)

Answer

(1) Castner's process

Solution

In Castner's process, fused NaOH is electrolysed at about 330 C (iron cathode, nickel anode):

Cathode: Na+ + e- Na

Anode: 4OH- 2H2O + O2 + 4e-

Downs process: electrolysis of fused NaCl (mixed with CaCl2) — the present commercial method for sodium.

Cyanide process: extraction of silver and gold by leaching with NaCN solution.

∴ The process is Castner's process.

Answer: (1)