Question

In the manufacture of caustic soda by Castner-Kellner process, the by-products formed are:

• A. $H_2,C{l}_2$
• B. $C{l}_2,O_2$
• C. $H_2,O_2$
• D. $N_2,C{l}_2$

Answer 1

The correct option is A $H_2,C{l}_2$

Chlorine should not comes in contact with NaOH during electrolysis of NaCl, otherwise following reaction will takes place.

$2NaOH+C{l}_2\to NaCl+NaOCl+H_{2}O$

To overcome this problem, the anode is separated from the cathode in the electrolytic cell by using a mercury cathode. The mercury cathode cell is known as Castner-Kellner cell.

The process of preparing NaOH solution by electrolysis of sodium chloride in Castner-Kellner cell is called Castner-Kellner process.

$2C{l}^{-}\to C{l}_2+2e^{-}\text{[Anode]}2N{a}^{+}+2e^{-}\to 2Na\text{[Cathode]}Na+Hg\to Na-Hg\text{[Amalgam]}2Na-Hg+2H_{2}O\to 2NaOH+2Hg+H_2$

The by-products obtained in the process are $H_2$ and $C{l}_2$ respectively.