Question

Sodium hydroxide or caustic soda is a useful industrial chemical and is manufactured by chlor-alkali process. In the process, a gas X is formed as the by-product. It reacts with slaked lime to give a compound Y which finds application as a bleaching agent for the clothes. Write the chemical equation involved in this process.

Answer 1

Chlor-alkali process is used for the manufacture of hydrogen $\left({\mathrm{H}}_2\right)$, chlorine $\left({\mathrm{Cl}}_2\right)$, and sodium hydroxide (NaOH).

Chemical equation:

$2\mathrm{NaCl}\left(\mathrm{aq}\right)+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\stackrel{\mathrm{electrolysis}}{\to }2\mathrm{NaOH}\left(\mathrm{aq}\right)+{\mathrm{H}}_2\left(\mathrm{g}\right)+{\mathrm{Cl}}_2\left(\mathrm{g}\right)$

In the above reaction, sodium chloride $\mathrm{NaCl}\left(\mathrm{aq}\right)$ decomposes when electricity is passed through it to form sodium hydroxide $\mathrm{NaOH}\left(\mathrm{aq}\right)$, hydrogen ${\mathrm{H}}_2\left(\mathrm{g}\right)$ and chlorine ${\mathrm{Cl}}_2\left(\mathrm{g}\right)$ as a by-product.

This process is called as Chlor-alkali process.