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. How is compound Y formed from gas X? Write the chemical equation.

Answer 1

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

Reaction involves:

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

Gas X:

Gas X is Chlorine$\left({\mathrm{Cl}}_2\right)$ which is the by-product of the concentrated sodium chloride solution$\mathrm{\left(}\mathrm{NaCl}\mathrm{\right)}$.

Compound Y:

When this chlorine gas $\left({\mathrm{Cl}}_2\right)$ is passed through the suspension of slaked lime $\left(\mathrm{Ca}{\left(\mathrm{OH}\right)}_2\right)$, it forms calcium oxychloride $\left({\mathrm{CaOCl}}_2\right)$ which is compound Y. This compound Y is a bleaching powder for the clothes.

Chemical Reaction:

$\mathrm{Ca}{\left(\mathrm{OH}\right)}_2\left(\mathrm{s}\right)+{\mathrm{Cl}}_2\left(\mathrm{g}\right)\to {\mathrm{CaOCl}}_2\left(\mathrm{s}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$

Therefore, calcium oxychloride is formed when gas $\left({\mathrm{Cl}}_2\right)$ is passed through the suspension of slaked lime.