Question

How is chloride of lime chemically different from calcium chloride? Why does the chloride of lime gradually lose its chlorine when kept exposed to air?

Answer 1

1. The chloride of lime is calcium oxychloride (${\mathrm{CaOCl}}_2$), which is highly alkaline in nature.
2. Calcium oxychloride is also known as bleaching powder.
3. Whereas calcium chloride is ${\mathrm{CaCl}}_2$ and it is neutral in nature.
4. When chloride of lime or bleaching powder is exposed to air, it reacts with the carbon dioxide present in the air to evolve its chlorine as gas. Also, calcium carbonate is formed as a product.

Reaction involved:

$\underset{(\mathrm{Bleaching}\mathrm{powder})}{\underset{\mathrm{Chloride}\mathrm{of}\mathrm{lime}}{{\mathrm{CaOCl}}_2\left(\mathrm{s}\right)}}+{\mathrm{CO}}_2\left(\mathrm{g}\right)\stackrel{\mathrm{air}}{\to }\underset{\mathrm{Calcium}\mathrm{carbonate}}{{\mathrm{CaCO}}_3\left(\mathrm{s}\right)}+\underset{\mathrm{Chlorine}\mathrm{gas}}{{\mathrm{Cl}}_2\left(\mathrm{g}\right)}$

Therefore, the chloride of lime loses its chlorine when kept exposed to air due to a reaction with carbon dioxide.