Question

How can temporary hardness of water be removed? Give proper chemical equation in support of you answer.

Answer 1

The presence of magnesium and calcium carbonates in water makes it temporarily hard.

• Hardness of water can be removed by boiling the water.
• When we boil the water the soluble salts of Mg(HCO₃)₂ is converted to Mg(OH)₂ which is insoluble and hence gets precipitated and is removed.
• To remove hardness by boiling the bicarbonates changes to insoluble carbonate and water becomes soft.
• $$\begin{gathered} \underset{\mathrm{calcium}\mathrm{bicarbonate}}{\underset{}{\mathrm{Ca}{\left({\mathrm{HCO}}_3\right)}_2}}\stackrel{\mathrm{boil}}{\to }\underset{\mathrm{calcium}\mathrm{carbonate}}{\underset{}{{\mathrm{CaCO}}_3}}\downarrow +{\mathrm{CO}}_2+{\mathrm{H}}_2\mathrm{O} \\ \underset{\mathrm{magnesium}\mathrm{bicarbonate}}{\underset{}{\mathrm{Mg}{\left({\mathrm{HCO}}_3\right)}_2}}\stackrel{\mathrm{boil}}{\to }\underset{\mathrm{magnesium}\mathrm{carbonate}}{\underset{}{{\mathrm{MgCO}}_3}}\downarrow +{\mathrm{CO}}_2+{\mathrm{H}}_2\mathrm{O} \end{gathered}$$