Question

Explain how temporary hardness of water can be removed by boiling ?

Answer 1

Temporary hardness

• Temporary hardness of water refers to the hardness of water that is induced by the presence of dissolved Calcium and Magnesium bicarbonates in it.

Removal of temporary hardness of water

• The hard water can be temporarily softened by simply boiling it.
• Boiling can be used to reduce temporary hardness induced by dissolved Calcium bicarbonate $\left[{\mathrm{Ca}\left({\mathrm{HCO}}_3\right)}_2\right]$ and Magnesium bicarbonate $\left[{\mathrm{Mg}\left({\mathrm{HCO}}_3\right)}_2\right]$ .
• Calcium bicarbonate and Magnesium bicarbonate compounds in water breakdown to generate $({\mathrm{CaCO}}_3)$ and Magnesium Carbonate $({\mathrm{MgCO}}_3)$ , respectively, when heated over a period of time.
• These carbonates are insoluble in water and must be filtered to be separated.

$\underset{\mathrm{Calcium}\mathrm{bicarbonate}}{\mathrm{Ca}\left({\mathrm{HCO}}_3\right)\left(\mathrm{aq}\right)}\underset{\mathrm{heat}}{\overset{\mathrm{boil}}{\to }}\underset{\underset{(\mathrm{insoluble}\mathrm{salt})}{\mathrm{Calcium}\mathrm{Carbonate}}}{{\mathrm{CaCO}}_3\left(\mathrm{s}\right)}+\underset{\mathrm{Carbon}\mathrm{dioxide}}{{\mathrm{CO}}_2\left(\mathrm{g}\right)}+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}$

$\underset{\mathrm{Magnesium}\mathrm{bicarbonate}}{\mathrm{Mg}\left({\mathrm{HCO}}_3\right)\left(\mathrm{aq}\right)}\underset{\mathrm{heat}}{\overset{\mathrm{boil}}{\to }}\underset{\underset{(\mathrm{insoluble}\mathrm{salt})}{\mathrm{Magnesium}\mathrm{Carbonate}}}{{\mathrm{CaCO}}_3\left(\mathrm{s}\right)}+\underset{\mathrm{Carbon}\mathrm{dioxide}}{{\mathrm{CO}}_2\left(\mathrm{g}\right)}+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}$