Question

How does water get temporarily hard in nature?Give proper reactions in support of your answer.

Answer 1

• The presence of calcium and magnesium bicarbonates Ca(HCO₃​)_2​ and Mg(HCO₃​)₂​ causes temporary hardness in water.
• The presence of soluble salts of calcium and magnesium, i.e., sulfates and chlorides of calcium and magnesium cause permanent hardness in water.
• The reactions involved during the removal of temporary hardness of water are
  $\underset{\mathrm{Calcium}\mathrm{bicarbonate}}{\mathrm{Ca}{({\mathrm{HCO}}_3)}_2\left(\mathrm{aq}\right)}\to \underset{\mathrm{Carbon}\mathrm{dioxide}}{{\mathrm{CO}}_2\left(\mathrm{g}\right)}+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}+\underset{\mathrm{Calcium}\mathrm{carbonate}}{{\mathrm{CaCO}}_3\left(\mathrm{s}\right)}$
• $\underset{\mathrm{Magnesium}\mathrm{bicarbonate}}{\mathrm{Mg}{\left({\mathrm{HCO}}_3\right)}_2\left(\mathrm{aq}\right)}\to \underset{\mathrm{Carbon}\mathrm{dioxide}}{{\mathrm{CO}}_2\left(\mathrm{g}\right)}+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}+\underset{\mathrm{Magnesium}\mathrm{carbonate}}{{\mathrm{MgCO}}_3\left(\mathrm{s}\right)}$
• Temporary hardness of water is due to the presence of bicarbonates of magnesium and calcium.
• It can be removed by boiling the water when soluble bicarbonates are converted into soluble carbonates which can be removed by filtration. This is shown by the above reactions.