Question

Name the substance which makes water (i) temporary hard and (ii) permanent hard.

Answer 1

(i) Substance that makes water temporary hard:

• The presence of magnesium and calcium carbonates in water makes it temporarily hard.
• In this case, the hardness of water can be removed by boiling the water.
• Calcium hydrogen carbonate($\mathrm{Ca}{\left({\mathrm{HCO}}_3\right)}_2$).
• Magnesium hydrogen carbonate($\mathrm{Mg}{\left({\mathrm{HCO}}_3\right)}_2$).

(ii) Substance that makes water permanent hard:

• When the soluble salts of magnesium and calcium are present in the form of chlorides and sulfides in water, we call it permanent hardness because this hardness cannot be removed by boiling.
• Calcium sulfate (${\mathrm{CaSO}}_4$)
• Calcium chloride (${\mathrm{CaCl}}_2$)
• Magnesium sulfate (${\mathrm{MgSO}}_4$)
• Magnesium chloride (${\mathrm{MgCl}}_2$).