Temporary hard water is converted into soft water by adding required amount of calcium hydroxide. In this method Mg2+ ions are precipitated as Mg(OH)2 and Ca2+ ions are precipitated as CaCO3.
Mg (HCO3)2 →Mg (OH)2 + 2CO2
Ca (HCO3)2→ 2CaCO3 → 2H2O + 2CO2.
The insoluble precipitates can be removed by filtration.
