During boiling, soluble Mg(HCO3)2 is converted into insoluble Mg(OH)2 and Ca(HCO3)2 is converted into insoluble CaCO3. This is because of high solubility product of Mg(OH)2 as compared to MgCO3 hence, Mg(OH)2 is precipitated. These precipitates can be removed by filtration. Thus, filtrate will be obtained in soft water. Mg(HCO3)2⟶Mg(OH)2↓+2CO2 Temporary hardness Ca(HCO3)2⟶CaCO3↓+CO2+2H2O Ksp of Mg(OH)2>Ksp of MgCO3 and hence, Mg(OH)2 precipitation first.