Solve this:
Q.(i) Describe one method for removal of temporary hardness of water.
Q.(i) Describe one method for removal of temporary hardness of water.
Temporary hardness : It is due to the presence of soluble bicarbonates of calcium and magnesium. It can be removed by following two methods:
(i) Boiling: During boiling, the soluble Mg(HCO3)2 present in water is converted into insoluble Mg(OH)2 and Ca(HCO3)2 is changed to insoluble CaCO3 which settle at the bottom as precipitates. These precipitates can be removed by filtration. Filtrate thus obtained will be soft water.
Heat
Mg( HCO3)2-----> Mg(OH)2 + 2CO 2
Heat
Ca( HCO3)2-----> CaCO3 + CO 2+ H2O
OR
(ii)Calcium hydroxide or Clark’ method: In this method calculated amount of lime is added to hard water. It precipitates out calcium carbonate and magnesium hydroxide which can be filtered off.
Mg( HCO3)2 + Ca(OH)2----> MgCO3 + CaCO3 + 2 H2O
Ca( HCO3)2 + Ca(OH)2 ---> 2CaCO3 + 2 H2O
Temporary hardness : It is due to the presence of soluble bicarbonates of calcium and magnesium. It can be removed by following two methods:
(i) Boiling: During boiling, the soluble Mg(HCO3)2 present in water is converted into insoluble Mg(OH)2 and Ca(HCO3)2 is changed to insoluble CaCO3 which settle at the bottom as precipitates. These precipitates can be removed by filtration. Filtrate thus obtained will be soft water.
Heat
Mg( HCO3)2-----> Mg(OH)2 + 2CO 2
Heat
Ca( HCO3)2-----> CaCO3 + CO 2+ H2O
OR
(ii)Calcium hydroxide or Clark’ method: In this method calculated amount of lime is added to hard water. It precipitates out calcium carbonate and magnesium hydroxide which can be filtered off.
Mg( HCO3)2 + Ca(OH)2----> MgCO3 + CaCO3 + 2 H2O
Ca( HCO3)2 + Ca(OH)2 ---> 2CaCO3 + 2 H2O
