What are different methods used for softening of hard water?
The hardness of water is of two types:
i) Temporary hardness
ii) permanent hardness
Temporary hardness:
Temporary hardness is due to the presence of magnesium and calcium hydrogen-carbonates. It can be removed by;
Boiling: During boiling, the soluble Mg(HCO3)2 is converted into insoluble Mg(OH)2 and Ca(HCO3)2 is changed to insoluble CaCO3. It is because of high solubility product of Mg(OH)2 as compared to that of MgCO3, that Mg(OH)2 is precipitated. These precipitates can be removed by filtration. Filtrate thus obtained will be soft water.
It is due to the presence of soluble salts of magnesium and calcium in the form of chlorides and sulphates in water. Permanent hardness is not removed by boiling. It can be removed by the following method:
Treatment with washing soda; Washing soda reacts with soluble calcium and magnesium chlorides and sulphate in hard water to form insoluble carbonates.
MCl2 +Na2CO3 --> MCO3 +2NaCl
(M =Mg, Ca )
