Temporary hardness is due to the presence of bicarbonates of calcium or magnesium. Permanent hardness is due to the presence of chlorides and sulphates of calcium or magnesium ions.
Clark’s method : This method is used for removing temporary hardness. 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.
Treatment with washing soda:
This method is used to remove permanent hardness. Washing soda reacts with soluble calcium and magnesium chlorides and sulphates in hard water to form insoluble carbonates.
