Hard water contains high levels of dissolved minerals. In Class 11 Chemistry (Hydrogen chapter), understanding the difference between temporary and permanent hardness is crucial.
Hard water does not lather easily with soap, leading to wastage of soap and the formation of scum. It also causes scaling in boilers and pipes.
Permanent hardness of water is caused by the presence of soluble chlorides and sulphates of calcium and magnesium (e.g., CaCl₂, MgCl₂, CaSO₄, MgSO₄).
Permanent hardness CANNOT be removed by BOILING.
Boiling only removes temporary hardness (which is caused by bicarbonates of Ca and Mg). When you boil water with permanent hardness, the chlorides and sulphates do not precipitate out; they remain dissolved.
To remove permanent hardness, chemical methods are required:
Temporary hardness is caused by dissolved **bicarbonates (hydrogen carbonates)** of calcium and magnesium: Ca(HCO₃)₂ and Mg(HCO₃)₂.
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