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Chemistry

(a) What do you understand by :

(i) temporary hardness

(ii) soft water

(iii) permanent hardness

(b) How are temporary and permanent hardness removed ?

Practical Chemistry

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Answer

(a) (i) Temporary hardness — Hardness of water due to the presence of calcium and magnesium bicarbonates — Ca(HCO3)2, Mg(HCO3)2 — that can be removed by boiling and filtration is called temporary hardness.

(ii) Soft water — Water that does not contain dissolved calcium and magnesium salts is called soft water. This water forms lather with ordinary soap.

(iii) Permanent hardness — Hardness of water due to the presence of calcium and magnesium chlorides and sulphates — CaCl2, MgCl2, CaSO4, MgSO4 — that cannot be removed by boiling is called permanent hardness.

(b) Temporary hardness can be removed by boiling followed by filtration and permanent hardness can be removed by addition of washing soda or caustic soda.

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