Question

Hardness in temporary water can be remove by boiling but hardness in permanent hard water can not

Answer 1

Hard water caused e.g. by dissolved magnesium sulfate or calcium sulfate is permanent hardness because the sulfate salts don't decompose on heating, so, the hardness is NOT removed on boiling the hard water.

Answer 2

Because bicarbonates decompose to give insoluble carbonates

Explanation:

Temporary hardness is the hardness caused by bicarbonates of calcium and magnesium. It is called as temporary hardness as it can be easily removed using simple methods such as boiling as they decompose to give insoluble salts.

$Ca(HCO_3)_2\overset{heat}\rightarrow CaCO_3(s)+H_2O+CO_2$

$Mg(HCO_3)_2\overset{heat}\rightarrow Mg(OH)_2(s)+2CO_2$

Permanent hardness is the hardness caused by chlorides and sulphates of calcium and magnesium. It is called as permanent hardness as it only be removed using chemicals such as lime and soda.

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