Question

The reagent(s) used for softening the temporary hardness of water is (are)(a) Ca₃ (PO₄)₂ (b) Ca(OH)₂(c) Na₂CO₃ (d) NaOCl

Answer 1

Temporary hardness is caused by presence of bicarbonates of calcium and magnesium. By adding calculated amount of lime, namely Calcium hydroxide,

the calcium carbonate and magnesium carbonates gets precipitated.

The answer is (b) Ca(OH)2

Answer 2

The reagent used for softening the temporary hardness of water is $Ca(OH)_2$

Explanation:

Temporary hardness is the hardness caused by bicarbonates of calcium and magnesium. It is also called as Carbonate hardness as it can be easily removed using simple methods.

Example: $Ca(HCO_3)_2$ and $Mg(HCO_3)_2$

Removal of temporary hardness is done using lime :

$Ca(HCO_3)_2+Ca(OH)_2\rightarrow 2CaCO_3+2H_2O$

$Mg(HCO_3)_2+2Ca(OH)_2\rightarrow Mg(OH)_2+2CaCO_3+2H_2O$

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