Question

Temporary hardness of water is due to of calcium and magnesium and it can be removed by.

• A. sedimentation
• B. boiling
• C. sulphates
• D. bicarbonates

Answer 1

Answer: (B), (D)

bicarbonates

Temporary hardness of water is due to the presence of soluble calcium bicarbonate $(Ca$($HC{O}_3{)}_2)$ and magnesium bicarbonate $(Mg$($HC{O}_3{)}_2)$.
It is called temporary because it can be easily removed by boiling.

$Ca\left(HC{O}_3{)}_2\right(aq)$ $\stackrel{boil}{\to }$ $CaC{O}_3(\downarrow )$ + $H_{2}O\left(l\right)$ + $C{O}_2\left(g\right)$

$Mg\left(HC{O}_3{)}_2\right(aq)$ $\stackrel{boil}{\to }$ $MgC{O}_3(\downarrow )$ + $H_{2}O\left(l\right)$ + $C{O}_2\left(g\right)$

On boiling, the bicarbonates of calcium and magnesium form their respective insoluble carbonates. These precipitates are removed by filtration.