Chemistry - Complete s-block Question with Solution | TestHub

Temporary hardness in water is due to the presence of magnesium and calcium hydrogen carbonates.

Clark’s method: In this method, the calculated amount of lime is added to hard water. It precipitates out calcium carbonate and magnesium hydroxide which can be filtered off.

$\mathrm{Ca}{\left({\mathrm{HCO}}_3\right)}_2+\mathrm{Ca}{\left(\mathrm{OH}\right)}_2\stackrel{}{\to }2{\mathrm{CaCO}}_3 \downarrow +2{\mathrm{H}}_2\mathrm{O}$

$\mathrm{Mg}{\left({\mathrm{HCO}}_3\right)}_2+2\mathrm{Ca}{\left(\mathrm{OH}\right)}_2\stackrel{}{\to }2{\mathrm{CaCO}}_3 \downarrow +\mathrm{Mg}{\left(\mathrm{OH}\right)}_2 \downarrow +2{\mathrm{H}}_2\mathrm{O}$