Question

How can the temporary hardness of water be removed? Give a proper chemical reaction in support of your answer.

Answer 1

Removing temporary hardness of water

By boiling: Soluble bicarbonates are converted into insoluble carbonates which are removed by filtration.

Reactions:$\mathrm{Ca}{\left({\mathrm{HCO}}_3\right)}_2\left(\mathrm{s}\right)\to {\mathrm{\Delta CaCO}}_3\left(\mathrm{s}\right)\downarrow +{\mathrm{H}}_2\mathrm{O}\left(\mathrm{aq}\right)+{\mathrm{CO}}_2\left(\mathrm{g}\right)$

$\mathrm{Mg}{\left({\mathrm{HCO}}_3\right)}_2\left(\mathrm{s}\right)\to {\mathrm{\Delta MgCO}}_3\left(\mathrm{s}\right)\downarrow +{\mathrm{H}}_2\mathrm{O}\left(\mathrm{aq}\right)+{\mathrm{CO}}_2\left(\mathrm{g}\right)$

By clarks method

Calcium hydroxide is Clark’s reagent. It removes the hardness of water by converting bicarbonates into carbonate.

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