Question

Explain with equation, when permanent hard water is treated with washing soda

Answer 1

Permanent hardness

• It occurs due to dissolved chlorides and sulfates of calcium and magnesium,
• This type of hardness cannot be removed by simple methods like boiling or filtration, so it is called permanent hardness.

Treatment with washing soda

• The permanent hardness of water can be removed by adding washing soda
• Washing soda reacts with soluble salts in hard water to form insoluble carbonates that can be filtered off

$$\begin{gathered} {\mathrm{MCl}}_2\left(\mathrm{s}\right)+{\mathrm{Na}}_2{\mathrm{CO}}_3\left(\mathrm{s}\right)\to {\mathrm{MCO}}_3\left(\mathrm{s}\right)\downarrow +2\mathrm{NaCl}\left(\mathrm{s}\right) \\ {\mathrm{MSO}}_4\left(\mathrm{s}\right)+{\mathrm{Na}}_2{\mathrm{CO}}_3\left(\mathrm{s}\right)\to {\mathrm{MCO}}_3\left(\mathrm{s}\right)\downarrow +{\mathrm{Na}}_2{\mathrm{SO}}_4\left(\mathrm{s}\right) \\ \mathrm{where},\mathrm{M}=\mathrm{Ca}\mathrm{and}\mathrm{Mg} \end{gathered}$$