Chemistry - Hydrogen and Its compound Question with Solution | TestHub

The Clark's method is used to remove temporary hardness of water. It involves adding slaked lime, calcium hydroxide, to hard water. This precipitates calcium carbonate and magnesium hydroxide, which can then be filtered out, reducing the hardness.

The chemical equation for the removal of calcium hardness is:

$$\mathrm{Ca}(\mathrm{HC}{\mathrm{O}}_3{)}_2(\mathrm{aq})+\mathrm{Ca}(\mathrm{OH}{)}_2(\mathrm{s})\to 2CaC{\mathrm{O}}_3(\mathrm{s})+2{\mathrm{H}}_2\mathrm{O}(\mathrm{l})$$

The chemical equation for the removal of magnesium hardness is:

$$\mathrm{Mg}(\mathrm{HC}{\mathrm{O}}_3{)}_2(\mathrm{aq})+2Ca(\mathrm{OH}{)}_2(\mathrm{s})\to \mathrm{Mg}(\mathrm{OH}{)}_2(\mathrm{s})+2CaC{\mathrm{O}}_3(\mathrm{s})+2{\mathrm{H}}_2\mathrm{O}(\mathrm{l})$$

Therefore, the chemical used in Clark's method is calcium hydroxide, $\mathrm{Ca}(\mathrm{OH}{)}_2$.