Question

What happens when the temporary hard water is boiled? Give chemical equation also.

Answer 1

Hard water: Water that does not give lather with soap is called hard water.

• The presence of soluble bicarbonates, of $\mathrm{Calcium}\left(\mathrm{Ca}\right)$ and $\mathrm{Magnesium}\left(\mathrm{Mg}\right)$ is the reason behind its hardness.

Removing Hardness of Water: The presence of biCarbonates of $\mathrm{Magnesium}\left(\mathrm{Mg}\right)$ and $\mathrm{Calcium}\left(\mathrm{Ca}\right)$ in water makes it temporarily hard. In this case, the hardness of water can be removed by boiling the water.

• When we boil water the soluble salts $\mathrm{Magnesium}\mathrm{bicarbonate}\left[\mathrm{Mg}{\left({\mathrm{HCO}}_3\right)}_2\right]$ are converted to insoluble$\mathrm{Magnesium}\mathrm{hydroxide}\left[\mathrm{Mg}{\left(\mathrm{OH}\right)}_2\right]$.
• These insoluble substances get precipitated and easily get removed.
• After filtration, we get soft water.

Chemical equation:

$$\begin{gathered} \mathrm{Mg}{\left({\mathrm{HCO}}_3\right)}_2\left(\mathrm{aq}\right)\stackrel{\mathrm{heat}}{\to }\mathrm{Mg}{\left(\mathrm{OH}\right)}_2\left(\mathrm{s}\right)+2{\mathrm{CO}}_2\left(\mathrm{g}\right) \\ \mathrm{Magnesium}\mathrm{Magnesium}\mathrm{Carbon} \\ \mathrm{bicarbonate}\mathrm{hydroxide}\mathrm{dioxide} \\ \left(\mathrm{soluble}\right)\left(\mathrm{insoluble}\right) \end{gathered}$$

Therefore, the temporary hardness of water can be removed by boiling.