Question

Temporary hardness can be removed by

• A. Boiling
• B. Cooling
• C. Adding $\mathrm{Calcium}\mathrm{carbonate}$
• D. Adding $\mathrm{Magnesium}\mathrm{carbonate}$

Answer 1

The correct option is A

Boiling

Temporary Hardness: The hardness of water due to the presence of dissolved $\mathrm{Calcium}\mathrm{and}\mathrm{Magnesium}\mathrm{bicarbonates}$ is called temporary hardness.

The explanation for the correct answer

Option A

• Temporary hardness of water can be removed by boiling.
• The soluble $\mathrm{Calcium}\mathrm{and}\mathrm{Magnesium}\mathrm{bicarbonates}$ decomposes to form the insoluble$\mathrm{Calcium}\mathrm{and}\mathrm{Magnesium}\mathrm{carbonates}$.
• The insoluble $\mathrm{Calcium}\mathrm{carbonate}\left({\mathrm{CaCO}}_3\right)$ and $\mathrm{Magnesium}\mathrm{carbonate}\left({\mathrm{MgCO}}_3\right)$ formed from the heated temporary hard water is then can be removed by filtration.

Chemical equation 1

$\underset{(solubleinhardwater)}{\underset{\mathrm{Calcium}\mathrm{bicarbonate}}{\mathrm{Ca}\left({\mathrm{HCO}}_3\right)\left(\mathrm{aq}\right)}}\underset{∆}{\to }\underset{(Insolubleinhardwater)}{\underset{\mathrm{Calcium}\mathrm{carbonate}}{{\mathrm{CaCO}}_3\left(\mathrm{s}\right)}}+\underset{\mathrm{Carbon}\mathrm{dioxide}}{{\mathrm{CO}}_2\left(\mathrm{g}\right)}+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}$

Chemical equation 2

$\underset{(solubleinhardwater)}{\underset{\mathrm{Magnesium}\mathrm{bicarbonate}}{\mathrm{Mg}\left({\mathrm{HCO}}_3\right)\left(\mathrm{aq}\right)}}\underset{∆}{\to }\underset{(Insolubleinhardwater)}{\underset{\mathrm{Magnesium}\mathrm{carbonate}}{{\mathrm{MgCO}}_3\left(\mathrm{s}\right)}}+\underset{\mathrm{Carbon}\mathrm{dioxide}}{{\mathrm{CO}}_2\left(\mathrm{g}\right)}+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}$

Thus, option A i.e., Boiling is the correct answer.