Question

How can the temporary hardness of water remove? Explain with equation.

Answer 1

Hard water

• The hardness of water is due to Chloride of calcium and Bicarbonate of magnesium
• Hard water contains soluble salts of calcium and magnesium.
• It does not give lather with soap. this is because of the precipitation of the insoluble soap

Temporary hardness

• It occurs due to the dissolved bicarbonate of calcium and magnesium. so it is called carbonate hardness
• This type of hardness is temporary because it can be easily removed by just boiling and filtering the water.

Removal of Temporary hardness - Boiling

• The temporary hardness of water can be removed by boiling. due to boiling $\mathrm{Mg}{\left({\mathrm{HCO}}_3\right)}_2$ is converted into insoluble $\mathrm{Mg}{\left(\mathrm{OH}\right)}_2$, whereas $\mathrm{Ca}{\left({\mathrm{HCO}}_3\right)}_2$ is converted into insoluble ${\mathrm{CaCO}}_3$ and gets precipitated.
• These precipitates can be removed by filtration or decantation

$$\begin{gathered} \underset{\mathrm{Magnesium}\mathrm{bicarbonate}}{\mathrm{Mg}{\left({\mathrm{HCO}}_3\right)}_2\left(\mathrm{aq}\right)}\stackrel{∆}{\to }\underset{\mathrm{Magnesium}\mathrm{hydroxide}}{\mathrm{Mg}{\left(\mathrm{OH}\right)}_2\left(\mathrm{aq}\right)\downarrow }+\underset{\mathrm{Carbondioxide}}{2{\mathrm{CO}}_2\left(\mathrm{g}\right)\uparrow } \\ \underset{\mathrm{Calcium}\mathrm{bicarbonate}}{\mathrm{Ca}{\left({\mathrm{HCO}}_3\right)}_2\left(\mathrm{aq}\right)}\stackrel{∆}{\to }\underset{\mathrm{Calcium}\mathrm{carbonate}}{{\mathrm{CaCO}}_3\left(\mathrm{s}\right)\downarrow }+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}+\underset{\mathrm{Carbondioxide}}{{\mathrm{CO}}_2\left(\mathrm{g}\right)\uparrow } \end{gathered}$$