Question

Temporary hardness can be removed by:

• A. boiling
• B. clark's process
• C. calgon's process
• D. permutit method

Answer 1

Answer: (A), (B)

boiling
clark's process

By boiling : - On boiling, soluble $Mg{\left(HC{O}_3\right)}_2$ is converted to insoluble $Mg{\left(OH\right)}_2$ and $Ca{\left(H{CO}_3\right)}_2$ to insoluble ${CaCO}_3$. It is because high solubility of $Mg{\left(OH\right)}_2$ as compared to $Mg{CO}_3$, than $Mg{\left(OH\right)}_2$ is precipitated. Precipitates can be removed by filtration.

By Clark's Method : Calculated amount of lime is added to hard water $\to Ca{CO}_3$ precipitates out & $Mg{\left(OH\right)}_2$ can be filtered off.