Question

What is the cause of hardness of water? Name the salts used for hardness of water.

Answer 1

Hard water

• The presence of specific dissolved Calcium $\left(\mathrm{Ca}\right)$ and Magnesium $\left(\mathrm{Mg}\right)$ salts in water causes water to be hard.
• These following are the salts that causes hardness in water.

1. Calcium sulphate $\left({\mathrm{CaSO}}_4\right)$
2. Magnesium sulphate $\left({\mathrm{MgSO}}_4\right)$
3. Calcium chloride $\left({\mathrm{CaCl}}_2\right)$
4. Calcium bicarbonate $\left[\mathrm{Ca}{\left({\mathrm{HCO}}_3\right)}_2\right]$
5. Magnesium bicarbonate $\left[{\mathrm{Mg}\left({\mathrm{HCO}}_3\right)}_2\right]$
6. Magnesium chloride $\left({\mathrm{MgCl}}_2\right)$

• There are 2 types of hardness of water -

1. Temporary hardness of water
2. Permanent hardness of water

Temporary hardness

• Temporary hardness of water refers to the hardness of water that is induced by the presence of dissolved Calcium and Magnesium bicarbonates in it.
• It can be removed by boiling.

Permanent hardness

• Permanent hardness of water refers to the hardness of water that is induced by the presence of dissolved Calcium and Magnesium Chlorides and sulphates in it.
• Chemicals like washing soda is used to remove permanent hardness of water.