Question

The water that does not lather readily with a soap is called __________ 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

Lather production by soap in hard water

• Hard water do not forms lather with soap because large amount of soap is used to neutralise the salts present in water, resulting in formation of scum which sticks to clothes.

So, The water that does not lather readily with a soap is called hard water.