Question

Name the following:-

Chemical compound that can be used to soften hard water.

Answer 1

Types of water on the basis of salts present in them:

• Hard water- It contains a high amount of calcium and magnesium compounds.
• Soft water- It does not contain compounds of calcium and magnesium.

When hard water is treated with washing soda-

• It is sodium carbonate (${\mathrm{Na}}_2{\mathrm{CO}}_3$).
• It removes both the temporary and permanent hardness of the water.
• When it reacts with sulphates and chlorides of calcium and magnesium, it forms an insoluble precipitate.
• This precipitate can be removed by filtration.
• Water left behind is soft water and forms a lather with soap.

Reaction involved-

$\underset{\mathrm{washing}\mathrm{soda}}{{\mathrm{Na}}_2{\mathrm{CO}}_3\left(\mathrm{s}\right)}+\underset{\mathrm{calcium}\mathrm{sulphate}}{{\mathrm{CaSO}}_4\left(\mathrm{l}\right)}\to \underset{\mathrm{insoluble}\mathrm{Calcium}\mathrm{carbonate}}{{\mathrm{CaCO}}_3(\downarrow )}+\underset{\mathrm{sodium}\mathrm{sulphate}}{{\mathrm{Na}}_2{\mathrm{SO}}_4\left(\mathrm{s}\right)}$

Hence,

Sodium carbonate (${\mathrm{Na}}_2{\mathrm{CO}}_3$) is a washing soda that can be used to soften hard water.