Question

Name the sodium compound which is used for softening hard water.

Answer 1

Softening of hard water:

1. The removal of calcium, magnesium and other metal cations from hard water is known as water softening.
2. Because soap is not wasted and is associated with calcium ions in soft water, it takes less soap to clean the same amount of dirt.
3. Water softening is required due to the fact that the calcium and magnesium ions in hard water react with the higher fatty acids in soap to form an insoluble gelatinous curd, resulting in soap waste.
4. Washing soda, or sodium carbonate (${\mathrm{Na}}_2{\mathrm{CO}}_3$), is capable of removing both temporary and permanent hardness.
5. It releases carbonate ions into the water since it is insoluble in water. Calcium carbonate precipitates when these carbonate ions react with the dissolved calcium ions.
6. The calcium ions in the final precipitate come from hard water, while the carbonate ions come from washing soda, resulting in softening of water. $\underset{\mathrm{Carbonate}\mathrm{ion}}{{{\mathrm{CO}}_3}^{2-}\left(\mathrm{aq}\right)}+\underset{\mathrm{Calcium}\mathrm{ion}}{{\mathrm{Ca}}^{+2}\left(\mathrm{aq}\right)}\to \underset{\mathrm{Calcium}\mathrm{carbonate}\mathrm{precipitate}}{{\mathrm{CaCO}}_3\left(\mathrm{s}\right)}$

Therefore, sodium carbonate is used in the softening of hard water.