Question

How is washing soda prepared from sodium carbonate(${\mathrm{Na}}_2{\mathrm{CO}}_3$)? Give its chemical equation. State the type of this salt. Name the type of hardness of water which can be removed by it?

Answer 1

Solvay's process:

• Washing soda(${\mathrm{Na}}_2{\mathrm{CO}}_3.10{\mathrm{H}}_2\mathrm{O}$) is synthesized through Solvay's process.
• It involves the reaction of sodium chloride($\mathrm{NaCl}$), ammonia(${\mathrm{NH}}_3$) and carbon dioxide(${\mathrm{CO}}_2$) in water.
• Carbon dioxide(${\mathrm{CO}}_2$) involved is produced through calcium carbonate(${\mathrm{CaCO}}_3$) and the calcium oxide($\mathrm{CaO}$) left is used in recovering ammonia(${\mathrm{NH}}_3$).
• At first, sodium bicarbonate(${\mathrm{NaHCO}}_3$) is obtained which is then converted to sodium carbonate(${\mathrm{Na}}_2{\mathrm{CO}}_3$) on heating.
• Finally, washing soda(${\mathrm{Na}}_2{\mathrm{CO}}_3.10{\mathrm{H}}_2\mathrm{O}$) is produced by the recrystallization of sodium carbonate(${\mathrm{Na}}_2{\mathrm{CO}}_3$).

$\underset{\mathrm{Sodium}\mathrm{chloride}}{\mathrm{NaCl}\left(\mathrm{s}\right)}+\underset{\mathrm{Ammonia}}{{\mathrm{NH}}_3\left(\mathrm{g}\right)}+\underset{\mathrm{Carbon}\mathrm{dioxide}}{{\mathrm{CO}}_2\left(\mathrm{g}\right)}+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}\to \underset{\mathrm{Sodium}\mathrm{bicarbonate}}{{\mathrm{NaHCO}}_3\left(\mathrm{s}\right)}+\underset{\mathrm{Ammonium}\mathrm{chloride}}{{\mathrm{NH}}_4\mathrm{Cl}\left(\mathrm{aq}\right)}$

$\underset{\mathrm{Sodium}\mathrm{bicarbonate}}{2{\mathrm{NaHCO}}_3\left(\mathrm{s}\right)}\stackrel{\mathrm{\Delta }}{\to }\underset{\mathrm{Sodium}\mathrm{carbonate}}{{\mathrm{Na}}_2{\mathrm{CO}}_3\left(\mathrm{s}\right)}+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}+\underset{\mathrm{Carbon}\mathrm{dioxide}}{{\mathrm{CO}}_2\left(\mathrm{g}\right)}$

$\underset{\mathrm{Sodium}\mathrm{carbonate}}{{\mathrm{Na}}_2{\mathrm{CO}}_3\left(\mathrm{s}\right)}+\underset{\mathrm{Water}}{10{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}\to \underset{\mathrm{Washing}\mathrm{soda}}{{\mathrm{Na}}_2{\mathrm{CO}}_3.10{\mathrm{H}}_2\mathrm{O}\left(\mathrm{aq}\right)}$

• ${\mathrm{Na}}_2{\mathrm{CO}}_3$ is formed by the combination of a strong base and a weak acid.
• Hence, ${\mathrm{Na}}_2{\mathrm{CO}}_3$ is a basic salt
• It can remove both temporary and permanent hardness.