Question

Describe how washing soda is produced starting from sodium chloride (common salt). Write equations of all the reactions involved.

Answer 1

1. Preparation of washing soda

1. A cold and concentrated solution of sodium chloride is reacted with ammonia (NH₃) and carbon dioxide to form sodium hydrogen carbonate (NaHCO₃) and ammonium chloride (NH₄Cl). Sodium hydrogen carbonate precipitates as a solid as it is slightly soluble in water.

                  NaCl + NH₃ + H₂O + CO₂ → NaHCO₃ + NH₄C

2. The sodium hydrogen carbonate precipitated is separated by filtration, and then dried and heated. On heating, it decomposes to form sodium carbonate (Na₂CO₃). The anhydrous sodium carbonate formed here is called soda ash.

                  2NaHCO₃ → Na₂CO₃ + CO₂+ H₂O

3. The soda ash is dissolved in water and recrystallised to get washing soda crystals containing 10 molecules of water of crystallisation.

           Na₂CO₃ + 10H₂O → Na₂CO₃.10H₂O