Formation of washing soda
Answers
In the following three steps, washing soda is prepared from sodium chloride or common salt.
Firstly, a cold and concentrated sodium chloride solution is reacted with ammonia and carbon dioxide to obtain sodium hydrogen carbonate.
The sodium hydrogen carbonate is slightly soluble in water, so it precipitates out as solid.
NaCl +NH3 +CO2 +H2O → NaHCO3 +NH4Cl
Secondly, now sodium hydrogen carbonate is separated by filtration, dried and heated. On heating sodium hydrogen carbonate decomposes to form sodium carbonate. This anhydrous sodium carbonate is known as soda ash.
2NaHCO3 → Na2CO3 +H2O +CO2
Soda ash
The preparation of Sodium Carbonate is also known as Solvay process. But before that calcium carbonate (limestone) was heated to release carbon dioxide
Thirdly, anhydrous sodium carbonate or soda ash is dissolved in water and recrystallised to get washing soda crystals containing 10 molecules of water of crystallisation.
Na2CO3 + 10H2O → Na2CO3.10H2O
Washing Soda