preparation of washing soda by solvay process

The Solvay process is used to manufacture sodium carbonate Na₂CO_3.

The steps involved in this process are:

1. Purify saturated brine

2. React it with gaseous ammonia

3. The ammoniated brine is carbonated with CO₂ to form NaHCO₃

4. This is insoluble in brine solution, so can be filtered out.

5. On heating, it decomposes to Na₂CO₃

6. CaCO₃ is also used to provide CO₂

Reactions: 1. CO₂ reacts with ammonia to form ammonium carbonate.

2NH₃ + CO₂ + H₂O -- (NH₄)₂CO₃

2.Ammonium carbonate further reacts with CO2 to form ammonium bicarbonate.

(NH₄)₂CO₃ + CO₂ + H2O -- 2NH₄HCO₃ (aq.)

3. Ammonium bicarbonate then react with NaCl to form sodium bicarbonate.

NH₄HCO₃ + NaCl -- NaHCO₃ + NH₄Cl

Due to exothermic nature of above reactions, solubility of NaHCO3 increases. To counter this effect , the solution is cooled, precipitate of NaHCO3 are separated by vacuum filtration and washed to remove ammonium salts.

4.Dry sodium bicarbonate is then heated to give anhydrous sodium carbonate. Carbon dioxide is then again recirculated.

2NaHCO3 -- Na₂CO₃ + CO₂ + H₂O