Question

Discuss the various reactions that occur in the Solvay process.

Answer 1

Solvay process is used to prepare sodium carbonate.

When carbon dioxide gas is bubbled through a brine solution saturated with ammonia, sodium hydrogen carbonate is formed. This sodium hydrogen carbonate is then converted to sodium carbonate.

1. Step 1: Brine solution is saturated with ammonia.
   \[\ce{2NH_3 + H_2O + CO_2 -> (NH_4)_2 CO_3}\]
   This ammoniated brine is filtered to remove any impurity.
2. Step 2: Carbon dioxide is reacted with this ammoniated brine to result in the formation of insoluble sodium hydrogen carbonate.
   \[\ce{NH3 + H2O + CO2 -> NH4HCO3}\]
   \[\ce{NaCl + NH4HCO3 -> NaHCO3 + NH4Cl}\]
3. Step 3: The solution containing crystals of NaHCO₃ is filtered to obtain NaHCO₃.
4. Step 4: NaHCO₃ is heated strongly to convert it into NaHCO₃.
   \[\ce{2NaHOC_3 -> Na_2CO_3 + CO_2 + H_2O}\]
5. Step 5: To recover ammonia, the filtrate (after removing NaHCO₃) is mixed with Ca(OH)₂ and heated.
   \[\ce{Ca(OH)2 + 2NH4Cl -> 2NH3 + 2H2O + CaCl}\]
   The overall reaction taking place in Solvay process is
   \[\ce{2NaCl + CaCO_3 -> Na_2CO_3 + CaCl_2}\]