Question

Describe various reactions that occur in the Solvay process.

Answer 1

We know that the Solvay process is used in the preparation of sodium carbonate. The Solvay process has several intermediate reactions. In this process, Ammonia gas is also used which forms an important intermediate product. Ammonia is again recycled in this reaction. Calcium carbonate is one of the reactants which undergoes heating.

Complete answer:
We know that the Solvay process is used in the preparation of sodium carbonate. This process is cost-effective compared to other processes of preparation of Sodium carbonate. This process involves several intermediate reactions.
Carbon dioxide is passed through a brine solution which is saturated with ammonia gas and ammonium bicarbonate is formed.
${ NH }_{ 3 }\quad +\quad { H }_{ 2 }O\quad +\quad C{ O }_{ 2 }\quad \to N{ H }_{ 4 }HC{ O }_{ 3 }$
This ammonium bicarbonate reacts with brine solution and forms sodium bicarbonate. Sodium bicarbonate is insoluble as the solution is already saturated.
$NaCl\quad +\quad N{ H }_{ 4 }HC{ O }_{ 3 }\quad \rightarrow \quad NaHC{ O }_{ 3 }\quad +\quad N{ H }_{ 4 }HCl$
Sodium bicarbonate is heated to form sodium carbonate liberating carbon dioxide.
$2NaHCO_{ 3 }\quad \quad \rightarrow Na_{ 2 }CO_{ 3 }\quad +\quad C{ O }_{ 2 }\quad +\quad { H }_{ 2 }O$
Calcium carbonate is heated and it liberates carbon dioxide.
$CaCO_{ 3 }\quad \to \quad CaO\quad +\quad C{ O }_{ 2 }$
Calcium oxide reacts with water and produces calcium hydroxide.
$CaO\quad +\quad { H }_{ 2 }O\quad \to \quad Ca\left( OH \right) _{ 2 }$
Ammonium chloride in the second step reacts with the calcium hydroxide produced in the above step and ammonia gas is recycled.
$2 NH_{ 4 }Cl\quad + \quad Ca \left( OH \right) _{ 2 }\quad \to \quad 2 NH _{ 3 }\quad +\quad CaCl _{ 2 }\quad +\quad 2 H_{ 2 }O$
Final reaction of the entire process will be
$2 NaCl\quad + \quad CaCO_{ 3 } \quad \to \quad Na_{ 2 }CO _{ 3 }\quad +\quad CaCl_{ 2 }$
The obtained sodium carbonate reacts with water and Washing soda is formed.
$Na_2 CO_3 + 10H_2 O \to Na_2 CO_3.10H_2 O$

Note: As there is an excess of carbon dioxide passed through ammoniated brine solution ammonium bicarbonate is formed. Sodium bicarbonate formed is insoluble in solution because the solution contains excess bicarbonate ion and due to the common ion effect, it is insoluble.