Question

Sodium carbonate is prepared by Solvay process but it is not extended to the manufacture of potassium carbonate because potassium bicarbonate is very soluble and does not crystallize like sodium bicarbonate.

Answer 1

Hint: Solvay process includes precipitation of the bicarbonate of the salt and then it is used for the preparation of required product. If the bicarbonate is soluble in water, there would not be any precipitate that we can separate from the solution.

Complete answer:
We use the Solvay process industrially for obtaining sodium carbonate from ammonia, limestone and brine. We also know this process by the name ammonia-soda process.
In the Solvay process, at first we pass carbon dioxide through a concentrated solution of sodium chloride and ammonia which gives us sodium bicarbonate precipitate. We can write the reaction as-
     $NaCl+C{{O}_{2}}+N{{H}_{3}}+{{H}_{2}}O\to NaHC{{O}_{3}}+N{{H}_{4}}Cl$
Industrially, the above reaction is carried out by passing concentrated salt water to the first tower where we bubble up ammonia through the salt water solution and then in the second tower we pass carbon dioxide through the ammoniated salt water solution to obtain sodium bicarbonate.
We add ammonia to make the solution basic because the formation of ammonium chloride will affect the precipitation of sodium bicarbonate. Ammonia helps us in maintaining the pH of the solution hence acts as a buffer. Also, in a basic solution sodium bicarbonate is less soluble than sodium chloride.
Then we convert the sodium bicarbonate into sodium carbonate through a process named calcination, which is basically heating of the ore at a very high temperature in presence of oxygen. This leaves us with the required product as well as water and carbon dioxide as by products. We can write the reaction as-
     \[2NaHC{{O}_{3}}\to N{{a}_{2}}C{{O}_{3}}+C{{O}_{2}}+{{H}_{2}}O\]
As we can see from the above discussion that precipitation of sodium bicarbonate plays an important role as it can be filtered out unlike potassium bicarbonate, which is soluble in water and we cannot obtain any crystals to filter.
Therefore, the given statement, sodium carbonate is prepared by Solvay process but it is not extended to the manufacture of potassium carbonate because potassium bicarbonate is very soluble and does not crystallize like sodium bicarbonate is true.

Note:
In the Solvay process, the obtained bicarbonate is not directly calcined to give the required product. Sodium bicarbonate is present with ammonium chloride therefore we separate the precipitate and the ammonium chloride solution is heated with calcium oxide which gives us ammonia. Ammonia obtained from here is recycled and then used for the first step of the process.