Question

Potassium Carbonate ( ${ K }_{ 2 }{ CO }_{ 3 }$ ) cannot be prepared by Solvay’s process because:

(A). $KH{ CO }_{ 3 }$ is less soluble that $NaH{ CO }_{ 3 }$

(B). $KH{ CO }_{ 3 }$ is too soluble to be precipitated by KCl and ${ NH }_{ 4 }{ HCO }_{ 3 }$

(C). ${ K }_{ 2 }{ CO }_{ 3 }$ is too soluble to be precipitated by KCl

(D). ${ K }_{ 2 }{ CO }_{ 3 }$ is less soluble than ${ Na }_{ 2 }{ CO }_{ 3 }$

Answer 1

In Solvay’s process, sodium carbonate ( ${ Na }_{ 2 }{ CO }_{ 3 }$ ) is prepared. There is a step in this process where $NaH{ CO }_{ 3 }$ is precipitated out using ${ NH }_{ 4 }{ HCO }_{ 3 }$ and NaCl. $KH{ CO }_{ 3 }$ is highly soluble in water.

Complete Step By Step Answer:

${ K }_{ 2 }{ CO }_{ 3 }$ cannot be prepared using Solvay’s process because $KH{ CO }_{ 3 }$ is highly soluble in water and it cannot be precipitated out using KCl and ${ NH }_{ 4 }{ HCO }_{ 3 }$ . Let us understand more about Solvay’s process.

Solvay’s process is used in industries to manufacture ${ Na }_{ 2 }{ CO }_{ 3 }$ . Sodium carbonate is also known as soda ash. This process occurs in two steps.

In the first step, sodium chloride is reacted with ammonium bicarbonate to form ammonium chloride and a precipitate of sodium bicarbonate. This precipitate is filtered out and is used in the next step.

$NaCl+{ NH }_{ 4 }{ HCO }_{ 3 }\longrightarrow Na{ HCO }_{ 3 }\downarrow +{ NH }_{ 4 }Cl$

In the second step, sodium bicarbonate is heated at ${ 160 }^{ \circ }C to { 230 }^{ \circ }C$ to form sodium carbonate. This process is known as calcination.

$2Na{ HCO }_{ 3 }\overset { \triangle }{ \underset { { 160 }^{ \circ }C - { 230 }^{ \circ }C }{ \longrightarrow } } { Na }_{ 2 }{ CO }_{ 3 }+{ H }_{ 2 }O+{ CO }_{ 2 }$

As we can see, sodium bicarbonate is precipitated out by using its chloride salt and ammonium bicarbonate in the first step. If we want to prepare potassium carbonate using this process, then we will also have to take chloride salt of potassium i.e. KCl and ammonium bicarbonate to precipitate potassium bicarbonate. But potassium bicarbonate is highly soluble in water and it cannot be precipitated using KCl and ammonium bicarbonate. Thus potassium carbonate cannot be produced using this process.

Therefore, Option (B) is correct.

Note:

Don’t confuse carbonate with bicarbonate in this process. In Solvay’s process, the bicarbonate salt is first precipitated and then it is heated at high temperatures to obtain the carbonate salt.