Question

Potassium carbonate cannot be prepared by Solvay process. Why?

Answer 1

In the Solvay process, we obtain Sodium carbonate from the solution because it is not soluble in the solution. When we try to dissolve Potassium carbonate in water, it gets dissolved easily.

Complete step by step answer:
Solvay process is used for industrial production of Sodium carbonate. Let’s see how the Solvay process produces sodium carbonate.
The overall chemical reaction involved in this process is as under.

$2NaC{l_{(aq)}} + CaC{O_3}_{(s)} \to N{a_2}C{O_3}_{(s)} + CaC{l_2}_{(aq)}$

We can see that cation exchange reaction takes place sodium carbonate and calcium chloride gets produced when sodium chloride and calcium carbonate is allowed to react.
Actually Solvay process is done in the following way:

First ammonia is allowed to react with concentrated brine (NaCl) solution. Then, Carbon dioxide is bubbled in the solution. Then, lime is added and we obtain Sodium carbonate as the final product.
We obtain Calcium chloride as a byproduct in the Solvay process.
Now, if we want to obtain Potassium carbonate from this process then, we can replace NaCl by KCl and follow the same procedure as we do for production of Sodium carbonate. The reaction is given below for potassium carbonate.

$2KC{l_{(aq)}} + CaC{O_{3(s)}} \to {K_2}C{O_{3(aq)}} + CaC{l_{2(aq)}}$

Here, one problem emerges here as Potassium carbonate is soluble in the aqueous medium. So, we cannot obtain it from solution easily while in case of Sodium carbonate, it is not soluble and as it gets formed, immediately it gets precipitated out. So, this is the reason why cannot produce Potassium carbonate by the Solvay process.
Solubility of potassium carbonate in water is 112gm per 100mL of water. While solubility of sodium carbonate is only 30gm per 100mL of water at normal temperatures. Thus we can say that we cannot obtain potassium carbonate as it will not get precipitated out in water as it has very high solubility.

Note: - Remember that even though sodium carbonate and potassium carbonate are salts of Na and K which have similar properties, do not have same solubility in water and that is the reason why potassium carbonate is not prepared by Solvay method. Sodium carbonate is very less soluble in water and potassium carbonate is well soluble in water.