Question

Sodium sulfate must be mix with what chemical to become sodium carbonate?

Answer 1

Sodium sulfate has formula $\mathrm{Na_2SO_4}$ and sodium carbonate $\mathrm{Na_2CO_3}$. Apparently, the only way to convert sodium sulfate into sodium carbonate is reaction of sodium sulfate with barium carbonate. The last one is not soluble compound, Ksp (solubility products constant) is $2.58\times 10^{-9}$, but barium sulfate is even less soluble: Ksp is equal to $1.08\times 10^{-10}$, this is the reason why the next reaction occurs:

$$\mathrm{Na_2SO_4} + \mathrm{BaCO_3} \rightarrow \mathrm{Na_2CO_3} + \mathrm{BaSO_4} \downarrow$$