Solutions of barium nitrate and sodium sulfate are mixed, and a precipitate of barium sulfate is formed. Why is barium sulfate the only compound that precipitates when the solutions are mixed?

Barium sulfate is the only compound that precipitates because the other product is sodium nitrate, which is soluble.

The overall equation is:

##Ba(NO_3)_(2(aq))+Na_2SO_(4(aq))rarrBaSO_(4(s))+2NaNO_(3(aq))##

All nitrates are soluble so the sodium and nitrate(V) ions remain in solution.

They take no part in the reaction so can be regarded as spectator ions.

The ionic equation is therefore:

##Ba_((aq))^(2+)+SO_(4(aq))^(2-)rarrBaSO_(4(s))##