Qualitative Analysis Problems - part 1
Separate Na2S and Na2SO4 solutions
Both of Na2S and Na2SO4 are solutions and also colourless. Therefore we can't identify it by colour.
Add BaCl2 to both solutions separately. We can see a white precipitate forms in a one solution (Na2SO4 solution). That precipitate is BaSO4. But BaS is soluble in water and colourless too.