Chem lab: Can I get a push in the right direction?

Take 2 small samples (aliquots) of each unknown. Each can be about 0.5 ml. Add a drop of Phenolphthalein to each. The only one that turns pink will be the sodium hydroxide. Now add a drop of the sodium hydroxide to each of the aliquots. The one that forms a precipitate is the barium nitrate. We have identified 2 of the 4 unknowns. The other 2 are the sulfuric acid and the nitric acid. Take a 0.5 ml aliquot of each of them and add a drop of the barium nitrate. The one that forms a precipitate is the sulfuric acid, the other is the nitric acid.