46. Solving a chemistry problem

6. Three bottles were brought to the laboratory assistant, from which the labels were torn off. It is known that they contain concentrated solutions of acids - sulfuric, nitric and phosphoric. The laboratory assistant took a small amount of liquid from each bottle, added the same substance to each sample and heated it. This was enough to determine which tube contains each of the acids. What substance was added? Write the equations for the reactions that take place.