Three unlabeled flasks contain solutions of potassium sulfate, potassium sulfide and potassium nitrate

Three unlabeled flasks contain solutions of potassium sulfate, potassium sulfide and potassium nitrate. How to chemically recognize which substance is in each of the flasks?

Barium chloride must be added to determine the composition of the tubes. If a characteristic white precipitate of barium sulfate falls out in one of the test tubes, then it is potassium sulfate.

Then add hydrochloric acid to the remaining two test tubes. The appearance of the smell of hydrogen sulfide will indicate that there is potassium sulfide in the test tube.

Concentrated sulfuric acid and copper can be added to confirm that potassium nitrate remains in the third tube, resulting in a brown smoke.