# Which procedure(s) will allow a student to differentiate between solid sodium sulfate and solid sodium sulfite?

I. Make solutions of each and look for a precipitate when added to 0.10 M Ba(NO3)2. II. Add crystals of each to 0.10 M HCl and watch for bubbles. III. Make solutions of each and test with a pH indicator.

The answer is II and III only. I understand how III works, but I don't see how sulfite and sulfate can be differentiated by adding HCl; don't both get reduced to SO2 bubbles?

• What's getting oxidized, then? – Yunfei Ma Apr 17 '16 at 4:05

Sodium sulfite and hydrochloric acid partially react to $\ce{SO2}$ which is gaseous and thus will form bubbles if not dissolved immediately.