How to distinguish between sodium nitrate, sodium nitrite, sodium sulphate and sodium sulphite?

If the unknown samples are solid, dissolve them separately in distilled water to form four aqueous solutions.


Test 1 :
Add separately a few barium chloride solution to each of the four unknown solutions in a test tube.

Only sodium sulphate solution gives a white precipitate of barium sulphate.
Ba²⁺(aq) + SO₄²⁻(aq) → BaSO₄(s)

The other three solutions give no observable change.


Test 2 :
Add separately a few dilute hydrochloric acid to each of three unknown solutions, which have not been identified, in a test tube. Warm the mixture if necessary.

Sodium nitrite solution gives off a brown gas of nitrogen dioxide.
2NO₂⁻(aq) + 2H⁺(aq) → H₂O(l) + NO(g) + NO₂(g)
2NO(g) + O₂(g) → 2NO₂(g)

Sodium sulphite solution gives off a colourless gas with choking smell of sulphur dioxide.
SO₃²⁻(aq) + 2H⁺(aq) → H₂O(l) + SO₂(g)

Sodium nitrate solution gives no observable change.

Nitrates have NO3.

Nitrites have NO2.

Sulphates have....I think you get it.