Chemical Properties of SO2

1. As an acid – It reacts with alkalis to form trioxosulphate (iv) salts.
2NaOH_(aq) + SO_2(g) →  Na₂SO_3(aq) + H₂O_(L)

2. As a reducing agent – It reduces oxidizing agents without leaving any traces of sulphur.
2KMnO_4(aq) + 5SO2_(g) + 2H₂O_(L)  → K₂SO_4(aq) + 2MnSO_4(aq) + 2H₂SO4

3. It can combine directly with metallic oxides to form salts.
PbO_2(s) + SO_2(g)  →  PbSO_4(aq)

NB: 2SO_2(s) + SO_2(g) →  2SO_3(g)

4. As an oxidizing agent –
C_(s) + SO_2(g) →  CO_2(s)

NB: SO2 bleaches by reduction unlike chlorine which bleaches by oxidation.