Sulphur dioxide is a reducing agent (which reduces ions such as Fe3+, MnO4-, and Cr2O72-:
2 FeCl3 + S02 + 2 H2O à 2 FeCl2 + H2SO4 + 2 HCl
2 KMnO4 + 5SO2 + 2H20 à K2SO4 2MnSO4 + 2H2SO4
K2Cr2O7 + 3SO2 + H2SO4 à K2SO4 + Cr(SO4)3 + 3H20
It is also an oxidising agent oxidising H2S and certain reactive metals such as Mg:
SO2 + 2 H2S à 3S + 2 H2O
Mg + SO2 à MgO + S