Sulphur dioxide (SO2) acts as a reducing agent in the presence of moisture.
- Sulphur dioxide, SO2 reduces halogens (X°) to haloacids (X1-).
I2 + 2H2O + SO2 → 2HI + H2SO4
- SO2 gas when passed through an acidified solution of KMnO4 it is decolourised due to reduction (Mn7+ to Mn2+).
2KMnO4 + 2H2O + 5SO2 → K2SO4 + 2MnSO4 + 2H2SO4
- Sulphur dioxide (SO2) reduces Fe3+ to Fe2+
2FeCl3 + SO2 + 2H2O → 2FeCl2 + H2SO4 + 2HCl