PbS

S

SO2    SO3 SO32–   SO42–

This part of the scheme illustrates two aspects of sulfur chemistry.

• Firstly, like other nonmetal oxides, the sulfur oxides are acidic. Thus they react with water as shown below to produce oxoacids having the structures shown at the right or, as shown in the scheme above, with OH^–(aq) to give the corresponding oxoanions.
  
  SO₂ + H₂O → H₂SO₃ (sulfurous acid)
  SO₃ + H₂O → H₂SO₄ (sulfuric acid)
• Secondly, sulfur(IV) is a good reductant.
  Thus, sulfur(IV) reacts with the oxidants O₂ and H₂O₂ to produce sulfur(VI).