Reactions releasing sulfur dioxide into the atmosphere:

» Iron (II) sulfate; commercially prepared from dilute sulfuric acid.

Dilute sulfuric acid – used to clean iron sheets before galvanizing.

When iron (II) sulfate is heated to 300^oC it decomposes into iron (III) oxide, sulfur dioxide and sulfur trioxide.

2 FeSO₄ → Fe₂O₃ + SO₂ + SO₃

» When hydrogen sulfide is oxidized during the decomposition of an organic matter or substance, it produces sulfur dioxide and water.

2 H₂S (g) + 3 O₂ (g) → 2 H₂O (g) + 2 SO₂ (g)

» By burning sulfur, sulfur dioxide is formed.

S₈ + 8 O₂ → 8 SO₂

» Sulfur dioxide is released by smelters in the process of sweltering sulfide ores such as copper, lead or zinc. The ore is heated in air and changes to a metal oxide which releases sulfur dioxide.

2ZnS + 3O₂ →2ZnO + 2SO₂

» Sulfur dioxide can be prepared in the laboratory by heating copper turnings with concentrated sulfuric acid. The two products are copper sulfate and water.

Cu (s) + 2 H₂SO₄ (aq) → CuSO₄ (aq) + SO₂ (g) + 2 H₂O (l)

» When sulfite such as sodium sulfite is mixed with dilute acid – sulfur dioxide is formed.

Na₂SO₃(s ) + 2 HCl(aq ) → 2 NaCl(s ) + SO₂(g ) + H₂O(l )

» Often, the sulfur in natural gases, coal or petroleum is burnt, the combustion produces sulfur dioxide.

S + O₂ →SO₂