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Sulfur dioxide (or Sulphur dioxide) has the chemical formula SO2. The gas is irritating to the lungs and is frequently described as smelling of burning sulphur.
It is produced by volcanoes and in various industrial processes. In particular, poor-quality coal and petroleum contain sulfur compounds, and generate sulfur dioxide when burned: the gas reacts with water and atmospheric oxygen to form sulfurous acid (H2SO3) and thus acid rain.
Preparation of sulfur dioxide for chemical production
Sulphur dioxide is often prepared by burning sulphur in air:
S(s) + O2 (g) → SO2 (g)
Hydrogen sulphide from crude oil may also be burned.
H2S (g) + O2 {g} → H2 (g) + SO2 (g)
Sulphide ores such as iron pyrites and sphalerite (zinc blende) may also be used:
4 FeS2 (s) + 11 O2 (g) → 2 Fe2O3 (s) + 8 SO2 (g)
2 ZnS (s) + 3 O2 (g) → 2 ZnO (s) + 2 SO2 (g)
When anhydrite, CaSO4, is heated with coke and sand in the manufacture of cement, CaSiO3, sulphur dioxide is a by-product.
2 CaSO4 (s) + 2 SiO2 (s) + C (s) → 2 CaSiO3 + 2 SO2 (g) + CO2
Flue gas desulphurisation in power stations releases SO2 for the process.
Uses
Sulfur dioxide is sometimes used as a preservative in alcoholic drinks, or dried apricots.
The word equation for the acid rain reaction:
sulfur dioxide + water = hydrogen sulfite
H2SO3 is also called "hydrogen sulfite" or sulfurous acid.
See also:
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