CIE AS Chemistry (9701) 2019-2021

Revision Notes

2.4.4 Sulfur: the Formation of Atmospheric Sulfur Dioxide, its Role in Acid Rain

Formation of Atmospheric Sulfur Dioxide

  • Fossil fuels are often contaminated with small amounts of sulfur impurities
  • When these contaminated fossil fuels are combusted, the sulfur in the fuels get oxidised to sulfur dioxide

S(s) + O2(g) → SO2(g)

  • The sulfur dioxide then dissolves in rainwater droplets to form sulfurous acid

SO2(g) + H2O(l) → H2SO3(aq)

  • Sulfurous acid can lead to acid rain which has damaging consequences

Sulfur Dioxide and its Role in Acid Rain

  • Sulfur dioxide forms acid rain as it dissolves in rainwater droplets to form sulfurous acid
  • This acidic rain can then react with metals and rocks (such as limestone) causing buildings and statues to get damaged
  • Acid rain also affects plants by damaging the waxy layer on the leaves of trees and plants
    • As a result, it gets more difficult to absorb minerals which plants require for healthy growth and may eventually lead to plant death
  • Acidic rain also causes the rivers and lakes to become too acidic endangering aquatic life
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