Acid Rain
Normally the pH of precipitation is controlled by the reaction of carbon
dioxide with water to form carbonic acid, which keeps the pH of ìcleanî
rain in the slightly acid range, of about 5.6:
CO2 (g) + H2O(l) H2CO3 (aq) H3O+(aq) + HCO3-(aq)
Sulfurous acid is produced by the reaction of sulfur dioxide with water,
and even though it is a weak acid, it does add to the acidity of rain.
A greater worry is the oxidation of the SO2 to form SO3 which reacts
with water to form the strong acid, sulfuric acid.
SO2 (g) + H2O(l) H2SO3 (aq)
2 SO2 (g) + O2 (g) 2 SO3 (g)
SO3 (g) + H2O(l) H2SO4 (aq)
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