The acidity of rain water is due to the CO2 in the atmosphere. The CO2 dissolves in rain water to produce carbonic acid.
CO2(g) + H2O (l) <--> H2CO3 (aq)
H2CO3 (aq) + H2O (1) <--> HCO3 - (aq) + H3O+ (aq)
Gases produced by motor cars and industry produce large amounts of sulfur dioxide and nitrogen oxides. When these are absorbed in rain water, the rain becomes acidic causing Acid Rain.
SO2 (g) --> SO3 (g) --> H2SO4 (aq)
2NO2 (g) + H2O (i) --> HNO2 (aq) + HNO3 (aq)
The pH of clean river water is between 6.5-8.5. Water flowing over limestone can make the river slightly basic.
CaCO3 (s) <--> Ca2+ (aq) + CO3 ^2- (aq)
CO3 ^2- (aq) + H2O(l) <--> HCO3- (aq) + OH- (aq)
ACID MINE DRAINAGE
•Acid mine drainage is a pollutant from mines, it contains a corrosive and toxic mixture of sulphuric acid and heavy metal ions.
•Can kill aquatic life
•Decreased light penetration in water.
•Damage to fish gills