Question

briefly describe the chemistry behind acid rain formation

Answer 1

Rain is naturally acidic due to the dissolution of carbon dioxide forming weak carbonic acid. Acid rain refers to rain that has a higher hydrogen ion concentration. Acid rain occurs due to the dissolution of acidic oxides in the atmosphere.

REACTION INVOLVES:-

Formation of Nitrogen Dioxide: N_2(g) + 2O_2(g) -> 2NO_2(g)
Both sulfur dioxide and nitrogen dioxide are acidic oxides and react with water to form acids.

Sulfur dioxide reacts with water to form sulfurous acid.
SO_2(g) + H₂O_(l) -> H₂SO_3(aq)

Substances in the upper atmosphere then catalyse the reaction between sulfurous acid and oxygen to form sulfuric acid.
2H₂SO_3(aq) + O_2(g) -> 2H₂SO_4(aq)

Similarly, nitrogen dioxide reacts with water to form a mixture of nitric acid and nitrous acid.
2NO_2(g) + H₂O_(l) -> HNO_3(aq) + HNO_2(aq)

Substances in the atmosphere then catalyse the reaction between nitrous acid and oxygen causing the formation of more nitric acid.
2HNO_2(aq) + O_2(g) -> 2HNO_3(aq)

Both sulfuric acid and nitric acid are soluble in water and are the major acids present in acid rain. As this forms and falls onto the Earth's surface, these strong acids are also brought to the surface causing harmful effects on the built and the natural environment.