Question

How does acid rain form ?

Answer 1

Acid rain forms when water molecules in the atmosphere react with sulfur dioxide or nitrogen oxides to form an acidic compound. The resulting compound has a lower pH.

The chemical reactions that occur when water molecules mix with sulfur dioxide and nitrogen dioxide are below:

$$SO_{2} + 1.2O_{2} + H_{2}O \rightarrow H_{2}SO_{4}$$

$$H_{2}SO_{2} \rightarrow 2H^{+} + SO_{4}^{2-}$$

Similarly,

$$2NO_{2} + 1/2O_{2} + H_{2}O \rightarrow 2HNO_{3}$$

$$HNO_{3} \rightarrow H^{+} + NO_{3}^{-}$$

Nitrogen oxides can be produced naturally by lightening strikes and sulfur dioxides is formed when volcanoes explode, but acid rain can also be caused by emissions due to humans.