Question

Acid rain is known to contain some acids. Name these acids and where from they come in rain?

Answer 1

Oxides of nitrogen and suphur which are acidic in nature can be blown by wind along with soild particles in the atmosphere and finally settle down either on the ground as dry deposition or in water, fog and snow as wet deposition.

Further these oxides i.e., $S{O}_2$ and $N{O}_2$ after oxidation and reaction with water are major contributors to acid rain becuse polluted air usually contains particulate matter that catalyse the oxidation. Hence, these two are the major contributors of acid rain.

$2S{O}_2\left(g\right)+O_2\left(g\right)+2H_{2}O\left(l\right)\to 2H_{2}S{O}_4\left(aq\right)$

$4N{O}_2\left(g\right)+O_2\left(g\right)+2H_{2}O\left(l\right)\to 4HN{O}_3\left(aq\right)$

Rainwater has a pH of 5.6 due to the presence of $H^{+}$ ions formed by the reaction of rainwater with carbon dioxide present in the atmosphere.

$H_{2}O\left(l\right)+C{O}_2\left(g\right)\to H_{2}C{O}_3\left(aq\right)$

$H_{2}C{O}_3\left(aq\right)\to H^{+}\left(aq\right)+HC{O}_3^{-}\left(aq\right)$

The acids commonly present in acid rain are nitric acid, sulphuric acid and carbonic acid.