4.16 understand how sulfur dioxide and oxides of nitrogen contribute to acid rain

Acids formed in the atmosphere can fall as acid rain. This can harm the environment and can also destroy limestone buildings and marble statues since they are made of limestone (Calcium Carbonate CaCO₃). Metals like iron are also attacked by acid rain.

- Sulfur dioxide in atmosphere from burning of fossil fuels can react with water and oxygen to make sulfuric acid (H₂SO₄):
2SO₂ (g)         +         2H₂O (l)         +         O₂ (g)         →         2H₂SO₄ (aq)

- If sulfur dioxide in the atmosphere reacts with just water, a weaker acid sulfurous acid (H₂SO₃) is formed:
SO₂ (g)         +         H₂O (l)         →         H₂SO₃ (aq)

- In car engines the temperature is high enough for nitrogen in air to react with oxygen to produce oxides of nitrogen, e.g:
N₂ (g)         +         O₂ (g)         →         NO₂ (g)
In the atmosphere these nitrogen oxides can produce nitric acid (HNO₃).