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3.2.3Organic Chemistry

Pollution from Combustion — Edexcel AS Chemistry Revision Notes & Topical Questions

5 min read 4 parts Lesson 21 of 42

📚 Edexcel AS Chemistry Hub / Topical Revision
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Part 1 of 4Pollutants and Their Sources

Carbon monoxide
  • Carbon monoxide Incomplete combustion in limited oxygen produces CO, a toxic gas that binds to haemoglobin in the blood.
Soot
  • Soot Particulates of carbon from incomplete combustion cause breathing problems and darken buildings.
Unburnt hydrocarbons
  • Unburnt hydrocarbons Fuel that escapes combustion contributes to smog and forms ozone at ground level.
Oxides of nitrogen
  • Oxides of nitrogen Nitrogen and oxygen from the air react at the high temperature inside engines: N₂ + O₂ → 2NO.
Sulfur dioxide
  • Sulfur dioxide Sulfur impurities in fuels burn: S + O₂ → SO₂.
Carbon dioxide
  • Carbon dioxide Complete combustion of any carbon fuel gives CO₂, a greenhouse gas that contributes to global warming.

Part 2 of 4Acid Rain

1
Sulfur dioxide dissolves in water droplets in the atmosphere to form sulfurous acid, H₂SO₃.
2
Oxidation in the air can convert it to sulfuric acid: 2SO₂ + O₂ + 2H₂O → 2H₂SO₄.
3
Nitrogen monoxide is oxidised in air to nitrogen dioxide: 2NO + O₂ → 2NO₂.
4
Nitrogen dioxide then reacts with water and oxygen to form nitric acid: 4NO₂ + O₂ + 2H₂O → 4HNO₃.
5
The acidic rain damages limestone buildings, kills trees and lowers the pH of lakes so that fish die.

Part 3 of 4Health and Environment

Health and Environment
CO
  • CO Carbon monoxide is colourless and odourless, so it is dangerous because victims do not notice it.
NOₓ
  • NOₓ Nitrogen oxides cause respiratory problems and also contribute to photochemical smog.
SO₂
  • SO₂ Sulfur dioxide irritates the lungs and is the main cause of acid rain.
CO₂
  • CO₂ Carbon dioxide absorbs infrared radiation from the Earth and enhances the greenhouse effect.
Particulates
  • Particulates Fine carbon particles damage the lungs and reduce visibility in cities.

Part 4 of 4Exam Checklist & Tips

3.2.3 – Key Points for the Exam

  • Pollutant A substance in the environment that causes harm.
  • Particulates Tiny solid particles, such as soot, suspended in air.
  • Acid rain Rain with a pH lower than normal because it contains dissolved acidic oxides.
  • Greenhouse gas A gas that absorbs infrared radiation and traps heat in the atmosphere.
  • Incomplete combustion Burning without enough oxygen, forming CO or C.

Common Mistakes

  • Saying that nitrogen oxides come from nitrogen in the fuel, when in engines they mainly come from air.
  • Confusing the global warming effect of CO₂ with acid rain, which is caused mainly by SO₂ and NOₓ.
  • Describing CO as an acidic gas that causes acid rain.
  • Leaving out that sulfur dioxide comes from sulfur impurities in the fuel.

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