Crude oil contains hydrocarbons with sulfur impurities. When these hydrocarbons are burned as fuels, sulfur dioxide is produced as well as other combustion products. Explain how the combustion of hydrocarbons containing sulfur impurities, and the combustion of hydrocarbons in insufficient oxygen, each cause harm to the environment or human health.

Pearson Edexcel International GCSE Chemistry (4CH1) — 4.2 Crude oil · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Crude oil fractions are widely used as fuels in transport and industry. The combustion of these fuels releases several pollutant gases and particles into the atmosphere.

Model answer (4 marks)

Sulphur impurities in the hydrocarbons give rise to sulphur dioxide (SO₂) when the fuel is burned. SO₂ reacts with water vapour in clouds to form sulphuric acid, which falls as acid rain. Acid rain damages or kills trees, harms aquatic life and corrodes buildings and metals.

When the fuel is burnt in insufficient oxygen, incomplete combustion occurs. This produces carbon monoxide (CO), a colourless, odourless gas that is toxic to humans because it binds haemoglobin more strongly than oxygen. Incomplete combustion also releases fine carbon particulates (soot). These particulates scatter sunlight, causing global dimming, and they are inhaled by humans, leading to respiratory problems and other health issues.

Examiner tips

  • Use the exact terms ‘sulphur dioxide’, ‘acid rain’, ‘carbon monoxide’, ‘carbon particulates’. Explain the chain of effects (SO₂ → acid rain → damage) and the health impact of CO. Show the two separate causes of harm – sulphur and incomplete combustion – as the question asks.
  • common_mistakes
  • :
  • Confusing sulphur dioxide with sulphuric acid; not linking SO₂ to acid rain. Forgetting that CO is toxic to humans. Omitting the health effects of carbon particulates or the environmental effect of global dimming.

Mark scheme (4 marks)

  1. Sulfur dioxide (from burning sulfur impurities) reacts with water vapour in clouds to form acid rain
  2. Acid rain damages/kills trees, aquatic life, or corrodes buildings/metals (named harmful effect of acid rain)
  3. Incomplete combustion (insufficient oxygen) produces carbon monoxide, which is toxic to humans
  4. Incomplete combustion also produces carbon particulates, which cause global dimming or health problems such as respiratory problems in humans

Key terms in this question

impurities · combustion

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