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Cambridge IGCSE Chemistry · 0620

Chapter 11: Organic Chemistry — Part 3

Topic 11.3 · Fuels and fractional distillation

Fossil Fuels and Hydrocarbons

  • Fossil Fuels: Include coal, natural gas, and petroleum (crude oil).
  • Natural Gas: Mainly consists of methane (CH4).
  • Hydrocarbons: Compounds containing hydrogen and carbon atoms only.
  • Petroleum: A finite resource consisting of a mixture of hydrocarbons.

Fractional Distillation of Petroleum

Petroleum is separated into useful fractions based on differences in boiling points. The crude oil is heated and vaporised; as it rises up a fractionating column, different components condense at different levels.

Trends from Bottom to Top of the Column:

  • Decreasing chain length.
  • Higher volatility (evaporates more easily).
  • Lower boiling points.
  • Lower viscosity (runs more easily).

Exam Traps

  • Do not reverse column trends — long-chain fractions (fuel oil, bitumen) collect at the bottom, not the top.
  • Do not confuse fractional distillation (physical separation by boiling point) with cracking (chemical breakdown of long chains).

Uses of Fractions

  1. Refinery Gas: Heating and cooking.
  2. Gasoline (Petrol): Fuel for cars.
  3. Naphtha: Chemical feedstock.
  4. Kerosene (Paraffin): Jet fuel.
  5. Diesel Oil: Fuel for diesel engines.
  6. Fuel Oil: Fuel for ships and home heating.
  7. Lubricating Oil: Lubricants, waxes, and polishes.
  8. Bitumen: Making roads.

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