Fractional Distillation - IGCSE Chemistry Revision Notes

Introduction to Fractional Distillation

• Crude oil is a mixture of hydrocarbons called fractions.
• Each fraction contains hydrocarbons of similar chain lengths and properties.
• Fractional distillation separates these fractions based on boiling points.
• Most fractions contain alkanes with single bonds between carbon and hydrogen.

Process of Fractional Distillation

• Fractionating Column: Utilized to separate crude oil into fractions.
  • Has a temperature gradient: hot at the bottom, cooler at the top.
  • Steps:
    1. Crude oil is heated and vaporizes.
    2. Hydrocarbon vapors enter the column.
    3. Vapors with high boiling points condense at the bottom.
    4. Vapors with lower boiling points rise and condense at the top.

Important Tips

• Higher boiling point compounds condense lower in the column.

Properties of Main Fractions

• Viscosity: Ease of flow of a liquid.
  • High viscosity = thicker liquid, flows less easily.
  • Increases with the carbon chain length.
• Color: Darkens with increased carbon chain length.
• Boiling Point: Increases with molecular size due to greater intermolecular attraction.
• Volatility: Tendency to vaporize.
  • Decreases with increased molecular size.

Boiling Point Trends of Main Fractions

Uses of Crude Oil Fractions

• Liquified Petroleum Gas: Domestic heating and cooking.
• Petrol: Car fuel.
• Kerosene: Jet fuel.
• Diesel: Diesel engines.
• Heavy Fuel Oil: Ships and power stations.
• Bitumen: Road and roof surfacing.

Key Points

• Names and uses of the main fractions are crucial for exam preparation.
• Gasoline is known as petrol in the UK and gasoline in the USA.