GCSE Chemistry - Crude Oil and Fractional Distillation

Explain that crude oil is a fossil fuel mixture of hydrocarbons, primarily alkanes containing hydrogen and carbon. Describe how crude oil formed naturally from dead plants and animals buried millions of years ago, transformed by high pressure and temperature underground.

Discuss how crude oil is extracted from rocks by drilling and pumping it to the surface. Emphasize that crude oil is a finite, non-renewable resource that will eventually be depleted at current extraction rates.

Feed crude oil into a heated chamber and apply heat until most of the oil converts into a gas. This gaseous mixture is then ready to be separated in the fractionating column.

Introduce the gaseous hydrocarbon mixture into a fractionating column that is hot at the bottom and progressively cooler toward the top. The hot gases rise up the column as cooler regions are encountered.

Long-chain hydrocarbons with high boiling points rapidly condense into liquids at the hot lower regions and drain out early. These fractions include bitumen for road surfacing and heavy fuel oils used for heating and lubrication.

Medium-chain hydrocarbons with moderate boiling points rise higher in the column before condensing into liquids. These fractions include diesel, petrol for vehicles, and kerosene for jet engines.

Short-chain hydrocarbons with very low boiling points remain gaseous throughout the column and exit at the top. These include LPG (liquefied petroleum gas) containing propane and butane, which are highly flammable and useful as fuels.

Compare the different hydrocarbon fractions by flammability and utility, noting that shorter-chain fractions make better fuels while longer-chain fractions can be used directly or cracked into smaller molecules. Explain that these petrochemicals also serve as raw materials for producing solvents, lubricants, polymers, and detergents.