Crude oil is a mixture of hydrocarbons. Explain why crude oil is separated into fractions by fractional distillation, and describe how the process works.

Crude oil contains many hydrocarbons with a wide range of boiling points, so the mixture cannot be used directly as a fuel or raw material.

To separate it, the crude is heated in a furnace until it vaporises.

The vapour is fed into a fractionating column that has a temperature gradient – hot at the bottom and cool at the top.

As the vapour rises, components with higher boiling points condense first near the bottom, while lower‑boiling components remain gaseous and rise further up, condensing at higher levels. Each condensed liquid is collected as a separate fraction.

This process yields distinct fractions such as naphtha, kerosene, diesel and residual oil, each with a useful boiling‑point range.