Explain how crude oil is split into fractions? Give an example of a substance collected at the top of the column. [5 marks]

Crude oil is made up of a mixture of substances.Crude oil is vapourised before it enters the column.The column is hotter at the bottom and cooler at the top (around 350 degrees at the bottom, and 50 degrees at the top).Substances travelling up the column condense as they reach their boiling point [so longer molecules with higher boiling points condense lower down the columm and smaller molecules with lower melting points condense higher].
Substances that collect at the top of the column are:any short chain hydrocarbons and low boiling point alkanes (used as fuel) e.g. methane, ethane, propane, butane etc[propane/ butane can also be known as petroleum gas].