Describe how a fractional distillation column separates crude oil fractions.

The column is hot at the bottom and cool at the top. Crude oil is evaporated and its vapours travel up the column condensing at different temperatures. Substances with high boiling points condense at the bottom and substances with lower boiling points condense on the way to the top. Each fraction then contains hydrocarbon molecules with a similar number of carbon atoms and a similar range of boiling points.