alkanes

• what is crude oil?

  a mixture of hydrocarbons that can be separated using fractional distillation.
• how is crude oil separated?

  the mixture is vapourised and fed into the fractionating column. The vapour rises, cools, and condenses.
• how are shorter chained hydrocarbons collected?

  shorter chain hydrocarbons have a lower boiling point so they rise to the top and cool towards the top of the column.
• how are longer-chain hydrocarbons collected?

  they have a higher boiling point therefore they condense towards the bottom of the column