Fractional Distillation

How are various fractions taken from crude oil by fractional distillation.

[4 marks]

Visual Mark Scheme Breakdown

• How do we prepare the crude oil for the fractional column? (1 mark)

  • It is heated in a furnace to vaporise

  (1 mark)

• How does the bottom and top of the column differ? (1 mark)

  • There is a temperature gradient (cool at the top, hot at the bottom)

    (1 mark)

• What happens to the gases? (1 mark)

  • The gases condense a different heights of the column

  (1 mark)

• Why? (1 mark)

  • Each gas has a different boiling point and therefore condenses at a different height

  (1 mark)

  • At the cooler top, short-chain hydrocarbons with low boiling point exit

  • At the hotter bottom, long-chain hydrocarbons with high boiling points exit