C7 CGP

Question 1

What is crude oil?

Answer 1

• fossil fuel
• mixture of hydrocarbons

Question 2

Explain fractional distillation.

Answer 2

1. The oil is heated until most of it has turned into gas
2. The gases enter a fractionating column (and the liquid bit is drained off)
3. In the column there’s a temperature gradient (it’s hot at the bottom and gets cooler as you go up)
4. The longer hydrocarbons have high boiling points. They condense back into liquids and drain out the column early on, when they’re near the bottom
5. The short hydrocarbons have lower boiling points. They condense and drain out much later on, near to the top of the column where it’s cooler.
6. You end up with the crude oil mixture separated out into different fractions. Each fractions contains a mixture of hydrocarbons that all contain a similar number of carbon atoms so have similar boiling points.