C7 Fractional Distillation (page 151)

Question 1

What can crude oil be used to make?

Answer 1

lots of things, such as fuels.

But you cant just put crude oil in your car. First the different hydrocarbons have to be separated. Thats where frational distillation comes in.

Question 2

What is crude oil?

Answer 2

it is a fossil fuel. Its formed from the remains of plants and animals, mainly plankton, that died millions of years ago and were buried in mud. Over millions of years, with high temperature and pressure, the remains turn to crude oil, which can be drilled up from the rocks where it’s found.

Question 3

What are fossil fuels like coal, oil and gas called?

Answer 3

Non-renewable fuels.

They take so long to make that they’re being used up much faster than they’re being formed. They’re fline resourses (see page 161) - one day they’ll run out.

Question 4

Fractional Distillation can be used to separate what?

Answer 4

Hydrocarbon Fractions

Question 5

Crude oil is a mixture of lots of different hydrocarbons, most of which are what?

Answer 5

Alkanes.

(Alkanes consist of hydrogen and carbon atoms arranged in a tree structure in which all the carbon- carbon bonds are single. Alkanes have the general chemical formular CnH2n+2

Question 6

How is Fractional Distillation used to separate Hydrocarbon Fractions?

Answer 6

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

Please see diagram on page 151

Question 7

Petrol drains further up a fractionating column that diesel. Use the diagram of the fractionating column to explain why the boiling point of petrol is lower than of diesel? (2 marks)

Answer 7

The hydrocarbons in petrol have a shorter chain length than the hydrocarbons in diesel (1 mark).

This means that petrol has a lower boiling point than diesel (1 mark)

Question 8

Describe the temperature gradient in the fractionating column used for fractional distillation?

Answer 8

Its hot at the bottom and cooler at the top (1 mark)