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Chemistry - Processing Crude Oil (AQA)

Crude oil is separated in a fractionating column. In GCSE Chemistry you learn how boiling points decide which fractions become fuels, feedstocks and materials we use daily.

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Fascinating Fact:

Main fractions include refinery gases, gasoline, naphtha, kerosene, diesel, fuel oil and bitumen.

In GCSE Science (Chemistry), you learn that fractional distillation separates crude oil into fractions with similar boiling points. Each fraction has different uses, from fuels for transport to feedstocks for the chemical industry.

Key Terms

Fractional distillation: A process that separates a mixture of liquids, such as crude oil, into fractions based on their different boiling points.
Fraction: A group of hydrocarbons from crude oil that boil within a similar temperature range and have related uses.
Boiling point: The temperature at which a liquid changes to a gas; used to separate crude oil in a fractionating column.

Frequently Asked Questions (Click to see answers)

What is fractional distillation of crude oil in GCSE Chemistry?

Fractional distillation is the process of heating crude oil so it vaporises, then condensing the vapours at different heights in a column to collect fractions with similar boiling points.

How does a fractionating column separate crude oil?

The column is hot at the bottom and cooler at the top. Vapours rise, then condense where the temperature is just below their boiling point, so different fractions are drawn off at different levels.

What products are made from crude oil fractions?

Crude oil fractions provide fuels like petrol, diesel and kerosene, as well as gas for heating, fuel oils for ships and bitumen for road surfaces and roofing materials.

Try These Related Quizzes

1 .

Where are the coolest temperatures in the fractionating column?

At the very bottom

Just above the bottom

Somewhere in the middle

At the very top

The column is cooler the higher up you go

2 .

Why does fractional distillation of crude oil work?

Because the chemicals in crude oil have the same melting points

Because the chemicals in crude oil boil at different temperatures

Because the chemicals in crude oil have different viscosities

Because the chemicals in crude oil are very volatile

This allows them to be condensed from hot, vapourised crude oil at different places in a fractional distillation column, thus separating the mixture

3 .

Which of the following statements best describes the molecules in crude oil?

The molecules in crude oil are not chemically combined

The molecules in crude oil are chemically combined

The molecules in crude oil are all very large

The molecules in crude oil are all very small

There is a wide range of sizes of molecules in crude oil, none of which are chemically combined with each other - crude oil is a mixture

4 .

The chemicals from crude oil are mainly alkanes. Which of the following statements best describes alkanes?

Alkanes are hydrocarbons with sulfur molecules attached

Alkanes are hydrocarbons with multiple bonds between the carbon atoms

Alkanes are hydrocarbons with single bonds between the carbon atoms

Alkanes are hydrocarbons made from carbon atoms alternating with hydrogen and oxygen atoms in a long chain

Hydrocarbons with only single bonds between the carbon atoms are called saturated

5 .

Which of the following is not required for cracking?

High temperatures

Hydrogen

A catalyst

Large hydrocarbon molecules

Cracking of the long carbon chain alkanes from crude oil produces a shorter carbon chain alkane and an alkene. As well as this 'catalytic' cracking, other methods such as steam cracking are also used

6 .

The demand for certain fractions of oil is greater or smaller than the output, for example, there is not enough of the fraction containing the chemicals used as fuel for cars, and there is more of the bitumen fraction than can be used. How is this problem solved?

Some of the gas molecules are joined together to make bigger molecules like petrol and diesel

More roads are built to use up the bitumen fraction

Some of the molecules in the bitumen fraction are cracked

More oil is distilled so that enough of each fraction is made, the unused products are then thrown away

Cracking of larger molecules breaks them down into smaller and more useful molecules which saves having to waste them

7 .

At an oil refinery, how often is oil put into the fractional distillation column?

Once a day

Twice a day

Every hour

All the time

You are expected to know that the process is continuous. The fractionating column at an oil refinery is only 'switched off' if there is a breakdown or if maintenance is required

8 .

Most of the fractions of crude oil are used as what?

Food

Fuel

Drugs

Plastics

About the only fraction not used as a fuel is the bitumen fraction

9 .

What happens to the chemicals in the crude oil vapour as they rise?

Nothing, they remain vapourised

As they reach an area that is the same temperature as their boiling point they condense

As they reach an area that is the same temperature as their melting point they condense

They react together to form fuels

When they condense, the chemicals form droplets of liquid that fall back down the column onto a collecting tray and can be removed from the fractionating column

10 .

Crude oil is put into the fractionating column in what form?

As a hot vapour

As a cold vapour

As a hot liquid

As a cold liquid

The crude oil is heated to a temperature where all of the chemicals have boiled and then injected into the fractional distillation column to rise and cool, allowing the different hydrocarbons to condense at different levels

You can find more about this topic by visiting BBC Bitesize - Crude oil, hydrocarbons and alkanes - AQA

Author: Kev Woodward (PGCE, Science & Chemistry Teacher, Quiz Writer)