GCSE Chemistry – Unit 1 Factsheets
1.3 How do we get fuels from crude oil?
a) What is crude oil?
Crude oil is a mixture of a very large
number of compounds. Most of the
compounds in crude oil are hydrocarbons.
Defn: Hydrocarbon – molecule made
up of hydrogen and carbon atoms
only.
b) Alkanes
Most of the hydrocarbons in crude oil are
saturated hydrocarbons called alkanes, which
have the
general formula, CnH2n+2
Defn: Saturated hydrocarbon –
contains only single covalent bonds.
Defn: General formula – shows the
ratio of different types of atoms in
a homologous series.
Defn: Mixture – two or more elements
or compounds not chemically joined.
Remember, chemical properties of each substance
in a mixture are unchanged. It is possible to
separate the substances in a mixture by physical
methods such as distillation.
Name
Molecular Structure
formula
Methane CH4
Ethane
C2H6
Propane
C3H8
Butane
C4H10
Pentane
C5H12
Hexane
C6H14
Defn: Homologous series – family of organic compounds such as alkanes.
c) Fractional Distillation
The many hydrocarbons in crude oil may be
separated into fractions, each of which
contains a similar number of carbon atoms, by
evaporating the oil and allowing it to condense
at a number of different temperatures. This
process is called fractional distillation.
Trends in fractions – hydrocarbons
which come off lower down the
fractionating tower:

Are larger molecules

Have lower boiling points

Burn less easily

Are more viscous

And are darker in colour than
those which come off above
d) How fractions are used as fuels
The properties of hydrocarbons which depend upon the size of their molecules
influence how they are used as fuels. For example:
 molecules with 3-4 carbons are gases and used for bottled gas fuel
 molecules with 7-9 carbons are used as petrol to fuel cars
 molecules with 11-18 carbons are used in kerosene heaters and aircraft fuel
 molecules with 20-27 carbons are used as fuel oil for ships or heaters
e) Environmental issues relating to fuels
Most fuels contain carbon
Substance
and/or hydrogen and may
Sulphur
also contain some sulphur.
dioxide
The gases released into
the atmosphere when a
fuel burns may include
carbon dioxide, water
(vapour), carbon monoxide
and sulphur dioxide.
Carbon
Particles may also be
dioxide
released.
Carbon
Problem
Solution
Contributes to acid
rain
Remove sulphur from
fuels before they are
burned, eg buy low sulphur
petrol. Sulphur dioxide
can be removed from the
waste gases after
combustion, eg in power
stations.
Use less fossil fuel –
develop alternative fuels.
Contributes to
global warming
Poisonous as it
binds to
haemoglobin
preventing red
blood cells carrying
oxygen.
Cause global
dimming
Ensure complete
combustion or ventilate
well.
monoxide
f) Alternatives
Hydrogen and ethanol may
both be used as fuels in
place of hydrocarbons.
Cut down on emission of
Particles
particles, ie use catalytic
Hydrogen burns very
converters, burn less fuel
cleanly, the only product
being water vapour. Obtaining hydrogen however will require energy – this could
come from burning fossil fuels or from a renewable source. Ethanol can be produced
from non-renewable fossil fuels or from the fermentation of plants. When ethanol
burns completely it gives off carbon dioxide and water vapour.
g) Consider …
 How does burning hydrocarbon fuels impact the environment?
 Why is it important we use fuels?
 What alternatives are there to fossil fuels?
 Why is crude oil so expensive?
 Which fuels do you think will be used most in 20 years time?
 What will the major consequences be to everyday life if gas and oil and coal
run out in the near future?
 How important or useful are hydrocarbons? Why?
 What makes a good fuel?
 Which is better, hydrogen or ethanol, as a fuel?
Typical AQA style Examination Questions
1. Describe the process by which crude oil is separated. You will be awarded 1 mark
for use of key terminology.
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2. Consider the data given below of different fuels. Order the fuels from which you
think is the best fuel to the worst fuel. What is your reasoning behind your
decision?
Fuel
A
B
C
D
Cost in
pence per
100g
6.0
4.0
3.5
18.0
Energy in
kJ per
100g
4800
1200
2800
14400
Energy
per penny
in kJ
800
300
800
800
Gas formed on burning
Carbon
dioxide
Yes
Yes
Yes
No
Sulphur
dioxide
No
No
Yes
No
Water
vapour
Yes
Yes
Yes
yes
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3. Why is it dangerous to leave a gas heater running all night in a locked basement
room?
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4. Explain how and why the boiling points of the alkane family are all different
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5. Describe the process by which fossil fuels are formed?
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6. What is the difference between metal oxides and non-metal oxides in terms of
pH? What is the reasoning for your decision? State an example of each!
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7. Draw a labelled diagram of the apparatus you would use for the cracking of a long
chain alkane.
8.
What is the chemical test and observations that you would carry out to identify the
product? What is another name for the type of reaction being carried out?
9. Alkenes can undergo addition reactions with hydrogen, what is another name for
this type of reaction? What is meant by the term addition? With an example
show what is formed in a reaction of this kind!
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