Crude Oil
5 marks · EasyHydrocarbons in crude oil are separated into different groups, called fractions, for different uses. These fractions have different properties.
State what a hydrocarbon is.
State one reason why crude oil is called a non-renewable resource.
Describe one way the boiling point and one way the colour of a hydrocarbon fraction would change as its molecules get bigger.
Explain why smaller hydrocarbon fractions are often used as fuels.
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(a) A compound containing only carbon and hydrogen atoms.
(b) Crude oil is non-renewable because it takes millions of years to form and cannot be replaced quickly once used.
(c) As molecules get bigger, boiling point increases and colour becomes darker.
(d) Smaller hydrocarbon fractions are more volatile and burn easily, making them suitable as fuels.
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Marking points
B1 (a) · 1 mark · States a hydrocarbon contains only carbon and hydrogen.
B1 (b) · 1 mark · Gives a correct reason for crude oil being non-renewable (takes millions of years to form/not replaced quickly).
B1 (c) · 1 mark · States boiling point increases as molecule size increases.
B1 (c) · 1 mark · States colour becomes darker as molecules get bigger.
B1 (d) · 1 mark · Explains why smaller hydrocarbons are good fuels (volatile, burn easily, ignite easily).
Worked solution
a) A hydrocarbon is a compound containing only carbon and hydrogen atoms.
b) Crude oil is non-renewable because it takes millions of years to form, so cannot be replaced quickly.
c) As molecule size increases, boiling point increases and colour becomes darker.
d) Smaller hydrocarbon fractions are more volatile and ignite easily, so are often used as fuels.