Crude Oil
5 marks · EasyCrude oil is very important in modern life. It is separated into fractions for different uses.
State what crude oil is mainly made of.
Crude oil is separated into fractions. Give one example of a product obtained from a fraction of crude oil and state its use.
Describe how the viscosity and colour of hydrocarbon liquids change as the size of their molecules increases.
Explain why larger hydrocarbon molecules have higher boiling points than smaller ones.
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(a) Crude oil is a mixture of hydrocarbons.
(b) Example: petrol (used as fuel in cars); diesel (fuel in vehicles); kerosene (aircraft fuel); bitumen (road surfacing); etc.
(c) As molecule size increases, viscosity increases (liquid becomes thicker, flows less easily) and colour becomes darker.
(d) Larger molecules have stronger intermolecular forces, so more energy is needed to separate them, resulting in a higher boiling point.
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Marking points
B1 (a) · 1 mark · States that crude oil is a mixture of hydrocarbons
B1 (b) · 1 mark · Gives a correct product and use from a crude oil fraction (e.g., petrol as car fuel)
B1 (c) · 1 mark · Describes correct viscosity trend with molecule size (e.g., increases)
B1 (c) · 1 mark · Describes correct colour trend with molecule size (e.g., becomes darker)
B1 (d) · 1 mark · Explains higher boiling point of larger hydrocarbons due to stronger intermolecular forces
Worked solution
a) Crude oil is a mixture of hydrocarbons.
b) Petrol (used as fuel in cars) is obtained from a fraction of crude oil. (Any correct example and use accepted.)
c) As the size of hydrocarbon molecules increases, the liquids become more viscous (they flow less easily) and also become darker in colour.
d) Larger hydrocarbon molecules have stronger intermolecular forces because they have more atoms, so more energy is needed to separate them, resulting in a higher boiling point.