How the physical properties of hydrocarbons change with molecule size
3 marks · EasyFuel oil and gasoline (petrol) are both hydrocarbon fractions collected from crude oil.
State which of the two fractions is expected to evaporate more quickly at room temperature.
Give a reason for your answer to part (a).
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(a) Gasoline (petrol)
(b) — · must show Gasoline has smaller molecules, Smaller hydrocarbons are more volatile and evaporate more easily
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Marking points
B1 (a) · 1 mark · Identifies gasoline (petrol) as the fraction that evaporates more quickly.
M1 (b) · 1 mark · States that gasoline (petrol) consists of smaller hydrocarbon molecules than fuel oil.
A1 (b) · 1 mark · Explains that smaller molecules are more volatile and evaporate more readily.
Worked solution
a) Gasoline (petrol)
b) Gasoline contains smaller hydrocarbon molecules, which are more volatile and evaporate more easily at room temperature than the larger molecules in fuel oil.