How the physical properties of hydrocarbons change with molecule size
2 marks · HardState two changes in the physical properties of hydrocarbon fractions as the number of carbon atoms in their molecules increases.
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Also accept: Boiling point increases; Volatility decreases (they become less volatile); Viscosity increases (they become more viscous); Colour becomes darker; Fractions burn less easily
Common mistakes: State only one change; Give chemical, not physical, changes
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Marking points
B1 · 1 mark · One correct property change stated (e.g. boiling point increases, viscosity increases, volatility decreases, colour gets darker, burns less easily)
B2 · 1 mark · A second correct property change stated (not a restatement of the first)
Worked solution
As the number of carbon atoms increases, the boiling point increases and the fraction becomes less volatile (more viscous, darker, or burns less easily are also acceptable).