How the physical properties of hydrocarbons change with molecule size
3 marks · EasyThe table shows information about three fractions from crude oil.
| Fraction | Approx. number of carbon atoms | Boiling point (°C) |
|---|---|---|
| Petroleum gas | 4 | −1 |
| Diesel | 16 | 260 |
| Bitumen | 70 | over 350 |
Which fraction is most volatile?
Describe the relationship between the number of carbon atoms and boiling point for these fractions.
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Show answer
(a) Petroleum gas
(b) — · must show Boiling point increases as number of carbon atoms increases, Bitumen: largest number of carbons, highest boiling point
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Marking points
B1 (a) · 1 mark · Correctly identifies petroleum gas as the most volatile fraction.
M1 (b) · 1 mark · States that boiling point increases as the number of carbon atoms increases.
A1 (b) · 1 mark · Links examples from the table (e.g., bitumen has the most carbon atoms and the highest boiling point).
Worked solution
a) Petroleum gas
b) As the number of carbon atoms increases, the boiling point increases. For example, bitumen has the most carbon atoms (70) and the highest boiling point (over 350 C).