How the physical properties of hydrocarbons change with molecule size
3 marks · EasyThe table shows two hydrocarbon fractions obtained from crude oil.
| Fraction | Approx. number of carbon atoms |
|---|---|
| Fuel gas | 3 |
| Lubricating oil | 20 |
Which fraction is more viscous?
Explain your answer to part (a).
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(a) Lubricating oil
(b) — · must show Fraction with more carbon atoms, Viscosity increases with molecule size
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Marking points
B1 (a) · 1 mark · Correctly identifies lubricating oil as the more viscous fraction.
M1 (b) · 1 mark · Recognises that lubricating oil has larger molecules (more carbon atoms).
A1 (b) · 1 mark · States that viscosity increases as the size (number of carbon atoms) increases.
Worked solution
a) Lubricating oil
b) Lubricating oil has a higher number of carbon atoms (20) than fuel gas (3). As the number of carbon atoms in a hydrocarbon increases, the molecules are larger and the liquid becomes more viscous.