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Crude oil is a mixture of alkanes which can be separated into different fractions - OCR Gateway - GCSE Chemistry: Combined Science - Question 14 - 2021 - Paper 10
Question 14
Crude oil is a mixture of alkanes which can be separated into different fractions. The different fractions have a range of different boiling points. The diagram sh... show full transcript
Worked Solution & Example Answer:Crude oil is a mixture of alkanes which can be separated into different fractions - OCR Gateway - GCSE Chemistry: Combined Science - Question 14 - 2021 - Paper 10
Step 1
Explain how fractional distillation separates the crude oil into fractions.
Answer
Fractional distillation operates by heating crude oil, causing it to vaporize. The vapor then rises through a column that is cooler at the top and hotter at the bottom. As the vapors ascend, they cool and condense at different heights depending on their boiling points. Alkanes with lower boiling points will condense higher up in the column, while those with higher boiling points will condense lower down. This process effectively separates the crude oil into distinct fractions based on the differing boiling points of the alkanes.
Step 2
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Step 5
Explain the similarities and differences in the boiling points of the alkanes.
Answer
The boiling points of methane, ethane, propane, and butane increase as the number of carbon atoms in the molecules increases. This is due to the increased Van der Waals forces, which result from larger molecular sizes and greater surface area. Methane, having one carbon atom, has the lowest boiling point at -162 °C, while butane, with four carbon atoms, has the highest boiling point at -0.5 °C. The differences in boiling points highlight the effect of molecular size and intermolecular forces in determining the physical properties of different alkanes.