Practise 28 exam-style questions on Fractional distillation and petrochemicals for AQA GCSE Chemistry. Write your answer as you would in the exam and get it marked in seconds against the mark scheme, point by point, with an AI tutor on hand if you get stuck.
28 questions
1–6 marks each
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20 questions, marked as you go
Sample questions with model answers
Here are 4 of the questions in this topic, each with a model answer, an explanation of why it earns the marks and the mark scheme an examiner would use.
Question 1
2 marks
Name two fuels that are produced from crude oil.
Model answer
Petrol and diesel oil.
Explanation
Many fuels we depend on come from crude oil: petrol, diesel oil, kerosene, heavy fuel oil and liquefied petroleum gases. Each comes from a different fraction.
Mark scheme
1 mark
petrol
max 2; ignore crude oil; do not accept coal or natural gas
1 mark
diesel oil
1 mark
kerosene
allow jet fuel / paraffin
1 mark
heavy fuel oil
allow fuel oil
1 mark
liquefied petroleum gases (LPG)
Question 2
2 marks
The petrol fraction contains alkanes with between 5 and 10 carbon atoms per molecule. Relative atomic masses (Ar): C = 12, H = 1
Give the molecular formula of the alkane in the petrol fraction with the largest molecules, and calculate its relative formula mass (Mr).
Model answer
The largest molecules have 10 carbon atoms. Using CₙH₂ₙ₊₂: (2 × 10) + 2 = 22 hydrogen atoms, so the formula is C₁₀H₂₂. Mr = (10 × 12) + (22 × 1) = 120 + 22 = 142
Explanation
Each fraction contains molecules within a range of sizes. Using the alkane general formula, you can work out the formula and Mr of any alkane in the range.
Mark scheme
1 mark
C₁₀H₂₂
allow C10H22; correct answer with no working scores full marks
1 mark
Mr = (10 × 12) + (22 × 1) = 142
allow ecf from an incorrect alkane formula
Question 3
3 marks
Hydrocarbons with larger molecules condense lower down in the fractionating column.
Explain why, in terms of the forces between molecules.
Model answer
Larger hydrocarbon molecules have stronger intermolecular forces between them. More energy is needed to overcome these forces, so they have higher boiling points. This means they condense at higher temperatures, and the higher temperatures are found lower down the column.
Explanation
During evaporation and condensation it is the weak forces between molecules that are overcome or formed, not the covalent bonds inside the molecules. Longer molecules have stronger intermolecular forces.
Mark scheme
1 mark
larger molecules have stronger intermolecular forces
allow forces between molecules; do not accept stronger covalent bonds
1 mark
so more energy is needed to overcome the forces / they have higher boiling points
1 mark
so they condense at higher temperatures, which are found lower down the column
Question 4
4 marks
Some people think that crude oil should be used mainly as a feedstock for making chemicals, rather than being burned as fuel.
Evaluate this view.
Model answer
Crude oil is a finite resource, so it will eventually run out. It is the feedstock for many materials that are hard to make any other way, such as polymers, solvents, lubricants and detergents, so using it as a feedstock makes the most of a limited resource. Burning it as fuel also releases carbon dioxide, which contributes to climate change. However, modern life depends heavily on petrol, diesel and kerosene for transport and on other fuels for heating, so it would be difficult to stop burning crude oil quickly. Because alternatives such as electric vehicles and renewable energy are available for many fuel uses, I agree that crude oil should increasingly be kept for making chemicals.
Explanation
An evaluation needs points for and against the view, followed by a conclusion that follows from them. Key ideas are that crude oil is finite, that feedstock uses have few alternatives, and that fuel use releases carbon dioxide.
Mark scheme
1 mark
crude oil is finite and will run out
max 4
1 mark
it is needed as a feedstock for useful materials such as polymers, solvents, lubricants and detergents
1 mark
burning fuels releases carbon dioxide (which contributes to climate change)
1 mark
but modern life depends heavily on fuels from crude oil for transport, heating and electricity
1 mark
alternatives exist or are being developed for fuels (e.g. electric vehicles, renewable energy, biofuels)
1 mark
a justified conclusion
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