AQA GCSE Chemistry
AQA GCSE Chemistry 4.7.1 Carbon Compounds as Fuels and Feedstock Exam Questions
Free AQA GCSE Chemistry exam questions for 4.7.1 Carbon Compounds as Fuels and Feedstock, with a mark scheme for every pack. Covers crude oil, alkanes, fractional distillation, properties and combustion of hydrocarbons, cracking and the test for alkenes.
4.7.1 Carbon Compounds as Fuels and Feedstock exam questions
4 question packs of real past exam questions, each with its mark scheme. Do not stop after a few: answer as many as you can without notes, then mark every answer with the mark scheme. The more questions you do, the more quickly you will spot how examiners ask about each idea.
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About AQA GCSE Chemistry 4.7.1 Carbon Compounds as Fuels and Feedstock
AQA GCSE Chemistry 4.7.1 introduces organic chemistry through crude oil. You learn that crude oil is a mixture of hydrocarbons, mostly alkanes, and how fractional distillation separates it into useful fractions used as fuels and as feedstock for the petrochemical industry. You explain trends in boiling point, viscosity and flammability, write combustion equations, and describe how cracking turns long-chain alkanes into shorter alkanes and alkenes. It is assessed on Paper 2 and links to alkenes and polymers in 4.7.2 and 4.7.3, and to atmospheric pollution in 4.9. Balancing cracking and combustion equations is a frequent exam task.
What you need to know
- Crude oil and alkanes Crude oil is a finite resource formed from the remains of plankton buried in mud. It is mainly hydrocarbons, most of which are alkanes with general formula CnH2n+2: methane, ethane, propane and butane are the first four.
- Fractional distillation Crude oil is heated and vaporised; the vapour rises up a column that is hotter at the bottom and cooler at the top. Fractions condense at different heights according to their boiling points. Fractions include petrol, kerosene, diesel oil, heavy fuel oil and liquefied petroleum gases.
- Properties of hydrocarbons As molecules get longer, boiling point and viscosity increase and flammability decreases. Short-chain hydrocarbons are more useful as fuels.
- Combustion Complete combustion of a hydrocarbon releases energy and forms carbon dioxide and water, with carbon and hydrogen oxidised. Example: CH4 + 2O2 → CO2 + 2H2O.
- Cracking Long-chain hydrocarbons are broken down into shorter, more useful molecules by catalytic cracking (vapour over a hot catalyst) or steam cracking (mixed with steam at very high temperature). Products include alkenes, used to make polymers and as starting materials.
- Test for alkenes Alkenes turn bromine water from orange to colourless; alkanes do not change its colour.
Common mistakes in 4.7.1 Carbon Compounds as Fuels and Feedstock
- Saying fractions are separated by different 'melting points' or 'densities'. They are separated by boiling points.
- Getting trends backwards: longer chains are more viscous and less flammable, with higher boiling points.
- Writing 'bromine water turns clear'. Clear can still be coloured; say it turns colourless.
- Unbalanced cracking equations. Check that carbon and hydrogen totals are equal on both sides, for example C10H22 → C8H18 + C2H4.
- Saying crude oil is a compound. It is a mixture of many compounds.
Try three 4.7.1 Carbon Compounds as Fuels and Feedstock exam-style questions
1. Decane, C10H22, is cracked to produce octane, C8H18, and one other product. Write a balanced equation and name the other product. (2 marks)
Show the mark scheme answer
C10H22 → C8H18 + C2H4; ethene.
2. Write a balanced equation for the complete combustion of propane, C3H8. (2 marks)
Show the mark scheme answer
C3H8 + 5O2 → 3CO2 + 4H2O; correct products (1), balanced (1).
3. Explain why crude oil can be separated by fractional distillation. (3 marks)
Show the mark scheme answer
Crude oil is a mixture of hydrocarbons with different chain lengths; which have different boiling points; the column has a temperature gradient so each fraction condenses at a different height.
4.7.1 Carbon Compounds as Fuels and Feedstock FAQs
What does AQA GCSE Chemistry 4.7.1 cover?
It covers crude oil, alkanes, fractional distillation, the properties and combustion of hydrocarbons, cracking and the bromine water test for alkenes.
Which paper is 4.7.1 examined in?
Section 4.7 Organic chemistry is assessed on AQA GCSE Chemistry Paper 2.
What should I learn about cracking?
Learn the two methods (catalytic and steam), the conditions in words, how to balance cracking equations and why cracking is needed: demand for short-chain fuels like petrol is greater than supply, and alkenes are needed to make polymers.
