Edexcel GCSE Chemistry
Edexcel GCSE Chemistry Topic 8: Fuels and Earth Science Exam Questions
Free Edexcel GCSE Chemistry exam questions for Topic 8: Fuels and Earth Science, with a mark scheme for every pack. Covers crude oil and hydrocarbons, fractional distillation, alkanes, combustion and pollutants, cracking, hydrogen as a fuel, the atmosphere and climate change.
Topic 8: Fuels and Earth Science exam questions
2 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 Edexcel GCSE Chemistry Topic 8: Fuels and Earth Science
Topic 8 of Edexcel GCSE Chemistry covers fuels from crude oil and the chemistry of the Earth's atmosphere. You learn that crude oil is a mixture of hydrocarbons separated by fractional distillation, describe trends in the properties of fractions, write combustion equations, and explain the pollutants produced, including carbon monoxide, soot, sulfur dioxide and oxides of nitrogen. You compare petrol with hydrogen as a fuel and explain cracking. The second half deals with how the atmosphere evolved, the greenhouse effect and climate change. Topic 8 is assessed on Paper 2 and links to energy changes in Topic 7 and organic chemistry in Topic 9.
What you need to know
- Crude oil Crude oil is a complex mixture of hydrocarbons, mostly alkanes, and is a finite resource. Fractional distillation separates it into fractions: gases, petrol, kerosene, diesel oil, fuel oil and bitumen.
- Properties of fractions Fractions with larger molecules have higher boiling points, are more viscous and are harder to ignite. Alkanes form a homologous series with general formula CnH2n+2, differing by CH2.
- Combustion and pollutants Complete combustion produces carbon dioxide and water. Incomplete combustion produces carbon monoxide (toxic, combines with haemoglobin and reduces oxygen transport) and soot. Sulfur impurities produce sulfur dioxide and acid rain; oxides of nitrogen form from nitrogen and oxygen in the air at high temperatures in engines.
- Fuels and cracking Hydrogen as a fuel produces only water but is hard to store and is often made using energy from fossil fuels; petrol is easy to store but produces carbon dioxide. Cracking breaks long-chain alkanes into shorter alkanes and alkenes, using a catalyst, to match supply to demand for fuels.
- The atmosphere The early atmosphere, from volcanoes, contained little or no oxygen and a large amount of carbon dioxide; water vapour condensed to form oceans, and carbon dioxide dissolved. Oxygen increased through photosynthesis by plants and algae. A simple test: oxygen relights a glowing splint.
- Greenhouse effect and climate change Carbon dioxide, methane and water vapour absorb heat radiated from the Earth and re-emit it. Human activities increase greenhouse gases; evidence comes from ice cores and temperature records, though historical data are less accurate. Effects include rising sea levels and changing weather patterns.
Common mistakes in Topic 8: Fuels and Earth Science
- Saying fractions are separated by different melting points. They are separated by boiling points.
- Saying carbon monoxide is dangerous because it causes acid rain. It is toxic because it binds to haemoglobin.
- Assuming hydrogen fuel is completely pollution-free. Its production may use fossil fuels.
- Confusing alkanes (CnH2n+2, saturated) with alkenes (CnH2n, unsaturated) when writing cracking products.
- Saying greenhouse gases reflect heat back. They absorb and re-emit infrared radiation.
Try three Topic 8: Fuels and Earth Science exam-style questions
1. Write a balanced equation for the complete combustion of methane. (2 marks)
Show the mark scheme answer
CH4 + 2O2 → CO2 + 2H2O; correct formulae (1), balanced (1).
2. Explain why cracking is carried out. (2 marks)
Show the mark scheme answer
There is more demand for short-chain hydrocarbons (such as petrol) than is supplied by crude oil; cracking converts less useful long-chain molecules into shorter alkanes and alkenes (used to make polymers).
3. Give one advantage and one disadvantage of hydrogen compared with petrol as a fuel for cars. (2 marks)
Show the mark scheme answer
Advantage: only produces water (no carbon dioxide); disadvantage: hydrogen is a gas so it is difficult to store or needs large tanks, or is often made using fossil fuels, or few refuelling stations.
Topic 8: Fuels and Earth Science FAQs
What does Edexcel GCSE Chemistry Topic 8 cover?
It covers crude oil, fractional distillation, alkanes, combustion and pollutants, hydrogen as a fuel, cracking, the evolution of the atmosphere, the greenhouse effect and climate change.
Which paper is Topic 8 on?
Topic 8 Fuels and Earth science is assessed on Edexcel GCSE Chemistry Paper 2.
What should I learn about pollutants?
For each of carbon monoxide, soot, sulfur dioxide and oxides of nitrogen, learn how it forms and its effect. Link sulfur dioxide and oxides of nitrogen to acid rain and carbon monoxide to toxicity.
