OxfordAQA International GCSE Chemistry: Carbon compounds as fuels (9202) – Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs – examination boards hold copyright in their own papers. Use these alongside the official past papers from your board or school.

Written for OxfordAQA International GCSE Chemistry (9202), this set follows the OxfordAQA International GCSE Chemistry (9202) specification, Version 6.2, for exams May/June 2018 onwards. It covers section 3.10.1 Carbon compounds as fuels (3.10.1.1 to 3.10.1.3) and the required practical on testing for a double bond. The qualification is untiered, so all the questions are for every candidate. Relative atomic masses: C = 12, H = 1, O = 16.

Links: study guide · revision notes · course hub · checklist · free diagnostics

Questions

1. This question is about crude oil.

(a) State what is meant by a hydrocarbon. [1] (b) Crude oil has no single boiling point. Explain why. [1]

2. Five substances are labelled A to E: A C₈H₁₈, B C₇H₁₄, C C₅H₁₂, D C₆H₆, E C₃H₈O.

(a) Identify the two alkanes. [1] (b) Identify the alkene. [1] (c) Explain why E is not a hydrocarbon. [1] (d) Draw the displayed formula of propane. [1] (e) Write the molecular formula of the alkane with 14 carbon atoms. [1]

3. Describe how crude oil is separated into fractions in a fractionating column. [6]

4. Use these values for four hydrocarbons.

Hydrocarbon	Carbon atoms	Boiling point / °C
P	3	−42
Q	6	69
R	10	174
S	16	287

(a) Give the letter of the hydrocarbon that is a gas at 25 °C. [1] (b) Describe the trend in boiling point shown by the data. [1] (c) Give the letter of the most viscous liquid. [1] (d) Give the letter of the liquid that ignites most easily. [1] (e) Estimate the boiling point of a hydrocarbon from the same series with 8 carbon atoms. [1]

5. Tetradecane, C₁₄H₃₀, and octane, C₈H₁₈, can be used as fuels.

(a) Tetradecane burns in excess oxygen. Write a balanced equation for this reaction. [2] (b) Write a balanced equation for the incomplete combustion of octane in which carbon monoxide and water are the only products. [2] (c) State what happens to the carbon and hydrogen atoms in a fuel during combustion. [1]

6. A power station burns coal that contains a small amount of sulfur.

(a) Explain why sulfur dioxide is released. [1] (b) Oxides of nitrogen are also released, even though the coal contains almost no nitrogen. Explain why. [2] (c) Name the environmental problem caused by each of these: sulfur dioxide; carbon dioxide; solid particles. [3]

7. The hydrocarbon C₂₁H₄₄ is cracked.

(a) Complete the equation: C₂₁H₄₄ → C₁₅H₃₂ + C₂H₄ + …… [1] (b) Describe the two ways in which the vapour can be cracked. [2] (c) Explain why oil refineries crack large hydrocarbons. [2]

8. A student has two colourless liquids, X and Y. One is an alkane and one is an alkene.

(a) Describe a test the student could do to identify the alkene. Give the result for each liquid. [3] (b) Identify one hazard in this experiment and say how the student could reduce the risk. [2] (c) Explain what the result tells you about the bonding in the alkene. [1]

9. Ethanol can be made by hydration of ethene or by fermentation of sugar.

(a) Write the equation for the hydration of ethene and name the catalyst. [2] (b) Calculate the maximum mass of ethanol that can be made from 8.4 tonnes of ethene. [2] (c) Compare the two methods in terms of raw material, type of process, purity of product and energy requirements. [4]

10. A brewer ferments 3.6 kg of glucose: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂

(a) Calculate the maximum mass of ethanol that can form, in kg. [3] (b) State the temperature range used, and explain why a much higher temperature is not used. [2]

11. A government plans to replace part of the country’s petrol with bioethanol made from sugar cane. Use these illustrative values for the total carbon dioxide released per unit of energy, counting production and burning: petrol 94 g; bioethanol 40 g.

(a) Calculate the percentage reduction in carbon dioxide when bioethanol replaces petrol. [2] (b) Evaluate the plan. Refer to renewable resources, land use and carbon footprint. [5]

12. Coal and natural gas are both used as fuels.

(a) State why the combustion of a fuel is useful. [1] (b) A fuel burns in plenty of air to give only carbon dioxide and water. Deduce which elements the fuel must contain. [1] (c) Explain why burning a fuel in a poor supply of air can produce soot. [2]

Answers

1. (a) A compound (molecule) made of hydrogen and carbon atoms only [1]. (b) It is a mixture of many compounds, each with its own boiling point [1]. Examiner insight: “Contains hydrogen and carbon” is not enough for (a); the word “only” is what earns the mark.

2. (a) A and C [1]. (b) B [1]. (c) It contains oxygen as well as carbon and hydrogen [1]. (d) Three carbons in a chain, each with four single bonds, and eight hydrogens [1]. (e) C₁₄H₃₀ [1]. Examiner insight: Draw every single bond in a displayed formula; count four bonds round each carbon and one round each hydrogen before you finish.

3. Any six of: crude oil is heated so it vaporises [1]; vapour enters the bottom of the column [1]; there is a temperature gradient, with the base hottest and the top coolest [1]; vapours rise up the column [1]; each substance condenses where the temperature is below its boiling point [1]; fractions are collected at different heights, with small molecules at the top and large molecules at the bottom [1]. Examiner insight: Aim for six distinct, linked points in a logical order; a short answer that only says “they separate by boiling point” earns very little credit.

4. (a) P [1]. (b) Boiling point increases as the number of carbon atoms increases [1]. (c) S [1]. (d) Q [1]. (e) Any value from 100 °C to 150 °C [1]. Examiner insight: In (d), P is a gas at room temperature, so the question asks about liquids; read the stem carefully before choosing the smallest molecule.

5. (a) Correct formulae of CO₂ and H₂O [1]; 2C₁₄H₃₀ + 43O₂ → 28CO₂ + 30H₂O (or C₁₄H₃₀ + 21½O₂ → 14CO₂ + 15H₂O) [1]. (b) Correct products CO and H₂O [1]; 2C₈H₁₈ + 17O₂ → 16CO + 18H₂O [1]. (c) They are oxidised (combine with oxygen) [1]. Examiner insight: Balance carbon, then hydrogen, then oxygen, and count every element on both sides before moving on; one wrong coefficient leaves the whole equation unbalanced.

6. (a) Sulfur in the coal is oxidised when it burns, forming sulfur dioxide [1]. (b) The furnace is at a high temperature [1], so the nitrogen and oxygen in air combine with each other [1]. (c) Sulfur dioxide: acid rain [1]. Carbon dioxide: climate change [1]. Solid particles: global dimming [1]. Examiner insight: For (b), name the high temperature and say the nitrogen comes from the air; blaming nitrogen in the coal contradicts the question.

7. (a) C₄H₈ [1]. (b) Pass the vapour over a hot catalyst [1]; or mix it with steam and heat to a very high temperature [1]. (c) There is more of the large hydrocarbons than is needed, and they are less useful as fuels [1]; cracking produces smaller molecules that are in demand as fuels, and alkenes [1]. Examiner insight: For (b), saying “heat it” alone is not enough; you need either the catalyst or the steam route described.

8. (a) Add bromine water to each liquid and shake [1]. The alkene turns the bromine water from orange to colourless [1]. The alkane leaves it orange [1]. (b) Bromine water is harmful or irritant [1]; wear eye protection and gloves (or use small volumes) [1]. Accept: hydrocarbons are flammable; keep away from naked flames. (c) The alkene has a carbon–carbon double bond, which reacts with bromine [1]. Examiner insight: “Goes clear” is a common slip; clear can still be coloured, so write colourless.

9. (a) C₂H₄ + H₂O → C₂H₅OH [1]; phosphoric acid [1]. (b) 28 t of ethene gives 46 t of ethanol, so 8.4 × 46 ÷ 28 [1] = 13.8 tonnes [1]. (c) Hydration uses ethene from crude oil, which is non-renewable; fermentation uses sugar, which is renewable [1]. Hydration is continuous; fermentation is a batch process [1]. Hydration gives pure ethanol; fermentation gives a dilute solution [1]. Hydration needs more energy for its high temperature and pressure; fermentation runs at 20 °C to 35 °C [1]. Examiner insight: Each comparison point should say something about both methods; describing one method alone leaves the comparison unmade.

10. (a) Moles of glucose = 3600 ÷ 180 = 20 mol [1]. Moles of ethanol = 2 × 20 = 40 mol [1]. Mass = 40 × 46 = 1840 g = 1.84 kg [1]. (b) 20 °C to 35 °C [1]. At much higher temperatures the enzymes in yeast stop working (are denatured) [1]. Examiner insight: Forgetting the 1 : 2 ratio halves the answer; write the mole ratio from the equation before using it.

11. (a) (94 − 40) ÷ 94 × 100 [1] = 57% [1]. (b) Sugar cane is renewable, while petrol comes from crude oil, which is not [1]. Plants absorb carbon dioxide as they grow, so the carbon footprint is lower [1]. The footprint is not zero, because farming, processing and transport release carbon dioxide [1]. Growing fuel crops uses land that could grow food or may lead to forest being cleared [1]. A judgement that weighs these points, for example: worthwhile if the cane is grown on land not needed for food [1]. Examiner insight: End with a judgement backed by reasons from both sides; a list of points with no conclusion is not an evaluation, and a bare opinion is not either.

12. (a) It releases energy [1]. (b) Carbon and hydrogen (it may also contain oxygen) [1]. (c) There is not enough oxygen to oxidise all the carbon to carbon dioxide [1], so some is left as carbon particles [1]. Examiner insight: In (b), you cannot rule out oxygen in the fuel, so answers that say “carbon and hydrogen only” are risky.

Where marks are usually lost

• Describing fractions as separated by melting point or by molecule shape.
• Forgetting that the column is cooler at the top.
• Writing trends for viscosity or flammability the wrong way round.
• Unbalanced combustion equations, or leaving water out of incomplete combustion.
• Matching each pollutant to the wrong environmental problem.
• Using “clear” instead of colourless for the bromine water result.
• Comparing only one method of making ethanol, or calling fermentation continuous.
• Skipping the mole ratio in fermentation calculations.
• Giving a one-sided answer on biofuels when asked to evaluate.

Next steps

• Recap fast with the revision notes.
• Go back over weak areas in the study guide.
• For extra reacting-mass work, try the quantitative chemistry practice set.
• See the whole course on the OxfordAQA IGCSE Chemistry hub and tick off topics on the printable checklist.
• Try one of the free 10-minute diagnostics.
• Book a free trial class.

Official syllabus

OxfordAQA International GCSE Chemistry (9202) specification, Version 6.2, for exams May/June 2018 onwards, published by OxfordAQA. This practice set covers section 3.10.1 Carbon compounds as fuels and the required practical on testing for a double bond.