Pearson Edexcel IGCSE Chemistry: Organic Chemistry — Practice Questions (4CH1)

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 available from your board.

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Questions

1. Ethanol can be made by the fermentation of glucose.

(a) State two conditions used for fermentation. [2]

(b) Explain why air must be kept out of the fermentation mixture. [1]

2. Describe how crude oil is separated into fractions by fractional distillation. [3]

3. Decane, C₁₀H₂₂, is cracked to form octane, C₈H₁₈, and one other product.

(a) Write an equation for this reaction. [1]

(b) Give one reason why cracking is carried out. [1]

4. Describe a test to distinguish between hexane and hexene, giving the result for each. [2]

5. Explain how burning some fossil fuels can cause acid rain. [2]

Answers

1. (a) A temperature of about 30 °C (30–40 °C) [1]; yeast (enzymes in yeast) [1]. (b) Oxygen in the air would oxidise the ethanol to ethanoic acid [1].

Mark-scheme insight (Pearson Edexcel 4CH1 June 2024 mark scheme, Paper 2CR, Question 4(a)): the credited conditions are a temperature (30 °C, or a value from 30 to 40 °C) and yeast; “glucose”, “anaerobic” and “pressure” are ignored, so they do not score as conditions. Try the real question next: Pearson Edexcel International GCSE Chemistry 4CH1, June 2024, Paper 2CR, Question 4.

Source for the mark-scheme insights on this page: Pearson Edexcel International GCSE Chemistry 4CH1 Paper 2CR mark scheme (Summer 2024) and Pearson Edexcel International GCSE Chemistry 4CH1 Paper 1CR mark scheme (Summer 2024), paraphrased.

2. Crude oil is heated so it vaporises and the vapour enters near the bottom of the column [1]; the column has a temperature gradient, hot at the bottom and cooler at the top [1]; each fraction condenses at the height where the temperature falls below its boiling point, so fractions are separated by boiling point [1].

3. (a) C₁₀H₂₂ → C₈H₁₈ + C₂H₄ [1]. (b) There is more long-chain hydrocarbon than is needed, and cracking makes more of the shorter-chain fuels in higher demand (such as petrol) (or: it makes alkenes for polymers) [1].

4. Add bromine water to each [1]. Hexene decolourises it (orange to colourless); hexane stays orange [1].

5. Some fuels contain sulfur impurities, which burn to form sulfur dioxide [1]; sulfur dioxide dissolves in rainwater to form an acidic solution (acid rain) [1].

Mark-scheme insight (Pearson Edexcel 4CH1 June 2024 mark scheme, Paper 1CR, Question 8(c)): the first mark is for the fuel containing sulfur, and nitrogen is rejected for that mark. (Nitrogen oxides come from nitrogen in the air, not from the fuel.) Try the real question next: Pearson Edexcel International GCSE Chemistry 4CH1, June 2024, Paper 1CR, Question 8.

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Where marks are usually lost

• Giving “anaerobic” as a fermentation condition instead of the temperature and yeast.
• Saying bromine water “goes clear” instead of “colourless”.
• Unbalanced cracking equations: count carbon and hydrogen on both sides.
• Blaming nitrogen in the fuel for acid rain.