Total marks: 100 · Duration: 105 minutes · Tier: Higher
Instructions to candidates
- Use black ink or black ball-point pen. Draw diagrams in pencil.
- Answer all questions in the spaces provided.
- In all calculations, show clearly how you work out your answer.
- You may use a calculator.
- Where a question describes apparatus, a graph or a chromatogram in words, you may find it helpful to sketch it.
Information
- The maximum mark for this paper is 100.
- The marks for questions are shown in brackets.
- You are expected to use good English and to organise information clearly, especially in questions marked with an asterisk (*).
- This paper covers AQA GCSE Chemistry topics 4.6 to 4.10: the rate and extent of chemical change; organic chemistry; chemical analysis; chemistry of the atmosphere; and using resources.
- Relative atomic masses (Ar): H = 1, C = 12, O = 16. One mole of any gas occupies 24 dm³ (24 000 cm³) at room temperature and pressure.
Paper
Question 1 — Rates of reaction (14 marks)
A student adds magnesium ribbon to excess dilute hydrochloric acid and measures the total volume of hydrogen produced.
| Time (s) | 0 | 10 | 20 | 30 | 40 | 50 | 60 |
|---|---|---|---|---|---|---|---|
| Volume of hydrogen (cm³) | 0 | 18 | 32 | 42 | 48 | 50 | 50 |
(a) Calculate the mean rate of reaction in the first 20 seconds. Give the unit. [2 marks]
(b) Explain why the rate of reaction decreases as the reaction goes on. [2 marks]
(c) The student repeats the experiment at a higher temperature. Explain, in terms of particles, why the rate increases. [3 marks]
(d) The gradient of the tangent to the graph of these results at 30 s is 0.8 cm³/s. What does this value represent? [1 mark]
(e) Explain how a catalyst increases the rate of a reaction. [2 marks]
(f) Calculate the mean rate of reaction over the first 50 seconds in mol/s. Give your answer in standard form to 3 significant figures. [2 marks]
(g) (i) State one variable the student must keep the same. [1 mark]
(ii) Suggest one improvement to the method that would give more accurate volume readings. [1 mark]
Question 2 — Reversible reactions and equilibrium (11 marks)
Ammonia is made by the Haber process: N₂(g) + 3H₂(g) ⇌ 2NH₃(g). The forward reaction is exothermic.
(a) Explain the effect of increasing the pressure on the yield of ammonia. [2 marks]
(b) Explain the effect of increasing the temperature on the yield of ammonia. [2 marks]
(c) Explain why a temperature of about 450 °C is used. [2 marks]
(d) What is meant by dynamic equilibrium? [2 marks]
(e) Hydrated copper sulfate (blue) can be heated to form anhydrous copper sulfate (white) and water. This reaction is endothermic. What can you say about the energy change when water is added to anhydrous copper sulfate? [1 mark]
(f) Ammonia reacts with sulfuric acid to make ammonium sulfate, a fertiliser. Write a balanced equation for this reaction. [2 marks]
Question 3 — Organic chemistry (15 marks)
(a) Octane, C₈H₁₈, is an alkane.
(i) Give the general formula of the alkanes. [1 mark]
(ii) Explain why octane is described as saturated. [1 mark]
(b) Decane, C₁₀H₂₂, can be cracked to form octane and one other product.
(i) Complete the equation: C₁₀H₂₂ → C₈H₁₈ + ______ [1 mark]
(ii) Describe a test to show that the other product is an alkene. Give the result. [2 marks]
(c) Name the product formed when ethene reacts with bromine. [1 mark]
(d) Name the organic product formed when ethanol is oxidised. [1 mark]
(e) Name the ester formed when ethanol reacts with ethanoic acid. [1 mark]
(f) Propene, CH₃CH=CH₂, forms the addition polymer poly(propene). Describe the repeating unit of poly(propene). [2 marks]
(g) Polyesters are condensation polymers. Explain how a condensation polymer differs from an addition polymer. [2 marks]
(h) Write a balanced equation for the complete combustion of propane, C₃H₈. [2 marks]
(i) Explain why the boiling points of the fractions from crude oil increase as the molecules get bigger. [1 mark]
Question 4 — Chemical analysis (13 marks)
(a) (i) What is meant by a pure substance in chemistry? [1 mark]
(ii) How could a student use melting point to show that a sample of aspirin is pure? [1 mark]
(b) A paint is described as a formulation. What is a formulation? [1 mark]
(c) A student uses paper chromatography to analyse a food colouring. A spot travels 3.6 cm and the solvent front travels 8.0 cm.
(i) Calculate the Rf value of the spot. [2 marks]
(ii) Explain why the start line is drawn in pencil, not ink. [1 mark]
(iii) Which is the mobile phase in paper chromatography? [1 mark]
(d) Describe the test for
(i) chlorine [1 mark]
(ii) oxygen. [1 mark]
(e) A student does flame tests on two unlabelled salts. Salt P gives a crimson flame and salt Q gives a lilac flame. Identify the metal ion in each salt. [2 marks]
(f) Sodium hydroxide solution is added to a solution of an iron(II) salt. Give the colour of the precipitate. [1 mark]
(g) Dilute nitric acid and silver nitrate solution are added to a solution of a bromide. Give the colour of the precipitate. [1 mark]
Question 5 — Chemistry of the atmosphere (12 marks)
(a)* Describe how the Earth's early atmosphere is thought to have changed to form the atmosphere we have today. [6 marks]
(b) Explain how greenhouse gases cause the temperature of the Earth to increase. [3 marks]
(c) Give two ways of reducing the carbon footprint of a product. [2 marks]
(d) Explain why carbon monoxide is a dangerous pollutant. [1 mark]
Question 6 — Using resources (15 marks)
(a) Some countries produce drinking water by distilling seawater. Explain why this method is expensive. [2 marks]
(b) Waste water treatment includes screening, sedimentation and anaerobic digestion. Describe what happens in sedimentation and in anaerobic digestion. [2 marks]
(c) The table shows life cycle assessment data for two shopping bags.
| Paper bag | Plastic (poly(ethene)) bag | |
|---|---|---|
| Raw material | Wood | Crude oil |
| Energy to make one bag (MJ) | 1.7 | 1.6 |
| Number of uses before disposal | 1 | 5 |
| Biodegradable? | Yes | No |
Use the data to evaluate which bag has the smaller environmental impact. [3 marks]
(d) Copper can be extracted from low-grade ores by phytomining. Describe how phytomining works. [3 marks]
(e) Iron can be protected from rusting by attaching blocks of zinc. Explain how this protects the iron. [2 marks]
(f) Explain why steel, an alloy of iron, is harder than pure iron. [2 marks]
(g) Give one property of a composite material that makes it more useful than its separate components. [1 mark]
Question 7 — Investigating the effect of concentration (10 marks)
Sodium thiosulfate solution reacts with dilute hydrochloric acid to form a yellow precipitate of sulfur, which makes the mixture cloudy.
(a)* Describe a method to investigate how the concentration of sodium thiosulfate affects the rate of this reaction. [6 marks]
(b) With 40 g/dm³ sodium thiosulfate, the cross disappeared after 20 s. With 20 g/dm³ it disappeared after 40 s. Calculate 1/time for each concentration, and describe the relationship between concentration and rate. [2 marks]
(c) Explain, in terms of particles, why rate increases with concentration. [2 marks]
Question 8 — Calculations in organic chemistry (10 marks)
(a) Propane burns: C₃H₈ + 5O₂ → 3CO₂ + 4H₂O
(i) Calculate the mass of carbon dioxide produced when 11 g of propane burns completely. [3 marks]
(ii) Calculate the volume of oxygen, at room temperature and pressure, needed to burn 11 g of propane. [2 marks]
(b) Ethanol can be made by fermentation or by the hydration of ethene.
Fermentation: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ Hydration: C₂H₄ + H₂O → C₂H₅OH
(i) Calculate the percentage atom economy of making ethanol by fermentation. Give your answer to 3 significant figures. [3 marks]
(ii) Give one advantage of making ethanol by fermentation. [1 mark]
(iii) Give one advantage of making ethanol by the hydration of ethene. [1 mark]