C9.2 · Greenhouse gases and climate change
Calculate — 5 marks
A chemical plant manufactures quicklime (calcium oxide) for use in steel production by thermally decomposing limestone in a rotary kiln. The process releases carbon dioxide gas into the atmosphere. The plant manager must calculate the mass of greenhouse gas emissions to comply with environmental regulations. The equation for the reaction is: CaCO₃(s) → CaO(s) + CO₂(g). Relative formula masses: CaCO₃ = 100, CO₂ = 44.
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(01.1) Calculate the maximum mass of carbon dioxide produced when 2.5 tonnes of pure calcium carbonate completely decomposes. Give your answer in tonnes.
[2 marks]
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(01.2) The limestone used in the plant is typically only 80% calcium carbonate, with the remainder being non-reactive impurities. Calculate the actual mass of carbon dioxide produced when 2.5 tonnes of this impure limestone is completely processed. Give your answer in tonnes.
[3 marks]
Show mark scheme
- (01.1) Correct use of mass ratio (44/100) or mole calculation
- (01.1) Correct answer: 1.1 tonnes (accept 1100 kg)
- (01.2) Correct calculation of mass of pure calcium carbonate: 2.0 tonnes (or 2.5 × 0.80)
- (01.2) Correct use of mass ratio or stoichiometry
- (01.2) Correct answer: 0.88 tonnes (accept 0.9 tonnes or 880 kg)
C10.1 · Sustainable development and life cycle assessment
Calculate — 5 marks
A manufacturing company produces plastic water bottles. They are conducting a life cycle assessment (LCA) to compare the environmental impact of their current production method with a proposed sustainable alternative. The current method uses virgin plastic and generates 2.4 kg of CO₂ equivalent per bottle produced. The proposed method uses 60% recycled plastic and generates 0.9 kg of CO₂ equivalent per bottle. The company produces 500,000 bottles annually.
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Calculate the total annual CO₂ equivalent emissions from the current production method for all bottles produced.
[2 marks]
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Calculate the total annual CO₂ equivalent emissions from the proposed sustainable method for all bottles produced.
[2 marks]
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Calculate the percentage reduction in CO₂ equivalent emissions if the company switches to the proposed sustainable method. Show your working.
[1 mark]
Show mark scheme
C10.3 · The Haber process and fertilisers
Describe — 2 marks
A farmer is planning to increase crop yields on their land. They decide to use nitrogen-based fertilisers produced using the Haber process. The farmer wants to understand how this industrial process works and why it is important for modern agriculture.
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Describe what happens to nitrogen gas and hydrogen gas in the Haber process.
[2 marks]
Show mark scheme
- {'mark': 1, 'description': 'Nitrogen and hydrogen react together / combine'}
- {'mark': 1, 'description': 'To form ammonia (or they produce ammonia)'}
C10.1 · Sustainable development and life cycle assessment
Suggest — 4 marks
A manufacturer produces reusable shopping bags made from organic cotton. The company claims these bags are more sustainable than single-use plastic bags. However, a life cycle assessment (LCA) shows that producing one organic cotton bag requires significantly more water and energy than manufacturing a plastic bag. The cotton bag must be reused approximately 150 times before its total environmental impact equals that of a single plastic bag.
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Suggest why the initial production stage of the organic cotton bag has a greater environmental impact than a single-use plastic bag. (1 mark)
[1 mark]
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Suggest two reasons why the reusable cotton bag becomes more sustainable than the plastic bag after 150 uses, considering the complete life cycle of both products. (2 marks)
[2 marks]
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Suggest how a consumer's purchasing decision and usage pattern would need to change for the organic cotton bag to be a genuinely sustainable choice compared to the plastic alternative. (1 mark)
[1 mark]
Show mark scheme
C10.1 · Sustainable development and life cycle assessment
Define — 4 marks
A chemical company manufactures biodegradable packaging from plant starch. The company wants to ensure their product is genuinely environmentally friendly by evaluating its impact from raw material extraction to disposal.
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(01.1) Define the term sustainable development.
[2 marks]
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(01.2) Define the term life cycle assessment.
[2 marks]
Show mark scheme
- (01.1) meeting the needs of the present/current generation
- (01.1) without compromising the ability of future generations to meet their own needs
- (01.2) assessing the environmental impact of a product
- (01.2) at all stages from raw material extraction through processing, manufacture, use, and disposal
C4.3 · Electrolysis
State — 3 marks
A student carries out an electrolysis experiment using copper sulfate solution with copper electrodes. A direct current power supply is connected to the electrodes, and the student observes changes at both the positive and negative electrodes during the experiment.
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State the name of the electrode connected to the positive terminal of the power supply.
[1 mark]
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State what is observed at the negative electrode during the electrolysis of copper sulfate solution with copper electrodes.
[1 mark]
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State why the copper electrode connected to the positive terminal gradually decreases in mass during this electrolysis.
[1 mark]
Show mark scheme
C7.2 · Polymers and alcohols
Evaluate — 3 marks
A packaging company is choosing between two materials for food containers. Poly(lactic acid) (PLA) is a biodegradable polymer made from plant starch through fermentation to produce lactic acid, which is then polymerised. Poly(ethene) is produced from crude oil through fractional distillation and cracking to make ethene, which is then polymerised. The company wants to evaluate which material is more suitable.
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(01.1) State one advantage and one disadvantage of using PLA instead of poly(ethene) for food packaging.
[2 marks]
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(01.2) Evaluate whether the company should choose PLA or poly(ethene) for food containers. Give a reason for your answer.
[1 mark]
Show mark scheme
- (01.1) Advantage: PLA is biodegradable / breaks down naturally / renewable resource used / less landfill waste (1)
- (01.1) Disadvantage: PLA is more expensive / requires land to grow crops / may compete with food production / needs specific industrial composting conditions (1)
- (01.2) Judgment with valid reason (1) — e.g., PLA is better for the environment, OR poly(ethene) is cheaper/more durable
C9.1 · The evolution of the atmosphere
Define — 4 marks
Geologists study volcanic rocks to understand how Earth's atmosphere formed billions of years ago. Volcanoes released gases that created the early atmosphere, and later processes changed its composition over time.
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(01.1) Define the term outgassing.
[2 marks]
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(01.2) Define photosynthesis. Explain how this process caused the amount of oxygen in the atmosphere to increase.
[2 marks]
Show mark scheme
- (01.1) Release of gases from the interior of the Earth / volcanoes
- (01.1) into the atmosphere
- (01.2) Process by which plants / algae / organisms use carbon dioxide and water to produce glucose and oxygen
- (01.2) (Credit) Oxygen accumulated / built up in the atmosphere over time as photosynthetic organisms increased in number
C6.1 · Rate of reaction
Define — 4 marks
A chemical manufacturer produces hydrogen gas by reacting zinc metal with dilute hydrochloric acid. The company needs to control the rate of this reaction to ensure a steady supply of hydrogen for use in the production of margarine.
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(01.1) Define the term rate of reaction.
[2 marks]
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(01.2) Give one reason why the manufacturer wants to control the rate of this reaction. State one measurement that could be used to determine the rate of this reaction.
[2 marks]
Show mark scheme
- (01.1) the change in concentration of reactants or products per unit time
- (01.1) or the amount of reactant used or product formed per unit time
- (01.2) safety reasons / to prevent explosion / to match production demand / to control supply (1)
- (01.2) volume of gas produced per unit time / mass of zinc lost per unit time / concentration of acid changed per unit time (1)
C1.1 · Atomic structure
Evaluate — 3 marks
In medical imaging, doctors use iodine compounds to monitor thyroid function. Two isotopes of iodine can be used: iodine-127, which is stable, and iodine-131, which is radioactive with a half-life of 8 days. Both isotopes have identical chemical properties and both contain 53 protons.
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(01.1) State how the atomic structure of iodine-131 differs from iodine-127.
[1 mark]
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(01.2) Evaluate the use of iodine-131 compared to iodine-127 for medical imaging.
[2 marks]
Show mark scheme
- (01.1) Iodine-131 has more neutrons than iodine-127 (accept: iodine-131 has 78 neutrons, iodine-127 has 74 neutrons)
- (01.2) Iodine-131 is radioactive so it can be detected/traced in the body (or: emits radiation that can be measured externally)
- (01.2) Risk of harm from radiation exposure OR conclusion that iodine-131 is more suitable despite the risk because it can be monitored/detected
C8.2 · Chromatography and tests for gases
State — 5 marks
A student is testing gases produced during different chemical reactions in the laboratory. They need to identify the gases using chemical tests and separate a mixture of coloured dyes using paper chromatography.
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State the name of the gas produced when a metal reacts with dilute hydrochloric acid.
[1 mark]
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State the test and the expected observation to identify oxygen gas.
[2 marks]
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A student uses paper chromatography to separate a mixture of food colourings. State the name of the liquid used to carry the dyes up the paper and state why this liquid must not be allowed to reach the top of the paper.
[2 marks]
Show mark scheme
C5.2 · Activation energy and reaction profiles
Calculate — 2 marks
A student investigates the decomposition of hydrogen peroxide (H₂O₂) into water and oxygen. This reaction is very slow at room temperature. When manganese dioxide is added as a catalyst, the reaction speeds up significantly. The student draws a reaction profile showing the energy changes for the uncatalysed reaction. The energy of the reactants is 150 kJ/mol, the energy of the products is 50 kJ/mol, and the energy of the transition state (peak) is 350 kJ/mol.
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(01.1) Calculate the activation energy for the uncatalysed reaction.
[1 mark]
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(01.2) A catalyst provides an alternative pathway with an activation energy of 100 kJ/mol. Calculate the energy change when the catalyst is used.
[1 mark]
Show mark scheme
- (01.1) 200 (kJ/mol)
- (01.2) 100 (kJ/mol)
GCSE Perfect