O Level Combined Science 5129 · Topic 21

Chemistry of the environment: past paper questions

35 real questionsasked in 8 of the last 10 exam series2019–2025usually: State, Explain, Name, Describe, Use

Real questions on chemistry of the environment

The newest 17 of 17 written questions, plus 18 multiple-choice. Open one to see it on the real paper.

5129/21 · October/November 2025 · Q10a[2]
Describe two effects of pollution by untreated sewage on freshwater ecosystems.
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5129/22 · October/November 2025 · Q2a[1]
State the percentage of oxygen gas, O 2 , in clean, dry air.
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5129/22 · May/June 2025 · Q4a(i)[1]
State the name of the component of cigarette smoke that increases the risk of a person developing lung cancer.
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5129/22 · May/June 2025 · Q4a(ii)[1]
State one other harmful condition which can result from smoking cigarettes.
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5129/21 · October/November 2024 · Q13a(ii)[1]
State one adverse effect of particulates of carbon on human health.
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5129/22 · October/November 2024 · Q12a(ii)[1]
State an adverse effect of carbon dioxide.
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5129/21 · May/June 2024 · Q12d[1]
Domestic water supplies are treated to make them safe to drink. Name the chemical that is added to the water to kill microbes.
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5129/22 · May/June 2024 · Q12b[1]
Explain why chlorine is used in the treatment of domestic water supplies.
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5129/21 · October/November 2023 · Q16a[2]
Explain what is meant by ‘background radiation’.
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5129/22 · October/November 2023 · Q12c[2]
Explain why deforestation increases global warming.
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5129/21 · May/June 2023 · Q15b[1]
State the difference between tap water and distilled water.
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5129/21 · October/November 2022 · Q2b[1]
State an industrial use of water.
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5129/22 · May/June 2021 · Q8d[1]
Explain why chlorine is used in the treatment of water supplies.
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5129/21 · October/November 2020 · Q1c[2]
Nitrogen dioxide is an atmospheric pollutant produced in car engines. Explain how nitrogen dioxide in the air causes buildings to erode.
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5129/22 · October/November 2020 · Q15b(i)[1]
Use Fig. 15.1 to determine the solubility of carbon dioxide in 100 cm 3 of water at 40 °C. solubility = g / 100 cm 3 of water
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5129/22 · May/June 2019 · Q5c[1]
A different oxide of nitrogen is produced in car engines during the combustion of petrol. State one environmental effect caused by oxides of nitrogen in the atmosphere. Question 6 starts over the page.
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5129/22 · May/June 2019 · Q14a(i)[1]
Name a different gas that has a variable percentage composition in clean air.
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What examiners said

Candidates should be guided by the two marks available in this question. Many candidates knew that background radiation is in the surroundings but only a few gave the name of a source such as rocks, the Sun or even the air.
— Examiner report, October/November 2023, 5129/21 Q16(a) (Cambridge)

Candidates needed to give this question more consideration. Many assumed that deforestation only occurs because of fire hence the carbon dioxide in the atmosphere increases. This is partially correct but does not gain credit. Trees remove carbon dioxide from the atmosphere. Candidates can also refer to photosynthesis. To gain both marks, candidates needed to refer to the mechanism of global warmin...
— Examiner report, October/November 2023, 5129/22 Q12(c) (Cambridge)

Most candidates knew that distilled water contains fewer impurities than tap water.
— Examiner report, May/June 2023, 5129/21 Q15(b) (Cambridge)

Practise this topic

Answer these questions online and get each one marked against the official mark scheme, with what you missed and how to fix it.

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In the syllabus

21.1 Water

Describe distillation as the separation of a liquid by evaporation and condensation
Explain that distilled water is used in practical chemistry rather than tap water because it contains fewer chemical impurities
State that water needs to be treated to make it suitable for drinking
Describe the treatment of the domestic water supply in terms of: (a) sedimentation and filtration to remove insoluble solids (b) use of carbon to remove tastes and odours (c) chlorination to kill microbes
Describe desalination as a process to obtain drinking water from sea water

21.2 Air quality and climate

State the composition of clean, dry air as approximately 78% nitrogen, N2, 21% oxygen, O2, and the remainder as a mixture of noble gases and carbon dioxide, CO2
State the source of each of these air pollutants: (a) carbon dioxide from the complete combustion of carbon-containing fuels (b) carbon monoxide and particulates from the incomplete combustion of carbon-containing fuels (c) methane from the decomposition of vegetation and waste gases from digestion in animals (d) gases from the burning of plastics
State the adverse effect of these air pollutants: (a) carbon dioxide: higher levels of carbon dioxide leading to increased global warming, which leads to climate change (b) carbon monoxide: toxic gas (c) particulates: increased risk of respiratory problems and cancer (d) methane: higher levels of methane leading to increased global warming, which leads to climate change (e) gases from the burning of plastics: toxic
State and explain strategies to reduce global warming, limited to increasing use of renewable energy, decreasing use of fossil fuels, limiting deforestation and reduction in livestock farming
State that a hydrogen–oxygen fuel cell uses hydrogen and oxygen to produce electricity, with water as the only chemical product
Describe the advantages and disadvantages of using hydrogen–oxygen fuel cells in comparison with gasoline/petrol engines in vehicles

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