IGCSE Chemistry: Chemistry of the Environment — 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 available free from your board.

Related: Chemistry of the Environment revision notes

Tier note: questions marked (0620 Extended, 5070 required) go beyond 0620 Core: how a catalytic converter removes oxides of nitrogen, with the equation (syllabus 10.3 outcome 8), and explaining how greenhouse gases cause global warming (10.3 outcome 7). Everything else is 0620 Core — water (10.1) and fertilisers (10.2) are entirely Core, and so are pollutant sources and effects and the strategies to reduce them (10.3 outcomes 1–4). 5070 has no tiers, so O Level candidates need all of it.

---

Questions

1. State the approximate composition of clean, dry air. [2]

2. For each pollutant, state its source and one harmful effect:

(a) carbon monoxide [2] (b) sulfur dioxide [2] (c) oxides of nitrogen [2]

3. Explain how sulfur dioxide leads to acid rain, and give two consequences. [4]

4. (0620 Extended, 5070 required) Explain how a catalytic converter reduces pollution, giving one equation. [3]

5. (0620 Extended, 5070 required) Explain the greenhouse effect and name two greenhouse gases with a source for each. (Naming the two gases and their sources is 0620 Core.) [5]

6. Water for domestic use is treated before supply.

(a) Describe the three main stages. [3] (b) Explain why chlorine is added and state one risk. [2]

7. Ammonium nitrate is used as a fertiliser.

(a) Explain why nitrogen is needed by plants. [1] (b) Explain how excess fertiliser causes eutrophication, and its effect on aquatic life. [2] (Give the outcome — oxygen depletion killing aquatic life — for full credit; the detailed step-by-step mechanism below is background, not required by the syllabus.)

8. Two chemical tests can confirm that a colourless liquid contains water.

(a) Name the two tests and state the colour change each gives. [2] (b) These tests only confirm the presence of water, not its purity. Describe how you would test whether a water sample is pure. [2]

9. The same hydrocarbon fuel can produce very different pollutants depending on how it burns.

(a) Write a word equation for its complete combustion, and state the pollutant risk. [2] (b) State the two pollutants produced instead when the fuel burns incompletely, and explain why incomplete combustion happens. [2]

10. State one named method used to reduce each of the following, and explain briefly how it works:

(a) climate change [2] (b) acid rain [2]

11. Explain how burning coal can lead to acid rain, and give one way power stations reduce this. [3]

---

Answers

1. About 78% nitrogen and 21% oxygen [1], with about 1% argon and small amounts of carbon dioxide and other gases [1].

2. (a) From incomplete combustion of carbon-containing fuels [1]; it is toxic, binding to haemoglobin and reducing oxygen transport [1]. (b) From burning sulfur-containing fossil fuels [1]; it causes acid rain and respiratory problems [1]. (c) From car engines [1] (how they form — nitrogen and oxygen from the air reacting at the high temperature inside the engine — is (0620 Extended, 5070 required)); they cause acid rain and photochemical smog [1].

3. SO₂ is released when sulfur-containing fuels burn [1]; it dissolves in rainwater to form acid rain [1] (background, not required: in the atmosphere SO₂ may first be oxidised to SO₃, which then dissolves in water to form sulfuric acid directly — this oxidation step is not part of the syllabus). Consequences, any two: acidified lakes killing aquatic life; damage to trees and soil; corrosion of limestone buildings [1] [1].

4. It provides a large surface area on which pollutant gases react [1], reducing nitrogen oxides while oxidising carbon monoxide [1]: 2NO + 2CO → N₂ + 2CO₂ [1].

5. Short-wavelength radiation from the Sun passes through the atmosphere and warms the Earth’s surface [1]. The Earth re-emits longer-wavelength infrared radiation [1], which greenhouse gases absorb and re-radiate, trapping heat in the atmosphere [1]. Two gases with sources: carbon dioxide from burning fossil fuels [1]; methane from livestock digestion, rice paddies or decaying waste [1].

6. (a) Sedimentation and filtration to remove suspended solids [1]; treatment with carbon to remove tastes and odours [1]; chlorination to kill bacteria [1]. (b) Chlorine kills bacteria, preventing waterborne disease [1]; the risk is that chlorine is toxic and can form harmful chlorinated compounds [1].

7. (a) Nitrogen is needed to make proteins for growth [1].

(b) Excess fertiliser is washed into rivers and lakes [1], ultimately depleting the dissolved oxygen, so fish and other aquatic organisms die [1]. (Background, not required: the fertiliser causes rapid algal growth, which blocks light; plants below die and are decomposed by bacteria, which multiply and use up the dissolved oxygen as they do so.)

8. (a) Anhydrous copper(II) sulfate turns from white to blue [1]; anhydrous cobalt(II) chloride turns from blue to pink [1]. (b) Compare the sample’s melting and boiling point with the known values for pure water (0 °C and 100 °C) [1]; dissolved substances lower the melting point and raise the boiling point, so a sample melting or boiling at the “wrong” temperature is impure [1].

9. (a) fuel + oxygen → carbon dioxide + water [1]; complete combustion’s CO₂ contributes to global warming/climate change [1]. (b) Carbon monoxide and particulates (soot) [1], produced because there is insufficient oxygen for the fuel to burn completely [1].

10. (a) e.g. increasing use of renewable/hydrogen energy [1], which reduces the amount of CO₂ released from burning fossil fuels, the main driver of the enhanced greenhouse effect [1]. (Also accept: planting trees, reducing livestock farming, reducing fossil fuel use.) (b) e.g. fitting catalytic converters to vehicles [1], which convert nitrogen oxides and carbon monoxide into less harmful gases before they reach the atmosphere [1]. (Also accept: using low-sulfur fuels; flue gas desulfurisation with calcium oxide.)

11. Coal contains sulfur, which burns to form sulfur dioxide [1]; sulfur dioxide dissolves in rainwater to form acid rain [1]. Power stations remove sulfur dioxide from waste gases by reacting it with calcium carbonate or calcium oxide (flue-gas desulfurisation) [1].

Try the real question next: Cambridge O Level Chemistry 5070, June 2025, Paper 22, Question 5.

---

Where marks are usually lost

• Giving the source of a pollutant without its effect.
• (0620 Extended, 5070 required) Describing the greenhouse effect without saying that the gases absorb thermal energy emitted by the Earth and re-emit it, reducing thermal energy loss to space.
• Forgetting that eutrophication kills aquatic life specifically through oxygen depletion (the detailed algal-bloom mechanism is background, not required).
• The water-treatment stages and chlorine’s specific role are a genuinely weak recall area — vague answers like “it is purified” or “chlorine cleans it” don’t get credit; name each stage in order and state exactly what chlorine does (kills bacteria/disease-causing microorganisms).
• Confusing the two water tests (which only detect the presence of water) with a purity test (which requires comparing melting/boiling point against the known values for pure water).
• Assuming the same fuel always produces the same pollutants — complete combustion gives CO₂, incomplete combustion (insufficient oxygen) gives carbon monoxide and particulates instead.