References only, not question text. Open Official paper ↗ where Cambridge publishes the paper,
or see the official Cambridge past-papers page; for other papers, ask your
school. “Paper 42” means Paper 4, variant 2.
Practice questions
Original questions written by HomiLabs in the style of the exam, with answers and mark schemes. They are not
Cambridge past paper questions and have not been reviewed by Cambridge. Try each one before opening the answer.
Q1Air quality & pollutants · Core · Paper 2 style · 5 marks
(a)State one source of each pollutant.(i) carbon monoxide(ii) sulfur dioxide(iii) oxides of nitrogen(iv) methane[4]
(b)State one adverse effect of particulates (soot) in the air.[1]
Show answer
(a) (i) incomplete combustion of carbon-containing fuels (ii) burning fossil fuels that contain sulfur compounds (iii) reaction of nitrogen and oxygen in hot car engines (iv) decomposition of vegetation / waste gases from digestion in animals (livestock)
1 mark each
(b) Increased risk of respiratory problems (and cancer).
B1
Q2Air quality & pollutants · Core · Paper 1 style · 1 mark
(a)[1]
Show answer
(a) B carbon monoxide
Incomplete combustion of the fuel in a shortage of oxygen gives carbon monoxide, which is toxic and has no colour or smell. Sulfur dioxide and nitrogen dioxide are toxic but have strong smells.
Q3Air quality & pollutants · Core · Paper 2 style · 4 marks
(a)Sulfur dioxide from a coal-fired power station dissolves in rainwater. Name the environmental problem this causes.[1]
(b)Describe two effects of this problem.[2]
(c)Suggest one way of reducing the sulfur dioxide released by power stations.[1]
Show answer
(a) acid rain
B1
(b) Any two of: damages/corrodes buildings and statues made of limestone or marble; corrodes metal structures; kills fish and other life in lakes; damages trees/plants.
1 mark each for any two
(c) Remove sulfur from the fuel / use low-sulfur fuel / flue gas desulfurisation (react SO₂ with calcium oxide).
B1
Q4Air quality & pollutants · Core · Paper 2 style · 5 marks
(a)Explain how oxides of nitrogen are formed in a car engine.[2]
(b)Write a balanced equation for the formation of nitrogen monoxide, NO.[1]
(c)State two adverse effects of oxides of nitrogen.[2]
Show answer
(a) Nitrogen and oxygen from the air react together at the very high temperature inside the engine.
Nitrogen and oxygen (from air) react B1; high temperature B1
Q5Air quality & pollutants · Standard · Paper 2 style · 4 marks
Modern cars have catalytic converters in their exhaust systems.
(a)Complete and balance the equation for the removal of carbon monoxide and nitrogen monoxide in a catalytic converter.__CO + __NO → __CO₂ + __[2]
(b)Identify the substance that is oxidised in this reaction. Explain your answer.[1]
(c)Name one other type of pollutant removed in the catalytic converter and state what it is converted to.[1]
Show answer
(a) 2CO + 2NO → 2CO₂ + N₂
N₂ as product B1; balancing B1
(b) Carbon monoxide; it gains oxygen (oxidation number of C increases from +2 to +4).
B1
(c) Unburned hydrocarbons; oxidised to carbon dioxide and water.
B1
Q6Air quality & pollutants · Standard · Paper 2 style · 4 marks
(a)In flue gas desulfurisation, waste gases from a power station pass through calcium oxide. Write the equation for the reaction of calcium oxide with sulfur dioxide.[1]
(b)Explain, in terms of the types of oxide, why this reaction happens.[2]
(c)Powdered calcium carbonate can be used instead. Suggest one advantage of using calcium carbonate.[1]
Show answer
(a) CaO + SO₂ → CaSO₃
B1
(b) Calcium oxide is a basic oxide and sulfur dioxide is an acidic oxide, so they react (neutralise) to form a salt.
CaO basic B1; SO₂ acidic, so neutralisation B1
(c) It is cheap and plentiful (limestone), and is safer to handle than calcium oxide.
B1
Q7Air quality & pollutants · Standard · Paper 2 style · 5 marks
During winter, Lahore often has thick smog. Measurements show high levels of particulates and oxides of nitrogen.
(a)Suggest two sources of the particulates.[2]
(b)Explain why smog is harmful to people.[1]
(c)Suggest two actions that would reduce smog.[2]
Show answer
(a) Any two of: diesel vehicle exhausts; burning crop stubble; brick kilns/industry burning coal or waste; burning rubbish.
1 mark each
(b) Particulates and NOₓ irritate the lungs and cause or worsen respiratory problems such as asthma.
B1
(c) Any two of: use catalytic converters; more public transport/electric vehicles; stop crop burning; cleaner kilns/filters on factory chimneys; low-sulfur fuels.
1 mark each
Q8Air quality & pollutants · Standard · Paper 1 style · 1 mark
(a)Which gas in car exhaust is NOT removed by a catalytic converter?[1]
Show answer
(a) A carbon dioxide
The converter changes CO, NO and unburned hydrocarbons into CO₂, N₂ and H₂O, so it removes B, C and D but actually produces more carbon dioxide. CO is removed by oxidation to CO₂.
Q9Air quality & pollutants · Challenge · Paper 2 style · 5 marks
A brick kiln burns 1000 kg of coal that contains 1.6 % sulfur by mass. All the sulfur is converted to sulfur dioxide: S + O₂ → SO₂[Ar: O, 16; S, 32; Ca, 40]
(a)Calculate the mass of sulfur in the coal.[1]
(b)Calculate the mass of sulfur dioxide produced.[2]
(c)Calculate the mass of calcium oxide needed to remove all of this sulfur dioxide (CaO + SO₂ → CaSO₃).[2]
Show answer
(a) 16 kg
1.6 % of 1000 = 16 kg B1
(b) 32 kg
16 000 ÷ 32 = 500 mol S M1; 500 × 64 = 32 000 g = 32 kg A1
(c) 28 kg
500 mol CaO M1; 500 × 56 = 28 000 g = 28 kg A1
Q10Air quality & pollutants · Challenge · Paper 4 style · 5 marks
An air-quality monitor next to a busy road records the average concentration of carbon monoxide each day for one week.Day | Mon | Tue | Wed | Thu | Fri | Sat | SunCO / µg per m³ | 1850 | 1920 | 1780 | 1890 | 2100 | 1150 | 860
(a)Calculate the mean concentration for Monday to Friday. Give your answer to the nearest whole number.[1]
(b)Calculate the percentage decrease from Friday to Sunday, to 3 significant figures.[2]
(c)Suggest a reason for the lower values at the weekend.[1]
(d)Explain why carbon monoxide is dangerous to health.[1]
Show answer
(a) 1908 µg per m³
(1850 + 1920 + 1780 + 1890 + 2100) ÷ 5 = 1908 B1
(b) 59.0 %
(2100 − 860) ÷ 2100 M1; × 100 = 59.0 % A1
(c) Less traffic (fewer people driving to work/school).
B1
(d) It is toxic: it reduces the blood's ability to carry oxygen.
B1
Q11Air quality & pollutants · Challenge · Paper 2 style · 5 marks
(a)When petrol (octane, C₈H₁₈) burns in a limited supply of air, carbon monoxide and water are formed. Write a balanced equation for this reaction.[2]
(b)Explain why a car engine running in a closed garage is particularly dangerous.[2]
(c)Write a balanced equation for the complete combustion of octane.[1]
Show answer
(a) 2C₈H₁₈ + 17O₂ → 16CO + 18H₂O
Correct formulae B1; balanced B1
(b) The oxygen in the garage gets used up, so combustion becomes more incomplete and more carbon monoxide forms; carbon monoxide is toxic and builds up in the closed space.
Less oxygen → more incomplete combustion/CO B1; CO toxic and accumulates B1
(c) 2C₈H₁₈ + 25O₂ → 16CO₂ + 18H₂O
B1
Q12Water (treatment, tests, pollution) · Core · Paper 3 style · 4 marks
(a)Describe a chemical test for water, giving the result.[2]
(b)Describe a physical test to show that a sample of water is pure.[2]
Show answer
(a) Add to anhydrous copper(II) sulfate: it turns from white to blue. (Or: cobalt(II) chloride paper turns from blue to pink.)
Reagent B1; colour change B1
(b) Measure its boiling point (100 °C) or melting point (0 °C); pure water boils at exactly 100 °C / melts at exactly 0 °C.
Measure boiling or melting point B1; correct value B1
Q13Water (treatment, tests, pollution) · Core · Paper 1 style · 1 mark
(a)Which stage of drinking-water treatment kills harmful microbes?[1]
Show answer
(a) A chlorination
Chlorine kills bacteria and other microbes. Filtration removes insoluble particles but does not kill microbes.
Q14Water (treatment, tests, pollution) · Standard · Paper 2 style · 4 marks
Water from the Indus is treated before it is supplied to homes.
(a)State the purpose of each stage:(i) sedimentation and filtration(ii) treatment with carbon(iii) chlorination[3]
(b)Even after treatment, tap water is not pure water. Explain why.[1]
Show answer
(a) (i) remove insoluble solids (ii) remove tastes and odours (iii) kill microbes
Each B1
(b) It still contains dissolved substances (salts/minerals and some chlorine).
B1
Q15Water (treatment, tests, pollution) · Standard · Paper 2 style · 5 marks
(a)Water from natural sources contains many substances. Name two substances in river water that are beneficial and explain why.[2]
(b)Name three substances found in polluted water that are harmful, and give one effect of one of them.[3]
Show answer
(a) Dissolved oxygen, which is needed by aquatic life; some mineral salts/metal compounds that provide essential minerals for life.
Dissolved oxygen for fish/aquatic life B1; mineral salts as essential minerals B1
(b) Any three of: some metal compounds (toxic); plastics (harm wildlife); sewage (contains harmful microbes, causes disease); harmful microbes; nitrates/phosphates from fertilisers (deoxygenation, damage to aquatic life). Effect e.g. sewage microbes cause diseases such as cholera.
Any three harmful substances B2 (two B1); one correct effect B1
Q16Water (treatment, tests, pollution) · Standard · Paper 2 style · 5 marks
(a)Excess nitrate fertiliser washes from farmland into a lake. Describe how this can lead to the death of fish.[4]
(b)Name one other type of compound from fertilisers or detergents that causes the same problem.[1]
Show answer
(a) Nitrates cause rapid growth of algae (algal bloom) on the surface; algae block light so plants below die; algae and plants die and are decomposed by bacteria; the bacteria use up dissolved oxygen, so fish die (deoxygenation).
Algae grow rapidly B1; plants/algae die B1; bacteria decompose them using oxygen B1; less dissolved oxygen so fish die B1
(b) phosphates
B1
Q17Water (treatment, tests, pollution) · Challenge · Paper 2 style · 5 marks
A student evaporates 250 cm³ of a tap-water sample to dryness in a weighed evaporating basin.Mass of empty basin = 52.316 gMass of basin + residue = 52.401 g
(a)Calculate the mass of dissolved solids in the sample.[1]
(b)Calculate the concentration of dissolved solids in g/dm³.[2]
(c)The sample boils at 100.1 °C. Explain what this, and the residue, show about the water.[1]
(d)Suggest why a balance reading to 0.001 g is needed.[1]
Show answer
(a) 0.085 g
52.401 − 52.316 = 0.085 B1
(b) 0.34 g/dm³
250 cm³ = 0.250 dm³ M1; 0.085 ÷ 0.250 = 0.34 A1
(c) It is not pure; dissolved substances raise the boiling point and leave a residue.
B1
(d) The mass of residue is very small, so a less precise balance would give a large percentage error.
B1
Q18Water (treatment, tests, pollution) · Challenge · Paper 4 style · 6 marks
A student compares the dissolved solids in three water samples. She evaporates 100 cm³ of each sample to dryness in a weighed basin.Sample | mass of empty basin / g | mass of basin + residue / griver water | 45.210 | 45.262tube-well water | 44.875 | 44.931bottled water | 46.020 | 46.035
(a)Calculate the mass of residue from each sample.[2]
(b)Calculate the concentration of dissolved solids in the tube-well water in g/dm³.[1]
(c)Which sample contained the most dissolved solids? State one other test she should do before deciding that this water is unsafe to drink.[2]
(d)Suggest one improvement to make the results more reliable.[1]
Show answer
(a) river 0.052 g; tube-well 0.056 g; bottled 0.015 g
All three B2; two B1
(b) 0.56 g/dm³
0.056 ÷ 0.100 = 0.56 B1
(c) Tube-well water; e.g. test for harmful microbes / test for toxic metal compounds or nitrates (dissolved solids are not all harmful).
Tube-well B1; sensible further test B1
(d) Repeat each sample and take a mean / use a larger volume of water.
B1
Q19Climate change & carbon cycle · Core · Paper 2 style · 4 marks
(a)Name two greenhouse gases.[2]
(b)For each gas, state one human activity that increases its amount in the atmosphere.[2]
Q20Climate change & carbon cycle · Core · Paper 1 style · 1 mark
(a)Which process removes carbon dioxide from the atmosphere?[1]
Show answer
(a) B photosynthesis
Green plants take in carbon dioxide during photosynthesis to make glucose. Combustion, respiration and decomposition all release carbon dioxide.
Q21Climate change & carbon cycle · Standard · Paper 2 style · 5 marks
(a)Explain how greenhouse gases cause the Earth's surface to warm up.[3]
(b)State two possible effects of climate change.[2]
Show answer
(a) Thermal energy from the Sun warms the Earth's surface, which emits infrared radiation; greenhouse gases absorb this infrared radiation; they re-emit it in all directions, including back towards the Earth, so less escapes to space and the surface warms.
Earth's surface emits infrared/thermal energy B1; greenhouse gases absorb it B1; re-emit it back towards Earth (less escapes to space) B1
(b) Any two of: rising sea levels; melting glaciers/ice caps; more frequent floods, droughts or heatwaves; changes in crop yields; loss of habitats.
1 mark each
Q22Climate change & carbon cycle · Standard · Paper 2 style · 5 marks
(a)Write the word equation and the balanced symbol equation for photosynthesis.[2]
(b)Name two processes in the carbon cycle that return carbon dioxide to the air.[2]
(c)Explain how cutting down large areas of forest affects the amount of carbon dioxide in the atmosphere.[1]
(b) respiration and combustion (also decomposition)
Each B1
(c) Fewer trees carry out photosynthesis, so less CO₂ is removed (and burning or decay of the trees releases CO₂), so the amount increases.
B1
Q23Climate change & carbon cycle · Standard · Paper 2 style · 4 marks
(a)Suggest three ways a country could reduce its emissions of carbon dioxide and methane.[3]
(b)Explain why using electric cars charged from coal-fired power stations does little to reduce carbon dioxide emissions.[1]
Show answer
(a) Any three of: use renewable energy (solar, wind, hydroelectric) instead of fossil fuels; increase use of hydrogen as a fuel; plant trees; reduce livestock farming; reduce waste in landfill; improve public transport/energy efficiency.
1 mark each for any three
(b) The coal burned in the power station still produces carbon dioxide.
B1
Q24Climate change & carbon cycle · Challenge · Paper 2 style · 4 marks
A household uses natural gas (methane) for cooking. In one month it burns 1.6 kg of methane.CH₄ + 2O₂ → CO₂ + 2H₂O[Ar: H, 1; C, 12; O, 16. One mole of gas occupies 24 dm³ at r.t.p.]
(a)Calculate the mass of carbon dioxide produced.[2]
(b)Calculate the volume of this carbon dioxide at r.t.p., in dm³.[1]
(c)Methane that leaks without burning is also a problem. Explain why.[1]
(c) Methane is a greenhouse gas (stronger than carbon dioxide), so leaks add to global warming.
B1
Q25Climate change & carbon cycle · Challenge · Paper 4 style · 5 marks
The table shows the average concentration of carbon dioxide in the atmosphere, measured at a remote observatory.Year | 1960 | 1980 | 2000 | 2020CO₂ / parts per million (ppm) | 317 | 339 | 370 | 414
(a)Calculate the average increase per year between 1960 and 1980, and between 2000 and 2020.[2]
(b)Calculate the average increase per year over the whole period 1960–2020, to 3 significant figures.[1]
(c)Describe the trend and suggest a reason for it.[2]
(c) The concentration increases, and the rate of increase is getting faster; more fossil fuels are burned (more energy use, vehicles, industry) and more deforestation.
Increasing at an increasing rate B1; reason B1
Q26Fertilisers · Core · Paper 2 style · 4 marks
(a)NPK fertilisers provide three elements needed for plant growth. Name the three elements.[2]
(b)Name one compound used in fertilisers to provide nitrogen.[1]
(c)Explain why farmers add fertilisers to their fields.[1]
(c) To replace elements removed by crops and improve plant growth / crop yield.
B1
Q27Fertilisers · Standard · Paper 2 style · 5 marks
[Ar: H, 1; N, 14; O, 16; S, 32]
(a)Calculate the percentage by mass of nitrogen in ammonium nitrate, NH₄NO₃.[2]
(b)Calculate the percentage by mass of nitrogen in ammonium sulfate, (NH₄)₂SO₄. Give your answer to 3 significant figures.[2]
(c)Suggest which fertiliser a farmer should choose to supply the most nitrogen per kilogram.[1]
Show answer
(a) 35.0 %
Mr = 80 M1; 28 ÷ 80 × 100 = 35.0 % A1
(b) 21.2 %
Mr = 132 M1; 28 ÷ 132 × 100 = 21.2 % A1
(c) ammonium nitrate
B1
Q28Fertilisers · Challenge · Paper 2 style · 6 marks
A farmer in Sahiwal compares two nitrogen fertilisers. (The prices are invented for this question.)Fertiliser | formula | mass of bag | price of bagurea | CO(NH₂)₂ | 50 kg | Rs 4800ammonium nitrate | NH₄NO₃ | 50 kg | Rs 4200[Ar: H, 1; C, 12; N, 14; O, 16]
(a)Calculate the mass of nitrogen in one bag of urea, to 3 significant figures.[2]
(b)Calculate the cost of 1 kg of nitrogen from each fertiliser, to the nearest rupee, and state which is better value.[3]
(c)The soil is also acidic. Explain why the farmer should not add lime at the same time as ammonium nitrate.[1]
Show answer
(a) 23.3 kg
Mr = 60; % N = 28 ÷ 60 = 46.7 % M1; 0.4667 × 50 = 23.3 kg A1
(b) urea Rs 206 per kg N; ammonium nitrate Rs 240 per kg N; urea is better value
Ammonium nitrate N = 0.35 × 50 = 17.5 kg M1; 4800 ÷ 23.33 = 206 and 4200 ÷ 17.5 = 240 A1; urea B1
(c) The base reacts with ammonium ions, releasing ammonia gas, so nitrogen is lost.
B1
Q29Composition of air · Core · Paper 1 style · 1 mark
(a)What is the approximate percentage by volume of nitrogen in clean, dry air?[1]
Show answer
(a) C 78 %
Clean dry air is about 78 % nitrogen and 21 % oxygen, with small amounts of argon and carbon dioxide. 21 % is the figure for oxygen.
Q30Composition of air · Standard · Paper 4 style · 5 marks
100 cm³ of dry air is pushed backwards and forwards between two gas syringes over a tube of heated copper powder. The copper turns black. The apparatus is allowed to cool and the volume is measured. This is repeated until the volume stops changing.Reading | 1 | 2 | 3 | 4Volume of gas / cm³ | 85 | 80 | 79 | 79
(a)Write a balanced equation for the reaction of copper with oxygen.[1]
(b)Calculate the percentage of oxygen in the air.[1]
(c)Explain why the apparatus is cooled before each reading.[1]
(d)Name the main gas left in the syringe and one other gas present in small amounts.[2]
Show answer
(a) 2Cu + O₂ → 2CuO
B1
(b) 21 %
(100 − 79) ÷ 100 × 100 = 21 B1
(c) Gases expand when hot, so a hot gas would give a volume that is too large.
B1
(d) nitrogen; argon (or carbon dioxide)
Each B1
Similar questions
Questions that test the same subtopic in different years, grouped so you can work on one skill at a time.
References only: find each question in its paper (official link where available, otherwise through your school).
Air quality & pollutantsBanker25 questions · 9/9 sessions
