OCR GCSE Chemistry A: Interpreting and interacting with earth systems (J248) – 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 from your board or school.

Practise C6.3 Interpreting and interacting with earth systems from OCR’s J248 specification for GCSE (9–1) Chemistry A (Gateway Science), Version 4.0 of August 2026, here. The set tests statements C6.3a to C6.3g with maths outcomes CM6.3i and CM6.3ii. C6.3 contains no Higher Tier only statements, so every question here is fair game on either tier. Topic C6 sits in Paper 2 for Foundation entrants and Paper 4 for Higher entrants.

Other J248 topics are on the OCR chemistry course hub; the J248 checklist lets you mark progress. To find gaps across chemistry, try the free 10-minute diagnostics.

Questions

1. Dry air today is very different from the Earth’s first atmosphere.

(a) Name the gas that makes up about 78% of dry air today. [1] (b) Name the two gases thought to have made up most of the Earth’s early atmosphere. [2]

2. Describe how the oceans formed and how the amount of carbon dioxide in the early atmosphere then decreased. [4]

3. Some very old rocks that formed on ancient seabeds contain thick red bands rich in iron oxide.

(a) Name the type of organism thought to have first released large amounts of oxygen. [1] (b) Write the balanced symbol equation for photosynthesis. [2] (c) Explain how the banded rocks suggest that oxygen did not build up in the air as soon as it was first produced. [2]

4. A leaflet says: “Carbon dioxide wraps the Earth like a blanket.” Explain the greenhouse effect in terms of radiation and molecules in the atmosphere. [4]

5. The table shows rounded annual mean carbon dioxide levels at a monitoring station.

Year	Carbon dioxide / ppm
1975	331
1995	361
2015	401

(a) Calculate the percentage increase from 1975 to 2015. Give your answer to 3 significant figures. [2] (b) Work out the average yearly rise for 1975–1995 and for 1995–2015. [2] (c) Use your answers to describe the trend. [1]

6. Use these values for the present-day atmosphere: carbon dioxide 425 ppm; methane 1.9 ppm.

(a) Convert 425 ppm into a percentage. [1] (b) Calculate how many times greater the carbon dioxide level is than the methane level, and state this as an order of magnitude. [2] (c) A student concludes that methane cannot affect the climate because there is so little of it. Suggest why this conclusion is wrong. [1]

7. A news article says: “Rising carbon dioxide levels match rising fossil fuel use, so human activity is changing the climate.” Evaluate this claim. Describe the evidence that supports it and the uncertainties in the evidence base. [6]

8. A government is choosing ways to respond to climate change.

(a) Describe two potential effects of increased levels of carbon dioxide and methane on the Earth’s climate. [2] (b) Three options are proposed: replace a coal-fired power station with offshore wind turbines; fit carbon capture and storage to the existing coal station; plant a large forest. Evaluate the options, considering scale and risk. [6]

9. A cargo ship burns 2500 tonnes of fuel oil on a voyage. The oil contains 0.50% sulfur by mass. Relative atomic masses: S = 32, O = 16.

(a) Calculate the mass of sulfur dioxide produced, assuming all the sulfur is converted. [3] (b) Explain one environmental problem caused by sulfur dioxide. [2] (c) The ship’s engine also releases nitrogen monoxide, NO. Write a balanced equation for its formation and state where the nitrogen comes from. [2]

10. Hexane, C₆H₁₄, is used as a fuel in a camping stove inside a tent.

(a) Balance this equation for incomplete combustion: C₆H₁₄ + O₂ → CO + H₂O [2] (b) Explain why carbon monoxide is especially dangerous in a closed tent. [2] (c) State one health problem caused by particulates from incomplete combustion. [1]

11. A small island needs 1500 m³ of potable water each day. Use these energy values (kWh per m³ of water): treated ground water 0.4; reverse osmosis 3.5; distillation 25.

(a) Describe how ground water is treated to make it potable. [3] (b) Explain how distillation produces potable water from sea water. [2] (c) Calculate the daily energy needed using reverse osmosis and using distillation. [2] (d) The island’s ground water is running low. Evaluate which desalination method it should choose. [3]

Answers

1. (a) Nitrogen [1] (b) Carbon dioxide [1] and water vapour [1] Examiner insight: Naming oxygen as a main early gas contradicts the whole point of C6.3a, so check your answer against the volcanic source.

2. Volcanoes released water vapour; as the Earth cooled it condensed to form oceans [1]. Carbon dioxide dissolved in the oceans [1] and was locked into carbonate rocks / sediments [1]. Photosynthesis by early organisms removed carbon dioxide, with carbon later stored in fossil fuels [1]. Examiner insight: Four separate, ordered points are needed; repeating “it dissolved” in different words gains nothing extra.

3. (a) Cyanobacteria (accept algae / bacteria that photosynthesise) [1] (b) 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂: correct formulae [1]; correct balancing [1] (c) The first oxygen reacted with dissolved iron in the sea, forming iron oxide that settled as the bands [1]; only after the dissolved iron was used up could oxygen collect in the air [1]. Examiner insight: In (c) link the bands to oxygen being used up by iron; simply saying “the rocks contain oxygen” does not explain the delay.

4. Incoming sunlight is mainly short-wavelength; most of it reaches the ground and heats it [1]. The surface emits longer-wavelength infrared radiation [1]. Carbon dioxide molecules absorb infrared [1] and re-emit it in all directions, some back to the surface, so less energy escapes to space [1]. Examiner insight: The word “reflect” is a common slip; the credited idea is absorption and re-emission of infrared.

5. (a) (401 − 331) ÷ 331 × 100 [1] = 21.1% [1] (b) 1975–1995: 30 ÷ 20 = 1.5 ppm per year [1]; 1995–2015: 40 ÷ 20 = 2.0 ppm per year [1] (c) The level is rising, and the rate of rise is increasing (1.5 to 2.0 ppm per year) [1]. Examiner insight: Divide by the starting value (331), not the final one; using 401 gives 17.5%, which is wrong.

6. (a) 425 ÷ 10 000 = 0.0425% [1] (b) 425 ÷ 1.9 = 224 times [1]; this is about two orders of magnitude (10²) [1] (c) Each methane molecule has a much larger warming effect than a carbon dioxide molecule, so a small amount still matters [1]. Examiner insight: For an order of magnitude, state the power of ten; “a lot bigger” does not use the data.

7. Any six points, including both sides and a judgement:

• Carbon dioxide has risen from about 280 ppm to over 430 ppm, alongside a steep rise in fossil fuel burning [1].
• Burning fossil fuels releases carbon dioxide, so there is a clear source [1].
• The greenhouse effect gives a mechanism: carbon dioxide absorbs and re-emits infrared [1].
• Correlation alone does not prove cause [1].
• Natural factors (the Sun’s output, volcanic eruptions, ocean cycles) also change climate [1].
• Past data come from proxies such as ice cores and from fewer measuring sites, so they are less certain; models are simplified [1]. Judgement: the claim is well supported because correlation and mechanism agree, but “match” overstates the certainty for exact effects. Examiner insight: An evaluation needs evidence on both sides; a one-sided list of reasons humans are to blame limits the credit.

8. (a) Sea-level rise and coastal flooding [1]; more extreme weather such as heatwaves or storms [1] (or changed rainfall affecting crops). (b) Wind turbines remove the station’s emissions [1] but output varies with the wind, so back-up is needed [1]. Carbon capture keeps the existing plant [1] but is expensive and risks leaks from storage; it is not yet used widely [1]. A forest absorbs carbon dioxide by photosynthesis [1] but needs a large area and takes decades to grow, so its scale is small compared with a power station’s output; best overall is wind with a stated reason [1]. Examiner insight: Each option needs a benefit and a drawback; a final choice with a reason is expected for “evaluate”.

9. (a) Mass of sulfur = 2500 × 0.50 ÷ 100 = 12.5 tonnes [1]; Mr of SO₂ = 64, so mass doubles [1]; 25 tonnes of SO₂ [1] (b) Sulfur dioxide dissolves in rain water to form acid rain [1], which damages trees, kills life in lakes or corrodes limestone buildings [1]. (c) N₂ + O₂ → 2NO [1]; the nitrogen comes from the air, reacting at the high engine temperature [1]. Examiner insight: In (a), keep the unit as tonnes throughout; converting to grams is not needed and invites errors.

10. (a) 2C₆H₁₄ + 13O₂ → 12CO + 14H₂O: correct carbon and hydrogen ratios [1]; correct oxygen [1] (b) Carbon monoxide is poisonous because haemoglobin picks it up in place of oxygen, so less oxygen reaches body tissues [1]; it has no colour or smell, so it builds up in the enclosed space without being noticed [1]. (c) Any one: lung damage / breathing problems / heart disease [1] Examiner insight: Check the oxygen count last: 13 × 2 = 26 on the left and 12 + 14 = 26 on the right.

11. (a) Filtration through beds of sand and gravel [1] removes insoluble particles (accept sedimentation first) [1]; sterilisation with chlorine, ozone or UV kills microbes [1]. (b) Sea water is boiled so water evaporates and leaves the salts behind [1]; the steam is condensed and collected as water [1]. (c) Reverse osmosis: 1500 × 3.5 = 5250 kWh [1]; distillation: 1500 × 25 = 37 500 kWh [1] (d) Reverse osmosis uses about seven times less energy than distillation [1], so lower fuel cost and fewer emissions [1]; but membranes need replacing and high pressure pumps, so choose reverse osmosis if equipment can be maintained [1]. Examiner insight: Use the numbers from (c) in (d); a judgement with no data reference is weaker.

Where marks are usually lost

• Saying greenhouse gases reflect heat rather than absorb and re-emit infrared.
• Leaving out the change from short-wavelength to infrared radiation.
• Dividing by the final value in a percentage increase.
• Quoting a trend with no values or units from the table.
• Treating correlation as proof in an “evaluate” question.
• Saying the nitrogen in NO comes from the fuel.
• Forgetting that sulfur dioxide mass is double the sulfur mass.
• Calling potable water “pure”.
• Missing the sterilisation stage in water treatment.

Next steps

• C6.3 revision notes and self-test
• C6.3 study guide
• Water separation techniques (purity topic)
• J248 course hub
• J248 statement checklist
• Book a free trial class
• All free 10-minute diagnostics

Official syllabus

This page follows OCR’s GCSE (9–1) Chemistry A (Gateway Science) specification J248, Version 4.0 (August 2026), first assessed in 2018, published by OCR. Content used: C6.3 Interpreting and interacting with earth systems (statements C6.3a–C6.3g; maths outcomes CM6.3i and CM6.3ii).