AQA GCSE Combined Science: Trilogy Chemistry Paper 2 (Higher), 2021: Question 4

✅ Correct answer

Production of copper is increasing.
It is increasing at an increasing rate.

💡 Key knowledge

• The line goes up from 1900 to 2020, so the amount produced is rising.
• The line gets steeper, so the rate of increase is also rising.

🧠 Exam technique

• Look for two separate points: direction and rate.
• Use precise graph language: increasing , decreasing , constant , steeper .

❌ Common errors

• Only saying “it goes up” — this usually gets 1 mark only.
• Describing the graph as “curved” without saying what that means.
• Writing “production is high” instead of describing the trend.

✅ Correct answer

Any one valid reason, for example:

• Increase in population / demand.
• More uses for copper.

💡 Key knowledge

Copper is used in wiring, electronics, plumbing and many products. More people and more technology mean more copper is needed.

🧠 Exam technique

Give a cause of the increase, not just a repeat of the graph. A short science reason is enough.

❌ Common errors

• Saying “because it increased” — this is not a reason.
• Writing something too vague like “economy” with no link to copper.

✅ Correct answer

Any one of these:

• More recycling may be used in the future.
• Copper is a finite resource and may run out.
• Alternative metals may be used in future.

💡 Key knowledge

Future production depends on human choices and resource availability, not just the past trend on the graph.

🧠 Exam technique

Examiners want a reason why the pattern may change. Mentioning uncertainty or a changing resource supply is strong evidence.

❌ Common errors

• “It is only an estimate” on its own is not enough unless linked to a reason.
• Waffling about the graph scale instead of future resource issues.

✅ Correct answer

B, D, C, A, E

• B Plants absorb metal compounds.
• D Plants are harvested.
• C Plants are burned.
• A Copper compounds from ash are dissolved in acid.
• E Solution of copper compound is electrolysed.

💡 Key knowledge

Phytomining uses plants to collect copper compounds from soil. The copper is later recovered from the ash and solution.

🧠 Exam technique

Follow the process logically: absorb → harvest → burn → dissolve → electrolyse.

❌ Common errors

• Putting burning before harvesting.
• Mixing up dissolution and electrolysis.
• Not recognising that plants must first take up metal compounds.

✅ Correct answers

Any two from:

• It is slower to produce copper.
• A large area of land is required.
• It gives an insufficient yield to meet demand.

💡 Key knowledge

Phytomining depends on plant growth, so it takes time. It also may not produce enough copper quickly for high demand.

🧠 Exam technique

You need two different disadvantages. Short bullet points work well. The mark scheme says not to refer to cost, carbon dioxide or global warming.

❌ Common errors

• Talking about cost — not allowed for this question.
• Writing a vague disadvantage like “bad for the environment” without a specific point.
• Repeating the same idea twice in different words.

📐 Calculations – step by step

Given:

• Total copper produced = 8.89 × 10⁹ kg
• 41.0% recycled, so 59.0% extracted
• Energy for recycled copper = 27.2 MJ per kg
• Energy for extracted copper = 70.4 MJ per kg

Step 1: Find energy used if all copper was recycled

27.2 × 8.89 × 10⁹ = 2.41768 × 10¹¹ MJ
Rounded to 3 s.f. = 2.42 × 10¹¹ MJ

Step 2: Find energy used in the actual year

Recycled part:
27.2 × 8.89 × 10⁹ × 41/100 = 9.914 × 10¹⁰ MJ

Extracted part:
70.4 × 8.89 × 10⁹ × 59/100 = 3.693 × 10¹¹ MJ

Total actual energy:
9.914 × 10¹⁰ + 3.693 × 10¹¹ = 4.6844 × 10¹¹ MJ

Step 3: Find the difference

4.6844 × 10¹¹ - 2.41768 × 10¹¹ = 2.26672 × 10¹¹ MJ

Answer = 2.27 × 10¹¹ MJ (3 significant figures)

✅ Correct answer

2.27 × 10¹¹ MJ

💡 Key knowledge

• 41.0% of the copper was recycled, so 59.0% was not.
• Use the correct energy value for each type of copper.
• Answers must be in MJ.

🧠 Exam technique

• Show every stage clearly: percentages, substitution, subtraction.
• Keep track of units all the way through.
• Use scientific notation carefully with large numbers.
• Round only at the end to 3 significant figures.

❌ Common calculation traps

• Using 41% for both recycled and extracted copper.
• Forgetting to calculate 59% for the extracted part.
• Subtracting in the wrong order.
• Giving the answer without units.
• Rounding too early and losing accuracy.

💡 What top answers did well

• Used precise trend language: increasing at an increasing rate.
• Gave one clear science reason for the graph trend.
• Sequenced phytomining logically.
• In the calculation, used the correct percentages and showed method clearly.

❌ Where marks were lost

• Describing the graph too vaguely.
• Giving reasons not linked to copper demand or resources.
• Mixing up the phytomining steps.
• Not giving two distinct disadvantages for phytomining.
• Making percentage and rounding mistakes in the calculation.