AQA GCSE Chemistry Chemistry Paper 2 (Foundation), June 2022: Question 10

💡 Key Knowledge: The 4 Stages of an LCA

• 1. Extracting raw materials: Limestone, sand, and sodium carbonate are mined/quarried (damages habitats, causes dust/noise). Crude oil is a finite resource that must be drilled and refined.
• 2. Manufacturing & Transport: Glass requires far more processing energy (6750 kJ vs 1710 kJ) and manufacturing energy (750 kJ vs 90 kJ). Glass is 10× heavier (200 g vs 20 g), using significantly more fuel to transport.
• 3. Use and lifetime: Glass bottles are reused 25 times on average; polymer bottles are used only once. Washing glass uses water and energy, but reuse conserves new materials.
• 4. Disposal: Both materials can be recycled, which diverts waste from landfill and saves energy compared to producing new materials.

🧠 Exam Technique: Securing Level 3 (5–6 Marks)

This is a level of response question marked holistically:

• Structure by LCA stage: Organize your answer using clear sub-points (Raw materials, Manufacturing/Transport, Use, Disposal).
• Compare both sides: Never write only about glass or only about plastic. Mention advantages and disadvantages for both.
• Per-use insight (Top Marks): While 1 glass bottle takes 7500 kJ total to produce, it is used 25 times ( 7500 ÷ 25 = 300 kJ per use ). The single-use polymer uses 1800 kJ per use!
• Include a clear judgement: End with a definitive conclusion weighing which bottle is better overall and why.

✅ Model Answer (Level 3 • 6/6 Marks)

Raw materials: Crude oil used for polymers is finite and non-renewable, whereas sand and limestone for glass are more abundant. However, quarrying raw materials for glass destroys habitats and requires more energy to process (6750 kJ vs 1710 kJ).

Manufacturing & Transport: Glass requires significantly more energy to manufacture (750 kJ vs 90 kJ). Furthermore, glass bottles are 10 times heavier (200 g vs 20 g), which increases vehicle fuel consumption and greenhouse gas emissions during transport.

Use: Glass bottles are reused 25 times, conserving raw materials and reducing packaging waste. Although washing them requires water and detergents, polymers are single-use.

Disposal: Both materials can be recycled into new products, reducing landfill use and saving raw materials.

Conclusion: Overall, glass is more sustainable if it is reused multiple times because the total energy per use ( 7500 kJ ÷ 25 = 300 kJ ) is far lower than the polymer bottle ( 1800 kJ per use).

❌ Common Mistakes to Avoid

• Merely copying the table: Writing "Glass uses 6750 kJ and polymer uses 1710 kJ" without explaining the environmental consequence (e.g. burning fossil fuels, releasing CO₂).
• Forgetting the conclusion: The command word is Evaluate. If you do not give a final justified judgement, you cannot achieve Level 3.
• Vague claims: Saying plastic is just "bad for the environment" instead of specifying that crude oil is a finite resource or that single-use products generate landfill waste.
• Missing the reuse factor: Overlooking that the glass bottle is reused 25 times, which completely offsets its higher initial production energy.

📐 Step-by-Step Calculation

Given in question:

• Volume = 40 cm³
• Density = 0.40 g/cm³
• Equation: density = mass ÷ volume

⚠️ Calculation Traps & Tips

• Wrong rearrangement: A very common error is dividing instead of multiplying (e.g. calculating 40 ÷ 0.40 = 100 g or 0.40 ÷ 40 = 0.01 g ). Use a formula triangle if unsure:
  Mass is at the top; Density and Volume are at the bottom.
• Unit consistency: Always check units match! Here, volume is in cm³ and density is in g/cm³ , so the calculated mass is directly in grams ( g ). No unit conversions needed.
• Show your working: Even if your final arithmetic is wrong, showing mass = 0.40 × 40 guarantees you pick up 2 out of the 3 marks!