AQA GCSE Chemistry Chemistry Paper 2 (Higher), November 2021: Question 8

✅ Correct Answer

• Lead is toxic (or lead is poisonous / harmful).

🧠 Exam Technique: Comparative Data

Always compare the rows in Table 4:

• Solder A: tin, copper, lead
• Solders B & C: tin, copper, silver

The difference is lead versus silver. Your answer must specifically address the hazard of lead.

❌ Common Errors

• Writing vague terms like "lead is dangerous", "lethal", or "deadly" (insufficient detail for GCSE science).
• Saying "silver is healthier" without identifying that lead is toxic.

✅ Correct Answer

• The proportions (or percentages / ratios) of the metals are different.

💡 Key Knowledge: What is an Alloy?

An alloy is a mixture, not a compound. Because the metals are not chemically combined in fixed ratios, changing the percentage of tin, copper, or silver changes the structure and alters the melting point.

❌ Common Errors

• Saying "they contain different metals" — Table 4 clearly shows both B and C contain tin, copper, and silver!
• Confusing mixtures with compounds and talking about "chemical bonds breaking differently".

✅ Correct Answers (Any 3)

• Conserves copper ores (copper ores are finite / non-renewable).
• Uses less energy than extracting copper from ores.
• Reduces waste / reduces the use of landfill sites.
• Reduces environmental impacts of mining / quarrying (e.g. less habitat destruction, less visual pollution, less dust/noise).

🧠 Exam Technique: "Sustainability" vs "Cost"

Sustainability refers to conserving natural resources and reducing environmental damage for future generations.

Examiners routinely reject "it is cheaper" or "makes more money" unless economic sustainability is explicitly asked for.

❌ Common Errors to Avoid

• Writing "it is cheaper / saves money" — ignored by the mark scheme!
• Vague claims like "it is better for the planet" without naming an impact (energy, waste, finite ores, habitat loss).
• Repeating the same point in different words (e.g. "saves ores" and "stops ores running out" count as 1 mark).

✅ Correct 4-Step Method

1. Grow plants on land containing low-grade copper ore (plants absorb copper compounds).
2. Burn the plants to produce ash (which contains concentrated copper compounds).
3. Dissolve the ash in acid to produce a solution of a copper compound (leachate).
4. Extract copper by electrolysis OR displacement using scrap iron.

💡 Key Knowledge: Why Scrap Iron?

Iron is more reactive than copper and is cheap/readily available as scrap. It displaces copper from solution:

Fe + CuSO₄ → FeSO₄ + Cu

Or ionic equation: Fe + Cu²⁺ → Fe²⁺ + Cu

🧠 Top-Scorer Strategy

Phytomining questions are almost always worth 4 marks. Memorise the 4 essential verbs:

• Grow (absorb copper)
• Burn (produce ash)
• Dissolve (in acid to get solution)
• Displace / Electrolyse (obtain pure metal)

❌ Common Errors

• Confusing phytomining (uses plants) with bioleaching (uses bacteria).
• Forgetting to state that the ash must be dissolved in acid before displacement or electrolysis can occur.
• Saying copper is obtained directly by burning the plant (burning only concentrates it into ash!).

✅ Correct Reasons (Any 2)

• High-grade ores are still available (traditional extraction is still viable).
• Phytomining is a slow process / takes a long time (plants need seasons to grow).
• Large areas of land are required (which could otherwise be used for agriculture/food).
• It is a new technology / not yet scaled up commercially.
• Copper yield is relatively small per harvest.

💡 Why We Need Alternative Methods

Traditional smelting requires high-grade ores, which are becoming scarce. Phytomining and bioleaching are designed to avoid traditional digging and smelting, but their primary trade-off is speed and scale.

❌ Common Errors

• Saying "it doesn't work" (it does work, it is just slow).
• Writing "it causes too much pollution" — phytomining actually produces far less environmental destruction than quarrying!