AQA GCSE Combined Science: Trilogy Chemistry Paper 1 (Higher), 2024: Question 6

✅ Correct answer

gold

Also accepted by the mark scheme: Au , silver / Ag , platinum / Pt , copper / Cu .

💡 Key knowledge

• Very unreactive metals can be found as the metal itself in the Earth.
• Gold is a classic example because it does not react easily.

🧠 Exam technique

This is a simple 1-mark recall question. Give one metal only. Do not waste time explaining.

❌ Common errors

• Naming a reactive metal such as magnesium or potassium.
• Giving a compound instead of a metal.

✅ Correct answer

reduction by carbon

Accepted: heating with carbon or reacting with carbon.

💡 Key knowledge

• In the figure, metal Z is below carbon in the reactivity series.
• If a metal is below carbon, its oxide can usually be extracted by reduction with carbon.
• Electrolysis is used for metals more reactive than carbon, but that is more expensive.

🧠 Exam technique

The key word is economical. Because metal Z is below carbon, carbon reduction is cheaper than electrolysis, so that is the best answer.

❌ Common errors

• Answering electrolysis just because the next parts are about aluminium.
• Not using the reactivity series shown in the question.

✅ Correct answer

cryolite

💡 Key knowledge

• Aluminium oxide is dissolved in molten cryolite during electrolysis.
• Cryolite lowers the melting point, so less energy is needed.

🧠 Exam technique

This is pure recall. Learn the exact word cryolite because it comes up often in aluminium extraction questions.

❌ Common errors

• Writing graphite or carbon — these are the electrodes, not substance X.
• Writing aluminium oxide — that is already named separately in the diagram.

✅ Correct answer

A full 3-mark answer would be:

• Oxygen is produced at the positive electrode.
• The oxygen reacts with the carbon electrode to form carbon dioxide.
• So the electrode is used up / burns away and must be continually replaced.

💡 Key knowledge

• Positive electrode = anode.
• Oxide ions lose electrons at the anode and form oxygen.
• The carbon anodes do not last forever because they react with oxygen.

🧠 Exam technique

For 3 marks, make sure your answer is a chain of ideas:

1. Say what is formed: oxygen.
2. Say what it reacts with: the carbon electrode.
3. Say the consequence: carbon dioxide forms and the electrode must be replaced.

Top answers are clear and linked. Do not just say “the electrode wears away” without explaining why.

❌ Common errors

• Saying aluminium forms at the positive electrode — aluminium forms at the negative electrode.
• Mentioning oxygen only, but not saying it reacts with carbon.
• Saying the electrode melts. The key idea is that it reacts and is used up.

✅ Correct answer

Al³⁺ + 3e⁻ → Al

💡 Key knowledge

• Negative electrode = cathode.
• Positive metal ions move to the negative electrode.
• Reduction means gain of electrons.
• Aluminium forms Al³⁺ ions, so each ion needs 3 electrons.

📐 Step-by-step method

1. Start with the ion present: Al³⁺
2. Because it is a positive ion, add electrons to the left side: + e⁻
3. The charge must balance, so you need 3 electrons: Al³⁺ + 3e⁻
4. Form the neutral metal atom: → Al

🧠 Exam technique

Always check both:

• Atoms balanced — one Al on each side.
• Charge balanced — left side total charge is 0 because +3 and 3 × −1 cancel, matching neutral Al on the right.

The mark scheme allows 1 mark for the idea of aluminium ion gaining electrons even if the balancing number is wrong, but full marks need the correct 3e⁻.

❌ Common errors

• Writing Al + 3e⁻ → Al³⁺ — this is the wrong direction.
• Forgetting the charge on aluminium ion.
• Using the wrong number of electrons, such as 1e⁻ instead of 3e⁻.
• Putting electrons on the right-hand side at the negative electrode.

Key answers for the whole question

• 06.1: gold
• 06.2: reduction by carbon
• 06.3: cryolite
• 06.4: oxygen is produced; it reacts with carbon to form carbon dioxide; the electrode is used up and replaced
• 06.5: Al³⁺ + 3e⁻ → Al

Examiner insight

• This question mainly rewards accurate recall plus one clearly written explanation.
• Students lose marks when they mix up positive and negative electrodes.
• Better answers use exact science terms: reduction by carbon, cryolite, oxygen, carbon dioxide, continually replaced.
• For the half equation, the best responses balance both charge and particles.