AQA GCSE Chemistry Chemistry Paper 2 (Foundation), June 2025: Question 3

✅ Correct Answer

The symbol ⇌ (or "the reversible sign / two opposite arrows").

💡 Key Knowledge

• A standard arrow (→) shows an irreversible reaction going from reactants to products.
• The double arrow ( ⇌ ) means the reaction goes both forwards and backwards.

🧠 Exam Technique

You can simply draw the symbol ⇌ or write "it has a reversible arrow". Keep it brief—there is only 1 mark available.

❌ Common Errors

Do not just write "it has an arrow" or "an equals sign (=)". You must specify that it is the reversible arrow or draw both arrows pointing in opposite directions.

✅ Correct Answer

Endothermic (thermal decomposition is also accepted).

💡 Key Knowledge

The law of conservation of energy applies directly here: If a reversible reaction is exothermic in one direction, it is always endothermic in the opposite direction by the exact same amount of energy.

🧠 Exam Technique

Commit this rule to memory: Opposite direction = opposite energy transfer. Exothermic pairs with endothermic.

❌ Common Errors

Writing irrelevant chemical processes like "reduction", "oxidation", or "neutralisation" instead of the energy term.

✅ Correct Answer

Energy released = 4.6 kJ

❌ Common Errors

• Multiplying instead of dividing: 20 × 4 × 23 (gives an unreasonably huge number).
• Forgetting to show clear workings: if you misread your calculator and wrote 4.8 without working, you score 0 marks. Writing (4/20) × 23 guarantees 1 method mark.

💡 Key Knowledge

• Most composites are made of two materials: the matrix / binder surrounding and binding together fibres or fragments of the other material, which is the reinforcement.
• In reinforced concrete, concrete acts as the binder/matrix, and steel rods/wires act as the reinforcement to resist tension.

❌ Common Errors & Rules

• Crucial Exam Rule: The mark scheme explicitly states: "do not accept more than one line from a box on the left". Drawing two lines from one box forfeits that mark!
• Do not connect anything to "Pre-stressed concrete"—that is the final composite itself, not an individual component.

✅ Correct Answer

Iron (or chemical symbol Fe ).

💡 Key Knowledge

Steels are alloys of iron containing specific amounts of carbon and sometimes other transition metals (e.g. chromium and nickel in stainless steel).

🧠 Exam Technique

Notice the question says "Which metal...". Carbon is often in steel, but carbon is a non-metal, so answering carbon scores 0.

❌ Common Errors

Writing "carbon" (not a metal), "aluminium", or "copper".

✅ Correct Answer

Tick (✔) box 2: Clay

💡 Key Knowledge

Clay ceramics (including bricks, porcelain, and pottery) are made by shaping wet clay and then heating it in a high-temperature furnace/kiln.

🧠 Exam Technique

The prompt asks to "Tick (✓) one box". If you change your mind, cross out the incorrect tick completely so the examiner knows which one you mean.

❌ Common Errors

Ticking poly(ethene), which is a polymer/plastic, or aluminium, which is a pure metal.