AQA GCSE Combined Science: Trilogy Chemistry Paper 1 (Higher), 2024: Question 8

💡 Big picture

• Nanotubes are cylindrical fullerenes made of carbon atoms.
• The carbon atoms are arranged in hexagonal rings.
• They have useful properties for materials, nanotechnology and drug delivery.
• They conduct because of delocalised electrons.

🧠 How marks are awarded

• 1-mark parts need a precise fact, not a long explanation.
• For the calculation, one mark is for the method and one for the correct answer.
• For the 3-mark explanation, you need a chain of ideas, not just “it has free electrons”.

✅ Correct answer

Hexagonal rings of carbon atoms.

💡 Key knowledge

The mark scheme accepts hexagonal or rings of carbon atoms. The key feature shown is the hexagonal arrangement.

🧠 Exam technique

For a 1-mark “describe” question, give the exact visible feature from the diagram. A short answer is best here.

❌ Common errors

• Saying only cylindrical – that describes the overall shape, not the arrangement of atoms.
• Saying layers – that is more relevant to graphite.
• Writing strong bonds – true in places, but it does not answer this question.

✅ Correct answers

Any one from:

• Nanotechnology
• Materials such as sporting equipment
• Materials such as body armour
• Drug delivery

💡 Key knowledge

Carbon nanotubes are useful because they are very strong and light, and can also be used on a very small scale in nanotechnology.

🧠 Exam technique

You only need one valid use. Be specific if you can, for example sporting equipment is better than just saying materials, although the mark scheme allows both.

❌ Common errors

• Repeating electronics – the mark scheme says ignore references to electronic use.
• Giving a property instead of a use, for example they are strong.
• Being too vague, like industry, without saying what for.

📐 Calculation

1. Use the relationship:
   number of moles = number of atoms ÷ Avogadro constant
2. Substitute the values:
   moles = 2380 ÷ (6.02 × 10²³)
3. Calculate:
   moles = 3.953488 × 10⁻²¹
4. Round suitably:
   3.95 × 10⁻²¹ mol

✅ Correct answer

3.95 × 10⁻²¹ mol

The mark scheme also allows values correctly rounded to at least 2 significant figures, for example 4.0 × 10⁻²¹ mol.

🧠 Exam technique

• Write the formula first to secure the method mark.
• Always include the unit mol.
• Check the power of 10 carefully: dividing by 10²³ gives a very small answer, so the answer must be 10⁻²¹ here.

❌ Common calculation traps

• Using multiplication instead of division.
• Forgetting the 10²³ part of the Avogadro constant.
• Writing the answer as 10²¹ instead of 10⁻²¹.
• Missing the unit mol.

✅ Full-mark answer

Each carbon atom forms three covalent bonds. This means one electron from each carbon atom is delocalised. These delocalised electrons can move through the structure and carry charge.

💡 Key knowledge

• Each carbon atom makes 3 covalent bonds.
• The remaining electron becomes delocalised.
• Delocalised electrons are free to move and so they carry electrical charge.

🧠 Exam technique

This is a 3-mark explanation, so build a logical sequence:

1. State the bonding: each carbon forms three covalent bonds.
2. Then link to electrons: one electron is delocalised.
3. Then link to conduction: the delocalised electrons move and carry charge.

Top answers include all three ideas in the correct order. Students often lost marks by missing the bonding point and only saying “it has free electrons”.

❌ Common errors

• Saying ions move – conduction here is due to electrons, not ions.
• Writing only it has electrons – not enough for 3 marks.
• Talking about layers sliding – that is a graphite property, not the reason for conductivity here.
• Forgetting to mention covalent bonding, even though the question specifically asks for bonding between carbon atoms.

💡 What examiners wanted

• 08.1: the precise word hexagonal.
• 08.2: any valid non-electronic use.
• 08.3: correct use of Avogadro constant and a tiny answer in mol.
• 08.4: a linked explanation from bonding to delocalised electrons to charge flow.

🧠 Best way to revise this topic

• Learn the key structure words for carbon allotropes: hexagonal, layers, giant covalent, delocalised electrons.
• Practise Avogadro calculations with powers of 10.
• For explain questions, write answers as a chain of cause and effect.

✅ Quick full-mark checklist

• Part (a): wrote hexagonal rings.
• Part (b): gave one valid use other than electronics.
• Part (c): showed 2380 ÷ 6.02 × 10²³ and got 3.95 × 10⁻²¹ mol.
• Part (d): included three covalent bonds, delocalised electron, and carry charge.