AQA A-Level Chemistry Paper 3, 2019: Question 31

1 mark · Easy difficulty · Multiple Choice

Identify which species or electrons are not responsible for the conduction of electricity.

Practise this question

Question

Multiple choice question asking 'Which is not responsible for conduction of electricity?' Options are: A 'The sodium ions in molten sodium chloride', B 'The electrons between layers of carbon atoms in graphite', C 'The bonding electrons in a metal', D 'The lone pair electrons on water molecules'.
Question text

31 Which is not responsible for conduction of electricity?

[1 mark]

A The sodium ions in molten sodium chloride

B The electrons between layers of carbon atoms in graphite

C The bonding electrons in a metal

D The lone pair electrons on water molecules

Mark scheme

Show the mark scheme Mark scheme table row for question 31 showing the correct answer as D with 1 mark.

31 D 1

How to answer it

Electrical Conductivity & Charge Carriers

What this question tests

This question assesses your understanding of the fundamental prerequisite for electrical conduction across different structures and bonding types (ionic, giant covalent, metallic, and simple molecular):

  • The requirement for mobile charge carriers (freely moving ions or delocalised electrons) to conduct electricity.
  • Why localised electrons, such as lone pairs in simple molecular substances, cannot carry an electric current.
Question 31

Identifying Species NOT Responsible for Conduction

Multiple Choice (1 Mark)

✅ Correct Answer

D: The lone pair electrons on water molecules

Award 1 mark for selecting option D.

💡 Key Knowledge

  • Condition for Conduction: A substance can only conduct electricity if it contains charged particles (ions or electrons) that are free to move throughout the structure.
  • Localised vs Delocalised: Lone pairs on H₂O are localised on the electronegative oxygen atom. Because they are held tightly within the molecule and cannot drift between molecules, they cannot carry charge.

🔍 Breakdown of Each Option

  • A (Molten NaCl): In the molten state, the giant ionic lattice breaks down. Both Na⁺ cations and Cl⁻ anions are mobile and migrate towards the electrodes when a voltage is applied. Hence, Na⁺ ions are responsible for conduction.
  • B (Graphite): Each carbon atom forms three covalent bonds; the fourth valence electron is delocalised in parallel p-orbitals between layers. These delocalised electrons are free to move across the planes, conducting electricity.
  • C (Metals): Metallic bonding consists of a lattice of positive metal ions embedded in a sea of delocalised valence (bonding) electrons that are free to flow through the lattice.
  • D (Water): Water is a neutral, simple molecular compound. While liquid water slightly self-ionises (2H₂O ⇌ H₃O⁺ + OH⁻), the lone pairs themselves remain localized and do not move through the bulk liquid to conduct charge.

🧠 Exam Technique

  • Spot the negative trigger: The word NOT is bolded. Always re-verify whether you are looking for the true or false statement before confirming your answer.
  • Elimination method: Identify substances that you know conduct electricity and cross out the valid charge carriers (molten ions, delocalised electrons in graphite, delocalised electrons in metals).

❌ Common Errors

  • Confusing presence of electrons with mobility: All molecules have electrons; students incorrectly assume that any valence or non-bonding electrons can conduct electricity. They must be delocalised.
  • Confusing pure water with tap water: Students often think water conducts electricity very well. Pure water is an extremely poor conductor, and any conductivity observed in impure water is due to dissolved mineral ions, never the oxygen lone pairs.

Topics

Physical Chemistry · 3.1.3 Bonding

Question and mark scheme from the AQA A-Level Chemistry examination, Paper 3, 2019. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.