AQA A-Level Chemistry AS Paper 1, June 2022: Question 23

1 mark · Easy difficulty · Multiple Choice

Identify which species or electrons are not responsible for conducting electricity.

Practise this question

Question

Multiple choice question 23 asks: 'Which is not responsible for conducting 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', and D 'The lone pair electrons in liquid water molecules'. Each option has a selection bubble next to it. Worth 1 mark.
Question text

23 Which is not responsible for conducting 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 in liquid water molecules

Mark scheme

Show the mark scheme Mark scheme for question 23 shows answer 'D (AO2)' with 1 mark, corresponding to 'The lone pair electrons in liquid water molecules'.

23 D (AO2) 1 The lone pair electrons in liquid water molecules

How to answer it

Electrical Conductivity and Mobile Charge Carriers

📌 What this question tests

Fundamental Bonding & Structure:

  • Understanding the prerequisites for electrical conduction (the presence of mobile charge carriers: either delocalised electrons or free-moving ions).
  • Distinguishing between localized electrons (lone pairs/covalent bonds) and delocalised electrons.
  • Recognising the electrical properties of ionic compounds (molten vs solid), giant covalent structures (graphite), metals, and simple covalent molecular substances (liquid water).
Question 23

Multiple Choice Analysis

Identifying particles not responsible for electrical conductivity [1 Mark]

✅ Correct Answer: D

The lone pair electrons in liquid water molecules

Pure water contains simple covalent molecules (H₂O). Lone pair electrons remain localized on individual oxygen atoms; they are not delocalised and cannot move freely through the structure to carry an electric charge.

Award 1 mark for selecting option D.

💡 Key Knowledge

For a substance to conduct electricity, it must contain charged particles that are free to move:

  • Molten ionic solids: The ionic lattice breaks down, freeing ions (such as Na⁺ and Cl⁻) to move and carry charge.
  • Graphite: Each carbon forms 3 covalent bonds. The fourth valence electron is delocalised across the plane between layers, allowing conduction.
  • Metals: A regular lattice of positive metal ions surrounded by a sea of delocalised valence ("bonding") electrons.
  • Covalent liquids (e.g. pure H₂O): Molecules are neutral and electron pairs (both bonding and lone pairs) are localized. Negligible auto-ionisation occurs (very poor conductor).

🧠 Exam Technique: Systematic Elimination

When an exam question contains a negative keyword like not:

  1. A (Sodium ions): In molten NaCl, mobile Na⁺ and Cl⁻ ions move to opposite electrodes. Responsible for conduction? YES .
  2. B (Graphite electrons): Delocalised electrons between graphene layers are mobile along sheets. Responsible? YES .
  3. C (Bonding electrons in metal): The metallic bond consists of delocalised valence electrons free to drift under potential difference. Responsible? YES .
  4. D (Lone pairs in water): Lone pairs are strictly localised around the oxygen nucleus and cannot flow as electric current. Responsible? NO (Correct choice) .

❌ Common Misconceptions & Traps

  • Overlooking the word "not": Candidates rushing under timed conditions often select Option A or B because they immediately spot a familiar conducting medium.
  • Confusing tap water with pure water: In everyday life, water conducts electricity due to dissolved mineral ions, not because of the water molecules or their lone pairs.
  • Believing all electrons conduct: Electrons only conduct if they are delocalised and mobile across a structure. Localised covalent bonds and lone pairs cannot carry current.

Topics

Physical Chemistry · 3.1.3 Bonding

Question and mark scheme from the AQA A-Level Chemistry examination, AS Paper 1, June 2022. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.