Explain why ionic compounds can conduct electricity when dissolved in water but not when solid.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
In a solid ionic compound the ions are arranged in a fixed lattice and cannot move.
Because the ions are immobile, charge cannot be carried and the solid does not conduct electricity.
When the compound is dissolved in water the lattice breaks apart and the ions become free.
The free ions can move through the solution and carry charge, so the solution conducts electricity.
Because the ions are immobile, charge cannot be carried and the solid does not conduct electricity.
When the compound is dissolved in water the lattice breaks apart and the ions become free.
The free ions can move through the solution and carry charge, so the solution conducts electricity.
Examiner tips
- Use the word "immobile" to show understanding of lattice structure. Mention that conduction requires mobile charge carriers. Show the contrast between solid and solution states. Keep answer concise and use correct terminology.
Common mistakes
- Confusing the role of electrons with ions in conduction. Saying the solid conducts because of electrons. Forgetting to mention that the lattice breaks apart in solution.
Mark scheme (4 marks)
- In a solid ionic compound, the ions are held in a fixed lattice / ions cannot move
- Because ions cannot move, charge cannot be carried / electricity cannot be conducted in the solid state
- When dissolved in water, the ionic lattice breaks apart and the ions are free to move
- The free-moving ions carry charge through the solution, allowing electrical conduction
Key terms in this question
Related
- All AQA GCSE Chemistry (8462) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →