Sodium chloride does not conduct electricity as a solid but does conduct electricity when dissolved in water. Explain why sodium chloride behaves differently in these two situations.

Pearson Edexcel International GCSE Chemistry (4CH1) — 1.6 Ionic compounds · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Sodium chloride is an ionic compound with a giant lattice structure. In its solid state it does not conduct electricity, but when dissolved in water it becomes a good electrical conductor.

Model answer (4 marks)

In solid NaCl the ions are fixed in a giant lattice held by strong electrostatic forces, so they cannot move.
Because the ions cannot move freely, charge cannot be carried and the solid does not conduct.
When NaCl is dissolved in water the lattice breaks apart and the ions dissociate into the solution.
The free‑moving ions in solution can carry charge, so the solution conducts electricity.

Examiner tips

  • Use the word ‘fixed’ or ‘immobile’ to show lack of movement in the solid.
  • Mention ‘dissociation’ when describing the solution state.
  • Explain that free ions carry charge, linking to conductivity.

Common mistakes

  • Confusing conductivity with conductivity of the solvent rather than the ions.
  • Omitting the term ‘dissociation’ or ‘lattice breaks apart’.

Mark scheme (4 marks)

  1. In solid sodium chloride, the ions are held in fixed positions in the giant lattice by strong electrostatic forces
  2. Because the ions cannot move freely in the solid, charge cannot be carried, so it does not conduct electricity
  3. When dissolved in water, the giant lattice breaks apart and the ions are released/dissociate into the solution
  4. The free-moving ions in solution can carry charge/current, so the solution conducts electricity

Key terms in this question

ion

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