Explain why copper(II) sulfate solution conducts electricity but solid copper(II) sulfate does not.

Cambridge International IGCSE Chemistry (0620) — 4.1 Electrolysis · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

Copper(II) sulfate solution contains free mobile ions.
These ions can move towards the electrodes and carry charge through the solution.
In solid copper(II) sulfate the ions are held in fixed positions and cannot move.
Therefore no charge can be carried and no current flows in the solid.

Examiner tips

Use the word "mobile" or "free" when describing ions in solution. Mention that ions move to the electrodes to carry charge. Contrast with ions being fixed in the solid lattice. Show the logical chain: ions present → mobile → current flows; ions fixed → no mobility → no current.

Common mistakes

Saying the solid conducts because it contains ions, ignoring that they are fixed. Forgetting to mention that the ions move to the electrodes. Using vague terms like "particles" instead of "ions".

Mark scheme (4 marks)

Copper(II) sulfate solution contains free/mobile ions
These ions can move towards the electrodes / carry charge through the solution
In solid copper(II) sulfate the ions are held in fixed positions / cannot move
Therefore no charge can be carried / no current flows in the solid

Key terms in this question

conduct