The electrical conductivity of ionic substances
2 marks · EasyExplain, in terms of ions, why calcium iodide conducts electricity when molten but not when solid.
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Common mistakes: Mentioning electrons instead of ions.
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Marking points
M1 · 1 mark · States or explains that in the solid, ions are fixed and cannot move, so no conduction.
M1 · 1 mark · States or explains that when molten, ions are free to move and can carry charge.
Worked solution
In solid calcium iodide, the ions are held in fixed positions and cannot move, so electricity cannot be conducted. When molten, the ionic lattice breaks down; the ions are free to move and can carry charge, so the substance conducts electricity.