Why things conduct electricity
4 marks · NormalExplain why molten zinc chloride can conduct electricity but solid zinc chloride cannot.
Describe what must be present in a substance for it to conduct electricity.
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(a) Molten zinc chloride contains ions that are free to move, allowing them to carry charge. In the solid, the ions are fixed in a lattice and cannot move.
(b) There must be charged particles (ions or electrons) that are free to move.
Common mistakes: Mentioning molecule movement; Saying solids conduct
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Marking points
M1 (a) · 1 mark · Explains that ions are free to move in the molten state.
M2 (a) · 1 mark · Explains that ions in the solid are not free to move / are held in a lattice.
B1 (b) · 1 mark · States the need for charged particles (ions or electrons).
B2 (b) · 1 mark · States that these must be free to move.
Worked solution
a) In molten zinc chloride, ions are free to move and carry charge, so it conducts electricity. In the solid, ions are fixed in the lattice and cannot move, so it does not conduct.
b) A substance must contain charged particles (such as ions or electrons) which are free to move in order to conduct electricity.