The electrical conductivity of ionic substances
4 marks · NormalCalcium fluoride is an ionic compound. State whether it will conduct electricity when in solid form and explain your answer.
Describe the arrangement and movement of ions in solid calcium fluoride.
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(a) No, solid calcium fluoride does not conduct electricity because the ions are fixed in the lattice and cannot move. · must show Does not conduct, Ions not free to move
(b) In solid calcium fluoride, the calcium and fluoride ions are arranged in a regular lattice structure and are fixed in position, so they are not able to move. · must show Regular lattice/giant ionic lattice, Ions fixed in place, No movement
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Marking points
B1 (a) · 1 mark · States calcium fluoride does not conduct electricity when solid.
B2 (a) · 1 mark · Explains this is because ions are not free to move.
B3 (b) · 1 mark · Mentions regular lattice or giant ionic structure.
B4 (b) · 1 mark · States ions are fixed in position and cannot move.
Worked solution
(a) Solid calcium fluoride does not conduct electricity as its ions are held in fixed positions within the lattice and cannot move.
(b) In solid calcium fluoride, the calcium and fluoride ions form a regular lattice structure and are fixed in place, so the ions cannot move.