Why does a solid ionic compound not conduct electricity?

Its ions are held in fixed positions and cannot move.

Why does a molten ionic compound conduct electricity?

The lattice breaks down so the ions are free to move and carry charge.

Why does an ionic compound conduct when dissolved in water?

The ions are free to move in the solution.

Why do many ionic compounds dissolve in water?

Water molecules attract the ions and pull them out of the lattice.

Name an insoluble ionic compound.

Calcium carbonate (limestone or chalk).

What must a substance have in order to conduct electricity?

Charged particles that are free to move.

What happens to the lattice when an ionic compound melts?

It breaks down and the ions gain enough energy to move freely.

What should you link every property to in an exam answer?

The structure (giant ionic lattice) and the bonding (electrostatic attraction between ions).

Properties of ionic compoundsIB MYP Chemistry: Flashcards

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Why do ionic compounds have high melting points?

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Why do ionic compounds have high melting points?: Strong electrostatic attraction between the oppositely charged ions needs a lot of energy to overcome.
What is the melting point of sodium chloride?: 801 °C.
Why does a solid ionic compound not conduct electricity?: Its ions are held in fixed positions and cannot move.
Why does a molten ionic compound conduct electricity?: The lattice breaks down so the ions are free to move and carry charge.
Why does an ionic compound conduct when dissolved in water?: The ions are free to move in the solution.
What carries the charge in a molten ionic compound?: Ions, not electrons.
Why do many ionic compounds dissolve in water?: Water molecules attract the ions and pull them out of the lattice.
Name an insoluble ionic compound.: Calcium carbonate (limestone or chalk).
What is the state of ionic compounds at room temperature?: Solid.
What must a substance have in order to conduct electricity?: Charged particles that are free to move.
A solid has a high melting point, does not conduct when solid but does when molten. What type is it likely to be?: An ionic compound.
What happens to the lattice when an ionic compound melts?: It breaks down and the ions gain enough energy to move freely.
What should you link every property to in an exam answer?: The structure (giant ionic lattice) and the bonding (electrostatic attraction between ions).

Exam questions on Properties of ionic compounds

A student in Cairo heats a few crystals of sodium chloride in a crucible over a Bunsen burner. The crystals do not melt, even though the flame is very hot. A furnace is needed to melt sodium chloride, at 801 °C.
Explain why sodium chloride has such a high melting point.2 marks
A teacher in Auckland gives students a white solid labelled X. They find that X does not conduct electricity when solid, melts only above 700 °C, and conducts electricity well when molten. X also dissolves in water, and the solution conducts electricity.
Explain why X does not conduct electricity when solid but does when molten.2 marks
A student in Kuala Lumpur investigates how well salt solutions conduct electricity. She dissolves 0 g, 2 g, 4 g, 6 g and 8 g of sodium chloride in separate 100 cm³ portions of distilled water and measures the current in each solution, using the same circuit and electrodes every time. The ammeter readings were 0.00 A, 0.18 A, 0.35 A, 0.52 A and 0.69 A. She predicted that the more sodium chloride dissolved, the greater the current.
Describe the trend in her results and explain it.3 marks

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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).