CAIE A Level Chemistry 9701 · States of matter
Substance X is a white crystalline solid with a melting point of 2852 °C. It does not conduct electricity when solid, but when molten it conducts electricity. When added to water, it reacts to form a solution that conducts electricity.
Explain the type of structure and bonding present in substance X, and explain why it has a high melting point and why its electrical conductivity changes between the solid and molten states.
4 marks, so the mark scheme is looking for about 4 separate creditworthy points. Making the same point twice in different words earns it once.
Explain means: Give the reasons or the mechanism: why or how something happens. Link each point to the next with because, so or which means. A list of facts with no links usually loses the reasoning marks.
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