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CAIE A Level Chemistry 9701 · States of matter

States of matter: compare question

Compare5 marksStandard

Magnesium oxide, MgO\ce{MgO}, and iodine, IX2\ce{I2}, are both crystalline solids at room temperature. MgO\ce{MgO} has a melting point above 2800 °C and does not conduct electricity when solid. Iodine sublimes at 113 °C and does not conduct electricity in any state. MgO\ce{MgO} dissolves in water to form a solution that conducts electricity, whereas iodine is only slightly soluble in water.

Compare the structure and bonding of these two solids. Explain how their structures account for the differences in their melting points, electrical conductivity, and solubility in water.

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5 marks, so the mark scheme is looking for about 5 separate creditworthy points. Making the same point twice in different words earns it once.

Compare means: Give similarities or differences between two things, and say which side each point belongs to. Write each point as a pair, for example: A is X, whereas B is Y. Two separate descriptions rarely earn the marks.

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