IB Chemistry SL Structure 3: Classification of matter questions

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Question 1

Multiple choiceMedium1 mark

The atomic radii of lithium and sodium are 152 pm and 186 pm, respectively. What is the percentage increase in atomic radius from lithium to sodium, and which element has the greater metallic character?

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Answer: A. The percentage increase is [(186 − 152)/152] × 100 = 22.4%. Metallic character increases down group 1, so sodium has the greater metallic character.

B: Calculates the percentage correctly but reverses the group 1 trend.
C: Uses the difference, 34 pm, as the percentage without dividing by the starting radius.
D: Expresses the final radius as a percentage of the starting radius but does not subtract the initial 100%.

Remember: calculate a percentage increase relative to the starting value.

Question 2

Multiple choiceMedium1 mark

Two successive members of a homologous series are CH₃CH₂CH₂OH and CH₃CH₂CH₂CH₂OH. What is the IUPAC name of the second compound, and how does its boiling point compare with that of the first?

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Answer: D. The second compound has a four-carbon chain, and numbering from the end nearest the hydroxyl group gives butan-1-ol. It has one more CH₂ group than the first compound; the longer chain has stronger intermolecular forces, so its boiling point is higher. A: names the compound correctly but reverses the boiling-point trend. B: places the hydroxyl group on carbon 2, although it is at the end of the displayed chain. C: assumes the boiling point stays the same because the compounds have the same functional group, overlooking the increase in chain length. Remember: boiling points generally increase with chain length within a homologous series.

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