In fractional distillation of crude oil, fractions with lower boiling points are collected at the top of the fractionating column. Which statement explains why this occurs?

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Question

In fractional distillation of crude oil, fractions with lower boiling points are collected at the top of the fractionating column. Which statement explains why this occurs?

Accepted Answer

Vapours with lower boiling points do not condense at higher temperatures — Award 1 mark for recognizing that low boiling point substances remain as vapours at temperatures where high boiling point substances condense. A is incorrect — molecular size affects boiling point but molecules do not 'rise faster'. C is partially correct but does not explain why they are collected at the top. D is incorrect — lower boiling points indicate weaker intermolecular forces.

Answer

Molecules with lower boiling points are smaller and rise faster

Answer

Vapours with lower boiling points do not condense at higher temperatures

Answer

Liquids with lower boiling points evaporate first and remain as vapours longer

Answer

Compounds with lower boiling points have stronger intermolecular forces

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