Question detail
In fractional distillation, what is the main reason that heavier fractions are collected at higher temperatures?
Try the question, check the answer, then read the explanation to understand the curriculum point.
At a glance
MCQ
Type
practice
Style
Topic
Alkanes
Question
- A. They have lower vapor pressures at a given temperature
- B. They have higher vapor pressures at a given temperature
- C. They have lower boiling points
- D. They have higher melting points
Answer
They have lower vapor pressures at a given temperature
Explanation
Lower vapor pressure at a given temperature means a component requires a higher temperature to reach its boiling point, so it condenses later in the distillation column.
Common mistake
Misunderstanding Fractional Distillation
Students often think that fractional distillation separates crude oil based solely on boiling points without considering the role of intermolecular forces.
Fractional distillation separates crude oil into fractions based on both boiling points and the strength of intermolecular forces. The formula for separation involves understanding that components with lower boiling points and weaker intermolecular forces vaporize first. For example, lighter fractions like gasoline have lower boiling points than heavier fractions like diesel. Therefore, as the crude oil is heated, the lighter fractions rise and condense at different levels in the fractionating column.
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