Question detail
During fractional distillation, at what stage is the lightest fraction, such as gasoline, collected?
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. When the distillation column is at its highest temperature
- B. When the column temperature is just above the boiling point of the lightest fraction
- C. When the column temperature is below the boiling point of the lightest fraction
- D. When the column temperature is at the boiling point of the heaviest fraction
Answer
When the column temperature is just above the boiling point of the lightest fraction
Explanation
Light fractions boil at lower temperatures; they are collected first when the column temperature rises to just above their boiling points.
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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