MCAT Organic Chemistry Question 166: Answer and Explanation

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Question: 166

1. Fractional distillation under atmospheric pressure would most likely be used to separate which of the following compounds?

  • A. Methylene chloride (boiling point of 40°C) and water (boiling point of 10°C)
  • B. Ethyl acetate (boiling point of 77°C) and ethanol (boiling point of 80°C)
  • C. Aniline (boiling point of 184°C) and benzyl alcohol (boiling point of 205°C)
  • D. Aniline (boiling point of 184°C) and water (boiling point of 100°C)

Correct Answer: B

Explanation:

Fractional distillation is the most effective procedure for separating two liquids that boil within a few degrees of each other. Ethyl acetate and ethanol boil well within 25°C of each other and thus would be good candidates for fractional distillation. Fractional distillation could also be used for the liquids in choice (C), but would require lower pressures because of their high boiling points.

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