Distillation - MCAT Chemical and Physical Foundations of Biological Systems

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Question

Consider the following solutions.

Solution A: 1M sodium chloride solution

Solution B: 1M calcium nitrate solution

Solution C: 1M sucrose solution

Equal volumes of the solutions are combined and the mixture is added to a distillation column. Which of the following solutions will separate first?

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Answer

Distillation is a process of separating a liquid from solutes or other liquids. It utilizes the boiling point differences to separate substances. A substance with a low boiling point will evaporate first in a distillation column and will be isolated first. The question is asking which solution will be isolated first; therefore, we need to figure out which solution has the lowest boiling point. Recall that the boiling point of a solution is elevated when there are more solutes present in the solution. Sodium chloride () contributes two solutes (sodium ions and chloride ions). Calcium nitrate () contributes three solutes (one calcium ion and two nitrate ions). Sucrose does not dissociate into ions in solution; therefore, it only contributes one solute. This means that the sucrose solution will have the lowest amount of molecules in solution, the lowest boiling point, and will be separated first.

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