Organic Chemistry MCAT Practice Exam

What type of distillation would you use to separate volatile substances from non-volatile impurities?

1. Simple distillation

2. Fractional distillation

3. Vacuum distillation

4. Steam distillation

The correct answer is: Simple distillation

Simple distillation is the appropriate technique to separate volatile substances from non-volatile impurities because it effectively takes advantage of differences in boiling points. In simple distillation, the mixture is heated, and the component with the lower boiling point vaporizes first, leaving behind the non-volatile impurities in the distillation flask. The vapor is then cooled and condensed back into a liquid, collected in a separate container. This method is ideal when the boiling point difference is significant (typically greater than 25-30°C) and is straightforward to implement for purifying liquids like solvents or essential oils that need to be separated from solutes or impurities that do not vaporize at the same temperature. In contrast, fractional distillation is more suited for separating mixtures of liquids with closer boiling points and involves using a fractionating column to enhance separation. Vacuum distillation is used to distill substances that have very high boiling points, and steam distillation is particularly useful for thermally sensitive substances or for extracting essential oils. However, when dealing with a simple separation of volatile from non-volatile materials, simple distillation is the best choice.