Which statement about distillation is true?

• A. It does not require any energy input.
• B. It relies solely on chemical reactions to separate components.
• C. It can separate components with identical boiling points.
• D. It uses differences in volatility to separate components and typically requires energy input.

Answer: (D)

Distillation relies on differences in volatility to separate components. The more volatile part of a mixture has a higher tendency to enter the vapor phase when you heat the liquid, so heating pushes vapor that is enriched in the lower-boiling-point component. As that vapor is condensed and often recycled through a column with multiple stages, the vapor becomes progressively richer in the more volatile component, yielding distinct fractions. Energy input is essential because you must supply heat to vaporize part of the liquid; without energy, no separation by distillation occurs. Components with identical boiling points won’t separate well in ordinary distillation since their volatilities are the same, though there are specialized techniques for special cases. The other statements conflict with the basic physical basis of distillation and the need for heat.