Fractional distillation relies on differences in what property to separate liquids?

• A. Boiling points
• B. Color
• C. Density
• D. Viscosity

Answer: (A)

Boiling point differences determine how fractional distillation separates liquids. When the mixture is heated, the liquid with the lower boiling point turns into vapor first. The fractional column promotes repeated condensation and vaporization, so the vapor becomes richer in the more volatile component and can be collected separately. This is why boiling point is the property that governs the process. Color, density, and viscosity don’t drive the separation—color is just appearance, density relates to how heavy a liquid is for its volume, and viscosity affects flow, not which component vaporizes first. For example, in a mixture of ethanol and water, ethanol boils at a lower temperature and is collected first.