Which technique is used to separate substances with similar boiling points, such as Ethanol and Water?

Which technique is used to separate substances with similar boiling points, such as Ethanol and Water?

• A. Simple Distillation
• B. Filtration
• C. Fractional Distillation
• D. Chromatography

Answer: (C)

When liquids have similar boiling points, you use fractional distillation because it lets the mixture separate through many vaporization-condensation cycles. The fractionating column provides a large surface area for vapor to condense and re-evaporate as it rises. The component with the lower boiling point—ethanol in this case—tends to vaporize and pass into the condenser first, while the higher-boiling component—water—condenses back and stays behind. With repeated cycles, the vapor that reaches the top is richer in ethanol, producing a distillate that is more ethanol-rich and the remaining liquid richer in water. Ethanol boils around 78°C and water around 100°C, which are close enough that simple distillation wouldn’t separate them well; the column makes the separation practical. Filtration isn’t relevant here because it targets solids, not liquids. Chromatography can separate components based on interactions with a stationary phase and is not the typical method for bulk liquid separation like ethanol and water.

When liquids have similar boiling points, you use fractional distillation because it lets the mixture separate through many vaporization-condensation cycles. The fractionating column provides a large surface area for vapor to condense and re-evaporate as it rises. The component with the lower boiling point—ethanol in this case—tends to vaporize and pass into the condenser first, while the higher-boiling component—water—condenses back and stays behind. With repeated cycles, the vapor that reaches the top is richer in ethanol, producing a distillate that is more ethanol-rich and the remaining liquid richer in water. Ethanol boils around 78°C and water around 100°C, which are close enough that simple distillation wouldn’t separate them well; the column makes the separation practical.

Filtration isn’t relevant here because it targets solids, not liquids. Chromatography can separate components based on interactions with a stationary phase and is not the typical method for bulk liquid separation like ethanol and water.