A student has a mixture of ethanol and water and wants pure ethanol. Simple distillation gives a mixture, but a taller column gives better separation. Which...
Question 1 Report
A student has a mixture of ethanol and water and wants pure ethanol. Simple distillation gives a mixture, but a taller column gives better separation. Which method gives the best separation of the two liquids?
Answer Details
Ethanol and water are miscible with boiling points of 78℃ and 100℃, which are close enough that simple distillation lets some water vapour through with the ethanol. Fractional distillation adds a tall packed column in which the vapour condenses and re-evaporates many times on the way up. Each of these cycles enriches the rising vapour in the lower boiling component, so fractional distillation gives the best separation.
A separating funnel only works for immiscible liquids that form two layers, and these two mix completely. Filtration separates by particle size and cannot act on two liquids, and crystallisation needs a dissolved solid. Reach for a fractionating column whenever two miscible liquids have similar boiling points.
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