During the fractional distillation of fermented sugar (aqueous ethanol), the concentration of ethanol reaches a rigid limit of approximately by volume. Why is it impossible to obtain absolute alcohol

Question

During the fractional distillation of fermented sugar (aqueous ethanol), the concentration of ethanol reaches a rigid limit of approximately $96\%$ by volume. Why is it impossible to obtain $100\%$ absolute alcohol by continuing this simple distillation?

Prashant Kotian · Accepted Answer

Correct answer: C. Ethanol and water show a large positive deviation, leading to a minimum boiling azeotrope at ~96%. At this point, the vapour produced has the identical mole fraction as the liquid phase, rendering fractional distillation completely ineffective.

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