During the fractional distillation of fermented sugar (initially dilute aqueous ethanol), the concentration of ethanol reaches a rigid maximum limit of approximately by volume. Fundamentally, why can'

Question

During the fractional distillation of fermented sugar (initially dilute aqueous ethanol), the concentration of ethanol reaches a rigid maximum limit of approximately $95.5\%$ by volume. Fundamentally, why can't $100\%$ absolute alcohol be obtained directly through further simple fractional distillation?

Prashant Kotian · Accepted Answer

Correct answer: C. Aqueous ethanol showing a large positive deviation forms a minimum boiling azeotrope at ~95.5% composition. At this specific composition, the vapor produced has the exact same mole fraction of ethanol and water as the liquid phase. Since distillation relies on differing phase compositions to separate components, no further concentration is possible.

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