Q.Explain the fractional distillation method of purification.
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Start your 14-day free trial to unlock the full solution →A fractionating column provides repeated cycles of vaporisation-condensation so the more volatile liquid distils off first, cleanly separating miscible liquids with close boiling points.
Fractional distillation is used to separate two (or more) miscible liquids whose boiling points are close to each other (differing by less than about 25C - for liquids with boiling points differing by more than 25C, simple distillation suffices). The mixture is placed in a distillation flask fitted with a fractionating column (a vertical column packed with glass beads, rings, or having a series of trays/plates that provide a large surface area for vapour-liquid contact) before the vapours reach the condenser.
As the mixture is heated, vapour rich in the more volatile (lower boiling) component rises through the column. As it rises, it partially condenses on the cooler surfaces of the packing; this condensed liquid drips back down, while further vapour rising from below reheats and revaporises the falling liquid. Because of this repeated cycle of partial condensation and revaporisation along the length of the column, the vapour that finally emerges from the top of the column becomes progressively richer in the more volatile component, while the liquid remaining in the flask becomes progressively richer in the less volatile component. …
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