The vapour above a solution. Raoult's law for volatile liquids and for a non-volatile solute, ideal and non-ideal solutions, and the azeotropes that distillation cannot separate.
3 lessons, about 1 h 35 min4 simulations11 problems5 practice questionsPython in every lesson
Created by StemPy LabClose a bottle that holds some liquid and the space above it fills with vapour. At a given temperature, the pressure of that vapour has a fixed value. Raoult's law tells you how much of it each liquid in a mixture supplies. It also tells you how a dissolved solid that cannot evaporate lowers it.
A mixture of two similar liquids obeys Raoult's law at every composition. A mixture of two unlike liquids does not. It gives more vapour than the law predicts, or less. The reason lies in the pull between neighbouring molecules, and it also fixes whether the mixture warms up or cools down.
Boil a mixture of two liquids and the vapour is richer in the more volatile one. Repeat the boiling, and you can separate an ideal pair. Some pairs refuse. At one composition the vapour has the same make-up as the liquid, and the mixture boils at one fixed temperature like a pure liquid. This is an azeotrope.
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