Vapour Composition

Vapour Composition1

Boiling Point Composition GraphsRecall: Boiling point is the temperature at which the vapour pressure of a liquid (in an open container) is equal to the atmospheric pressure.

More volatile liquids have more molecules in the vapour phase at any temperature, therefore, they will have lower boiling points.

2Boiling Point Composition Graphs

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TATATBTBNon-Ideal MixturesNon-ideal behaviour is observed in many mixtures. The intermolecular forces are NOT the same before and after mixing of liquids.

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Non-Ideal Mixtures

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Positive DeviationNegative DeviationWhat if we plotted boiling point against mole fractions?Colligative Properties: Boiling Point Elevation6Colligative Properties: Freezing Point Depression7Freezing Point Depression & Boiling Point Elevation

8Phase Diagram of Pure Liquid and Solution Containing Non-volatile Solute

9Boiling Point Elevation: ExampleWhat is the molality of an aqueous glucose solution if the boiling point of the solution at 1 atm pressure is 101.27 C?

Ans: 2.5 m

10Freezing point: ExampleThe freezing point of a 0.010 m aqueous solution of a non-volatile solute is -0.072 C. What would you expect the normal freezing point of this same solution to be?11