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Pure A has a vapour pressure of 30.0 kPa and pure B has 20.0 kPa…

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Pure A has a vapour pressure of $30.0\ \text{kPa}$ and pure B has $20.0\ \text{kPa}$ . For a solution with a mole fraction of A of $0.40$ , the measured partial pressures are $14.4\ \text{kPa}$ for A and $13.2\ \text{kPa}$ for B. Find the total pressure and the mole fraction of A in the vapour. Compare each partial pressure with Raoult's law and say what kind of solution this is.

Need a reminder? The key ideaShow

An ideal solution obeys Raoult's law at every composition, with $\Delta_{mix}H = 0$ and $\Delta_{mix}V = 0$ . A positive deviation has a pressure above the Raoult line, a weaker A–B attraction, $\Delta_{mix}H > 0$ and $\Delta_{mix}V > 0$ . A negative deviation is the opposite. The deviation is $\dfrac{P_{measured} - P_{Raoult}}{P_{Raoult}} \times 100\ \%$ .

The worked solution

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