At a fixed temperature the vapour pressure of pure A is $300 torr$ and that of pure B is $250 torr$ . A solution with $x_{A} = 0.50$ shows a measured total vapour pressure of $380 torr$ . Which statements are correct?

AThe solution shows positive deviation from Raoult's law
B $Δ H_{mix}$ for this system is positive
CThe vapour pressure expected for an ideal solution at this composition is $275 torr$
DThe solution boils at a higher temperature than an ideal solution of the same composition would

Answer: A, B, C

Ideal value

= 0.5 \times 300 + 0.5 \times 250 = 275

torr (statement 3 true). The measured

380 > 275

means positive deviation, which comes with weaker A-B attraction and endothermic mixing (statements 1 and 2). Higher vapour pressure means the solution reaches

1 atm

at a lower temperature, so statement 4 is false. Answer: 1, 2 and 3.

Practice Solutions and Colligative Properties More on Raoult's law, ideal and non-ideal solutions, azeotropes

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At a fixed temperature the vapour pressure of pure A is 300 torr and that of pure B is 250 torr. A solution with xA​=0.50 shows a measured total vapour pressure of 380 torr. Which statements are correct?

Answer: A, B, C

More questions on Raoult's law, ideal and non-ideal solutions, azeotropes

At a fixed temperature the vapour pressure of pure A is $300 torr$ and that of pure B is $250 torr$ . A solution with $x_{A} = 0.50$ shows a measured total vapour pressure of $380 torr$ . Which statements are correct?