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ChemistryNEET 2025Concentration terms, Henry's and Raoult's laws

Solutions

5 moles of liquid X and 10 moles of liquid Y make a solution having a vapour pressure of 70 torr. The vapour pressures of pure X and Y are 63 torr and 78 torr respectively. Which of the following is true regarding the described solution?

  1. A.The solution shows positive deviation.
  2. B.The solution shows negative deviation.✓
  3. C.The solution is ideal.
  4. D.The solution has a volume greater than the sum of the individual volumes.

Solution

Raoult's law predicts p=515(63)+1015(78)=21+52=73p = \frac{5}{15}(63) + \frac{10}{15}(78) = 21 + 52 = 73 torr. The observed 70 torr is lower, so the solution shows negative deviation (stronger A–B interactions).

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