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?
- The solution is ideal.
- The solution has volume greater than the sum of individual volumes.
- The solution shows positive deviation.
- The solution shows negative deviation.
Answer
(4) The solution shows negative deviation.
Solution
xX = 515 = 13, xY = 1015 = 23
Ideal (Raoult's law): p = 63 13 + 78 23 = 21 + 52 = 73 torr
Observed 70 torr < 73 torr, so the solution shows negative deviation ( mix V < 0, not greater volume).
Answer: (4)