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The vapour pressures of two pure liquids A and B are 50 torr and 40 torr respectively. When 8 moles of A is mixed with x moles of B, the vapour pressure of the resulting ideal solution is 48 torr. Find the value of x.
- 4
- 0.5
- 1
- 2
Correct answer: 2
Solution
By Raoult's law: P = x_A*P_A⁰ + x_B*P_B⁰. Here x_A = 8/(8+x), x_B = x/(8+x), P_A⁰ = 50, P_B⁰ = 40, P = 48. So 50*8/(8+x) + 40*x/(8+x) = 48. (400 + 40x)/(8+x) = 48. 400 + 40x = 48(8+x) = 384 + 48x. 400 - 384 = 48x - 40x = 8x. 16 = 8x. x = 2.
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