Question
The vapour pressure of two pure liquids A and B that form an ideal solution, are 400 and 800 ~mm of Hg respectivelyat a temperature t^ C . The mole fraction of A in a solution of A and B whose boiling point is t^ C will be
BITSAT
Chemistry
Solutions
2020
BITSAT 2020
BITSAT Chemistry Question (2020) — Solution
Options
- A. 0.4
- B. 0.8
- C. 0.1
- D. 0.2
Answer
C. 0.1
Step-by-step solution
V.P. of solution at t^ C =760 ~mm [at b.p., V.P. of solution =atompheric pressure] Thus = P _ A ^ x _ A + P _ B ^ x _ B or P = P _ A ^ 0 x _ A + P _ B ^ 0 (1- x _ A ) [ x _ A + x _ B =1 ] or 760=400 X _ A +800 (1- X _ A )[ P =760 mmofHg ] or -800+760=-400 x_ A or -40=-400 x _ A or x_ A = 40 400 =0.1 Thus mole fraction in solution is 0.1
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