Liquids A and B form ideal solution for all compositions of A and B at 25°C. Two such solutions with 0.25 and 0.50 mole fractions of A have the total vapor pressures of 0.3 and 0.4 bar, respectively. What is the vapor pressure of pure liquid B in bar?
Answer: 0.2
Solution
For an ideal solution, Raoult's law applies:
For solution 1 (, bar):
For solution 2 (, bar):
From equation (ii):
Substituting (iii) into (i):
From (iii):
For solution 1 (, bar):
For solution 2 (, bar):
From equation (ii):
Substituting (iii) into (i):
From (iii):
JEE Advanced · 2020 · 27 Sep 2020 · Paper 2 · Numerical answer