Solutions Question 398
Question: The vapour pressure of two pure liquids A and B which form an ideal solution are 1000 and 1600 torr respectively at 400 K. A liquid solution of A and B for which the mole fraction of A is 0.60 is contained in a cylinder by a piston on which the pressure can be varied. The solution use slowly vapourised at 400 K by decreasing the applied pressure. What is the composition of last droplet of liquid remaining in equilibrium with vapour-
Options:
A) $ X_{A}=0.30,X_{B}=0.70 $
B) $ X_{A}=0.40,X_{B}=0.60 $
C) $ X_{A}=0.70,X_{B}=0.30 $
D) $ X_{A}=0.50,X_{B}=0.50 $
Show Answer
Answer:
Correct Answer: C
Solution:
$ p_A^{0}=1000 $ torr $ p_B^{0}=1600 $ $ X_{A}=0.6 $
$ Y_{A}=0.6 $ (from graph) $ Y_{A}=\frac{p_A^{0}X_{A}}{p_A^{0}X_{A}+p_B^{0}(1-X_{A})} $ $ 0.6=\frac{1000X_{A}}{1000X_{A}+1600(1-X_{A})} $ $ XX_{A}=0.70XX_{B}=1-X_{A}=0.30 $
