Question
Chemistry Question on Solutions
The vapour pressures of two liquids A and B in their pure states are in the ratio of 1:2. A binary solution of A and B contains A and B in the mole proportion of 1:2. The mole fraction of A in the vapour phase of the solution will be
A
0.33
B
0.2
C
0.25
D
0.52
Answer
0.2
Explanation
Solution
Given, pA:PB=1:2
∴pB=2pA
Similarly nBnA=21
∴xA=1+21=31 and xB=1+22=32
Total pressure, pT=PAxA+pBxB
=pA×31+2pA×32
=31pA+34pA
=35pA
Mole fraction in vapour phase
yA=prpAxA
=35pApA×31=51=0.2