The pressure of two pure liquid A and B which form an ideal solutions are 400 mm Hg and 800 mm Hg respectively at temperature T.A liquid containing 3:1 molar composition pressure can be varied.The solutions is slowly vapourized at temperature T by decreasing the applied pressure starting with a pressure of 760 mm Hg.A pressure gauge (in mm) Hg is connected which give the reading of pressure applied.
The reading of pressure Gauge at bubble point is

Options

A. 500
B. 600
C. 700
D. None

Answer

A

Explanation

`X_A=0.75 " " X_B=0.05` above 500 mm Hg only liquid phase exists.
`P_("bubble") "point"=X_A P_A^@+X_B^@ P_B^@`
`P_("cqycqfyr fcUnq") =X_A P_A^@+X_B^@ P_B^@`
=0.75+400+0.25x800=500 mm
`y_A=0.75 , " " y_B=0.5`
At dew point
`1/P_T=y_A/P_A^@+y_B/P_B^@implies1/P_T=0.75/400+0.25/800=(1.5+0.25)/800`
`implies P_T=800/1.75=457.14` mm Hg
Below dew point only vapour phase exists