Question

The vapor pressure of a pure substance is measured to be 812mmHg at a specific temperature. A non-volatile solute is added to this substance and the vapor pressure is measured to be 400mmHg. What is the mole fraction of the non- volatile solute

Answer 1

Answer:

According to Raoult's law,

P

0

P

0

−P

s

=

n+N

n

Let m be the molecular mass of the solid substance.

n=

m

2.175

;N=

78

39

=0.5

(molecular mass of benzene = 78)

P

0

=640mm;P

s

=600mm

Substituting the values in above equation,

640

640−600

=

m

2.175

+0.5

m

2.175

=

2.175+0.5m

2.175

m=

0.5

2.175×16−2.175

=65.25