Question

A solution of 3 moles of carbon disulfide in 10 moles of ethyl acetate has a vapor pressure of 170 torr at 28°c. the vapor pressure of pure carbon disulfide at 28°c is 390 torr. what is the vapor pressue of pure ethyl acetate at 28°c

Answer 1

Total pressure of solution = (P⁰carbon sulfide * X carbon sulfide) + (P⁰ethyl acetate * X ethyl acetate)
where:
P⁰ carbon sulfide is vapor pressure of pure Carbon sulfide
X carbon sulfide is mole fraction of carbon sulfide = (number of moles of carbon sulfide / total number of moles)
P⁰ ethyl acetate is vapor pressure of pure ethyl acetate
X ethyl acetate is mole fraction of ethyl acetate = (number of moles of ethyl acetate / total number of moles)

P soln = (P⁰CS₂ * X CS2) + (P⁰ethyl acetate * X ethyl acetate)
170 torr   = (390 torr * 3 / 13) + (P⁰ ethyl acetate * 10 / 13 )
P⁰ ethyl acetate = 104 torr