A chem quiz question- About Mole Fraction?

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At a given temperature you have a mixture of benzene (vapour pressure of pure benzene = 745 torr) and toluene (vapour pressure of pure toluene = 290 torr). The mole fraction of benzene in the solution is 0.77. Assuming ideal behaviour, calculate the mole fraction of toluene in the vapour above the solution.

Thanks a lot for the answer
 
someone asked this question before... a couple minutes before you did here's what the answer was

p = p°X ( Raoult's law)
mole fraction toluene = 1 - 0.77= 0.23
p ( benzene) = 0.77 x 745 =574 torr
p ( toluene) = 0.23 x 290=66.7 torr

total vapour pressure above the solution = 574 + 66.7 =640.7 torr

66.7 / 640.7 = 0.104 = mole fraction toluene above the solution
 
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