Question

Biphenyl, C12H10, is a nonvolatile, nonionizing solute that is soluble in benzene, C6H6. At 25 °C, the vapor pressure of pure benzene is 100.84 torr. What is the vapor pressure of a solution made from dissolving 19.4 g of biphenyl in 33.0 g of benzene?

Answer 1

Moles of Biphenyl = mass of biphenyl / Molar mass of biphenyl = 19.4 / 154.21 =0.1258

benzene moles = 33 /78.11 = 0.4225

Mol fraction of biphenyl = ( biphenyl moles / biphenyl + benzene moles)

               = ( 0.1258 /0.1258+0.4225) = 0.22945

Now we have formula Po-Ps = Po x Xb

where Po = Vapor pressure of solvent = 100.84 ,

Xb = mol fraction of solute = 0.22945 ,

we find Ps i.e vapor pressure of solution

100.84 -Ps = 100.84 x 0.22945

Ps = 77.7 torr