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 15.7 g of biphenyl in 27.3 g of benzene?

Answer 1

According to Raoult's law

Vapor pressure of benzene Solution = vapor pressure of pure benzene X mole fraction of benzene in solution

mole fraction of benzene= number of moles of benzene in solution/ total moles of solution

= (27.3 gram/78.11 gram/mole)/ (27.3 gram/78.11 gram/mole)+ (15.7 gram/154.21 gram/mole)

= 0.349/0.349 +0.102 = 0.775

Since

Vapor pressure of benzene Solution = vapor pressure of pure benzene X mole fraction of benzene in solution

=100.84 torr X 0.775 = 78.21 torr Answer