Biphenyl, C 12 H 10 , C12H10, is a nonvolatile, nonionizing solute that is soluble in benzene, C 6 H 6 . C6H6. At 25 ∘ C, 25 ∘C, the vapor pressure of pure benzene is 100.84 Torr. What is the vapor pressure of a solution made from dissolving 19.0 g 19.0 g of biphenyl in 27.8 g 27.8 g of benzene?

Vapor pressure of solution = 75.02 Torr

Explanation:

Vapor pressure of pure solvent (P°) - Vapor pressure of solution = P° . Xm . i

As the solute is nonvolatile and nonionizing, i = 1

Let's determine the Xm (mole fraction)

Moles of solute → 19 g . 1mol/154g = 0.123moles

Moles of solvent → 27.8 g . 1mol / 78 g = 0.356 moles

Total moles = 0.123 + 0.356 = 0.479

Xm = 0.123 / 0.479 = 0.256

Let's replace in the formula

100.84 Torr - Vapor pressure of solution = 100.84 Torr . 0.256 . 1

Vapor pressure of solution = - (100.84 Torr . 0256 - 100.84 Torr) → 75.02Torr