Question

Biphenyl, C12H10, is a nonvolatile, nonionizing solute that is soluble in benzene, C6H6. At 25

Answer 1

Vapour pressure of pure benzene = 100.84 torr

amount of biphenyl dissolved = 15.4 g

molecular wt of biphenyl = 154

so mole of biphenyi = 154 / 154 = 0.1 moles

amount of benzene = 34.8 g

molecular wt of benzene = 78

so moles of benzene = 0.446

Mole fraction of solute = 0.1 / 0.446 + 0.1 = 0.183

we know that

Lowering of vapour pressure is a colligaive property i.e it depends upon the number of molecules

Lowerign of vapour pressure = Pressure of solvent X mole fraction of solute = 100.84 torr X 0.183 = 18.45 torr

so vapour pressure of benzen = 100.84 - 18.45 = 82.39 torr