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 17.3 g of biphenyl in 27.4 g of benzene?

Answer 1

Answer – We are given the, vapor pressure of pure benzene = 100.84 torr

Mass of biphenyl = 17.3 g , mass of benzene = 27.4 g

First we need to calculate the moles of both

Moles of biphenyl = 17.3 g / 154.21 g.mol^-1 = 0.112 moles

Moles of benzene = 27.4 g / 78.11 g.mol^-1 =0.351 moles

So, total moles = 0.112 moles + 0.351 moles = 0.463 moles

So, moles fraction of benzene = 0.351 /0.463 = 0.758

We know the Raoult's law –

P of solution = mole fraction of solvent * pure vapor pressure of solvent

P solution = 0.758 *100.84 torr

                  = 76.4 torr

So, the vapor pressure of a solution made from dissolving 17.3 g of biphenyl in 27.4 g of benzene is 76.4 torr