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 10.0 g of biphenyl in 25.9 g of benzene?

Answer 1

Molar mass of C6H6,

MM = 6*MM(C) + 6*MM(H)

= 6*12.01 + 6*1.008

= 78.108 g/mol

Molar mass of C12H10,

MM = 12*MM(C) + 10*MM(H)

= 12*12.01 + 10*1.008

= 154.2 g/mol

n(C6H6) = mass/molar mass

= 25.9/78.108

= 0.3316

n(C12H10) = mass/molar mass

= 10.0/154.2

= 0.0649

n(C6H6),n1 = 0.3316 mol

n(C12H10),n2 = 0.0649 mol

Total number of mol = n1+n2

= 0.3316 + 0.0649

= 0.3964 mol

Mole fraction of each components are

X(C6H6) = n1/total mol

= 0.3316/0.3964

= 0.8364

According to Raoult’s law:

P = Po*X(solvent)

p = 100.84*0.8364

p = 84.34 torr

Answer: 84.34 torr