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 10.9 g of biphenyl in 25.3 g of benzene?

The correct answer is - 83. torr

Explanation:

We know that:

p = X solvent * P pure solvent,

where, X solvent = number of moles of solvent / total number of moles.

in this solution, solute is 10.9 g of C12 H10 and the solvent is 25.3 g C6H6.  

molar mass of C6H6 = 6 * 12 g/mol + 6 * 1g/mol = 78 g/mol ( =>  moles of solvent = mass in grams / molar mass)

moles of solvent = 25.3 g / 78 g/mol = 0.3243 mol

molar mass of C12H10 = 12 * 12g/mol + 10*1g/mol = 154 g/mol

moles of solute = 10.9 g / 154 g/mol = 0.07077 mol

=> X solvent = 0.3243 / (0.3243 + 0.07077) = 0.8208

=> p = 0.8208 * 100.84 torr = 82.77 torr ≈ 83.0 torr

83.0 torr