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 18.9 g of biphenyl in 26.4 g of benzene?

mols biphenyl = g/molar mass

mols benzene = g/molar mass
mol fraction benzene = Xbenzene = mols benzene/total mols.
Then pbenzene = Xbenzene*Ponormal v.p.

To calculate the vapor pressure of a solution made by dissolving biphenyl in benzene, you can use Raoult's Law, which states that the vapor pressure of a solvent above a solution is directly proportional to the mole fraction of the solvent.

First, let's calculate the number of moles of biphenyl and benzene in the solution:

1. Calculate the molar mass of biphenyl (C12H10):

Molar mass of C = 12.01 g/mol
Molar mass of H = 1.01 g/mol

Molar mass of biphenyl = (12.01 x 12) + (1.01 x 10) = 154.23 g/mol

Now, calculate the number of moles of biphenyl in 18.9 g:

moles of biphenyl = 18.9 g / 154.23 g/mol = 0.1227 mol

2. Calculate the molar mass of benzene (C6H6):

Molar mass of C = 12.01 g/mol
Molar mass of H = 1.01 g/mol

Molar mass of benzene = (12.01 x 6) + (1.01 x 6) = 78.11 g/mol

Now, calculate the number of moles of benzene in 26.4 g:

moles of benzene = 26.4 g / 78.11 g/mol = 0.3378 mol

Next, calculate the mole fraction of benzene in the solution:

Mole fraction of benzene = moles of benzene / total moles of solute and solvent

Total moles of solute and solvent = moles of benzene + moles of biphenyl

Total moles of solute and solvent = 0.3378 mol + 0.1227 mol = 0.4605 mol

Mole fraction of benzene = 0.3378 mol / 0.4605 mol = 0.7337

Finally, use Raoult's Law to calculate the vapor pressure of the solution:

Vapor pressure of solution = mole fraction of benzene x vapor pressure of pure benzene

Vapor pressure of solution = 0.7337 x 100.84 torr

Vapor pressure of solution = 73.86 torr

Therefore, the vapor pressure of the solution made from dissolving 18.9 g of biphenyl in 26.4 g of benzene is approximately 73.86 torr.