Question

I'm confused with this chemistry problem?

Answer 1

I believe you used the mole fraction of the solute as opposed to the mole fraction of the solvent. It's a common mistake.

Explanation:

`P_(sol n) = chi_i P_0`

where chi is the mole fraction of solvent and P naught is the pure solvent's vapor pressure.

`chi_(C_6H_6) = (32.8g * (mol)/(78g))/((32.8g * (mol)/(78g) + 19.5g * (mol)/(154g)) approx 0.769`

is the mole fraction of benzene in our solution.

Hence,

`P_(sol n) = 0.769 * 100.84t o rr approx 77.50t o rr`

is the vapor pressure of that solution given those data.