# I'm confused with this chemistry problem?

Nov 30, 2017

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:

${P}_{s o l n} = {\chi}_{i} {P}_{0}$

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,

${P}_{s o l n} = 0.769 \cdot 100.84 t o r r \approx 77.50 t o r r$

is the vapor pressure of that solution given those data.