A solution is 40.0% by volume benzene (C₆H₆)in carbon tetrachloride at 20°C. The vapor pressure of pure benzene at this temperature is 74.61 mmHg and its density is 0.87865 g/cm³; the vapor pressure of pure carbon tetrachloride is 91.32 mmHg and its density is 1.5940 g/cm³. If this solution is ideal, its total vapor pressure at 20°C is A)84.64 mmHg B)84.30 mmHg C)82.96 mmHg D)81.63 mmHg E)165.93 mmHg

Question

Quizplus · Accepted Answer

First, calculate the mole fraction of benzene:
Mole fraction of benzene = (volume fraction of benzene x density of CCl4) / (volume fraction of benzene x density of CCl4 + volume fraction of C6H6 x density of C6H6)
Mole fraction of benzene = (0.4 x 1.5940) / (0.4 x 1.5940 + 0.6 x 0.87865) = 0.373
Next, use Raoult's law to calculate the total vapor pressure:
Total vapor pressure = mole fraction of benzene x vapor pressure of benzene + mole fraction of CCl4 x vapor pressure of CCl4
Total vapor pressure = (0.373 x 74.61) + (0.627 x 91.32) = 84.30 mmHg

A Solution Is 40