The boiling point of pure benzene at 760. torr is 80.1°C. What is the vapor pressure of benzene over a solution containing 4.40 mol of nonvolatile hydrocarbon and 11.80 mol of benzene at 80.1°C? A) 6.04 × 10² torr B) 5.54 × 10² torr C) 2.06 × 10² torr D) 7.60 × 10² torr E) 1.42 × 10² torr

Question

Quizplus · Accepted Answer

According to Raoult's Law:

P_benzene = X_benzene * P°_benzene

where P_benzene is the vapor pressure of benzene over the solution, X_benzene is the mole fraction of benzene in the solution, and P°_benzene is the vapor pressure of pure benzene.

To find X_benzene, we need to first calculate the total moles of solute and solvent:

n_total = n_benzene + n_hydrocarbon
n_total = 11.80 mol + 4.40 mol
n_total = 16.20 mol

Then, we can calculate X_benzene:

X_benzene = n_benzene / n_total
X_benzene = 11.80 mol / 16.20 mol
X_benzene = 0.728

Now we can use Raoult's Law to find P_benzene:

P_benzene = X_benzene * P°_benzene
P_benzene = 0.728 * 760. torr
P_benzene = 553. torr

Therefore, the vapor pressure of benzene over the solution is 553. torr, which corresponds to choice B.

The Boiling Point of Pure Benzene at 760