Chem 301 Problem Day #8
Fall 2008
1. A mixture contains 3.00 moles CCl4 and 7.50 moles CHCl3. The vapor pressure of pure CCl4 is
0.0445 bar and that of pure CHCl3 is 0.0795 bar. Assume an ideal solution.
a. What is the vapor pressure of CHCl3 above the solution?
xCHCl3 = 7.50/(3.00+7.50) = 0.714
PCHCl3 = xCHCl3 P*CHCl3 = (0.714)(0.0795) = 0.0568 bar
b. What is the vapor pressure of CCl4 above the solution?
xCCl4 = 3.00/(3.00+7.50) = 0.286
PCCl4 = xCCl4 P*CCl4 = (0.286)(0.0445) = 0.0127 bar
c. What is the composition of the vapor?
Ptotal = PCHCl3 + PCCl4 = 0.0695 bar
yCHCl3 = (PtotalP*CHCl3 – P*CHCl3P*CCl4)/(Ptotal(P*CHCl3 – P*CCl4))
= (0.0568 × 0.0795 – 0.0795 × 0.0445) / (0.0568(0.0795 – 0.0445))
= 0.82
yCCl4 = 1 – yCHCl3 = 0.18
OR yCHCl3 = PCHCl3 / Ptotal = 0.0568/0.0695 = 0.82
2. Using the diagrams below, estimate the pressure required to cause a xbenz=0.50 solution of
toluene/benzene to boil at room temperature. What is the composition of the vapor phase at that
point?
At what temperature would this solution boil at atmospheric pressure? What is the
composition of the vapor phase under these conditions?
T=298K P=1atm
Ptot = 65 Torr Tbp = 365 K
ybenz = 0.76 ybenz = 0.74
