CH 102/104 - Practice problems – 10/03/12
Colligative properties and binary liquid mixtures.
1. Suppose that 25.0 g of solid NaOH is added to 1.50 L of an aqueous solution that is already 2.40
M in NaOH. Then water is added until the final volume is 4.00 L. Determine the concentration of
the NaOH in the resulting solution.
2. Pure toluene (C7H8) has a boiling point has a normal boiling point of 110.60 °C. A solution of 7.80
g of anthracene (C14H10) in 100.0 g of toluene has a boiling point of 112.06 °C. Calculate the boiling
point elevation constant (kb) for toluene.
3. At 25 °C, some water is added to a sample of gaseous methane (CH4) at 1.00 atm pressure in a
closed vessel, and shaken until as much methane as possible dissolves. Then 1.00 kg of the
solution is removed and boiled to expel the methane, yielding a volume of 3.01 L of CH4(g) at 0 °C
and 1.00 atm. Determine the Henry’s Law constant for methane in water.
4. At 40 °C, the vapor pressure of pure carbon tetrachloride (CCl4) is 0.293 atm and the vapor
pressure of pure dichloromethane (C2H4Cl2) is 0.209 atm. A nearly ideal solution is prepared by
mixing 30.0 g of carbon tet with 20.0 g of DCM.
a. Calculate the mole fraction of carbon tet in the solution.
b. Calculate the vapor pressure of the solution at 40 °C.
c. Calculate the mol fraction of carbon tet in the vapor in equilibrium with the solution.
5. Match each of the solute-solvent combinations below with a pressure diagram (Ileft/middle/right)
and explain your answer.
Mixture A: _____________________________
Mixture C: _____________________________
Mixture B: _____________________________
Mixture D: ____________________________
6. Determine the van’t Hoff factor for the ionic solute dissolved in water in the
beaker on the right.
7. Use the following data for three acqueous solutions of CaCl2 to calculate the
empirical value of the van’t Hoff factor.
Molality
0.0225
0.0910
0.278
Tf depression (°C)
0.110
0.440
1.330
8. In the winter of 1994, record low temperatures were registered throughout the US. For example,
in Champaign, IL, a record low of -29 °F was registered. At this temperaturecan salting icy roads
with CaCl2 be an effective method of melting ice?
a. Assume that i = 3 for CaCl2 in water
b. Assume for i the value you calculated in problem 7.
Answers - Q1: 1.06 mol/L. Q2: 3.34 K mol / kg. Q3: 4.13x102 atm.
Q4: 0.491; 0.250 atm; 0.575. Q5: middle, left, right, left. Q6: 1.67. Q7: 2.63. Q8: a. yes; b. no.