University of Texas, Arlington

CHEM 1442

Chapter 12 Questions

Useful Information:

R = 0.08206 L.atm/mol.K = 8.314 J/mol.K

1 atm = 760 torr = 760 mm Hg

 

 

P_soln = (P_solv) (X_solv)                                                                             π = MRT ( R = 0.0821 Latm/mol K)

 

T_f = imK_f ( or T_b )

 

 Psoln = (Psolv) ( Xsolute)

 

P_total = P_AX_a + P_bX_b (two volatile liquids)

 

 

Molality

 

1. 45 g of NaOH is dissolved in 100 ml of water. (a) What is the m of the solution. The density of water is 1g/ml. (b) If the density of the NaOH solution is 1.5 g/ml, what is the M of the solution?

 

2. A certain aqueous solution is 50% HCl by mass. The density of the solution is

1.2 g/cm³. What is the concentration of HCl expressed in molality?

 

Colligative Properties van’t Hoff factor, i. How an ionizing compound works.

 

3. Which of the solutions below, at the same concentration of 0.1 m in an aqueous solution, would have the highest van’t Hoff factor, i.
   1. NaCl (b) CH₃CH₂CH₃ (c) CaCl₂ (d) KBr

 

4. Which of the following would have the lowest boiling point?
   1. 0.08 m glucose ( a non-electrolyte) (b) 0.05 m CaCl₂ (c) 0.02 m K₃PO₄

(d) 0.007 m AlCl₃

 

 

Colligative Properties and Raoult’s Law : Determining Molar Mass

 

5. A solution of 0.5 g of an unknown is dissolved in 30 ml of benzene. The solution exhibits an osmotic pressure of 8.92 torr at 27^oC. What is its molecular mass?

 

6. A solution is prepared by dissolving 31.4 g of a nonvolatile, nonelectrolyte solute in 85.0 g of water. The vapor pressure of the solution at 60^o C is 142 torr. What is the molar mass of the solute? ( Given: the vapor pressure of water at 60^o C

is 150 torr.)

 

Mole Fraction, X

 

7. A solution is made by mixing ethyl alcohol and water. If the mole fraction of water is .7, what is the mole fraction of ethyl alcohol?

 

8. A solution of benzene and toluene obey Raoult’s Law. The vapor pressures at 20^oC are: benzene = 76 torr    toluene = 21 torr

What is the mole fraction of benzene in a solution whose total vapor pressure is 50 torr at 20^oC?

 

 

Freezing Point Depression and Boiling Point Elevation

 

9. The freezing point of ethanol (C₂H₅OH) is –114.6^oC. The molal freezing point                      depression constant for ethanol is 2.00^oC/m. What is the freezing point (in C) of a    solution prepared by dissolving 50.0 g of glycerine (C₃H₈O₃), a nonelectrolyte, in          200 g of ethanol? ( Molar mass of C₃H₈O₃ is 92 g/mol )

 

10. 20.7 g of magnesium chloride were dissolved in 100g of water. What is the boiling point of this solution, assuming complete dissociation?

(K_b for water is 0.51 ^oC/m)

 

Henry’s Law: Solubility of gases in liquids

 

11. The partial pressure of CO₂ in air is approximately 4.0 X 10^-4 atm. The solubility of CO₂ in water under these conditions is 1.3 X 10^-5 M. What is CO₂ solubility at 1 atm?