Chem 2/5 Labs FS2001
Colligative Properties Post-Laboratory Questions

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  1. Raoult’s law states that the vapor pressure of the solvent in a solution, P1, is equal to the mole fraction of the solute in solution, X1, to the vapor pressure of pure solvent, P°1, as follows:

P1 = X1 P°1.

In the ideal case, this leads to a linear plot of the vapor pressure of the solvent, P1, versus the mole fraction of solvent, X1. However nonideal solutions deviate from linearity either negatively or positively as shown below:

 
  1. What would cause positive deviations from Raoult’s law?

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  2. What would cause negative deviations from Raoult’s law?

 

 

 

 

 

 

 

  1. Lanthanum (III) chloride (LaCl3), dissociates into ions as it dissolves in water:

    2. LaCl3 (s) --> La3+ (aq) + 3 Cl- (aq)

    Suppose 0.2453 grams of LaCl3 is dissolved in 100.0 grams of H2O. What is the boiling point of the solution at atmospheric pressure?

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

  2. When 6.30 grams of a nonvolatile hydrocarbon of unknown molar mass is dissolved in 150.0 grams of benzene, the boiling point of the solution is 80.696 °C. The boiling point of pure benzene is 80.099 °C. What is the molar mass of the hydrocarbon?

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  3. When 5.50 grams of biphenyl (C12H10) is dissolved in 100.0 grams of benzene, the boiling point of the solution exceeds the boiling point of pure benzene by 0.903 °C. What is Kb for benzene?