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Chapter 10 & 11 Test Review

Questions 1-2

     A) Hydrogen Bonding           C) Ionic Bonding    E) London Dispersion Forces
     B) Hybridization                    D) Resonance

1.   (3 pts)  Is used to explain why iodine molecules are held together in the solid state.

2.   (3 pts)  Is used to explain why the boiling point of HF is greater than the boiling point of HBr.

3.   (3 pts)  Which of the following is true at the triple point of a pure substance?

     A)   The vapor pressure of the solid phase always equals the vapor pressure of the liquid phase.
     B)   The temperature is always 0.01 K lower than the normal melting point.
     C)   The liquid and gas phases of the substance always have the same density and are therefore
          indistinguishable.
     D)   The solid phase always melts if the pressure increases at constant temperature.
     E)   The liquid phase always vaporizes if the pressure increases at constant temperature.

4.   I.   Difference in temperature between freezing point of solvent and freezing point of solution
     II.  Molal freezing point depression constant, Kf, for solvent

     (3 pts)  In addition to the information above, which of the following gives the minimum data required to
     determine the molecular mass of a nonionic substance by the freezing point depression technique?

     A)   No further information is necessary.           C)   Mass of solute and mass of solvent.
     B)   Mass of solute.                                          D)   Mass of solute and volume of solvent
                                                                            E)   Mass of solute, mass of solvent, and vapor
                                                                                     pressure of solvent

5.   (4 pts)  A solution of toluene (molecular weight 92.1) in benzene (molecular weight 78.1) is prepared.  The mole
     fraction of toluene in the solution is 0.100.  What is the molality of the solution?

     A) 0.100 m     B) 0.703 m     C) 0.921 m     D) 1.28 m E) 1.42 m

Questions 6-8

6.   (3 pts)  The normal boiling point of the substance represented by the phase
     diagram above is

     A)  -15C     C) 140C
     B)  -10C     D) greater than 140C
                       E) not determinable from the diagram

7.   (3 pts)  The phase diagram above provides sufficient information for
     determining the

     A)   entropy change on vaporization               D)   latent heat of vaporization
     B)   conditions necessary for sublimation              E)   latent heat of fusion
     C)   deviations from ideal gas behavior of the gas phase

8.   (3 pts)  For the substance represented in the diagram, which of the phases is most dense and which is least dense
     at -15C?

          Most Dense          Least Dense
     A)   Solid               Gas
     B)   Solid               Liquid
     C)   Liquid              Solid
     D)   Liquid              Gas
     E)   The diagram gives no information about densities.

Free Response

9.   (6 pts)  The freezing points and electrical conductivities of three aqueous solutions are given below.
 
 

Solution Freezing Point Electrical conductivity
0.010 m sucrose -0.0186 C almost zero
0.010 m formic acid -0.0213 C low
0.010 m sodium fomate -0.0361 C high

     Explain the relationship between the freezing point and electrical conductivity for each of the solutions above.
     Account for the differences in the freezing points among the three solutions.

10.  Elemental analysis of an unknown pure substance indicates that the percent composition by mass is as follows:  Carbon, 49.02%; Hydrogen, 2.743%; Chlorine, 48.23%

     A solution that is prepared by dissolving 3.150 grams of the substance in 25.00 grams of benzene, C6H6, has a
     freezing point of 1.12 C.  (The normal freezing point of benzene is 5.50 C and the molal freezing-point
     depression constant, Kf, for benzene is 5.12 C/molal.)

     A)   (3 pts)  Determine the empirical formula of the unknown substance.
     B)   (5 pts)  Using the data gathered from the freezing point depression method, calculate the molare mass of the unknown substance.
     C)   (3 pts)  Calculate the mole fraction of benzene in the solution described above.
     D)   (3 pts)  The vapor pressure of pure benzene at 35øC is 150. millimeters of Hg.  Calculate the vapor
          pressure of benzene over the solution described above at 35øC.

11.  Discuss the following phenomena in terms of the chemical and
     physical properties of the substances involved and general principles
     of chemical and physical change.

     A)   (5 pts)  As the system shown on the right approaches
          equilibrium, what change occurs to the volume of water in the
          beaker with pure water?  What happens to the concentration
          of the sugar solution in the other beaker?  Explain why these
          changes occur.

     B)   (5 pts)  A bell jar connected to a vacuum pump is shown on the right.  As the
          air pressure under the bell jar decreases, what behavior of water in the beaker
          will be observed?  Explain why this occurs.

12.  Explain each of the following in terms of atomic and molecular structures and/or
     intermolecular forces.

     A)   (3 pts)  The normal boiling point of CCl4 is 77 C, whereas that of CBr4 is 190 C.

     B)   (3 pts)  NaI(s) is very soluble in water, whereas I2(s) has a solubility of only 0.03 gram per 100 grams of
          water.

Freebie:  (3 pts)  If you had your choice of any career what would it be?


Selected Answers

1.  E
2.  A
3.  A
4.  C
5.  E
6.  C
7.  B
8.  D
9.  Sucrose is a covalent compound and does not split up in water.  Therefore there are no ions presents so the electrical conductivity is low, and there are relatively few particles present so the freezing point depression is not as great.

Formic acid and sodium formate are both electrolytes, but judging from their electrical conductivity, the formic acid must not dissociate 100% (or at least not as much as the sodium formate).  Therefore, there are fewer particles present and it has less of a freezing point depression.

10.  A.  C3H2Cl
        B.  147.3 g/mol
        C.  .937
        D.  140.6 mmHg

11. A.   The pure water level will decrease because it has a higher vapor pressure when compared to the sugar solution.  Eventually, all of the water will be transferred into the sugar solution.

B.  As the pressure drops, the boiling point of the water will drop.  If the water is warm enough, it will begin to boil.

12.  A.  Both compounds are non polar, therefore both are affected only by London Dispersion Forces.  LDF's are stronger with bigger atoms, so CBr4 has larger LDF's, therefore it is harder to separate into a gas, therefore it has a higher boiling point.

    B.  NaI is ionic (and therefore polar) while I2 is non polar.  Water is a polar solvent.  Polar solvents tend to dissolve polar solutes, thus, NaI is very soluble while I2 is not.

A teacher!!