CHM 1046                           TEST  2          Name _______________________
June 21, 1996                                   (please print)                  
                                                   Soc.Sec.Num. ________________

      This exam consists of four pages.  Make sure you
have one of each.  Print your name at the top of each
page now.  A fifth page contains a periodic chart. 
You may tear this sheet off and use it for scratch
paper.  Show your work on calculations, and give
answers to the correct number of significant figures. 
You may use atomic weight values rounded to the
nearest 0.1 amu.

      If anything confuses you or is not clear, raise
your hand and ask!

Points

1.    Question 1 concerns the following chemical reaction:

           N2O4(g)  þ   2 NO2(g)

      A 1.00 L container is filled with 0.0400 moles of N2O4 with no NO2
      present.  The reaction is allowed to come to equilibrium at 25oC,
      and the concentration of N2O4 is measured to be 0.0055 mol/L.

(6)   (a)  Calculate Kc for this reaction.












(3)   (b)  Calculate Kp for the same reaction (R=0.08205 L-atm/mol-K).







(3)   (c)  The volume in the container is compressed to 0.50 L.  Will the
           equilibrium shift toward forming more NO2 or more N2O4?




(3)   (d)  The reaction is endothermic, þH = + 56 kJ/mol.  Will
           increasing the temperature shift the equilibrium toward
           forming more NO2 or more N2O4?





(9)2. Consider the following reaction at equilibrium in a metal
      container:

           2 SO2(g)  +   O2(g)   þ     2 SO3(g)

      Tell whether the amount of SO3 present at equilibrium will
      increase, decrease, or remain the same with the following changes
      in the system:

      (a)  Additional oxygen is added to the container.


      (b)  The pressure is increased by decreasing the volume of the
           container.


      (c)  The pressure is increased by adding nitrogen to the container.



(14)3.The equilibrium constant for the reaction

           2 NO(g) þ  N2(g)  +  O2(g)

      is Kc = 2.4 x 103 at 2000oC.

      A 1.00 L chamber is filled with 0.065 moles of NO  with no N2 or O2
      present.  The chamber is heated to 2000oC and the reaction allowed
      to come to equilibrium.  What will be the concentration of N2 and
      O2 in the flask at equilibrium?
      
      
      















(6)4. For each of the following [H+] values, circle the pH value that is
      written to the correct number of significant figures.

        [H+]                          pH

      2.25 x 10-5     5     4.6     4.64     4.648    4.6478

      4.7  x 10-11    10   10.3    10.33    10.328   10.3279

      0.009           2     2.0     2.05     2.046    2.0458


(12)5.Calculate the [OH-], pOH, and pH of the following solutions:

      (a)  0.036 M NaOH






      (b)  0.025 M Ca(OH)2






      (c)  10-8 M KOH







(12)6.You find a bottle in the laboratory labeled "0.25 M ammonia".  Kb
      for ammonia is 1.8 x 10-5.  Calculate the pH of the solution. 
      (Note, you should write an equation expressing the equilibrium
      involved, write an expression for Kb in terms of the concentrations
      of the relevant components.  You will probably find it easier to
      solve for [OH-] first, and then convert to pH)
      
      
      
      
      
      
      
      
      
      
      
      
      
      
      
      
      
      
(12)7.A 0.2 M solution of ascorbic acid (vitamin C) has a pH of 2.40. 
      Calculate Ka for ascorbic acid.

















(8)8. Predict whether solutions of the following salts should be acidic,
      basic, or neutral.

      KBr

      lithium acetate

      dimethylammonium chloride

      NaClO


(6)9. In each of the following pairs of compounds, circle the weaker
      base.

      (a)  ClO3-   and   ClO2-

      (b)  HS-     and   HSe-

      (c)  OH-     and   NH3


(6)10.Lactic acid, the substance produced when muscles are worked
      anaerobically, is listed in a biochemistry textbook as having a pKa
      of 3.85.  Calculate Ka and Kb for lactic acid.