CHM 1046                           TEST  2          Name _______________________
October 18, 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, be sure to
include units in the calculations, and give answers
to the correct number of significant figures.  

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

Points

1.    Question 1 concerns the following chemical
      reaction:

           2 NH3   þ   N2   +   3 H2

      A 1.00 L container is filled with 0.400 moles of NH3 with no N2 or
      H2 present.  The reaction is allowed to come to equilibrium at
      472oC, and the concentration of N2 is measured to be 0.174 M.

(3)   (a)  Write the equilibrium expression for Kc.






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













(3)   (c)  The volume in the container is compressed to 0.50 L.  Will the
           equilibrium shift toward forming more N2 or  less N2?





(3)   (d)  The reaction is endothermic, delta H = + 92.38 kJ/mol.  Will
           increasing the temperature shift the equilibrium toward
           forming more N2 or less N2?



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

           2 CO (g)   +   O2(g)  þ    2 CO2(g)

      Tell whether the amount of CO2 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.



(15)3.The equilibrium constant for the reaction

           N2(g)  +  O2(g)  þ    2 NO (g)

      is Kc = 4.17 x 10-4 at 2000oC.

      A 1.00 L chamber is filled with 0.750 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

      9.1 x 10-5      4     4.0     4.04     4.041    4.0410

      4.70  x 10-11   10   10.3    10.33    10.328   10.3279

      0.007           2     2.2     2.15     2.155    2.1549



(8)5. In each of the following pairs of compounds, circle the weaker
      base.

      (a)  HSO3-   and   HSO4-

      (b)  F-      and   Cl-

      (c)  NH3     and   acetate ion

      (d)  OH-     and   HCO3-



(16)6.Calculate the [OH-], pOH, and pH of the following solutions:

      (a)  0.045 M KOH






      (b)  0.033 M Ba(OH)2






      (c)  10-8 M NaOH






      (d)  1.5 x 10-3 M HCl






(12)7.You find a bottle in the laboratory labeled "0.15 M pyridine". 
      Pyridine is a base with a Kb of 1.7 x 10-9.  Calculate the pH of
      the solution.  (You will probably find it easier to solve for [OH-]
      first, and then convert to pH)
















(10)8.Predict whether solutions of the following salts should be acidic,
      basic, or neutral.

      NaHCO3

      lithium formate

      ammonium iodide

      KBrO

      FeCl3


(9)9.Citric acid, an important intermediate in metabolism, is a
      triprotic acid listed in biochemistry textbooks as having pK's of
      3.13, 4.77, and 6.40.  Calculate the three Ka's for the three
      protons of citric acid.