Hour Test 3 (pink)                          Name__________________________

CHM 1045 (Dr. Light)                     Soc.Sec.Num._____________________

April 12, 1996                   8:00 am         Recitation Section_______

PLEASE NOTE:    The final exam in this course is a
                block exam scheduled from 3-5 on
                Wednesday, April 24, in this room. 
                This is not the regularly scheduled
                time for an 8:00 MWF class.

This exam consists of 4 pages.  Make sure you have
one of each.  A fifth page has some data you may need
for some of the problems.  You may tear it off and
use it as scratch paper.

Be sure to read all instructions carefully.  If
anything is not clear, raise your hand and ask!

Points

(10)1.Draw two resonance structures for the each of the following
     molecules or ions, and indicate the formal charge on each atom in
     each structure:

     NO3-1                           SO2









(10)2.Give the molecular geometry of each of the following molecules,
     sketch a picture of the structure, use an arrow to indicate the
     polarity of each bond, and indicate whether the molecule as a whole
     would be polar or non-polar.

     BCl3                                  SO3






(5)3.Draw two resonance structures for SCN-1 (carbon is the central
     atom).  Circle the structure which you believe is the better of the
     two, and explain why.
(15)4.For each of the following compounds or ions, draw the best Lewis
     dot structure.  (If more than one resonance structure is "best",
     draw only one).  The central atom is underlined.  Give the electron
     pair geometry, the molecular geometry, and the hybridization about
     the central atom.


CompoundLewis Structure    electron pair   molecular       hybridization
                             geometry       geometry


XeF2









HNO3
(H attached to O)








CO32-









(7)5.There are two bonds between carbons and four C-H bonds in the
     compound ethylene (C2H4).  Identify each bond by its type
     (indicated by a Greek letter), and by the type of atomic orbital
     from each atom used in forming the bond.

     Bond       Bond type            C atomic orbital(s)   H atomic orbital

     C-C

     C-C

     C-H
(16)6.Calculate þH for the following reactions using the table of bond
     energies on the last page.

     (a)   C2H2     +     2 H2    ----->     C2H6














     (b)   N2        +        3H2       ---->      2NH3















(13)7.The following chemical reaction occurs when the Nickel-Cadmium
     battery is charged with electrical current.  Calculate the
     oxidation number of every atom in each reactant and product, and
     place the value in the blanks below the molecule.  Then indicate
     what atoms are being reduced and what atoms are being oxidized
     during the reaction.

     Cd(OH)2(s)  +   Ni(OH)2(s)      ---->  Cd(s)  +   2 H2O   +   NiO2(s)

     Cd ____         Ni ____               Cd ____   H ____     Ni ____

      O ____          O ____                         O ____      O ____

      H ____          H ____



Atom(s) oxidized in the reaction _______


Atom(s) reduced in the reaction ________


(8)8.A tank containing 4.5 moles of carbon monoxide gas and 1.2 moles of
     argon gas at 25 oC has a pressure of 7.8 atmospheres.  

     (a)   What are the partial pressures of carbon monoxide and argon?






     (b)   What would the total pressure in the tank be if an additional
           1.2 moles of argon were added to the tank, and the temperature
           were raised to 65 oC?







(8)9.What volume of oxygen, measured at 263 K and 1.00 atm pressure,
     must be used to completely burn 85.9 grams of C2H2.?  (Write the
     balanced equation for the reaction).
















(8)10.The empirical formula for cyclopentane is CH2.  If 5.2 g of
     cyclopentane has a volume of 2.00 L at 0.984 atm and 50.0oC,
     determine the molecular formula of cyclopropane.  (Show your work).










The following data may be of use to you in answering some of the
questions.  
R = 0.08206 L-atm/mol-K;  1 atmosphere = 760 torr = 101.325 kPa

Average Bond Energies (kJ/mol)

Single Bonds:

C-H   413       N-H  391        O-H  463        F-F   155
C-C   348       N-N  163        O-O  146        
C-N   293       N-O  201        O-F  190        Cl-F  253
C-O   358       N-F  272        O-Cl 203        Cl-Cl 242
C-F   485       N-Cl 200        O-I  234   
C-Cl  328       N-Br 243                        Br-F  237
C-Br  276                       S-H  339        Br-Cl 218
C-I   240       H-H  436        S-F  327        Br-Br 193
C-S   259       H-F  567        S-Cl 253        
                H-Cl 431        S-Br 218        I-Cl  208
Si-H  323       H-Br 366        S-S  266        I-Br  175
Si-Si 226       H-I  299                        I-I   151
Si-C  301
Si-O  368


Multiple Bonds:

C=C   614       N=N  418        O2   495
CðC   839       NðN  941
C=N   615                       S=O  523
CðN   891                       S=S  418
C=O   799
CðO  1072

Some Electronegativities

H  2.1      (2A)      (3A)       (4A)       (5A)      (6A)       (7A)
Li 1.0     Be 1.5    B  2.0     C  2.5     N  3.0    O  3.5     F  4.0
Na 0.9     Mg 1.2    Al 1.5     Si 1.8     P  2.1    S  2.5     Cl 3.0
K  0.8     Ca 1.0    Ga 1.6     Ge 1.8     As 2.0    Se 2.4     Br 2.8
           [Transition Metals 1.0-2.4]
Rb 0.8                                               Te 2.1     I  2.5
Cs 0.7                                               Po 2.0     At 2.2