This will be the last group problem for the term.  It is due at the
end of class on Wednesday, April 10.

This problem attempts to illustrate that everything you have
learned should  not be considered isolated facts or procedures
unconnected from each  other.  See how you can put several
different things together to solve an  "almost" real-life type of
problem.  

        Group Exercise Four    --   Analytical Sleuths

  You are a group of chemists who have set up a consulting
analytical  laboratory.  Your friend stops by with a sample of what
seems to be an  unusual material, at least it has slightly unusual
properties.  Immersed in  ice, it solidifies, left outside on a hot
day it forms a liquid, but immersed in a water bath with the water
near to the boiling point it turns into a vapor.  Your friend found
that it seems to be great for  removing paint from old furniture,
and he wants to know what it is.  Maybe  it is something he should
commercialize as a paint remover!  Or maybe it is toxic, and one
should be very careful with it.

  Now in a modern analytical laboratory there are some very
sophisticated  instruments (mass spectrometers, nuclear magnetic
resonance spectrometers,  ultraviolet and infrared
spectrophotometers) that would make identification very simple and
routine.  Since you can't afford this instrumetation, you  will try
to see what you can find out "the old fashioned way"  (i.e., 
before such instruments).  So you set each group member to a task.

Person one is assigned to determine elemental analysis by
combustion.

     You carefully weigh out 585.2 mg of the substance and burn it
     in a  combustion furnace.  You collect 1.390 g of CO2 and
     711.2 mg of water from  the combustion.  Additional tests tell
     you that the only elements present are carbon, hydrogen and
     oxygen.


Person two is assigned to get a molecular weight estimate by
measuring gas  density.

     You put some of the material in a Dumas-bulb and immerse the
     bulb in a boiling water bath until all of the material has
     turned to vapor.  Upon  cooling the bulb you find that 321 mg
     of material has condensed from the vapor in the bulb.  The
     bulb has a volume of 133 mL which you determined in another
     experiment by filling it with water and measuring the weight
     of  water it holds.  (See the figure in the book describing
     such an experiment,  figure 10.23, page 366).  The barometer
     on the wall tells you the  atmospheric pressure during the
     experiment just happened to be 760 mm.  From this data you can
     determine gas density and molecular weight.


Person three is assigned to measure some physical properties which
might  give a lead to identity.

     You measure the melting point of the substance to be 25.5
     degrees Celsius,  and the boiling point to be 82.2 degrees
     Celsius.  The density of the  material at room temperature is
     0.7856 g/mL.  The substance is soluble in  water, mixing with
     water in all proportions.   



     Everybody reports back with the results.  As a group now you
need to  answer the following questions.  (Your assignment is to
submit answers for  the questions, showing how you arrived at your
conclusions in each case).

1.  What is the empirical formula of the compound?

2.  What is the molecular formula of the compound?

3.  Can you draw a Lewis Dot structure corresponding to the
molecular  formula?  Can you draw more than one?  How many can you
draw?  (Compounds  with the same molecular formula and different
structures are called  structural isomers.  The question is how
many structural isomers are there for this substance.)

4.  Draw all the structures you can, indicating as much as you can
about the shape of each structure and whether or not it should be
polar.

5.  Look up these possible isomers in the Merck Index (found
several places in the Science Library as well as in your laboratory
stockroom).  You can find compounds listed by molecular formula in
the formula index, and from  there look up each substance by name. 
Which substance best fits the properties you have measured?  

6.  What do you tell your friend about the substance?