graphs in exp 14 reports

[robert zellmer]

I've discussed grading of exp 14 with TAs and had to opportunity to see
some of them.  There were some good reports but many had problems.
Of course the TAs may have shown me mostly those with problems to
figure out how to grade them.

In any case, there's a couple of things I wanted to say.

Many of the graphs had problems with spacing. The graphs did not take up
the whole page or the points didn't occupy most of the space on the page.
Some didn't have the boiling points included on the graphs or labeled.  Some
did have the b.p. but did not include them in the best-fit line.

There seemed to be some problems with sig. fig. in the table (especially
for Ps or lnPs) and s.f. on the axes of the graphs.

Also, many people didn't include what should have been included in the
Results/Discussion and Conclusion sections (just labeled Conclusion section
on rubric). I pointed out in class some of what you should be discussing for
exp 14 in terms of the Hv values for the knowns and attractive forces.  
I went
over this while discussing the Clausius-Clapeyron Eqn and the graph in the
notes.  I also explained in some detail what you should be doing with the
graphs, significant figures (especially for Ps and lnPs) and what should
be in the Results/Discussion/Conclusion section for this exp.

Do a "scatter" graph with points only (no connecting lines). Then do a
trend line.  You don't want to play "connect the dots" with the data.

Many people did not include inherent errors.  I believe I explained in
lecture at some point what this means.  These are errors due to the way
the experiment is being carried out which you have minimal to no control
over.  For instance, for exp 6 in Chem 1210 (coffee-cup calorimeter) the
most obvious inherent error would be it was a simple coffee cup.  While
it really didn't to a terrible job, it wasn't a "perfect" calorimeter 
and heat
could get in or out, especially via the lid.  Another one would be the 
fact the
thermometer could only be read to the first decimal place. For post parts
that limited the delta T to 2 (maybe 3) s.f.  That ultimately limited 
the sig. figs.
in the heat capacity for the calorimeter and the enthalpies for the 
reactions.
Not swirling the solution in the cup to equilibrate the temperature 
throughout
the solution would not be an inherent error.  That's your mistake. Splashing
water out of the cup when you dropped in the copper cylinders is not an
inherent error (again this is your error).  This doesn't mean "human" error
can not be considered inherent error.  It depends on the experiment.

This is not all inclusive of the problems I saw but some of the main
ones (many of the same errors repeated by multiple students).

Dr. Zellmer
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