graphs in exp 14

[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