report and graphs exp 14

[robert zellmer]

I've discussed grading of exp 14 with TAs for many years and had the
opportunity to see lots of them.  There are always 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 few things I wanted to say.

Many graphs have often had problems with spacing. The graphs didn't
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. plotted but did not include them in the
best-fit line.  You need to make sure when you import your graph from
Excel into Word the margins you set in Excel (preferably set them to
"0" in or no more than 0.1 in if it won't let you set it to zero) don't 
change.
Also, use "Lanscape" mode in Excel and make sure it stays that way
when you import it into Word.

You should 7 data points for each compound, the 5 Ps values you calculate
using eqn 6 from the manual using the T-V data you got from the syringe
and the two b.p. values, the one you measured in lab and the normal b.p.
you look up.

By they way, for the normal b.p. in the CRC (or other on-line
sources) you are looking for n-hexane, n-heptane, n-octane, 1-propanol,
ethanol and methanol.  The "n" stands for "normal", meaning the isomer
with all the C atoms in a straight chain (no branching, which gives isomers
with the same number of C atoms).  The "1" in 1-propanol means the
-OH group in the alcohol is the the #1 carbon atom (the end one).  There
is an isomer with 3 C atoms with the -OH on the 2nd carbon (the middle
carbon) which is 2-propanol (common name of isopropyl alcohol, which
you know as the alcohol in a mixture of water and called rubbing alcohol).
See section 2.9 in the textbook for simple organic compounds and how
they're named.

There seemed to be some problems with sig. fig. in the tables (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. I pointed out in class some
of what you should be discussing for exp 14 in terms of the delta(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
sections for this exp.  This is also in the "Points to Consider" in the 
manual.

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 most 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 discussion of inherent
errors applies to all the reports.

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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