graphs in exp 14 reports

[Robert Zellmer]

The following is based on reports I've seen in the past for exp 14.
There are always some good reports but many people have problems.

There seemed to be some problems with sig. fig. in the table (especially
for Ps or ln(Ps)) and s.f. on the axes of the graphs.  See my on-line 
discussion
of s.f. for Ps and for logarithms (and appendix A of the textbook).

*Exp 14 - Help for Exp 14* 
<http://chemistry.osu.edu/%7Erzellmer/chem1220/faq/exp14.txt>

*Manipulating Logs and Sig. Figs.* 
<http://chemistry.osu.edu/%7Erzellmer/chem1220/faq/sig_fig_logs.txt>


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 ln(Ps)) and what should be in the Results/Discussion and 
Conclusion
sections for this exp.

In the Discussion section you should include the delta(Hv) values for 
the knowns.
You should discuss if you got the correct order for the delta(Hv) values 
for the
compounds and how you know based on the attractive forces present between
the molecules and what those AF forces are.  If you get the wrong order
you should explain what the order should be and how you know based on the
AF present.  You can use the b.p. from the CRC to back up your discussion.
However, the b.p. data should not be used as your primary line of reasoning.
You can find the on-line CRC link on Carmen ("Content" tab) or my web
pages,

*CRC Handbook of Chemistry and Physics* 
<http://hbcpnetbase.com.proxy.lib.ohio-state.edu>


For the graph, do a "scatter" graph with points only (no connecting 
lines).  Then
do a trend line (linear).  You don't want to play "connect the dots" 
with the data.
Print the equation for each line (and R^2).  See my example for exp 14.

*Using MS EXCEL for Chem Lab - exp. 14 example (Vapor Pressure exp. - 
old exp 13)* <http://chemistry.osu.edu/%7Erzellmer/chem1220/lab/exp14.pdf>

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.  The
boiling points should be included in the data set and labeled on the graph.
Some did have the b.p. but did not include them in the best-fit line and 
did not
label them.  The boiling points are your best data points, particularly 
for the
known compounds since you are looking these up in the CRC manual.

Many people did not include inherent errors.  I believe I explained in 
lecture
at some point and my web page and e-mails 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 (coffee-cup calorimeter) the most
obvious inherent error would be, it was a simple coffee cup. While it really
didn't do 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.

Make sure you look at the "Points to Consider" section in the manual (at the
end of the write-up for 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 over
multiple years).

Dr. Zellmer
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