exp 14 reports - things to be aware of

[Zellmer, Robert]

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.

I'll start with, NO group work on reports.  They must be done individually.
This includes sharing of Excel files, graphs, etc.

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).  This was
sent out before the pre-lab but people still make these mistakes.

Exp 14 - Help for Exp 14<https://www.asc.ohio-state.edu/zellmer.1/chem1250/faq/exp14.txt>

Manipulating Logs and Sig. Figs.<https://www.asc.ohio-state.edu/zellmer.1/chem1220/faq/sig_fig_logs.txt>


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 compounds 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
compounds.  You should discuss if you got the correct order for the delta(Hv)
values for the cmpds 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 (although, as pointed out in a previous e-mail, it's not working so I sent
the normal b.p. data in the e-mail),

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

You don't need to formally source this data if it comes from the CRC (just mention
it's from the CRC).  If you use any other source you will need to have a more
extensive reference in your report.


You are required to discuss all of the data recorded and not just their own.  You're

suppose to be doing the calculations and graphing for all the data.  Then you are

discussing whether all the del(Hv) values are reasonable both in terms of their

size for del(Hv)s (based on the book, lab manual and lecture) and relative to each

other and the attractive forces present.  The points of interest state to discuss the

del(Hv)values and b.p. data.

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 and the
what the graph should look like (it should have 7 data points).

Using MS EXCEL for Chem Lab - exp. 14 example (Vapor Pressure exp. - old exp 13)<https://www.asc.ohio-state.edu/zellmer.1/chem1250/lab/exp14.pdf>

Exp 14 (dHv) - Example Graph for Compounds<https://www.asc.ohio-state.edu/zellmer.1/chem1250/lab/exp14_final_graphA.pdf>

Many of the graphs have 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 the normal
b.p. from the CRC manual (that's your best point).  Don't include your exp.
b.p. in the fit if it's way off from where it should be but still include it on the
graph.  This also applies to other "bad" data points.  They should be included
on the graph but not when doing the best-fit line.  This is a little tricker since to
leave a point out of the best-fit line you have to plot it as a separate data set.

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.  Matching colors
for a result has a human element to it but it could be considered an inherent
error depending on how it's done and what it's used for.

Make sure you look at the "Points to Consider" section in the manual (at the
end of the write-up for the experiment in the manual).  These give some idea of
things to consider and discuss.  It is not all inclusive and there may be other things
you need to address.   You should ALWAYS address whether your results are
correct or reasonable (since you don't always know if they're correct) and support
your analysis with data, your results and information from the book, lab manual
and lecture.  This should be in paragraph form, not in "question and answer" form.

You should also discuss if the b.p. data looks correct in relation to the
5 lnP-(1/T) data points and with respect to each other.  Is your exp b.p.
higher or lower than the normal b.p. from the CRC?  Which way should
it be based on the barometric pressure in the lab that was recorded.

You're not being graded on correctness for anything.  You're being graded
on your Discussion in terms of the things I mentioned in lecture and the
Points to Consider in the manual.

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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osu.edu/pipermail/cbc-chem1250/attachments/20220319/9f12d696/attachment-0001.html>