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 (just labeled Conclusion section
on rubric). 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.
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.  You don't want to play "connect the dots" with the 
data.  Include
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've explained what these are
on my web page and some of the links I've sent. 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 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: <https://lists.osu.edu/mailman/private/cbc-chem1220/attachments/20150118/574d43f7/attachment.html>