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I always get a number of questions about Exp 16 and what to do for
the<br>
average MW if two of the trials are close and one isn't. Should you
include<br>
all three in the average in this case?<br>
<br>
Sometimes the answer is pretty obvious. If you have 150, 155, 220
hopefully<br>
you realize something may be wrong with the 220 since the other two
are<br>
so close. I suppose it could happen the 220 is the correct one and
somehow<br>
one got two wrong results out of three which were close but this
would be<br>
unusual (at least we hope). In this case the 220 would not be
included in<br>
calculating the average MW. In the discussion section one would
list all three<br>
MW and the average and explain the one MW was left out of the
calculation<br>
of the average. <br>
<br>
Sometimes what to do isn't quite so obvious. What if the results
were 150,<br>
160 and 190. Should the 190 be included. If you do the average
rounds to<br>
170 (2 s.f.). If you don't it rounds to 160 (2 s.f.). Which is
correct? I would<br>
probably go with the 160. However, to get a correct answer one
needs to<br>
do an error analysis and see if the 190 should be included in
getting the<br>
average.<br>
<br>
I have a link under the "Laboratory" link. This is a copy of
Appendix F<br>
in the current lab manual. Here's the direct link,<br>
<br>
<a
href="http://chemistry.osu.edu/%7Erzellmer/chem1220/lab/App_D_122_lab_manual.pdf"><b>Treatment
of Numerical Data (Error Analysis, sig. fig., graphing)</b></a><br>
<br>
The discussion about how to determine if a data point can be ignored
in<br>
such cases is discussed in Section III, "Reporting Results" on pages
F-3<br>
through F-5.<br>
<br>
By the way, I can't tell you if leaving in one "bad" experimental
result will lead<br>
to a better or worse average. That depends on your results and how
careful<br>
you were being. Besides, I don't know what any of the actual true
results are<br>
for any of the experiments. Even if I did, I couldn't tell you
under penalty of<br>
death (well maybe not that severe a punishment but close).<br>
<br>
For the post-lab data entry you have to enter your data as is. Then
on the<br>
report sheet for the average list what you get from just the two
"good"<br>
MW values. Discuss this in the Discussion section and leave a
comment<br>
when you submit it asking the TA to grade the average MW based on
your<br>
report sheet.<br>
<br>
Dr. Zellmer
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