Exp 16 sig fig.

[Zellmer, Robert]

I often receive questions about the sig. fig. in exp 16 when it comes
to averaging the f.p. determinations to get the average f.p. which you
report on your data sheet and in the on-line pre-lab and data-entry post-lab.
I mentioned this in a previous e-mail about exp 16 but got a question
about it.

In class we discussed how you can average several numbers and gain sig.
fig.  That is correct.  That's why we take lots of measurements and average
them.  However, in practice when dealing with experimental data including
an additional sig. fig. in an average or from a graph really can't safely be
done with only 2 or 3 numbers.

Think about exp 1 in which you were plotting your data.  The purpose of
a best-fit line is to average out the random error in your data.  If you had
only 2 pts the line would go through both points and wouldn't have show
any effect of random errors.  Adding one more point wouldn't make it much
better. Having at least 4 data points would make it more plausible to gain a
sig. fig. (both when averaging and from a graph).  Even this may not be safe
as it actually depends on the magnitude of the numbers.  However, I stated
for the purposes of this class if you have 4 or more data points you can
gain a s.f.

I discussed this back in week 1 when discussing s.f. in class and for exp 1.

When you add up your determinations for the f.p. for each trial adding only
2-3 values isn't enough to give confidence in reporting an extra s.f.  If you
did five determinations and averaged those I would say you could maybe
report 1 extra s.f., but that depends on the actual data.  This will certainly
not be the case for the pre-lab since it gives the f.p. of the cyclohexane and
in each trial (it's already "averaged" some unseen determinations).  As
directed in previous e-mails, report ONE decimal place for your average
f.p. in all parts.

Dr. Zellmer
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osu.edu/pipermail/cbc-chem1250/attachments/20220328/ce0d0365/attachment-0001.html>