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<big><font size="2"><big>In Chem 1210 you may have discussed how you
can average several<br>
numbers and gain sig. fig. That is correct according to our
sig. fig.<br>
rules. That's why we take lots of measurements and average
them.<br>
However, in practice when dealing with experimental data
including<br>
an additional sig. fig. in an average or from a graph really
can't safely<br>
be done when averaging or graphing only 2 or 3 numbers.<br>
<br>
Think about an experiment in which you would be plotting your
data.<br>
The purpose of a best-fit line is to average out the random
error in your<br>
data. If you had only 2 pts the line would go through both
points and<br>
wouldn't have averaged out random errors. Adding one more
point<br>
wouldn't make it much better. Having at least 4 data points
would make<br>
it more plausible to gain a sig. fig. (both when averaging and
from a graph),<br>
but even that can be tenuous depending on the size of the
numbers.<br>
<br>
When you add up your determinations for the f.p. for each
trial adding only<br>
three values isn't enough to give confidence in reporting an
extra s.f. If you<br>
did five determinations and averaged those I would say you
could maybe<br>
report 1 extra s.f. in the f.p. This will certainly not be
the case for the pre-lab.<br>
Even for the post-lab you are averaging 3 determinations so
don't report an<br>
extra s.f.<br>
<br>
Dr. Zellmer</big></font></big>
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