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Someone asked about where the axes should start for the graphs for
exp 1.<br>
<br>
Since the volumes (and masses) from the beaker are different than
those <br>
for the other glassware the graph would have a lot of empty space if
you <br>
include the origin. It is not necessary to include the origin on
the graph, <br>
for any of the graphs. In order to have essentially the same
scaling for your <br>
data points on all four graphs you can do one of the following: <br>
<br>
1) Have the graphs for the buret, pipet and grad. cyl. start at the
origin. <br>
Since these graphs start around 5 mL (and around 5 g) perhaps
and <br>
the first data point is about 5 units from the origin you can
start the graph <br>
for the beaker at around 15 mL and a mass of around 15 g or so.
For <br>
visual purposes this will give the graphs about the same
scaling on the axes. <br>
You do have the R<sup class="moz-txt-sup"><span
style="display:inline-block;width:0;height:0;overflow:hidden">^</span>2</sup>
values to look at but it's nice to be able to visualize <br>
how well the points fit the best-fit line. <br>
<br>
2) You could start each graph about 1 unit away from your first
data point. <br>
This means for the buret, pipet and grad. cyl. your graphs
would start <br>
at about 4 mL and 4 g. The one for the beaker would start at
about 19 mL <br>
and 19 g. Of course this all depends on exactly where the
first data point <br>
winds up. <br>
<br>
This latter method would allow the points to spread out more.
It wouldn't show <br>
the origin but you don't need it as the eqn. gives you the
y-intercept for your <br>
data. You need this intercept for your discussion. <br>
<br>
Whenever possible, it's a good idea to spread out your data as much
as possible <br>
and that may mean not starting at the origin (the 0,0 point). This
allows you to see <br>
if you perhaps have a "bad" data point, which perhaps shouldn't
actually be included <br>
in determining the best-fit line or in further calculations. <br>
<br>
3) A couple of people have asked whether the lines on the graphs
should be <br>
forced through the origins. We understand they should go through
the origin.<br>
However, you shouldn't force them through the origin (this can be
done in Excel<br>
and you will do it for one of the graphs later in the semester).
The fact the<br>
y-intercept doesn't go through the origin tells you something (one
type of error<br>
you may have can cause it to not pass through the origin like it
should).<br>
<br>
Dr. Zellmer
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