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I'm getting a lot of questions about exp 17, the calculations,<br>
the graphs, etc.<br>
<br>
Just a reminder to look at my files for instructions about what to <br>
do for exp 17, especially the graphs. You do different things if <br>
you are graphing by hand versus doing things in Excel. <br>
<br>
If using Excel you need to put the data for ALL 4 solns on <br>
the zero, first and second-order graphs. <br>
<br>
For the zero-order graph you should use an exponential or <br>
parabola fit to get a smooth curve. <br>
<br>
For the first and second-order graphs (graphs 3 and 4) you <br>
should use LINEAR fits for both graphs. Do NOT go back <br>
and fit either to something other than linear. You are looking <br>
to see which graph has lines that are more closely parallel. <br>
Generally speaking if you have good data you will see a distinct <br>
difference between the two graphs. Also, which ever one produces <br>
lines that are more closely parallel those lines will fit the points
better. <br>
<br>
Sometimes one of the lines on the graphs will cross the others. <br>
In that case the data for that soln is probably "bad" and you will <br>
notice the slope isn't as similar to the other three slopes. <br>
In this case you should report all four rate constants on the <br>
report sheet but might consider not including the "bad" rate <br>
constant in your average. It depends on how different it is <br>
from the other three. <br>
<br>
Don't forget to discuss how you chose the order based on <br>
graphs 3 and 4. You should also discuss WHY the lines should<br>
be parallel.<br>
<br>
If the slope of your Beer's Law plot is a lot lower than 200 <br>
or a lot greater than 250 you may have done something wrong. <br>
Also, if your zero-order graph shows all 4 lines pretty much <br>
emanating from the same point (initial conc) or crossing early <br>
on (at early times) you've likely made a mistake with your <br>
initial concentrations. The initial Cr^3+ in each test tube after<br>
mixing is NOT what it was on the reagent bottle in lab.<br>
<br>
Make sure each graph take up the whole page and your data <br>
points occupy pretty much the whole graph area. Look at <br>
my Excel example for graph 2 (zero-order graph). <br>
<br>
Remember, I sent out a couple of other e-mails about exp 17<br>
already and I have the following help files,<br>
<br>
<a
href="http://chemistry.osu.edu/%7Erzellmer/chem1250/lab/lab_1250.htm"><b>Laboratory</b></a>
(see stuff dealing with exp 17)<br>
<br>
<a
href="http://chemistry.osu.edu/%7Erzellmer/chem1250/faq/exp17_help.txt"><b>Pre
and Post-lab Help for Exp 17 - (Answers to Students' Questions)</b></a><br>
<br>
<a
href="http://chemistry.osu.edu/%7Erzellmer/chem1250/lab/exp17_tips.pdf"><b>Handout
for Exp. 17 - Report Tips (Data Analysis)</b></a><br>
<br>
<a
href="http://chemistry.osu.edu/%7Erzellmer/chem1250/lab/exp17/exp17.htm"><b>Exp
17 - Using MS Excel</b></a><br>
<br>
<br>
Dr. Zellmer
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