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The next exp is exp 3 (DRL). This is a modified version of an older<br>
exp which used 4 solutions with different concentrations which are<br>
now used. Dr. Moga has sent an e-mail about this via Carmen. Some<br>
of what's below may simply be a reiteration. <br>
<br>
This is a reminder to look at my help files for exp 3 (DRL). I have
both pre-lab <br>
and post-lab hints and help. I've tried to change things from my
old files to<br>
coordinate with the new modified exp. Let me know if you see
something<br>
which doesn't seem to match up with the new exp.<br>
<br>
There is both a pre-lab and post-lab on Carmen for exp 3.<br>
<br>
Please look at the pre-lab help before going to lab. You are
making three<br>
solutions by mixing Cr^3+ and EDTA- resulting in different conc. of
Cr^3+<br>
in each solution. You should have a table like Table 3.1 of the
manual in<br>
your notebook. You may not necessarily have the exact values given
in<br>
Table 3.1 for the volumes of the Cr(NO3)3 since you are using a
buret<br>
(you shouldn't even try to get those exact volumes since it can take
longer<br>
than necessary). You will record the actual volumes of the Cr(NO3)2<br>
solution you measure. <br>
<br>
A <b>10</b>-mL pipet is being used for the EDTA. You use it to
measure out a<br>
total of 20-mL of EDTA in each test tube.<br>
<br>
Each partner should have 3 LARGE test tubes (the ones marked as
75-mL<br>
with the large openings), marked 1-3. One partner measures out the
Cr^3+<br>
and the other measures out the EDTA.<br>
<br>
For the data collection of the absorbances of the three solutions,
you want a<br>
<b>SINGLE</b> table for the time and absorbance data for the four
solutions on a<br>
single page. You should have a table with 8 columns, in groups of
two for<br>
each solution, marked something like <br>
<br>
<table cellspacing="2" cellpadding="2" height="97" width="474"
border="1">
<tbody>
<tr>
<td valign="top">soln 1</td>
<td valign="top"><br>
</td>
<td valign="top">soln 2<br>
</td>
<td valign="top"><br>
</td>
<td valign="top">soln 3</td>
<td valign="top"><br>
</td>
</tr>
<tr>
<td valign="top">time (min)<br>
</td>
<td valign="top">Abs<br>
</td>
<td valign="top">time (min)</td>
<td valign="top">Abs</td>
<td valign="top">time (min)</td>
<td valign="top">Abs<br>
</td>
</tr>
<tr>
<td valign="top"><br>
</td>
<td valign="top"><br>
</td>
<td valign="top"><br>
</td>
<td valign="top"><br>
</td>
<td valign="top"><br>
</td>
<td valign="top"><br>
</td>
</tr>
</tbody>
</table>
<br>
This table should be big enough to record at least 15 lines of time
and Abs data.<br>
This info is in the manual in the Data to Collect section.<br>
<br>
You will also need to have space for recording the initial conc. of
the Cr^3+ in<br>
each soln., the conc. of the CrEDTA- product and the absorbance
values for the<br>
product in the boiled solutions.<br>
<br>
The following links should be helpful. I spent several hours
updating the old<br>
link to hopefully coincide with the new modified experiment.<br>
<br>
<a
href="http://chemistry.osu.edu/%7Erzellmer/chem1220/lab/lab_1220.htm"><b>Laboratory</b></a>
(see stuff dealing with exp 3)<br>
<br>
<a
href="http://chemistry.osu.edu/%7Erzellmer/chem1220/faq/exp3_DRL_help.txt"><b>Pre
and Post-lab Help for Exp 3 - (Answers to Students' Questions)</b></a><br>
<br>
<a
href="http://chemistry.osu.edu/%7Erzellmer/chem1220/lab/exp3_DRL_tips.pdf"><b>Handout
for Exp. 3 - Report Tips (Data Analysis)</b></a><br>
<br>
I HIGHLY suggest you use Excel (or something similar) to do the data
tables,<br>
calculations and graphs. I have NOT updated this site so it still
refers to 4<br>
solutions and shows this in the pictures and graphs.<br>
<br>
<a
href="http://chemistry.osu.edu/%7Erzellmer/chem1220/lab/exp17/exp17.htm"><b>Exp
3 - Using MS Excel</b></a><br>
<br>
There are a lot of calculations (a minimum of 180). If you make a
mistake you<br>
often don't realize it until you do graph 2 (1st-order plot). Then
you have to go<br>
back and redo almost all the calculations. Using Excel makes the
whole process<br>
easier, even if you don't make a mistake.<br>
<br>
More to follow...<br>
<br>
Dr. Zellmer
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