Exp 3 (DRL) help - both pre and post lab, using Excel

[robert zellmer]

The next exp is exp 3 (DRL).  This is a modified version of an older
exp which used 4 solutions with different concentrations which are
now used.  Dr. Moga has sent an e-mail about this via Carmen.  Some
of what's below may simply be a reiteration.

This is a reminder to look at my help files for exp 3 (DRL).  I have 
both pre-lab
and post-lab hints and help.  I've tried to change things from my old 
files to
coordinate with the new modified exp.  Let me know if you see something
which doesn't seem to match up with the new exp.

There is both a pre-lab and post-lab on Carmen for exp 3.

Please look at the pre-lab help before going  to lab.  You are making three
solutions by mixing Cr^3+ and EDTA- resulting in different conc. of Cr^3+
in each solution.  You should have a table like Table 3.1 of the manual in
your notebook.  You may not necessarily have the exact values given in
Table 3.1 for the volumes of the Cr(NO3)3 since you are using a buret
(you shouldn't even try to get those exact volumes since it can take longer
than necessary).  You will record the actual volumes of the Cr(NO3)2
solution you measure.

A *10*-mL pipet is being used for the EDTA.  You use it to measure out a
total of 20-mL of EDTA in each test tube.

Each partner should have 3 LARGE test tubes (the ones marked as 75-mL
with the large openings), marked 1-3.  One partner measures out the Cr^3+
and the other measures out the EDTA.

For the data collection of the absorbances of the three solutions, you 
want a
*SINGLE* table for the time and absorbance data for the four solutions on a
single page.  You should have a table with 8 columns, in groups of two for
each solution, marked something like

soln 1 	
	soln 2
	
	soln 3 	
time (min)
	Abs
	time (min) 	Abs 	time (min) 	Abs

	
	
	
	
	


This table should be big enough to record at least 15 lines of time and 
Abs data.
This info is in the manual in the Data to Collect section.

You will also need to have space for recording the initial conc. of the 
Cr^3+ in
each soln., the conc. of the CrEDTA- product and the absorbance values 
for the
product in the boiled solutions.

The following links should be helpful.  I spent several hours updating 
the old
link to hopefully coincide with the new modified experiment.

*Laboratory* 
<http://chemistry.osu.edu/%7Erzellmer/chem1220/lab/lab_1220.htm> (see 
stuff dealing with exp 3)

*Pre and Post-lab Help for Exp 3 - (Answers to Students' Questions)* 
<http://chemistry.osu.edu/%7Erzellmer/chem1220/faq/exp3_DRL_help.txt>

*Handout for Exp. 3 - Report Tips (Data Analysis)* 
<http://chemistry.osu.edu/%7Erzellmer/chem1220/lab/exp3_DRL_tips.pdf>

I HIGHLY suggest you use Excel (or something similar) to do the data tables,
calculations and graphs.  I have NOT updated this site so it still 
refers to 4
solutions and shows this in the pictures and graphs.

*Exp 3 - Using MS Excel* 
<http://chemistry.osu.edu/%7Erzellmer/chem1220/lab/exp17/exp17.htm>

There are a lot of calculations (a minimum of 180).  If you make a 
mistake you
often don't realize it until you do graph 2 (1st-order plot).  Then you 
have to go
back and redo almost all the calculations.  Using Excel makes the whole 
process
easier, even if you don't make a mistake.

More to follow...

Dr. Zellmer
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