Collect enough 50 ml volumetric flasks to make up all of your knowns and the unknown.  You will not need to transfer them to any other containers.  You will sample them directly in the volumetrics as well.

 

Do not confuse the # of drops of citrate test (performed in a beaker and thrown away) with the actual preparation of the knowns and unknown.

Your calibration curve will only be as good as your technique.  Exact volume transfers are critical.

The only delay in this lab is that there is only one instrument you all must share.  So although it is critical you be careful in transferring volumes, if you want to get out on time it is also important you do the dilutions efficiently.  I suggest you build a flow chart to help you in the preparation of the knowns and unknown.  If you do the same step to all of the volumetrics, add the iron solution to all the volumetrics, then add the sodium citrate to all the volumetrics, then add the o-phenanthroline then dilute them all, then let them sit while you are standing in line for your turn at the UV-vis.

You will not need to perform the determination of the working wavelength at maximum absorbance.  The wonderful instrument you will be using will do this for you automatically.

All you need to do is record the numbers (absorbance and maximum wavelength) as they come up, or use the Maximum function in Excel on your table of data.

Perform only the second paragraph of the "Construction of a Calibration Curve and Analysis of the Unknown."  Excel will be of great use here.  After plotting the data right click on a data point, select insert trendline, select options and check the display equation on graph.  You can also check display insert R².  This will give you an idea of how good your calibration curve is.  1.000 is a perfect calibration curve.

Computer Procedure to follow for use with the Varian Cary 50 UV-vis Spectrophotometer

I.   Click on the Iron Icon on the vertical toolbar at the right
     Alternately click on the Iron Icon on the Desktop

a.  Click on the Setup tab on the left side of the Cary Display
b.  Click on OK

II.  Data Acquisition

a.  Insert the probe into the blank solution
b.  Gently shake the bubble out of the inspection region of the probe
c.  Click on the Baseline tab on the left side of the Cary Display
d.  Click on OK
e.  Wipe the probe clean with a Kimwipe
f.  Insert the probe into the first solution, shake gently to remove the air bubble
g.  Press the red button once on the probe
h.  Change the run name
i.   Click on OK, or press Enter

Do not remove the probe after step II.f. wait until the spectrophotmeter finishes scanning after step II.i.

j.   After the scan is finished remove the probe repeat steps II.e. thru II.j. until all solutions have been scanned.

III. Saving your Data and preparing the instrument for the next student

a.  Insert floppy into drive
b.  Select File at the top right of the Display
c.  Select Save Data As
d.  Select Drive A
e.  Select .csv File Type
f.  Name File
g. Click on Save
h. Select the  button
i.  Remove all check marks next to runs
j.  Click on OK

IV.  Next Student Repeat II - III