INSTRUMENTAL ANALYSIS OF PROCESS PRODUCTS
CHFEN 5503
UV/Vis Spectra and Analysis Lab
Fall, 2004
STUDENT OBJECTIVES
1.
2.
3.
4.
5.
This series of lab exercises is intended to give you:
More experience preparing "standard" volumetric solutions.
Experience preparing an analysis calibration curve.
An opportunity to use several different UV/Vis spectrophotometers.
An opportunity to determine the "correct" wavelength for a UV/Vis analysis.
An opportunity to "solve" an analytical problem using Beer's Law .
INTRODUCTION
Manganese can be determined as MnO4- using the techniques of UV/Vis spectrophotometry. The
usual approach is to prepare a set of analyte "standards" and then develop a calibration curve of
Absorbance vs. Concentration of analyte. This curve can then be used to determine an unknown
concentration of analyte based on its Absorbance. Calibration curves are developed for a specific
wavelength, which should also be determined experimentally.
TASKS (Sept 20,22)
1.
Prepare a standard solution of 0.1000 g/L KMnO4. Using this solution you are to prepare five
solutions of lesser concentration. Dilute to 0.0100 g/L as your weakest solution. You will need
at least 25 ml of each solution. This may be done in the same teams (three or 4 persons) we used
for the AA lab. Your previously calibrated glassware should be used.
2.
Using the 0.1000 g/L (or the next most concentrated) standard, run a spectral scan of absorbance
vs. wavelength in the visible region on the GBC Cintra-10 spectrometer. You can save and print
out an absorbace spectrum. Note: the Cintra runs best under Windows-95, so keep the other
software and open windows to a minimum on that old computer.
3.
Prepare a calibration curve (again as a team) of Absorbance vs Concentration for the KMnO4 at
the appropriate wavelength as determined in #2. Use at least the Spectronic 21 single beam, the
Cintra-10 and the Perkin Elmer (P.E.) double beam instruments. The calibration curve on the
Cintra-10 should have at least seven experimental points including 0.0 (i.e. pure solvent). Get as
many points as possible for the older Spectronic 21 and P.E. machines.
4.
When you have completed 1-3 above as a team (possibly during the first lab), you will be given
an individual (numbered) unknown solution of KMnO4. Your individual assignment is to
determine the concentration of Manganese in the unknown using both double beam and single
beam techniques.
UV/Vis Spectra and Analysis Lab
Page 2
REPORT (Due Mon Oct 4)
Your MEMO report for this set of lab activities should be brief but include the following:
1.
A copy of the wavelength scan from the Cintra-10 spectrometer (photocopies are OK). On the
scan you should clearly mark the appropriate wavelength(s) for developing a calibration curve.
2.
A copy of a wavelength scan for KMnO4 taken from the literature (not our text), and an
explanation of any significant differences between your lab scan and the literature one.
3.
KMnO4 calibration curves (plots) based on your experimental data using the single beam and the
double beam instruments. Each plot must be accompanied by a table of experimental values.
4.
The concentration of manganese (and permanganate) in grams/L in the unknown liquid assigned
to you and an explanation of how you determined it based on single and double beam
instrumental techniques.
5
A comparison of the single beam and double beam instrumental techniques and any discussion
appropriate regarding precision of results.
6.
Any other comparisons of instruments, methods, etc. as appropriate.