Ocean Optics Overture - Manual (Page 45)

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Appendix A
Sample Experiments
Beer’s law analysis of KMnO
4
Equipment Needed:
 Ocean Optics CCD array spectrometer with lamp/cuvette holder
 Equipment for making aqueous solutions of different concentrations of KMnO
4
 Cuvettes
Objectives:
 To find the molar absorbance coefficient (ε) for potassium permanganate, potassium manganate
(VII), by plotting a calibration curve using the Beer Lambert Law.
 Using the calibration to find the concentration of an unknown sample.
Procedure:
1. Set the spectrometer in A (Absorbance) mode.
2. Click on the concentration wizard icon before setting dark and reference readings. The wizard will
help you set the correct integration time.
3. From a stock solution of known concentration in Moles per liter, make up a range of dilutions of at
least three precisely known concentrations. Use solutions which have absorbance numbers between
0.5 and 2.5.
4. Measure these solutions in A mode. Potassium permanganate has a very high molar absorbance
coefficient (ε), so solutions have to be very dilute. As Absorbance numbers reach 3, Beers Law starts
to become less reliable.
5. Find λ
max.
For potassium permanganate this should be about 534nm (you will see two peaks at 524
and 544nm).