7/28/2019 The Objective of This Particular Experiment Was to Investigate the Concentration of a Potassium Permanganate S

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Determining concentrations of potassium permanganate within solutions using the Beer-Lambert

Law.

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The objective of this particular experiment was to investigate the concentration of a potassium

permanganate solution using its light absorbance values measured using a spectrophotometer. The

Beer-Lambert law used in previous studies has shown there is a correlation between light

absorbance and concentration. Using the Beer-Lambert law and a spectrophotometer the

concentrations of solutions A,B, C and D were determined.

To begin the experiment a 3ml UV plastic cuvette containing a volume of distilled water was placed

into a Cecil CE2041 spectrophotometer and used to record and store a baseline. Next, a spectrum

was run of a solution of 0.25mM of potassium permanganate (diluted with dH20) using the Cecil

CE2041 spectrophotometer from the wavelengths 450-600nm. These results were then analysed.

They clearly displayed two peaks; this indicated the two wavelengths at which light was absorbed at

its strongest. The following step involved preparing nine 4ml, 0.4mM potassium permanganate

solutions in individual test tubes. The nine tubes all contained a different amount of potassium

permanganate, they are as follows; 0.0ml,0.5ml,1.0ml,1.5ml,2.0ml,2.5,3.0ml,3.5ml and 4.0ml; all of

these solutions were diluted by using dH20. Using the test tube containing the 4ml of dH20 the

spectrophotometer was zeroed. The spectrophotometer was then used to read the absorbance of

the remaining 8 solutions at the wavelength of the first peak. This process was then copied using a

fresh cuvette for the wavelength of the second peak. Finally, after zeroing the spectrophotometer

again using dH20, the spectrophotometer was set to the wavelength that registered the biggest

extinction coefficient and using that value the absorbance of A,B,C and D were measured.

Results

The wavelengths at which light was absorbed strongest were recorded as 525nm and 543nm. These

figures will be used for the data in the following graphs.

Tube Water (ml) Stock KMnO4(ml)

(X) Conc.(mM)

(Y)Abs. @525nm

(Y)Abs. @543nm

1 4.0 0.0 0.0 0.0 0.0

2 3.5 0.5 0.05 0.129 0.11

3 3.0 1.0 0.1 0.271 0.223

4 2.5 1.5 0.15 0.379 0.319

5 2.0 2.0 0.2 0.496 0.448

6 1.5 2.5 0.25 0.612 0.563

7 1.0 3.0 0.3 0.748 0.671

8 0.5 3.5 0.35 0.863 0.793

9 0.0 4.0 0.4 0.981 0.905

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A positive correlation between molarity and absorbance was observed on both graphs. As molarity

increases, absorption also increases, this indicates that its directly proportional.

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0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45

Abso

rbance(ArbitraryUnits)

Molarity (mM)

Molarity of Potassium permanganate vs absorbance

at 525nm

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Previous applications of the Beer-Lambert Law seem to support the findings of this experiment. The

trend of both of the graphs have a strong correlation with the Beer-Lambert Law although results

from this experiment seem to be slightly off the Beer-Lambert law. This is probably due to simple

errors during the completion of the experiment itself.

References

A. Reid (2012), Prac 2: Extinction Coefficient data for coursework assignment, 4010GNBMOL,Skills for Biomolecular Scientists, Blackboard, 10/01/13

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0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45

Absorbance(ArbitraryUnits)

Molarity (mM)

Molarity of Potassium permanganate vs absorbance

at 543nm

Solution Absorption Concentration fromstandard curve (mM)

Concentration fromBeer-Lambert law(mM)

A 0.06 0.03234 0.02427

B 0.562 0.25351 0.22735

C 0.455 0.41274 0.3692

D 0.583 0.52552 0.47168

Wavelength 525nm 543nm

Absorbance 0.657 0.618

Extinction Co-eff. from Beer-Lambert Law

2.628 2.472

Extinction Co-eff. From Graph 2.4377 2.2697