The Objective of This Particular Experiment Was to Investigate the Concentration of a Potassium...
Transcript of The Objective of This Particular Experiment Was to Investigate the Concentration of a Potassium...
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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