Ultraviolet/Visible (UV-Vis) Spectroscopy of Potassium Permanganate
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Ultraviolet/Visible (UV-Vis) Ultraviolet/Visible (UV-Vis) Spectroscopy of Potassium Spectroscopy of Potassium
PermanganatePermanganateBy Robert BohmanBy Robert Bohman
November 4November 4thth 2006 2006
CH EN 4903CH EN 4903
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Importance to industryImportance to industry
• Potassium Permanganate is used to kill bacteria in reclaimed water
• Use UV-Vis to ensure that the concentration of Potassium Permanganate is at acceptable limit
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OverviewOverview
• Theory
• Light Absorption Spectrum
• Experimental Procedure
• Results
• Conclusion
• Q & A
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THEORYTHEORY
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Properties of LightProperties of Light11
• c = λν c = speed of light in vacuum (2.998 x 108 m/s)
λ = wavelength (m)
v = frequency (Hz) • E = hc/ λ = hcv`
h = Planck’s constant (6.626 x 10-34 J•s)
v` = wavenumber (m-1)
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Understanding Beer’s LawUnderstanding Beer’s Law22
• Transmittance T = P/P0
Schematic of Single-Beam Spectrophotometer, P0 is the irradiance entering sample, P is the irradiance leaving sample, and b is pathlength2
P = irradiance (energy per unit area of light beam)
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Understanding Beer’s LawUnderstanding Beer’s Law33
• Absorbance A = log (P/P0) = -log (T)
• Beer’s Law A = εbc
ε = molar absorptivity (M-1 cm-1)
b = pathlength (cm)
c = concentration (M)
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LIGHT ABSORPTION LIGHT ABSORPTION SPECTRUMSPECTRUM
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Absorption Spectrum of LightAbsorption Spectrum of Light44
Wavelength of maximum absorption (nm)
Color Absorbed Color Observed
380 – 420 Violet Green-Yellow
420 - 440 Violet-Blue Yellow
440 – 470 Blue Orange
470 – 500 Blue-Green Red
500 – 520 Green Purple
520 – 550 Yellow-Green Violet
550 – 580 Yellow Violet-Blue
580 – 620 Orange Blue
620 – 680 Red Blue-Green
680 - 780 Purple Green
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EXPERIMENTAL EXPERIMENTAL PROCEDUREPROCEDURE
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Detecting Potassium Detecting Potassium PermanganatePermanganate
• Potassium permanganate (KMn04) in solution is purple / violet color meaning maximum absorption should be at 500 – 550 nm
• Prepared 5 known concentrations of KMnO4: 1ppm, 20ppm, 40ppm, 60ppm, 80ppm
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Detecting Potassium Detecting Potassium PermanganatePermanganate
• Calibration Standards measured first on a Perkins-Elmer Lambda 35 over entire UV-Vis region to determine max absorption
• KMnO4 absorbed best at ≈ 520 nm
• A Bausch & Lomb Spectronic 21 was used to make all measurements
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RESULTSRESULTS
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UV-Vis Absorbance Readings for UV-Vis Absorbance Readings for Potassium Permanganate at 520 nmPotassium Permanganate at 520 nm
Average %A (after 3 runs)
Standard Deviation (%A)
1 ppm 0.015 0.004
20 ppm 0.256 0.001
40 ppm 0.520 0.004
60 ppm 0.753 0.002
80 ppm 1.046 0.001
Unknown #4 0.462 0.001
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Calibration Curve for KMnOCalibration Curve for KMnO44 using UV-Vis using UV-Vis
Spectroscopy, Absorption vs. ConcentrationSpectroscopy, Absorption vs. Concentration
y = 0.0129x
R2 = 0.9990
0.2
0.4
0.6
0.8
1
1.2
0 20 40 60 80 100
Concentration (ppm)
%A
bso
rban
ce
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Determination of Unknown Determination of Unknown Concentration of KMnOConcentration of KMnO44
• Used cuvette of 1cm length
• ε = slope of line = 0.029 ppm-1 cm-1
• Unknown #4 concentration found using
c = A/0.029
• 36 ppm = 0.462 %A / 0.029 ppm-1
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Error AnalysisError Analysis
• Used 10.00 ± 0.05mL volumetric pipette to make all solutions
• Measured density of water with:
= (999.8392 + 16.945176t – 7.9870401*10-3t2 – 46.170461*10-6t3 + 105.56302*10-9t4 – 280.54253*10-12t5)/(1 + 16.879850*10-3t)5
H2O = 0.997883 g/mL at 21.5°C
• Measured accuracy of scale to be 0.0005g
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Error in UnknownError in Unknown
• Errors determined graphically from calibration curve
• A = ± 0.01%
• Concentration = ± 1.00 ppm
• Final concentration of Unknown #4 was
36 ± 1.00 ppm
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CONCLUSIONCONCLUSION
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ConclusionConclusion
• How accurate are results?
Can be determined by R2 value for slope of calibration curve.
For this example R2 = 0.999
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ConclusionConclusion
• Use Beer’s law to determine concentration of unknown concentration
• Find the molar absorptivity through the slope of calibration curve
• Determined ε = 0.029 ppm-1 cm-1
• Determined Unknown #4 concentration to be 36 ± 1.00 ppm
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Q & AQ & A
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Special ThanksSpecial Thanks
To Triston Thorpe and Jason To Triston Thorpe and Jason Judkins in helping with the Judkins in helping with the
experimentexperiment
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ReferencesReferences
1. Harris, Daniel C. Sixth Edition Quantitative Chemical Analysis. Pg. 408-409. New York: W.H. Freeman and Company, 2003.
2. Harris, Daniel C. Sixth Edition Quantitative Chemical Analysis. Pg. 410. New York: W.H. Freeman and Company, 2003.
3. Harris, Daniel C. Sixth Edition Quantitative Chemical Analysis. Pg. 411-412. New York: W.H. Freeman and Company, 2003.
4. Harris, Daniel C. Sixth Edition Quantitative Chemical Analysis. Pg. 413. New York: W.H. Freeman and Company, 2003.
5. CRC Handbook of Chemistry and Physics. Pg. F-6. Cleveland, Ohio: The Chemical Rubber Co., 1968.
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RelaxRelax