Ultraviolet/Visible (UV-Vis) Spectroscopy of Potassium Permanganate

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Ultraviolet/Visible (UV-Vis) Spectroscopy of
Potassium Permanganate

• By Robert Bohman
• November 4th 2006
• CH EN 4903

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Importance 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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Overview

• Theory
• Light Absorption Spectrum
• Experimental Procedure
• Results
• Conclusion
• Q A

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THEORY
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Properties of Light1

• c ??
  c speed of light in vacuum (2.998 x
  108 m/s)
• ? wavelength (m)
• v frequency (Hz)
• E hc/ ? hcv
  h Plancks constant (6.626 x
  10-34 Js)
• v wavenumber (m-1)

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Understanding Beers Law2

• 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 Beers Law3

• Absorbance A log (P/P0) -log (T)
• Beers Law A ebc
• e molar absorptivity (M-1 cm-1)
• b pathlength (cm)
• c concentration (M)

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LIGHT ABSORPTION SPECTRUM
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Absorption Spectrum of Light4
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 PROCEDURE
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Detecting Potassium Permanganate

• 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 Permanganate

• 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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RESULTS
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UV-Vis Absorbance Readings for Potassium
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 KMnO4 using UV-Vis
Spectroscopy, Absorption vs. Concentration
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Determination of Unknown Concentration of KMnO4

• Used cuvette of 1cm length
• e 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 Analysis

• Used 10.00 0.05mL volumetric pipette to make
  all solutions
• Measured density of water with
• ? (999.8392 16.945176t 7.987040110-3t2
  46.17046110-6t3 105.5630210-9t4
  280.5425310-12t5)/(1 16.87985010-3t)5
• ?H2O 0.997883 g/mL at 21.5C
• Measured accuracy of scale to be ? 0.0005g

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Error 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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CONCLUSION
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Conclusion

• 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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Conclusion

• Use Beers law to determine concentration of
  unknown concentration
• Find the molar absorptivity through the slope of
  calibration curve
• Determined e 0.029 ppm-1 cm-1
• Determined Unknown 4 concentration to be 36
  1.00 ppm

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Q A
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Special Thanks

• To Triston Thorpe and Jason Judkins in helping
  with the experiment

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References

• Harris, Daniel C. Sixth Edition Quantitative
  Chemical Analysis. Pg. 408-409. New York W.H.
  Freeman and Company, 2003.
• Harris, Daniel C. Sixth Edition Quantitative
  Chemical Analysis. Pg. 410. New York W.H.
  Freeman and Company, 2003.
• Harris, Daniel C. Sixth Edition Quantitative
  Chemical Analysis. Pg. 411-412. New York W.H.
  Freeman and Company, 2003.
• 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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Relax