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Ultraviolet/Visible (UV-Vis) Spectroscopy of Potassium Permanganate. By Robert Bohman November 4 th 2006 CH EN 4903. Importance to industry. Potassium Permanganate is used to kill bacteria in reclaimed water

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

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Ultraviolet visible uv vis spectroscopy of potassium permanganate l.jpg

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

By Robert Bohman

November 4th 2006

CH EN 4903


Importance to industry l.jpg

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


Overview l.jpg

Overview

  • Theory

  • Light Absorption Spectrum

  • Experimental Procedure

  • Results

  • Conclusion

  • Q & A


Theory l.jpg

THEORY


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Properties of Light1

  • 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 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 Beer’s Law3

  • 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 SPECTRUM


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Absorption Spectrum of Light4


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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


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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

  • 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 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 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 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 & 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


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