Ch13 - CHEM 4241 Tuesday, October 18th 2011...

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CHEM 4241 Tuesday, October 18 th 2011 1 Announcements/business 1. Independent Research Project (50 points) Two parts: paper (30), video presentation (20) Guidelines on Gaview 2.HPLC lab starts this week: See lab manual for schedule Lab note books returned at end of class Seminar: “ Carbene, Carbenes, Every Where Nor Any That React? Tridentate CCC-N-Heterocyclic Carbene Pincer Complexes ” Dr. Keith Hollis, Ole Miss. Thursday, October 20 from 12:30pm - 1:30pm in Room 3228. Chapter 13 2.Molecular absorbance spectroscopy
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Chapter 13 Introduction to UV/vis Molecular Absorption Spectrometry 1. Optical properties of sample cuvettes 2. Chemistry-related limitations to Beer’s law Concentration effects Chemical deviations 1. Instrumental limitations to Beer’s law Polychromatic radiation Presence of stray radiation 1. Radiation Sources for molecular spectroscopy Deuterium lamps Tungsten lamps 1. Design of absorption spectrometers Single-beam instruments Double-beam instruments
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Beer’s Law Review/Sample Question A solution containing 6.23 ppm KMnO 4 (f.w. = 158.034 g/mol) had a transmittance of 55.2% in a 1.50 cm cell at 520 nm. Calculate the molar absorptivity of KMnO 4 at 520 nm. Remember: ppm=mg/L c b P P A P P T o o = - = = ε ) log( Absorbance Effect Simulation
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Sample cuvettes cause beam attenuation Quite high proportions (up to ~10%) of incident radiation can be lost to refection at surfaces and scattering.
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How are P and P o really measured? Intensity Measured after light beam passes through: P o cuvette + solvent (solvent blank) P cuvette + solvent + sample in solution For analytical work, the solvent blank and the sample must be placed in ‘matched’ cuvettes.
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Applications of Beer’s law to mixtures Imagine that the mixture being analyzed contains two species that absorb at the wavelength of analysis
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This note was uploaded on 10/20/2011 for the course CHEM 4241 taught by Professor Kreller during the Spring '11 term at Georgia Southern University .

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Ch13 - CHEM 4241 Tuesday, October 18th 2011...

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