LS7_a - Unit 2 How do we analyze chemical change?...

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Chemistry XXI Unit 2 How do we analyze chemical change? Absorption Spectroscopy
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Chemistry XXI Lab Session 7 How can we use light to quantify amount of substance?
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Chemistry XXI Your Challenge Imagine that you work for the FDA and you have been asked to monitor the amount of coloring added to different food products. Your task is to use absorption spectroscopy to quantify the mass of dye in commercial food products. How much dye is added per gram of food product?
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Chemistry XXI Absorption Spectroscopy Chemical substances absorb “ electromagnetic radiation ( EM ) of specific wavelengths. Dyes absorb EM in the visible portion of the spectrum.
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Chemistry XXI Spectra can also be used to quantify the concentration of different substances in a system Quantitation How would you compare the concentration of the different solutions? How would you expect the absorbance ( A ) change with the concentration ( C )?
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Chemistry XXI Measuring Concentrations For many materials, the absorbance ( A ) at a given λ is proportional to the concentration of the absorbing species (number of moles or molecules per unit volume; C ). log o i I Absorbance I = b (path length) How would you expect A to change with b ? How can we convert this proportionalities into a math relationship?
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Chemistry XXI Putting this all together we come up with the Beer – Lambert Law: For any particular wavelength, A bC ε = Beer’s Law Absorbance Molar absorptivity L/(mol cm) Path length cm Concentration Mol/L
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How can we use this type of data to determine the actual concentration of dye in a solution? A
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This note was uploaded on 04/09/2009 for the course CHEM 151 taught by Professor Staff during the Fall '08 term at University of Arizona- Tucson.

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LS7_a - Unit 2 How do we analyze chemical change?...

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