SOLUTIONS to Spectroscopy Practice Problems

# SOLUTIONS to Spectroscopy Practice Problems - Additional...

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1 Additional Practice Problems: SPECTROSCOPY Chem 241-Section 1 Fall 2006 Professor Jorgenson c = 3.00 x 10 8 meters/second h = 6.63 x 10 -34 joule-seconds λν = c/n E = h ν A = ε bC A = -Log (T) = 2-Log (%T) 1) 0.461grams of a compound “Z” with a molecular weight of 154.12 g/mole was dissolved in 50.0 ml of water. A 10.00 ml aliquot was withdrawn, placed in a 100.0 ml volumetric flask and diluted to the mark with water buffered at pH 5.40. 4.00 ml of this solution was transferred to a cuvette with a 1.00 cm pathlength, and the transmittance was measured at 470 nm to be 53.1 %T. A second solution with an unknown concentration of “Z” has a transmittance of 29.3 %T. A) Calculate the molar absorptivity of “Z” at 470 nm. 0.461 / 154.12 = 2.99 x 10 -3 moles 1/5 of this is used, which is 5.98 x 10 -4 moles 5.98 x 10 -4 moles in 0.100 L = 5.98 x 10 -3 Molar Abs = -Log(T) = -Log (0.531) = 0.275 ε = A/bC = (0.275) / (1.00)( 5.98 x 10 -3 ) = 46.0 B) Calculate the concentration of “Z” in the unknown solution. A = -Log(0.293) = 0.533 C = A/ ε b = (0.533) / (46.0)(1.00) = 1.16 x 10 -2 M

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2 2) Below is a diagram showing hypothetical energy levels and processes that can occur in a molecule. Each level or process is indicated by a letter. For each letter, give the name of the state or process associated with it. A) ground singlet electronic energy level B) first excited singlet electronic energy level C) first excited triplet electronic energy level D) absorption E) vibrational relaxation F) fluorescence G) internal conversion H) vibrational relaxation I) intersystem crossing J) vibrational relaxation K) intersystem crossing L) phosphorescence A B C D E F G H I J L K
3 3, A) Draw a graph of relative photometric error (relative error in measuring concentration by photometry) versus transmittance. Relative

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## This note was uploaded on 08/27/2011 for the course CHEM 101 taught by Professor Smith during the Spring '11 term at East Carolina University .

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SOLUTIONS to Spectroscopy Practice Problems - Additional...

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