Chemistry 105 - Fall 2003 - Marcin Majda - Midterm 1

Chemistry 105 - Fall 2003 - Marcin Majda - Midterm 1 -...

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Chemistry 105 November 3, 2003 Midterm Exam - Solutions 1 . (20 pts.) Consider atomic absorption (AA) and atomic emission (AE) spectroscopies. A . Draw the schematic diagrams of both AA and AE spectrometers and identify all the major components. 6 pts. The drawing should include: AA: light source, atom cell monochromator and detector AE: source/atom cell, monochromator, tetector B . Would the same monochromator used in AA be also well suited for the AE spectrometer? Explain your answer focusing on the role of the monochromator in each of these two techniques. 7 pts. No, in atomic absorption the spectral resolution is achieved by means of the narrow linewidth of the hollow cathode lamp. In AA, the monochromator is used to limit the amount of light emitted by the flame reaching the detector. In atomic emission, however, the resolution is achieved by the monochromator which must have several orders of magnitude better resolving power than the one used in AA. C . Flame is commonly used as an “atom cell” in AA but only occasionally in AE. What limits the usefulness of the flames as sources (atom cells) in AE? 7 point. The temperature of the flames is insufficiently high. The temperature determines, via Boltzmann distribution, the relative population of the atoms in the excited state and thus the sensitivity of AE determinations. ICP source are used instead since plasma offers higher temperatures. 2
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This note was uploaded on 05/07/2010 for the course CHEM 101 taught by Professor Dick during the Spring '08 term at Academy of Art University.

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Chemistry 105 - Fall 2003 - Marcin Majda - Midterm 1 -...

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