UMD CHEM 425 - sample_1_o15 (10 pages)

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sample_1_o15



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sample_1_o15

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Pages:
10
School:
University of Maryland, College Park
Course:
Chem 425 - Instrumental Methods of Analysis
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INSTRUMENTAL METHODS OF ANALYSIS MID TERM EXAM II XXX 125 Points CALCULATIONS 60 Points 1 30 pts The chelate CuA22 exhibits maximum absorption at 480 nm When the chelating reagent is present in at least a 10 fold excess the absorbance is dependent only upon the analytical concentration of Cu II and conforms to Beer s law over a wide range A solution in which the analytical concentration of Cu2 is 2 30x10 4 M and that for A2 is 8 60x10 3 M has an absorbance of 0 690 when measured with a 1 00 cm cell at 480 nm A solution in which the analytical concentrations of Cu2 and A2 are 2 3x10 4 M and 5 00x10 4 M respectively has an absorbance of 0 540 when measured under the same conditions Use this information to calculate the formation constant K for the reaction Cu2 2 A2 CuA22 2 20 pts The fluorescence lifetime of a compound without quenching is 6 0 ns while with a quencher concentration of 1 00x10 2 M the fluorescence lifetime is 2 0 ns The rate constant Page 1 of 10 for intersystem crossing is 1 00x108 s 1 while that for internal conversion from S1 to S0 is negligible Calculate A the rate constant for fluorescence kr B the quenching rate constant kq C the Stern Volmer quenching constant K kq units of M 1 D the fluorescence quantum yield of the quenched compound 3 10 pts Calculate the resolution required for a mass analyzer to resolve peaks for a CH2N MW 28 0187 and N2 MW 28 0061 Page 2 of 10 b C2H4 MW 28 0313 and CO MW 27 9949 INSTRUMENTS 25 points 4 A 5 pts Provide a block diagram of a photodiode array UV Vis absorption spectrophotometer clearly labeling each of the components Page 3 of 10 B 5 pts Provide a diagram of a monochromator clearly labeling each of the components C 5 pts Provide a block diagram of a scanning spectrofluorometer clearly labeling each of the components Page 4 of 10 D 5 pts Provide a block diagram of a capillary electrophoresis system clearly labeling each of the components E 5 pts Provide a block diagram of a double beam scanning UV Vis spectrophotometer clearly labeling each of the components Page 5 of 10 SHORT ANSWERS 40 points Mass Spectrometry 10 points 5 A 2 pts What ionization source is used in the mass spectrometer in the 425 laboratory Page 6 of 10 B 2 pts Name the two ionization sources that are used most commonly for the analysis of high molecular weight polar compounds such as proteins C 2 pts What mass analyzer is employed in the GC MS in the 425 laboratory D 2 pts For what reason is this mass analyzer employed in the GC MS in the 425 laboratory E 2 pts Name three other mass analyzers Ultraviolet Visible Absorption Spectrophotometry 10 points 6 A 2 pts Name two instrumental factors that can produce deviations from Beer s Law Page 7 of 10 B 2 pts Name two light sources that are commonly employed in UV Vis spectrophotometry to provide light in UV Vis range Visible range C 2 pts Name two types of electronic transitions that have very low molar absorptivities D 2 pts What detector is employed in the spectrophotometer in the 425 lab E 2 pts Name one advantage of using a photodiode array spectrophotometer and one advantage of using a scanning spectrophotometer Advantage of a photodiode array spectrophotometer Advantage of using a scanning spectrophotometer Fluorescence Spectroscopy 10 pts 7 A 2 pts Under what condition is fluorescence intensity proportional to concentration Page 8 of 10 B 3 pts What is the ratio mode in spectrofluorometry and why is it employed C 2 pts Explain the difference between a fluorescence emission spectrum and a fluorescence excitation spectrum Which resembles an absorption spectrum and why D 3 pts Name three possible relaxation pathways for a molecule in its first excited singlet state Capillary Electrophoresis 10 Points 8 A 4 pts Provide the order of elution of cations anions and neutral species using capillary zone electrophoresis Can neutral species be separated by this technique Why or why not Page 9 of 10 B 3 pts What is electroosmotic flow and why does it occur Suggest a way in which electroosmotic flow can be 1 suppressed 2 reversed C 3 points Name two advantages of using capillaries in electrophoretic separations Name one major disadvantage Advantages Disadvantage END of EXAM Page 10 of 10


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