UMD CHEM 425 - sample_2_o14 (6 pages)

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INSTRUMENTAL METHODS OF ANALYSIS MID TERM EXAM II XXX 125 Points CALCULATIONS 60 Points 1 20 points A mixture of chelating reagent B with Ni II gives rise to the formation of a highly colored NiB22 complex solutions of which obey Beer s law over a wide range Provided the analytical concentration of the chelating reagent exceeds that of Ni II by a factor of five or more the cation exists within the limits of observation entirely in the form of the complex Use the accompanying data to evaluate the formation constant Kf for the reaction Ni2 2 B NiB22 Concentrations M Ni2 B Absorbance A 395 nm 1 cm cell 2 5x10 4 2 20x10 1 0 765 2 5x10 4 1 00x10 3 0 360 2 25 points When measured with a 1 00 cm cell a 7 50 x 10 5 M solution of species A exhibited absorbances of 0 155 and 0 755 at 475 and 700 nm respectively A 4 25 x 10 5 M solution of species B gave absorbances of 0 702 and 0 091 under the same circumstances Calculate the concentration of A and B in a solution that yielded the following absorbance data in a 2 5 cm cell 0 439 at 475 nm and 1 025 at 700 nm 3 15 points If the fluorescence quantum yield and lifetime of compound X were 0 5 and 200 nanoseconds respectively under anaerobic conditions what would the quantum yield and lifetime be under aerated conditions assuming that O2 quenches the excited singlet state with a rate constant of 1x1010 M 1s 1 and the solution concentration of O2 is 1 5 mM When the solution concentration of O2 is 250 M INSTRUMENTS 25 points 2 A 5 points Provide a block diagram of a photodiode array UV Vis absorption spectrophotometer clearly labeling each of the components B 5 points Provide a diagram of a monochromator clearly labeling each of the components C 5 points Provide a block diagram of a fluorescence spectrometer clearly labeling each of the components D 5 points Provide a block diagram of a mass spectrometer clearly labeling each of the components E 5 points Provide a block diagram of a single beam scanning UV Vis scanning spectrophotometer clearly labeling each of the components SHORT ANSWERS 40 points Mass Spectrometry 18 points 3A 2 points Name two gas phase ionization sources B 2 points What ionization source is used in the mass spectrometer in the 425 laboratory C 2 points In chemical ionization which reaction proton transfer hydride abstraction or charge exchange produces the M 1 ion Which reaction produces the M 1 ion D 2 points Name two ionization sources that are used most commonly for the analysis of high molecular weight polar compounds such as proteins E 2 points Name four mass analyzers F 2 points What mass analyzer is employed in the GC MS in the 425 laboratory G 2 points For what reason is this