UMD CHEM 425 - midterm2-4 (7 pages)

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midterm2-4



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midterm2-4

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Pages:
7
School:
University of Maryland, College Park
Course:
Chem 425 - Instrumental Methods of Analysis
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Ccccccccccccccccccccccccccccccccc INSTRUMENTAL METHODS OF ANALYSIS MID TERM EXAM II xxx semester 140 Points CALCULATIONS 40 Points 1 The acid base indicator HIn undergoes the following reaction in dilute aqueous solution HIn H Incolor 1 color 2 The following absorbance data were obtained for a 5 00x10 4 M solution of HIn in 0 1 M NaOH and 0 1 M HCl Measurements were made at a wavelength of 485 nm and 625 nm with 1 00 cm cells 0 1 M NaOH A485 0 052 A625 0 823 0 1 M HCl A485 0 454 A625 0 176 In the NaOH solution essentially all of the indicator is present as In in the acidic solution it is essentially all in the form of HIn A 10 points Calculate the molar absorptivities for In and HIn at 485 and 625 nm CHEM 425 midterm II xxx 1 B 15 points Calculate the acid dissociation constant for the indicator if a pH 5 00 buffer containing a small amount of the indicator exhibits an absorbance of 0 472 at 485 nm and 0 351 at 625 nm 1 cm cells C 15 points What is the pH of a solution containing a small amount of the indicator that exhibits an absorbance of 0 530 at 485 nm and 0 216 at 625 nm 1 cm cells INSTRUMENTS 50 points CHEM 425 midterm II xxx 2 2 A 10 points Provide a block diagram of an ultraviolet visible UV VIS diode array spectrophotometer clearly labeling each of the components B 10 points Provide a block diagram of a scanning duel beam UV VIS spectrophotometer clearly labeling each of the components C 10 points Provide a diagram of a monochromator clearly labeling each of the components CHEM 425 midterm II xxx 3 D 10 points Provide a block diagram of a capillary electrophoresis system clearly labeling each of the components E 10 points Provide a block diagram of a mass spectrometer clearly labeling each of the components CHEM 425 midterm II xxx 4 SHORT ANSWERS 50 points 3 Mass Spectrometry 19 points 1 3 points Name three ionization sources 2 2 points Name one hard ionization source and one soft ionization source 3 2 points What complementary information can be obtained by the combined use of a hard and a soft ionization sources 4 2 points What ionization source is used in the mass spectrometer in the 425 laboratory 5 2 points What type of ionization source is used most commonly for the analysis of high molecular weight polar compounds such as proteins 6 4 points Name four mass analyzers 7 2 points What mass analyzer is employed in the gas chromatograph mass spectrometer GC MS in the 425 lab 8 2 points Why is this type of mass analyzer named in question G used in GC MS 4 Capillary Electrophoresis 14 points CHEM 425 midterm II xxx 5 1 3 points Provide the order of elution of cations anions and neutral species using capillary zone electrophoresis 2 3 points Name a capillary electrophoretic method that can be used to separate neutral species on the basis of their polarity 3 2 points Define isoelectric point pI 4 3 points In isoelectric focusing would the species with the highest pI focus closer to the cathode or the anode 5 3 points Indicate a way in which electroosmotic flow can be a repressed and b reversed 5 Ultraviolet Visible Absorption Spectrophotometry 17 points CHEM 425 midterm II xxx 6 1 2 points Provide an equation that relates beam intensity to the transmittance of a sample 2 3 points Provide an equation that relates transmittance to the absorbance of a sample 3 3 points Provide an equation that relates absorbance to concentration What is this equation called 4 3 points Name three factors that can produce deviations from the relationship provided in Question C 5 2 points Name two types of electronic transitions that have very low molar absorptivities 6 2 points What two light sources are commonly employed in UV Vis spectrophotometry to provide light in the ultraviolet and visible wavelength ranges respectively 7 2 points What detector is employed in the spectrophotometer in the 425 lab I pledge on my honor that I have not given ort received any unauthorized assistance on this exam Signature CHEM 425 midterm II xxx 7


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