611ProblemSet102010

611ProblemSet102010 - CHEMISTRY C6”: ELECTROANALYTICAL...

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Unformatted text preview: CHEMISTRY C6”: ELECTROANALYTICAL CHEMISTRY Fall, 2010 Problem Set 10 l . At a recent conference it was proposed by one participant that the clectrochemistry of a certain organometallic species A Follows an " ECEI mechanism " according to the scheme: Species A is reduced to species B (131,»; = +0.43 V vs. SCI-Z). Product B reacts in an irreversible. first-order chemical process to give C which undergoes oxidation to D (Em = —0.26 V vs. SCE). Consider a thin-layer cgilic voltammetric experiment in which a solution 01A is studied. Suppose that the potential is scanned from +0.8 to —0.8 and then back to +0.8 V vs. SCE. (a) It‘thc rate of scan of potential is m compared to the rate ol‘convcrsion of B to C. sketch an accurately labeled film-Lam cyclic voltammogram for this ex- periment. Give as much information as possible about the quantitative character— istics of the curve. (b) If the rate of scan ofpotentia] is verv slow compared to the rate of conversion of B to C. sketch an accurately labeled thinslayg cvclic voltammoaram for this ex- periment. Give as much infomiz-ltion as possible about the quantitative chart-letter istics ofthe curve. 2. 1.9-) 6. Consider the use of electrochemical detectors for high—performance liquid chromatog raphy (HPLC). (a) Detection limits for oxidizable species tend to be approximately 10 times lower than those for reducible species. Why? (b) Name two classes of organic compounds that have been determined electrochemi- cally in an HPLC separation. (c) Sketch one possible geometry or configuration for the working, reference, and auxiliary electrodes in a thin-layer electrochemical detector for HPLC. . [Explain or define. using appropriate diagrams or sketches it‘desired. each of the following terms associated with photoelectrochemistry and semiconductor electrodes. (a) band gap (b) p-type semiconductor (c) photovoltaic cell (d) dye sensitization (e) Fermi level . Explain or define, using appropriate diagrams or sketches il'desired, each ofthe following terms associated with elcctrocheniilumincscence. (a) energy-deficient process (b) triplet-triplet annihilation (c) S (singlet) route (d) sequential generation ot’ reagents . A semiconductor electrode is placed into a solution containing 1.00 x 10—"1 M concen- trations of both Fe(CN)(,4" and FetCN)(,3_ in water containing 0.10 M supporting elec- trolyte (’HCI); the formal potential for the ferricyanide-ferrocyanide rcdox eouple is approximately +0.46 V vs. SCE. Using the axes provided on the next page, sketch the current-voltage curves if the semiconductor is: (a) n-type Fe203, hvgnl, = 2.2 eV. Emubmd == —0.l(] V vs. SCE. and for the situations where the system is (i) in the dark and (ii) illuminated with radiation of energy (by) that is greater than hng (b) p-type Gal). 1wgap = 2.24 eV. Enamm = +0.80 V vs. SCE and for the situations where the system is (i) in the dark and (ii) illuminated with radiation ol‘ energy (hv) that is greater than hvgap. With reference to the preceding problem and using energy-level diagrams. explain the effect of illumination on the observed current for the n-type electrode. Be sure to de- scribe the redox process occurring at the semiconductor—solution interface. ' —. I i II Eli]: : :i! :I 't1'r*'r*t'='£i' - ' f '* ::== - :=- .- flu: Illiai .._; g I I I II Easing: IIIIIII ifl .41 ‘ I:§.: .EE.§ I EI I. -§l .:- 5.. III II I iiiii E E2; ‘ii _ -.= .5! :- III-II III.- E. J TI“ 1 + .I i" :.' F'" f a . . I l 7‘ '. ' L ' - * T' irIl ' I III II E;- "'-‘ i. +. _--+‘r t1 hm _ . . I ii??? L T T-pn ' .. L ...
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This note was uploaded on 01/18/2012 for the course C 611 taught by Professor Dennisg.peters during the Fall '10 term at Indiana.

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611ProblemSet102010 - CHEMISTRY C6”: ELECTROANALYTICAL...

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