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Publication Type
Journal Article
UWI Author(s)
Author, Analytic
Holder, Alvin A.; Dasgupta, Tara P.
Author Affiliation, Ana.
Department of Biological and Chemical Sciences
Article Title
Kinetics and mechanism of the reduction of the molybdatopentaamminecobalt(III) ion by aqueous sulfite and aqueous potassium hexacyanoferrate(II)
Medium Designator
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Connective Phrase
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Journal Title
Inorganica Chimica Acta
Translated Title
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Reprint Status
Refereed
Date of Publication
2002
Volume ID
331
Issue ID
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Page(s)
279-89
Language
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Connective Phrase
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Location/URL
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ISSN
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Notes
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Abstract
A detailed investigation on the oxidation of aqueous sulfite and aqueous potassium hexacyanoferrate(II) by the title complex ion has been carried out using the stopped-flow technique over the ranges, 0.01 [S(IV)]T 0.05 mol dm-3, 4.47 pH 5.12, and 24.9 q 37.6 C and at an ionic strength 1.0 mol dm-3 (NaNO3) for aqueous sulfite and 0.01 [Fe(CN)64-] 0.11 mol dm-3, 4.54 pH 5.63, and 25.0 q 35.3 C and at an ionic strength 1.0 or 3.0 mol dm-3 (NaNO3) for the hexacyanoferrate(II) ion. Both redox processes are dependent on pH and reductant concentration in a complex manner, that is, for the reaction with aqueous sulfite, kobs = {(k1K2K3+k2K1K4[H+] )[S (IV)]T]/([H+]2 + K1[H+] + K1K2) and for the hexacyanoferrate(II) ion, kobs = {(k1K3K4K5+k2K3K6[H+] )[Fe(CN)64-]T]/([H+]2 + K3[H+] + K3K4). aT 25.0 C, the value of k'1 (the composite of k1K3) is 0.77 0.07 mol-1 dm3 s-1, while the value of k'2 (the composite of k2K4) is (3.78 0.17) X 10-2 mol-1 dm3 s-1 for aqueous sulfite. For the hexacyanoferrate(II) ion, k'1 (the composite of k1K5) is 1.13 0.01 mol-1 dm3 s-1, while the value of k'2 (the composite of k2K6) is 2.36 0.05 mol-1 dm3 s-1 at 25.0 C. In both cases there was reduction of the cobalt(III) centre to cobalt(II), but there was no reduction of the molybdenum(VI) centre. k22, the self-exchange rate constant, for aqueous sulfite (as SO32-) was calculated to be 5.37 X 10-12 mol-1 dm3 s-1, while for Fe(CN)64-, it was calculated to be 1.10 X 109 mol-1 dm3 s-1 from the Marcus equations.....
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