Spectrophotometric and potentiometric study of the cobalt(II)-thiocyanate system in aqueous medium |
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Authors: | Nina Coichev Ferreira Velloso Eduardo Almeida Neves Ivano G R Gutz |
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Institution: | Instituto de Química da Universidade de São Paulo, Caixa Postal 20.780—CEP 01498, São Paulo—SP, Brasil |
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Abstract: | The cobalt(II)—thiocyanate system was spectrophotometrically studied at 2.0 M ionic strength (NaClO4) and 25°C. The following formation constants were obtained: β1 = 6.9 M?, β2 = 28.9 M?2, β3 = 12.1 M?3 and β4 = 1.30 M?4. Three wavelengths were considered, 515, 590 and 615 nm, and the molar absorptivities of each species were calculated. Linear relationships were obtained for vs and αi. There is strong evidence that the tetrahedral Co(SCN)4]2? is virtually the only species absorbing at 590 and 615 nm. An indirect potentiometric method led to comparable equilibrium constants. The cadmium(II)—thiocyanate formation constants used in the indirect method, under the same conditions, were found to be β1 = 21.51 ± 0.09 M?1, β2 = 123 ± 1 M?2, β3 = 130 ± 3 M?3 and β4 = 173 ± 1.2 M?4, in good agreement with earlier literature data. |
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Keywords: | Author to whom correspondence should be addressed |
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