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Master's Dissertation
DOI
10.11606/D.46.1993.tde-30072008-072805
Document
Author
Full name
Horacio Dorigan Moya
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
São Paulo, 1993
Supervisor
Committee
Neves, Eduardo Fausto de Almeida (President)
Angnes, Lúcio
Ortega, Manuel Molina
Title in Portuguese
Estudo potenciométrico dos equilíbrios no sistema manganês (II) / azoteto
Keywords in Portuguese
Azoteto
Constantes de equilibrio
Manganês
Métodos eletroquímicos
Potenciometria
Abstract in Portuguese
Foram estudados os equilíbrios dos complexos de Mn (II) com íons azoteto, em meio aquoso, por método potenciométrico indireto, através de medidas de pH, em meio de azoteto 0 a 1,8 M, e a 25,0 ºC, utilizando força iônica 2,00 M mantida com perclorato de sódio. Nas diferentes concentrações de íon metálico empregadas, 20, 40, 60, 80 e 100 mM, obteve-se uma mesma curva de formação de número médio de ligantes vs. concentração de ligante livre, o que configura a inexistência de complexos polinucleares nessas condições experimentais. Os valores de número médio de ligantes n¯, e de concentração de ligante livre, [L], foram utilizados para a integração de função de Bjerrum, obtendo-se a função de Fronaeus, F0(L), a partir da qual calcularam-se, por métodos gráficos e matemáticos, as quatro sucessivas constantes globais de equilíbrio: β1 = 4,15 ± 0,02 M-1 , β2 = 6,61 ± 0,04 M-2 , β3 = 3,33 ± 0,02 M-3 , β4 = 0,63 ± 0,01 M-4 . Avaliando os valores das constantes, observa-se que os complexos formados são fracos e, em obediência à regra de Irving e Williams, são menos estáveis que os complexos de cobalto (II) e de níquel (II). Em concentrações de ligante superiores a 1M há condições para lenta oxidação espontânea dos complexos de manganês(II) a manganês(III) com significativas mudanças espectrais.
Title in English
The potentiometric study of complex formation in the manganese (II)/azide system
Keywords in English
Azide
Manganese
Potentiometry
Stability constants
Abstract in English
The equilibria of complex formation between manganese(II) cations and azide anions were studied in aqueous medium by an indirect potentiometric method, at 25°C and ionic strengh 2.0 M (NaClO4). The equilibrium data were based on pH measurements of Mn(II) in N3¯/HN3 buffers. Metal ion concentration changing from 20 to 100 mM have defined one single formation curve of n_ (Bjerrum function) vs. [N 3 ¯ ] which is an evidence that only mononuclear species ara present in the working solutions. Integration of the formation curve from the best n¯vs. [N3¯] data leads to Fronaeus function data. They were properly treated to obtain the formation by a variety of methods (graphic and mathematical). The best set formed is: β1 = 4,15 ± 0,02 M-1 , β2 = 6,61 ± 0,04 M-2 , β3 = 3,33 ± 0,02 M-3 , β4 = 0,63 ± 0,01 M-4 . The complex are weaks and are is agreement with the Irving and Williams rule, i. e., less stable than the corresponding complexes of Ni(II) and Co(II). At ligand concentration higher t than 1,0 M there were conditions for a slow spontaneous oxidation of manganese(II) complexes to manganese to manganese(III), with remarkable spectral changes.
 
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Publishing Date
2008-08-08
 
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