Issue |
J. Chim. Phys.
Volume 75, 1978
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Page(s) | 476 - 483 | |
DOI | https://doi.org/10.1051/jcp/1978750476 | |
Published online | 29 May 2017 |
Influence de la formation de complexes chlorures sur la réduction électrochimique de SnIV en milieu perchlorique acide
(Laboratoire d’Électrochimie. Université Pierre et Marie Curie, Équipe de recherche associée au CNRS n° 310, 4, place Jussieu, 75230 Paris Cedex 05), France.
La détermination des constantes apparentes de stabilité des six complexes chlorostanniques [SnCln]4-n, dans des solutions d’acide perchlorique 5N de force ionique constante, permet l'analyse cinétique des vagues polarographiques obtenues dans les mêmes conditions expérimentales en fonction de la concentration des ions chlorures, ce qui aboutit à proposer des schémas réactionnels en corrélation avec la structure des solutions.
Abstract
The mechanism of electrochemical reduction of SnIV may be elucidated only in acid solutions, which prevent the formation of mixed hydroxylated complexes, more difficult to reduce.
Thus, in a HCIO4 5N solution of constant ionic strength, the presence of chloride ions increases substancially the rate constants, so that polarographic waves can be obtained whose limiting current is controlled by the diffusion of SnIV.
The determination of apparent stability constants of chloro-stannate complexes from potentiostatic measurements of « free » chloride ions, enables the kinetic analysis of these waves as a function of the « free » Cl-, from which the structure of the solutions depends exclusively.
The following conclusions have been reached :
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The reduction rate of the stannic ion being very slow, we only observe on the dropping mercury electrode, without chloride ions, the beginning of a reduction wave of Sn4+ before that of the protons.
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For Cl- « free » concentrations below 1.10-3 N, the reduction proceeds with direct formation of metallic tin. The species responsible for this mechanism could be the [math] complex, whose standard rate constant, k° is equal to 5.1.10-7 ms-1.
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For higher Cl- concentrations, a prewave appears corresponding to the reduction of SnIV to SnII. The species involved in that step up to a « free » chloride ion concentration of about 10-1 N, could be mainly the [math] complex.
© Paris : Société de Chimie Physique, 1978