The acidity constants of citric acid and the stability constants of the citrate complexes of copper(II), iron(II), and iron(III) have been measured at 25 °C in 0.1 M KNO3 background. The measurements were based on mass balances on hydrogen ions, supplemented in the case of Cu(II) and Fe(III) complexes by measurements of free metal concentration with a solid-state copper-ion-sensitive electrode and a redox electrode respectively. The data required the assumption of a binuclear copper complex, but all complexes characterized were of 1:1 stoichiometry.
TERRENCE B. FIELD and W. A. E. MCBRYDE. Can. J. Chem. 59,555 (1981). Conditional formation constants were determined at 25' C and with a background electrolyte of 0.1 mol dm-) NaNO, for the proton, nickel(II), copper(II), and zinc(I1) complexes of glycine, iminodiacetic acid, and nitrilotriacetic acid in 0,20,50, 80, and 95 volume percent methanol mixed with water. Similar measurements were made for triethylenetetramine in all but 95% methanol, and the formation constants s o determined were used to determine K M N , by a competitive method.The variation of all constants with solvent composition was examined from the point of view that complex formation is accompanied by solvent displacement. Accordingly it should be possible to correlate the observations by means of an over-all formation constant, valid for any solvent concentration. It was concluded that for two solvents as similar as water and methanol, both of which appear to be involved in solvation or desolvation in the reaction, the correlations sought could not very precisely fix the amounts of solvents displaced or taken up. The goodness of fit to the attempted correlations suggests that they would be useful for interpolations to solvent compositions other than those studied. TERRENCE B. FIELD et W. A. E. MCBRYDE. Can. J. Chem. 59,555 (1981). Operant a 25°C et utilisant comme electrolyte de base une solution de NaNO, a 0,l mol dm-3, on a determine les constantes de formation conditionnelle des complexes du proton, du nickel(II), du cuivre(I1) et du zinc avec la glycine, les acides iminodiacktique et nitritotriacetique dans des melanges methanol-eau a 0,20,50,70et 95% en volume. On a fait des determinations identiques pour la trikthylamine mais sans recourir au melange methanol-eau a 95% et on a utilise les constantes de formation ainsi obtenues pour determiner K M N , par une m6thode competitive.On a examine la variation de toutes les constantes avec la composition du solvant en tenant compte du fait que la formation des complexes s'accompagne d'un dtplacement du solvant. En consequence il devra Ctre possible de faire concorder les observations au moyen d'une constante globale deformation, valable pour n'importe quelle concentration de solvant. On a conclu que pour deux solvants aussi semblables que I'eau et le methanol, qui semblent itre impliques dans la solvatation ou la desolvatation au cours de la reaction, les correlations recherchees ne peuvent pas fixer avec precision les quantites de solvant deplace ou elitnine. Les meilleurs correlations obtenues suggkrent qu'elles seraient utiles pour faire des interpolations dans les compositions de solvant differentes de celles CtudiCes.[Traduit par le journal]
, 1202 (1978). Data from simulated titrations (pH, titer, and pM) were generated from literature values of equilibrium constants, and then submitted to various published methods of calculation to regenerate the indicated equilibrium constants. These calculations were done with error-free input data, and the same with imposed random errors. In other experiments data from real titrations were subjected to the same analysis, and additional checks were made on the output of the calculations with an ion-selective electrode as a probe for pM. One method of data analysis was prone to cause errors in the finally recovered constants, and causes for this are suggested. Introduction plexes. Certain features of the ~r o c e d u r e have come For collecting data with which to evaluate acidity t o light during extensive use of it, and these are deconstants of weak acids or bases or stability con-scribed here for the benefit of other prospective users. stants of metal complexes titrations are often preferred because of their capability of furnishing a Data Treatment large amount of experimental information from the At any point in a titration designed to study metalinteraction of a small number of standardized solu-complex formation there will be three stoichiometric tions. The subsequent numerical inanipulation of the concentrations: C,,, C,, and C,. C, is the net condata so collected can take various forms according centration of ionizable hydrogen, i.e., the total iont o the amount and kind of information available. izable hydrogen put in as ligand, mineral acid, etc., This paper reports a study of one recently described way of conducting titrations and utilizing the results for the calculation of metal complex stability constants, and compares this with some longer established practices.Sarkar and Kruck (1) recently extended a procedure developed by Osterberg (2) to determine p L in the presence of metal ions by p H titration, showing that it could also be applied to determine pM. This proposal possesses two desirable characteristics;
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