Activity corrections for ionic equilibria in aqueous solutions

Abstract

for ionic equilibria in aqueous solutions at 2S°C and ionic strengths up to 0.5 have been investigated. An empirical formula for activity corrections was generated by statistically fitting stability constant data for approximately 540 complexes. for which both thermodynamic and concentration stability constants were known, to a modified Debye-Huckel relationship. The general formula isx > 0, where A log K is the difference in the logarithms of the stability constants at infinite dilution and finite I ( I 5 0.5), and x is an even integer dependent only on the stoichiometry and charge of the ions involved. Activity correction formulae for ionic equilibria involving classes of ligands (amino acid, inorganic, amine, and organic acid) also were developed. The general formula predicts stability constant corrections within 0. I log unit for 87% of the data used at ionic strength 0. I and 64%of the data at ionic strength 0.5. In addition, single ion activity coefficients as a function of ionic strength, O< I < 0.5, are presented. Chem. 58, 1253Chem. 58, (1980. On a etudii les corrections d'activite pour I'equ~libre ionique en solution aqueuse a 25°C e t a des forces ioniques allant jusqu'i 0.5. Les donnees relatives aux constantes de stabilite de 540 complexes pour lesquelles on connait les constantes de stabilitk thermodynamique et concentration. ajustees d'un point de vue statistique ont permis de produire une formule empirique du type Debye-Hiickel de correction des activites. Cette formule genirale est la suivante:x > 0 dans cette formule A log K est la differencedes logarithmes des constantes de stabilite a dilution infinie et finie I ( I I 0.5) etx est un nombre entier pair qui dipend seulement de la stoechiomCtrie et de la charge des Ions impliques. On a egalement developpe des formules de correction d'activite des equilibres ioniques qui font intervenir les classes de ligands (acide arnine, inorganique, amine et acide organique). La formule generale permet de pridire a 0.1 unite logarithmique pres pour 87% des donnees utilisees les corrections de constantes de stabiliti a une force ionique de 0.1 et pour 64% des donnees a une force ionique de 0.5. On presente de plus des coefficients d'activite d'un ion unique comme etant une fonction de la force ionique comprise entre O< I 5 0.5.[Traduit par le journal]

Quantitative 27Al NMR spectroscopic studies of Al (III) complexes with organic acid ligands and their comparison with GEOCHEM predicted values

“…GEOCHEM calculations for an A1 oxalate solution (Al:ox molar ratio 1:2, pH 3.9), in which NMR integration estimated 11.3% of the A1 to be present as the Alox3 species, gave low estimates for this species suggesting that the constants in the databases are incorrect. Editing the database of GEOCHEM-PC v. 2.0 with other literature constants (Perrin, 1979), corrected to zero ionic strength (Sun et al, 1980), for all three A1 oxalate complexes gave results that more closely matched the NMR integral values (Table 1).…”

Radiochemical Studies of Iron Binding and Stability in Ferrimycobactin S

“…Combination of Equilibria (1) -(4) with the thermodynamic equilibrium constant Kl corrected for the changes in ionic strength according to Eq. (9) from [12] furnishes very concordant values of the various parameters for all curves with the exception of the isohydric at C H = 0.5 M. The parameters derived when fitting all curves together are given in Table 2 and the calculated curves are shown as solid lines in Figs. 1 and 2 and as dashed lines in Fig.…”

Binding of Divalent Cations to Aqueous Acetate: Molecular Simulations Guided by Raman Spectroscopy

“…It is important to notice that the Raman-derived binding constants for the contact ion pairs (or equivalently binding free energies) are obtained at finite ionic strength (between ~0.3 and ~1.5 M), while calculated binding free energies correspond to a standard binding free energy in the infinite dilution limit. Hence, to compare measured and calculated binding free energies, we first extrapolated the experimentally-derived binding free energies to zero ionic strength, using a refined Davies 45,46 -like equation fitted on a large set of ion-ion binding constants measured at different ionic strengths. 46 We thus report in Table 1 the extrapolated experimental binding free energy, which can be directly compared with the computed contact binding free energy, that encompasses both monodentate and bidentate binding geometries.…”

“…Hence, to compare measured and calculated binding free energies, we first extrapolated the experimentally-derived binding free energies to zero ionic strength, using a refined Davies 45,46 -like equation fitted on a large set of ion-ion binding constants measured at different ionic strengths. 46 We thus report in Table 1 the extrapolated experimental binding free energy, which can be directly compared with the computed contact binding free energy, that encompasses both monodentate and bidentate binding geometries. Note that these extrapolated binding free energies are still quite small, around −3.2 kJ mol −1 for Ca 2+ , −3.4 kJ mol −1 for Mg 2+ , and only −6.9 kJ mol −1 for Zn 2+ .…”