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]
Formation constants for metal complexes of Cu(II), Ni(II), and Ag(I) with some substituted pyridine ligands were determined in a nitrate salt solution of the ligand (0.5 F KNO3 + 0.1 F HL) at 25 °C by pH measurement. The linear relationship shown by a logarithmic plot of the formation constant versus the basicity of the ligands characterizes qualitatively the dΠ → pπ-bonding capacity for each metal ion. The 2-substituents, such as —CH3 and —NH2, on these pyridine ligands have a very profound steric effect upon the stabilities of Cu(II) and Ni(II) complexes, but have no such effect upon that of Ag(I) complexes. An explanation is given which may be useful in selecting analytical reagents.
There is no purified nitromethane on the market, and to obtain pure nitromethane for research purposes seems to be a problem. It has been said1 that conventional methods of purification were inadequate for the removal of impurities in commercial grade nitromethane. The impurities are usually higher nitroalkanes plus trace cyanoalkanes and are distinguishable from nitromethane by nmr spectroscopy (Fig. 1). We have tried the reported methods of purifying nitromethane, such as the chemical treatments2 and the azeotropic distillations,2*3 but the results were unsatisfactory. Now we find that a treatment of crystallization from ether at -60-78°C eliminates all the impurities which appear in the nmr spectrum of the commercial product (Fig. 2).
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