Formation Constants at

K j is the effective formation constant at a fixed pH and fixed concentration of auxiliary complexing agent. Box 12-2 describes the influence of metal ion hydrolysis on the effective formation constant. 

Formation constants for EDTA are expressed in terms of [Y4-], even though there are six protonated forms of EDTA. Because the fraction (aY4 1 of free EDTA in the form Y4 depends on pH, we define a conditional (or effective) formation constant as K = aYj Kf = MY" 4 /[M"+ [EDTA], This constant describes the hypothetical reaction Mn+ + EDTA MY 1-4, where EDTA refers to all forms of EDTA not bound to metal ion. Titration calculations fall into three categories. When excess unreacted M"+ is present, pM is calculated directly from pM = — log M l+]. When excess EDTA is present, we know both [MY"-4] and [EDTA], so IM"+] can be calculated from the conditional formation constant. At the equivalence point, the... 

Fig. 14.12 Formation constants at 25 C for 1 1 chelates of Lrrl+ ions with various aminepoly-carboxylate ions (ida, iminodiacetate nta, nilnlo-triacetate , A -hydroxy-elhyleihylenediaminetri-acelute edta, ethylene-dinminetetraacelate cdta, traru-1,2-cycIohcxane-diamineletraacctale dtps, diethylenetnammepenta-acetate). [From Moeller. T. J. Chem. Educ. 1970. 47, 417-430. Reproduced with permission.]...

Phillips, S. L. "Hydroloysis and Formation Constants at 25°C, LBL-14313, Lawrence Berkeley Laboratory, University of California, Berkeley, California, 1982. 

Lind, C. J. Polarographic determination of lead hydroxide formation constants at low ionic strength. Environ. Sci. Technol. (in press). 

Appendix 4 Formation Constants at 25°C A-10 Appendix 5 Standard and Formal Electrode Potentials A-12 Appendix 6 Use of Exponential Numbers and Logarithms A-15 Appendix 7 Volumetric Calculations Using Normality and Equivalent Weight A-19... 

The conditional formation constant for the calcium-EDTA chelate was calculated for pH 10 in Example 9.4 to be 1.8 X 10 °. Calculate the conditional formation constant at pH 3. Compare this with that calculated for lead at pH 3 in Problem 8. Could lead be titrated with EDTA at pH 3 in the presence of calcium ... 

Potentiometric measurements of the nickel(II) - cyanide system are described. The addition of Ni(CN)2, NiS04 or Ni(N03)2 to sodium cyanide solution resulted in the formation of a single nickel(II) containing species, Ni(CN)J . Its formation constant at 25°C and in 0.78 M NaCN solution was found to be log, fi = (11.83 + 0.17). The author used nickel metal as the working electrode. Since the electrode reactions involving nickel(II) are not reversible [50HUM/KOL], the reported formation constant is not reliable. 

These semi-thermodynamic formation constants (at 7 = 0) are not equivalent to the values obtained by extrapolation to zero ionic strength using the SIT, except for the case when the ratio ... 

The measured values of the formation constant for Cu-NTA at intermediate pH will then be 10 which is significantly less than the value of 10 measured at high pH. The same is true for the humic substance-metal ion complex equilibrium constants measured at low pH values. Morgan estimates that at pH 2 to 3 the —COO groups, which are important in forming fulvic acid-metal ion complexes, are virtually all in the —COOH or protonated form. Thus to obtain the value of the formation constant at intermediate pH for metal ion fulvic acid complexes, when the carboxyl groups are ionized, we should divide the equilibrium constant values presented in Table 5-13 by the dissociation constant of the —COOH group, that is,... 

The antitumour agent Cu(kts) (kts = 3-ethoxy-2-oxobutyraldehyde dithio-semicarbazonate) has an extremely large apparent formation constant at pH... 

The values in the tables have not been corrected for complexation with medium ions for the most part. There are insufficient data to make corrections for most of the ligands, and In order to make values between ligands more comparabie, the correction has not been made in the few cases where it could be made. In general the listed formation constants at constant ionic strength include competition by ions from KNO3 and NaC104 and are somewhat smaller than they would be If measured in solutions of tetraalkylammonium salts. 

Coefficient has a physical meaning of logarithm of formation constant at e -> °o related to the standard ionic strength I = 0. In Figure 9.21, this dependence is presented. 

Phillips, S.L., 1982, Hydrolysis and Formation Constants at 25°C, Report LBH4313... 

Conductometric and n.m.r. spectrometric data have allowed calculation of formation constants (at 30 °C) of cyclohexa-amylose-4-methyl cinnamate anion complexes with 1 1 and 2 1 stoicheiometries. The data suggest direct binding of the carboxylate terminal of 4-methyl cinnamate by cyclohexa-amylose in the 1 1 complex, while the structure of the 2 1 complex involves occlusion of the anion between two cyclohexa-amylose molecules in a head-to-head orientation. 

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