Hydrolysis constant, derivation

Table A-6 Hydrolysis constants derived from the work of [66BIL/BRA2], Uncertainties where given are 3a.

Nevertheless this paper is helpful to judge hydrolysis constants derived by cation exchange methods. The different pH-dependence of the sorption behaviour of Th(IV) onto different cation exchange materials shows that the evaluation of pH-dependent distribution (sorption) coefficients requires not only the fitting of the forma-tion constants logj (or log ) of the hydroxide complexes formed in solution but also of their equilibrium constants logio A ,m for the sorption onto the cation exchange material (CE) ... 

Knauss, K.G., Dibley, M.J., Bourcier, W.L., and Shaw, H.E (2001) Ti(IV) hydrolysis constants derived from rutile solubility measurements made from 100 to 300 °C. Appl. Geochem., 16, 1115-1128. 

Proceeding further using the arguments given in the first case, the following relationship can be derived for the hydrolysis constant (fCh) ... 

In the system Th(IV)-H20 three sets of thermodynamic quantities can be derived from experimental data (1) the hydrolysis constants l°gio j3° and log10 /34 of ThOH3+ and Th(OH)4(aq), respectively, have been determined potentiometrically by several authors over a wide range of ionic strength (for references see Hummel et al. 2002) (2) the thermodynamic properties of Th02(cr) have been determined by calorimetry, and thus a solubility product logio K°s 0 (cr) for... 

The standard notation for successive acid dissociation constants of a polyprotic acid is Kt, K2, K2, and so on, with the subscript a usually omitted. We retain or omit the subscript as dictated by clarity. For successive base hydrolysis constants, we retain the subscript b. The preceding examples illustrate that Kal (or K ) refers to the acidic species with the most protons, and Kbl refers to the basic species with the least number of protons. Carbonic acid, a very important diprotic carboxylic acid derived from COz, is described in Box 6-4. 

Kinetics of the transformations of the N-F class of fluorinating agents in water, acetonitrile, alcohols, and aqueous solutions of alkali metal hydroxides have been studied.159 Other kinetic studies include die reactions of triphenylphosphine with 3-methoxy- or 3-acctoxy-4,4,5,5-tetrasubstitutcd-1,2-dioxolanes,160 the reactions of 2-amino-5-chlorobenzophenone witii HC1 in MeOH-H20 (die aspect of nucleophilic aliphatic substitution lies in certain products arising from attack of AH2 on CH3OH there are six products in all, and rate constants are evaluated for die formation of each of them),161 and the hydrolysis of derivatives of diazidophenyhnethane.162... 

The determinations of hydrolysis constants from conductance measurements cannot be regarded as accurate the assumption has to be made that the added free acid or free base has a negligible conductance. This is reasonably satisfactory if the acid or base is very weak, e.g., a phenol or an aniline derivative, but for somewhat stronger acids or bases, e.g., acetic acid, an appreciable error would be introduced it is sometimes possible, however, to make an allowance for the conductance of the added acid or base. 

The principal disadvantage of TMS derivatives is the ease of postreaction hydrolysis in the presence of water. Most of these compounds cannot exist in aqueous media. Other types of derivatives, namely dimethyl-tert-butyl silyl ethers, have approximately 10 times lower hydrolysis constants, owing to steric hindrance of Si — O bonds by tert-butyl groups. Unfortunately, their mass spectra are not so informative for elucidation of the structures of unknown analytes, because the base peaks for all of them belong to noncharacteristic ions [C4Hg] with m/z 57 and [M — C4Hg]. ... 

Comparison of eq 16 and 17 indicates that neither electronic nor hydro-phobic factors play an important part in the inhibition. Thus it appears that the phosphonates interact with the enzyme in such a way that they cannot come in contact with a hydrophobic region of the protein. The range of electronic forces covered by the R groups was small so that a may be more important than eq 17 would indicate. Some overlap between E and a constants tends to obscure the role of a. The fact that, a constant derived from hydrolysis studies under homogeneous conditions, should apply to heterogeneous catalysis is surprising and indicates much more use for this parameter than one would have had reason to expect. 

The acidity constant (hydrolysis constant) can be derived by multiplying the numerator and denominator by [OH ] ... 

A recent review on the aqueous complexes of zirconium has been published by Nagra/Paul Scherrer Institute (PSI) as part of an update to their thermochemical database [2002HUM/BER]. For the hydrolysis species, these authors included in the Nagra/PSI update the stability constants proposed by [76BAE/MES] for ZrOH, Zr(OH)4 and Zr(OH)j. As indicated above, the stability constant derived for Zr(OH)4 may be questionable due to the fact it was obtained from solutions that may contain a... 

However, for each set of four constants only nine data points are available in a very narrow pH range. It is hard to believe that all species are present in sufficient quantity to be clearly distinguished. The method chosen for the derivation of the stability constants is very susceptible to accumulation of errors initially the first hydrolysis constant is developed, then, by successive fits the other constants. For the first hydrolysis constant one could obtain by SIT extrapolation a value for log y0°, = (0.85 0.02) based on data from perchlorate and nitrate media and As = - 0.79 or - 1.00 kg-mof assuming perchlorate or nitrate media, respectively. However, even these constants are not very reliable because, based on data of other authors, it is rather unlikely that at pH... 

For example, in several hydrolysis studies, allowance is made for complexation of Ni with chloride, using an association constant, the calculated activity of water. An interaction coefficient of NiOH with Cf is then derived as part of the same calculation that defines a value for the first hydrolysis constant for Ni. Conversely, association between Ni " and CF could have been neglected, an interaction coefficient for Ni " with cr then would have been specified, along with a different interaction coefficient for NiOH with cr. In theory, there should be no effect on the value of the selected hydrolysis constant, K°, at / = 0. 

Three publications [49GAY/GAR], [80TRE/LEB2], [89ZIE/JON] report thermodynamic properties for the Ni(OH)2(aq) and Ni(OH), species. The hydrolysis constants for reactions (V.26) and (V.27) can be derived from solubility equilibria ... 

Though the values for ai,m, etc. in equation (1) can of course be expressed in terms of the hydrolysis constants for the separate bonds, the treatment becomes extremely complicated as a different constant will be required for each polypeptide in which the particular bond occurs. In other words, the constant will vary as the reaction proceeds. Thus Kuhn et al. (1932) found that a three line formula was required to express the rate of hydrolysis of tetraglycine. Thus it does not seem that any rigid mathematical approach can be given at present, and we shall have to be content with a few generalizations derived largely from experimental observations. 

For these reasons, hydrolysis constants simply fitted to solubility data for Th(IV) hydroxide or hydrous oxide or crystalline Th02(cr), e.g., those in [1964NAB/KUD], [1989MOO], are not reliable and usually in strong contradiction to values derived using other methods. Therefore the present review at first selects the hydrolysis constants from studies based on potentiometric and solvent extraction studies. In a second step the selected hydrolysis constants are used to re-evaluate the published solubility data at pH < 5, i.e., to calculate the corresponding solubility constants. The recalculation of the pH-dependent solubility curves provides furthermore a test of the consistency of the selected data set, in particular for the neutral complexes predominant in the neutral and alkaline pH range. 

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