Correction to zero ionic strength

According to the specific ion interaction model the following equation is used to correct for ionic strength for the reaction considered here  

The ionic strength / and the molality m (/ cio- pressed in molal units, 3 M NaC104 corresponding to 3.5 m NaC104 (see Section 11.2), giving D = 0.25. This results in  

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Estimated from corrected to zero ionic strength as in Table B1 (Baes and Mesmer, 1981). "Assume 2 = 0-3 /3i-... 

Morse et al. (1987) also recomputed these constants based largely on Berner s data. Their results are identical to those listed above, except for mackinawite, for which they give p eq = 3.55. Bagander and Carman (1994) measured the in situ solubility of amorphous FeS in near-shore bottom sediments of the Baltic Sea between 13 and 19 C. Corrected to zero ionic strength and 25°C their measurements lead to = 2.55 for FeS(am) in reasonable agreement with the value given above. 

Discrepancies are principally treated as described in Section C.4. Again, two cases can be defined. Case I Only two data are available. Case II An outlier cannot be discarded. If only one data point is available, the procedure for correction to zero ionic strength outlined in Section C.6 should be followed. 

Correction to zero ionic strength (Appendix B) gives log,p K° (A.47) = (2.88 0.30), where the uncertainty has been assigned in the present review. The small Ae correction has been based on the value for s(Na, HPO4") from Table B-5 (rather than using the equation in Table B-6), and s(Ni, NOj ) = 0.18 kg-mol. ... 

Van de Graaf B, Hoefnagel AJ and Wepster BM, Substituent effects. 7. Microscopic dissociation constants of 4ramino- and 4-(dimethylamino)benzoic acid, /OC, 46(4), 653-7 (1981). NB The method gave a pJC value for benzoic acid of 4.21 (comparable to the best in the literature) and hence file mefiiod was well validated. Results at low ionic strengfiis (0.04 to 0.06) were corrected to zero ionic strength. 

It should be pointed out that most of the equilibrium constants listed in this table refer to solutions of constant ionic strength with the exception of Butler s data which have been corrected to zero ionic strength. The effect of ion association has also been neglected. The data of Pavarov et were obtained by radiotracer techniques at 18 2°C. 

The derivation of p a values from pH measurements is too familiar an exercise to be repeated here. Since pH values refer to a standard state for activities in methanol, the acidity constants will likewise have this reference state, i.e. they will be Ka values. When measurements are made in very dilute solutions (ca. 10" AO, not only are corrections to zero ionic strength small but ion-pairing of buffer salts becomes negligible. Some results of Juillard s measurements, based on the de Ligny standard buffers, are given in Appendix 3.5.5. 

In a small number of cases, a stability or solubility constant is available for a particular species or phase from a single study only. In these cases, the constant will be accepted if it can be related to other similar data (e.g. a lanthanide metal ion being compared with the data of other lanthanide metal ions). If the single study relates to measurement of the stability or solubility constant at a fixed ionic strength (and no other data are available at other ionic strengths), it can be corrected to zero ionic strength if similar data are available for like metal ions where... 

Data reported for the stability constant of BaOH are listed in Table 7.24. As with strontium(II), the data cover only a relatively small range of temperature (5-45 °C). There are few data that have been obtained in media that are fixed at high ionic strength, most likely due to the low stability of the species. The majority of data that were obtained at fixed ionic strength were at low concentration and were corrected to zero ionic strength by the authors or in subsequent studies. 

As was the case for strontium(II), all of the studies on the hydrolysis of bar-ium(II) were undertaken many years ago. As with strontium(II), the data were corrected to zero ionic strength in the studies in which the stability constants were determined, even though they may have been calculated from previously published data. There appears to be only a single study where the stability constant of BaOH has been reported in solutions of fixed ionic strength. 

The stability constant for U(OH)4(aq) given by Manfredi et al. (2006) from measurements in a medium of 3.0 mol 1 perchlorate and at 25 °C of log /l4 = -7.70 0.04 obtained from emf measurements is inconsistent with any of the data determined from solubility measurements. Moreover, the stability constant corrected to zero ionic strength proposed by these authors was log 4° = -4.93 0.35, more than five orders of magnitude more positive than any of the accepted values determined from the solubility measurements. On this basis, the value of Manfredi et al. (2006) is not retained by this review. 

Stability constant data are available for four monomeric species of zinc, ZnOH to Zn(OH) . The reported stability constants are listed in Table 11.61 and cover the temperature range of 12.5-350 "C. Majority of the data accepted by Powell et al. (2013) were corrected to zero ionic strength by the authors of the studies. Data at fixed ionic strength are extremely variable. As was done by Powell... 

There have been a number of studies of the hydrolytic reactions of thalliumfl). The majority of data were either corrected to zero ionic strength in the original study (or recalculated in a later study) or utilised perchlorate media. The studies of Kul ba, Yakovlev and Kopylov (1970) and Sipos et al. (1997) both postulated the formation of TlOH(aq) and Tl(OH)2 although the latter species is only minor, it was needed to describe the acquired data at high ionic strengths. The reported data are listed in Table 13.27. 

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