Prediction of Hydrolysis Stability Constants

The coefficient of determination is very high (r = 0.9939) demonstrating that the function can be used effectively to describe the variation in the stability of the species (there are 72 data values). The calculated intercept is Int = 

The ionic radii used in the g z r + 2) function are the same for both the M(0H)2 and species, except for the ionic radii used for zinc(ll). 

Powell et al. (2013) suggested that zinc(II) changed coordination states, from octahedral to tetrahedral, when transitioning from ZnOH to Zn(OH)2(aq). Such a transition would result in a reduction in the ionic radius and an increase in the stability of Zn(OH)2(aq) as was indicated by Powell et al. (2013). The ionic radius utilised for the monomeric hydrolysis species of zinc(II) (other than for ZnOH ) is 0.64 A. 

There are three ionic radii that change in the transition from M(OH) species to M(OH)3 species. The ionic radii of the small ions Be and Fe become larger (0.38 and 0.71 A, respectively) and that of AP becomes smaller (0.48 A). It is possible that the former two undergo hydroxide ion-hydroxide ion repulsion because of their small size, leading to a reduced stability. Aluminium(III) also likely has the same repulsive forces between the bound hydroxide ions but changes its coordination state from octahedral to tetrahedral. For these ions, the ionic radii are retained for all higher monomeric hydrolysis species. 

On the basis of the intercept values for the three monomeric species, the values calculated for log U12 and log Ui are 1.35 and 4.30, respectively. From these values, the calculated value for log k in Eq. (2.89) is -1.05 from log U12 and -1.17 from log The average of these two values leads to a value for k of 0.078. If this value is utilised, then the calculated value for log Ui is 8.04 from which an intercept of Int = -66.12 and a slope of Sip = 0.5632 (assuming that the intercept 

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