Acid dissociation constants , theoretical phase

Shibukawa et al. [109] published a new liquid chromatographic method for the determination of acid dissociation constants. On the basis of theoretical equations regarding the effect of background mobile phase ions on the retention of ionic analytes on a non-ionic polymer packing, they could determine simultaneously the dissociation constants (p/fa) and the charges of analyte molecules. They used chloride and perchlorate ions in the mobile phase as they exhibit large differences in the retention on the hydrophilic polymer packings used, so that the effect of the mobile phase electrolyte on the retention factor of an ionic analyte could be clearly evaluated. 

In deriving theoretical equations of the current-potential (or time) curves of ion transfer of an acid we shall make essentially the same assumptions as the assumption 1-6 above. It is noted here that theoretical equations of the more general case, that is, of a dibasic acid, such as expressed by AH2 = AH + H, AH = A + H, can be derived [24], but are not included here, to save space. The formal formation constant, and formal dissociation constant,, in the a phase is defined by... 

Theoretical considerations show that the free energy of dissociation of an acid in water, and hence the dissociation constant, is governed by the algebraic sum of the free energies for the solution of the undissociated acid in water, for vaporisation of the acid, for the formation of a free proton and an anion from the molecule of acid in the gas phase, and for hydration of the proton and anion. Thus the true acidity, given by the third of these... 

Figure 27. The zeta potential and surface charge density of HgQgCdQgTe as a function of pH. The solid line is the best fit theoretical curve to the acid dissociation model with pK = 12.7, pK = 2.4, pK = 7.6, and y = 0,30. The pK values correspond to the dissociation constants of the different phases of tellurous acid and y is proportional to the total acid site density. The surface oxide chemistry is HTeOg" (positive zeta potential, H2Te03 (zero zeta potential), HTeOg (first step in the zeta potential), and TeOa" (second step in the zeta potential). (With permission of American Institute of Physics.)...

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