Acid strength of inorganic ion exchangers

Case (a), implying random orientation or free rotation, is apparently realized in the high-temperature form of KOH. The transformation from (b) to (c) is to be expected with increasing dissociation of the proton. 

Amphoteric behavior can be deduced by following the progressive dissociation reaction of the acid formed in reaction (11). From Eqs. (10) and (11). 

When the concentrations in the ion exchanger of E-0 M and EOHJX are equal, the equiadsorption point (lAP), pHj, can be defined by 

With its determination carried out at constant ionic strength the pH, value, so obtained, provides an assessment of the acidity of the amphoteric ion exchanger. This pH, relatable to the average value of pKj and pK2 with Eq. (16), is very close to the value of the isoelectric point 0 )- Paries [105] has pointed out that the relationship between the lEP of a solid surface and the valency-effective ionic radii, when corrected for crystal field effects, coordination, hydration, and other factors, is quite good. He also has indicated that the broad probable lEP range characteristic of a cation oxidation state may be selected from the data in Table 2 as shown below. It is known that the lEP for amphoteric oxides is affected by the presence of impurities, crystallinity and the chemical species under investigation. 

Hydrous aluminum oxide is used frequently in chromatographic columns. Hydrous oxides of Ga, In, and the lanthanides may also be employed as inorganic ion exchangers. However, substantive research of these oxides has not been performed. 

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