Techniques for Measuring Acidity

The role of any technique used for characterizing acidity is to give a quantitative measurement of the number of acid sites (extensive factor) and their strength (intensive factor). In addition, it should ideally be able to differentiate between Brpnsted and Lewis types of acid sites. Of the techniques most commonly used for this purpose, few are able to characterize the acid sites accurately and quantitatively. Thus, in most instances a combination of characterization techniques become necessary. 

Many techniques have been used for measuring the acid characteristics of catalysts. In general, they can be classified into three types  

The use of these techniques in the recent literature is discussed in the next section. 

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It can be seen from the foregoing discussion that the interpretations of the observed acidities leave something to be desired even for such a fundamental series of compounds as the simple hydrides. The matter has been reopened in recent—, years by the development of techniques for measuring acidities in the gas phase.86 The available results reemphasize the fact, already well known from previous work, that solvation factors have a profound influence on the course of acid-base reactions. But the gas-phase experiments do more than this they call into question some of the fundamental assumptions and interpretations that haVe long been used to account for observed acidities in terms of molecular structure. 

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