Specific Solute-Solvent Interactions and Proton Transfer Reactions

4-3 SPECIFIC SOLUTE-SOLVENT INTERACTIONS AND PROTON TRANSFER REACTIONS 

Conjugate add-base pairs Recall from Chapter 3 that the definition of adds and bases most useful to analytical chemistry is that of Bronsted, in which a conjugate acid-base pair is related by the reaction 

Equation (4-7) represents an add-base half-reaction, which involves protons, analogous to an oxidation-reduction half-reaction (Chapter 15), which involves electrons. Protons, even less than electrons, do not exist in a free state to an appreciable extent. Therefore an add dissociates to yield protons only when a base is available to accept them that is, two conjugate pairs are necessary for an acid-base reaction. Several conjugate add-base pairs, arranged in order of decreasing acidity of HA and therefore increasing basicity of A , are listed in Table 4-1. 

The equilibrium constant of the acid-base half-readion (4-7) could be taken to be a measure of the intrinsic addity of HA, and its reciprocal a measure of the intrinsic basidty of A . Thus  

For a complete acid-base reaction, two add-base half-reactions are combined in the correct way, 

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