Bases, chemical polyprotic

The acidity or basicity of a solution is frequently an important factor in chemical reactions. The use of buffers of a given pH to maintain the solution pH at a desired level is very important. In addition, fundamental acid-base equihbria are important in understanding acid-base titrations and the effects of acids on chemical species and reactions, for example, the effects of complexation or precipitation. In Chapter 6, we described the fundamental concept of equilibrium constants. In this chapter, we consider in more detail various acid-base equilibrium calculations, including weak acids and bases, hydrolysis, of salts of weak acids and bases, buffers, polyprotic acids and their salts, and physiological buffers. Acid-base theories and the basic pH concept are reviewed first. 

Table 7.3 pK values at 25 °C of some acids and bases (upper section) and some large organic zwitterions (lower section) commonly used in buffer solutions. For polyprotic acids, where more than one proton my dissociate, the p/fa values are given for each ionization step. Only the trivial acronyms of the larger molecules are provided their full names can be obtained from the catalogues of most chemical suppliers... 

Among the most important chemical properties of amino acids are their acid-base properties. All are weak polyprotic acids because of the presence of both —COOH and —NHg groups. Given in Table 18.2 are p. values for each ionizable group of the 20 protein-derived amino acids. 

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