Acid-base polyprotic equations

Polyprotic Systems In the same fashion as equation 91 has been derived, expressions for the buffer intensity of polyprotic acid-base systems can be developed. In Table 3.8, the buffer intensity of a diprotic acid-base system is derived. A polyprotic acid can be treated the same way as a mixture of indi-... 

Calculating acid-base titration curves Strong acids, strong bases (Table 8.1), p. 266 Spreadsheet calculations, p. 269 Weak acids, weak bases (Table 8.2), p. 272 Spreadsheet calculations, p. 277 Indicators (key equations 8.4, 8.5), p. 270 Titration of Na2C03, p. 280 Titration of polyprotic acids (Table 8.3), p. 281 Titration of amino acids, p. 286... 

In addition, the equilibria on the left hand side of eqn (8.20) can sometimes be defined by the dissociation constants Kdissj (j = 1, 2,. .., m), that are very familiar from acid-base reactions (the acidity constants Kgj for polyprotic acids are in fact dissociation equilibrium constants). The relationships between all these constants are given by the sets of eqn (8.21). In certain cases, it is more convenient to use one type of equilibrium constants or another, and the choice is typically made based on the simplicity of the mathematical equations describing a system of interest. Definitions and uses of all equilibrium constants in determination of concentrations of all species present in a complex system are given in many monographs on coordination chemistry. ... 

The equivalent expression for polyprotic acids, zwitterions and weak bases are qiven in ref. 339. Froe equation (4.24) it can be seen that the relationship between k and pH is sigmoidal with an inflection point at the pH corresponding to the pK, of the acid. A snail change in the pH near the pK, value for the acid results in a large change in k but at extrene values with respect to the pl ... 

The titration curve of a polyprotic acid can be obtained by using the same approach as for monoprotic weak acids or weak bases. The mass and charge balance equations... 

Equation (5.164) can be rearranged for mono- and polyprotic weak acids (or weak bases) as follows ... 

Drugs may also have more than two pKa values, such as polyprotic or polybasic compounds (e.g., minocycline), and such drugs exhibit a complex pH solubility profile. It is essential to know per se pH of the drug solution during preformulation studies. The pH is measured or theoretically calculated if the pKa and drug concentration C are known. The pH of a weak acid or the salt of a weak base and a strong acid can be calculated using the equation... 

The equilibrium constants to be determined in this example are protonation constants, introduced in Chapter 20. The protonation constant of a base L is the reciprocal of the acid dissociation constant Kg for the corresponding conjugate acid HL. For a polyprotic acid, the general expression for the protonation constant is given by equation 22-5. 

In picturing reactions of a polyprotic acid with a strong base, we shall assume that enough base is added to react with all of the acidic hydrogen atoms. The following complete equations describe the reactions of the diprotic acid sulfuric acid and the triprotic acid phosphoric acid with sodium hydroxide. Each equation represents the sum of a series of reactions in which the acidic hydrogen atoms are removed one at a time. 

This ability to act as a base or an acid is called amphoterism. Any anions of polyprotic acids, such as HCO3, H2P04, and HP04, which contain replaceable hydrogen ions, are amphoteric. Some hydroxides, such as A1(0H)3 and Zn(OH)2, are also amphoteric, reacting with a base or acid, as illustrated by the following equations ... 

A general method for estimating dissociation values, given a set of solubility and pH measurements for tyrosine and 2,8-dihydroxyadenine, is presented. Equations are derived extending solubility, pH and dissociation constant relationships from weak acids and bases to polyprotic, amphoteric compounds. Included in ttie estimation procedure is a subroutine for approximating ttiermodynamic dissociation constants."... 

When the neutralization steps of a polyprotic acid or polybasic base are sufficiently separated, the titration has multiple equivalence points. T FIGURE 17.12 shows the two equivalence points corresponding to Equations 17.13 and 17.14. 

Some polyprotic acids can form more than one salt, depending on the number of H s that react with base. Write balanced molecular, total ionic, and net ionic equations to represent the following neutralization reactions between KOH and... 

A Write stepwise equations for protonation or deprotonation of each of these polyprotic acids and bases in water, (a) C03 (b) H3ASO4 (c) NH2CH2C00 (glycinate ion, a diprotic base). 

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