Acids ionization constants and

If tautomerism occurs in dilute aqueous acid, then K and K l will be the thermodynamic acid ionization constants and (26) will hold thus... 

Remember Thc strongest acids dissociate most readily. Of the 9 acids listed in Table 10-5, the strongest is sulfuric (1), with the highest acid ionization constant, and the weakest is phosphoric (3). 

Ross, D.L. and Riley, C.M. Physicochemical properties of the fluoroquinolone antimicrobials II. Acid ionization constants and their relationship to structure. Int. /. Pharm., 83,267-272,1992. 

An important relationship between the acid ionization constant and the ionization constant of its conjugate base can be derived as follows, using acetic acid as an example ... 

Specific examples of important equilibrium systems include sparingly soluble salts, weak acids, and weak bases. For salts, the solubility product constant, K, provides a way to calculate equilibrium concentrations and molar solubilities. Weak acids and bases also have specifically named equilibrium constants the acid ionization constant, and the base ionization constant, Aj,. 

Enantiomers have identical physical and chemical properties in achiral environments. The enantiomers of tartaric acid (Table 6.1), for example, have the same melting point, the same boiling point, the same solubilities in water and other common solvents, and the same values of pif (the acid ionization constant), and they all undergo the same acid-base reactions. The enantiomers of tartaric acid do, however, differ in optical activity (the ability to rotate the plane of polarized light), a property that is discussed in the next section. 

Hammett plots. For phenylacetic acid ionization constants and for benzoic acid in ethanol. Data to generate these plots were taken from Bright W. L., and Briscoe, H. T. "The Acidity of Organic Acids in Methyl and Ethyl Alcohols." J. Phys. Chem., 37,787 (1933), and Dippy, J. F., and Williams, F. R. "Chemical Composition and Dissociation Constants of Mono-Carboxylic Acids. Part I. Some Substituted Phenylacetic Acids." /. Chem. Soc., 161 (1934). 

Acidity constants are also called acid ionization constants and. less appropriately, dissociation constants. 

Scott, S. L., W.-J. Chen, A. Bakac et al. 1993. Spectroscopic parameters, electrode potentials, acid ionization constants, and electron exchange rates of the 2,2 -azinobis(3-ethylbenzothiazolineine-6-sulfonate) radicals and ions. J. Phys. Chem. 97 6710-6714. 

What are diprotic and triprotic acids List an example of each. Define the acid ionization constant and explain its significance. Write an equation for the autoionization of water and an expression for the ion product constant for water (Ky,). What is the value of a at 25 °C ... 

The ionization eonstant should be a function of the intrinsic heterolytic ability (e.g., intrinsic acidity if the solute is an acid HX) and the ionizing power of the solvents, whereas the dissoeiation constant should be primarily determined by the dissociating power of the solvent. Therefore, Ad is expeeted to be under the eontrol of e, the dieleetrie eonstant. As a consequenee, ion pairs are not deteetable in high-e solvents like water, which is why the terms ionization constant and dissociation constant are often used interchangeably. In low-e solvents, however, dissociation constants are very small and ion pairs (and higher aggregates) become important species. For example, in ethylene chloride (e = 10.23), the dissociation constants of substituted phenyltrimethylammonium perchlorate salts are of the order 10 . Overall dissociation constants, expressed as pArx = — log Arx, for some substanees in aeetie acid (e = 6.19) are perchloric acid, 4.87 sulfuric acid, 7.24 sodium acetate, 6.68 sodium perchlorate, 5.48. Aeid-base equilibria in aeetie acid have been earefully studied beeause of the analytical importance of this solvent in titrimetry. 

Assume that the reaction occurs between the two uncharged species, MNNG and Am, with a rate constant kN. Express ks as a function of tN, K m, Kan, and [H. Sketch the anticipated pH profile. Actually, this situation is further complicated because kN, although constant over some pH range, shows a further variation that can be attributed to an acidic intermediate. Derive an expression for kN as a function of [H + ] from the scheme shown, denoting the acid ionization constant of the steady-state intermediate as Knl. 

For the purpose of systematizing kinetic and equilibrium data, for literally hundreds of reactions, it is desirable to have a single reference series for all. Hammett adopted as the standard the acid ionization constants for substituted benzoic acids in aqueous solution at 25 °C. This choice was fortunate because the compounds are stable and for the most part readily available. Also, their pA"a s can easily and precisely be measured for nearly every substituent. Thus, one constructs a plot according to either of the following equations, in which Eq. (10-4) constitutes a further example ... 

The values of Hn and E are zero for water, by virtue of the constants 1.74 and 2.60. In these definitions, pKa refers to the acid ionization constant of the conjugate acid of the nucleophile, and E° to the standard electrode potential for the two-electron half-reaction ... 

The ability of an acid to lose a proton (acid strength) is experimentally measured by its acid ionization constant the higher the value of this constant the higher is the concentration of H30+ ions, and the stronger the acid. 

Long, F. A. Ballinger, P, Acid ionization constants of alcohols in the solvents water and deuterium oxide, in Pesce, B. (ed.), Electrolytes, Pergamon Press, New York, 1962, pp. 152-164. 

Group 6A hydrides dissociate in two stages. Their acid ionization constants, Kx and K2, are shown below ... 

A graphical depiction of log(kjp) plotted as a function of log( Xa/p), where is the rate constant for general acid catalysis, is the acid ionization constant, p is the number of equivalent protons on the acid, and q is the number of equivalent positions where a proton can be... 

Table 10-3 gives acid ionization constants for several familiar acids at 25 C. The values for the strong acids are not well defined. Examine the Ions column and see how every acid yields a hydrogen ion and a complementary anion in solution. 

Phosphoric acid behaves as a triprotic acid, having three ionizable hydrogen atoms. The hydrogen ions are lost sequentially. The chart below provides the ionization constants and their logs. 

Isoxsuprine HCl has been found to exhibit two acid ionization constants, with pKa values of 8.0 and 9.8 being reported [3]. 

Relative quantitative strengths of acids and bases are given either by their ionization constants, and K, or by their pK and pK values as defined by ... 

Moreover, many hydrogen compounds, when dissolved in such solvents, ionize more or less completely lo give solvated protons and anions, In the case uf polybasic acids, ionization constants are reported for each step in this dissociation. 

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