Acid ionization constants

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 ... 

Hydroxyl radicals. The acid ionization constant of the short-lived HO transient is difficult to determine by conventional methods but an estimate can be made because HO, but not its conjugate base, O -, oxidizes ferrocyanide ions HO + Fe(CN) — OH- + Fe(CN)g . Use the following kinetic data26 for the apparent second-order rate constant as a function of pH to estimate Ka for the acid dissociation equilibrium HO + H20 =... 

Ka is also widely called the acid ionization constant or acid dissociation constant. 

One of the most important types of aqueous equilibrium involves proton transfer from an acid to a base. In aqueous soiutions, water can act as an acid or a base. In the presence of an acid, symbolized HA, water acts as a base by accepting a proton. The equilibrium constant for transfer of a proton from an acid to a water molecule is caiied the acid ionization constant (Zg) ... 

The strength of a weak acid is measured by its acid ionization constant,. This equilibrium constant can be calculated from the measured pH of the solution, as illustrated in Example. ... 

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. 

The symbol for the equilibrium constant is K. It is called the acid ionization constant. 

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

Acetic acid, HC2H302, which is represented as HA, has an acid ionization constant Ka of 1.74 x 10 5. 

In dilute solutions, the concentration of water is almost constant. Multiplying both sides of the equilibrium expression by [H2O] gives the product of two constants on the left side. This new constant is called the acid dissociation constant, K. (Some chemists refer to the acid dissociation constant as the acid ionization constant. With either name, the symbol is Xg.)... 

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

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. 

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). 

Acetic acid, HC2H3O2, which is represented as HA, has an acid ionization constant of 1.74 x 10 (a) Calculate the hydrogen ion concentration, [H ], in a 0.50 molar solution of acetic acid. 

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

Kg refers to the acid dissociation constant which is the measure of an acid s strength. Some references call the acid ionization constant. 

Carbonates. Carbonic acid H CO, is present to the extent of (1.27 i of the total CO present in ihe solution that is formed by dissolving CO in H 0 ai room temperature. The CO may be expelled fully upon boiling. The solution reads with alkalis to form carbonates, e.g. sodium carbonate, sodium hydrogen carbonate, calcium carbonate, calcium hydrogen carbonate. The acid ionization constant usually cited for carbonic... 

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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