Base ionization constant table

Kjj is the base dissociation constant, or base ionization constant, that measures a base s strength. Some values are given for bases in Table 3. 

The constant is called the base ionizahon constant. The base ionization constant is the value of the equilibrium constant expression for the ionizahon of a base. The smaller the value of K, the weaker the base. values and ionization equahons for several weak bases are listed in Table 19-4. 

Step 3 From the preceding discussion and Table 15.3 we write the equibbrium constant of hydrolysis, or the base ionization constant, as... 

The next step is to calculate the pH of the solution that results from the hydrolysis of the CH3C00 ions. Following the procedure described in Example 15.13 and looking up the base ionization constant (Ky,) for CH3COO in Table 15.3, we write... 

Suppose you wish to calculate the pH of 0.10 M NaCN. As you have seen, the solution is basic because of the hydrolysis of the CN ion. The calculation is essentially the same as that for any weak base (Example 17.5). You would require the base-ionization constant of the cyanide ion. However, frequently the ionization constants for ions are not listed directly in tables, because the values are easily related to those for the conjugate molecular species. Thus, the Kb for CN is related to the Ka for HCN. 

Like ammonia, amines are weak bases. Table 16.2 gives base-ionization constants of some amines. 

Finding the [OH ] and pH of a weak base solution is analogous to finding the [H30 ] and pH of a weak acid. Similarly, we can neglect the contribution of the autoionization of water to the [OH ] and focus solely on the weak base itself. We find the contribution of the weak base by preparing an ICE table showing the relevant concentrations of all species and then use the base ionization constant expression to find the [OH ]. Example 15.12 shows how to find the [OH ] and pH of a weak base solution. 

Substitute the value of the base ionization constant (from Table 15.8) into the expression and solve for x. 

Table 23.2 lists the base ionization constants for several amines. We know that alkyl groups donate electrons to carbocations, and that they donate electrons in electrophilic aromatic substitution reactions. We might expect alkyl-substituted amines to be slightly stronger bases than ammonia because the inductive donation of electrons to the nitrogen atom by alkyl groups makes the unshared pair of electrons more available to a proton. However, the order of basicities does not increase in a simple order. 

It follows that Kt can be theoretically calculated from Kt and the ionization constant of either of the alkylated derivatives. In practice, however, this can only be done if there is an appreciable difference between the constant for the alkylated derivative and the value of Kt. Mason has argued that it is better to use the ionization constants of both alkylated forms in the equation Kt = Xmethyl groups can be base-weakening as well as base-strengthening the data shown in Table I indicate that the base-weakening inductive... 

Section 3.3.4 pointed out that cosolvents alter aqueous ionization constants as the dielectric constant of the mixture decreases, acids appear to have higher pKa values and bases appear (to a lesser extent than acids) to have lower values. A lower dielectric constant implies that the force between charged species increases, according to Coulomb s law. The equilibrium reaction in Eq. (3.1) is shifted to the left in a decreased dielectric medium, which is the same as saying that pKa increases. Numerous studies indicate that the dielectric constant in the region of the polar head groups of phospholipids is 32, the same as the value of methanol. [381,446-453] Table 5.2 summarizes many of the results. 

Since NH4+ is a stronger acid than N02 is a base, the solution will be acidic. The ionization constants were computed from data in Table 17-3 and with the relationship Kw = Ktx Kb. 

Kv is the self-ionization constant for water (Table 3.2) and equation (3.18) reflects the not surprising inverse relation between Ka and Kh. It is only when Ka and Kv for a compound are of different magnitudes that it may be classified as an acid or a base. An example which is difficult to classify is hypoiodous acid (HOI) where K = 2.5 x lO11 mol dm 3 andKh = 3.2 x 10 10 mol dm3. Although Kb has been widely used in the past, it is a quantity which is largely redundant, for Ka (or pKa) may be used to express the strength of bases as well as acids, see Table 3.3. 

Strong et al. [8] have determined the ionization constant of benzoic acid in H2O as a function of ternperamre by conductance methods. Their data are listed in Table 20.3, with the pK based on a hypothetical standard state of 1 mol dm. Temperature was controlled to +0.002°C. 

The ionization constants of a number of 1,2,4-thiadiazoles have been determined potentiometrically87,88 or by Hammett s method205 based on the measurement of ultraviolet absorption spectra in media of different hydrogen ion concentration.126 The results are given in Table VTI. 2- and 4-Aminopyrimidine differ in their basicities (pA ... 

Table 10 The Nucleic Bases, Their Proton Ionization Constants (pit,), and the Nomenclature of Their Nucleoside and Nucleotide Derivatives...

The ionization constants for selected pharmaceutical drugs and reference weak acids and weak bases are listed in Table 2.1. 

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