Ionization constant degree

Sect. 7 Ka a Abbreviations AAc BIS ConA DDS DMSO DLS IPN ionization constant degree of ionization acrylic acid N, N -methylene- bisacry lamide concanavalin A dextran sulfate dimethylsulfoxide dynamic light scattering interpenetrating network... 

I = a factor depending upon the average molecular size B = degree of ionization a = degree of ionization m, n, and / = constants... 

This chapter considers ionizable drug-Uke molecules and the effect of such ionization on pharmaceutic properties. Most medicinal substances are ionizable [1]. The biological medium into which these substances distribute embraces a range of pH values. The ionization constant, pK, can teU the pharmaceutical scientist to what degree the molecule is charged in solution at a particular pH. This is important to know, since the charge state of the molecule strongly influences its other physicochemical properties. 

Very precise, classic, measurements of the ionization constant of acetic acid were made many decades ago [2]. The dependence of In K on temperature is illustrated in Eigure 10.2. As the temperature is increased from 273 K, In K and the degree of ionization increases gradually, reaching a maximum just below 298 K, and then... 

The same phenomenon is responsible for the decrease in the ionization constant of a polymeric acid such as poly(acrylic acid) with increasing degree of ionization [Kawaguchi et al., 1990, 1992 Morawetz and Wang, 1987]. This effect is somewhat moderated for acrylic acid-ethylene copolymers, since charge density on the ionized polymer is decreased. The basicity... 

The molecular conductivity of periodic acid in soln. containing one mol. in v litres of water has been determined by W. Ostwald,14 A. Rosenheim, and E. Lowenthal. The two sets of determinations are concordant. F. Kohlrausch gives 48 and 64 for the mobilities of the 10/ and C10/-ions respectively on the assumption that this ionization is HI04=H-+I0/, the calculated ionization constant K does not change much with. .dilution. Assuming the mobility of the hydrogen is 338 at 25°, V. Rothmund and K. Drucker have calculated the degrees of ionization, a, and the ionization constants K, from W. Ostwald s eq. conductivities A ... 

The phosphorescence spectra of the phenanthrolines have also been studied. The spectra of 1,7-phenanthroline,22,78 1,10-phenanthroline,22,78-80,82,87-89 substituted 1,10-phenanthrolines,80 and 4,7-phen-anthroline22,78 have been measured in a variety of conditions. The phosphorescence spectra of all the parent phenanthrolines have been obtained in heptane.84 The degree of polarization of the phosphorescence has also been investigated.78, 84,90 The lifetime of the phosphorescence of 1,10-phenanthroline, which is less than that of phen-anthrene,88 has been well investigated.54,55,80,89 91 The ionization constants of the excited triplet state of 1,10-phenanthroline have been calculated from the phosphorescence spectra. 22,88... 

This equation involves the assumption that mobilities of the ions coming from the electrolyte are constant from infinite dilution to the concentration in question. From the degree of dissociation and the concentration, the ionization constant or protolysis constant of a weak electrolyte can be obtained. 

The percentage degree of ionization, a and the ionization constant K% are also indicated. Hence, the first ionization constant is rather weaker than that of ammonium hydroxide, being somewhere near A1=3xl0-8. I. M. Kolthoff calculated for the second ionization constant of hydrazine, i 2—2-8 X10 3 and E. C. Gilbert said that it should be less than 10 12. P. Drude gave 53 for the dielectric constant at 22°. 

The results for the pyro-acid are so much like those for hypophosphoric acid, that E. Cornec argued a like complexity for the molecules of the two acids. G. A. Abbott and W. C. Bray calculated that with soln. containing c millimols of pyrophosphoric acid per litre, the degree of ionization, and the ionization constants, are ... 

Another observation that underlines the importance of drug-membrane interactions in tumor therapy is the increase in antineoplastic activity against resistant cell lines with increasing lipophilicity of the cytotoxic drugs at constant degree of ionization (pit, -8.4). Independently of the anthracycline used to induce resistance, cross-... 

For polyelectrolyte, in general, the following relationship is given in the degree of ionization, a, and the apparent ionization constant, pKa, which is popularly called the modified Henderson-Hasselbach equation (51). 

In dilute aqueous solutions, the three halides, HC1, HBr, and HI, are essentially fully ionized, but in the poorer ionizing solvent, methanol, ionization is partial. In the latter solvent, HC1 is the most weakly ionized of the three whereas HI is the most strongly ionized this order of acidities has already been discussed (p. 90 see also Exercise 14). The ionization constant for hydrofluoric acid in dilute solutions is 7.2 X 10 4, but in very concentrated solutions the degree of ionization appears to rise sharply, a behavior opposite to that of almost all other weak electrolytes. This increase in acid strength is almost certainly due to the increase in concen-... 

Ionization constants of polysilicic acids. The ionization constant Ki for equilibrium a) of a species of ionization degree i is the product of i ionization constants k corresponding to successive dissociation reactions. He aesume that all tetrahedra within any species dissociate once before the second possible dissociation of any tetrahedron occurs, and so on for successive dissociations. 

Eq. (4-10) can be used only for solvents of equal acid and base strength, because only the effect of the solvent relative permittivity on the degree of ionization is considered. Under these conditions, Eq. (4-10) predicts that the logarithm of the ionization constant of HA should be inversely proportional to the relative permittivity of the solvent in which HA is dissolved. However, one has to take into account the fact that the relative permittivities near solute ions can differ considerably because of the effect of dielectric saturation, which hinders the precise calculation of electrostatic interactions. Because of these restrictions, Eq. (4-10) can be expected to yield only semiquantitative results. Nevertheless, it allows us to predict qualitatively how the charge type of an acid affects the ionization constant in solvents of different relative permittivities. 

The reason for employing alternative treatments to ortho-substituted aromatic molecules is that changes in rate or ionization constants mediated by meta or para substituents are mostly changes in or because substitution does not affect AS or AS". Ortho substituents affect both enthalpy and entropy the effect on entropy is noteworthy because entropy is highly sensitive to changes in the size of reagents and substituents as well as degree of solvation. Bolton et al. examined the ionization of substituted benzoic acids and measured accurate values for AG, and A S... 

Acid ionization constants As you have learned, a weak acid produces an equilibrium mixture of molecules and ions in aqueous solution. Thus, the equilibrium constant, provides a quantitative measure of the degree of ionization of the acid. Consider hydrocyanic acid (HCN), a deadly poison with applications in the steel industry and in the processing of metal ores. See Figure 19-9. The ionization equation and equilibrium constant expression for hydrocyanic acid are... 

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