Ionization: constant: decrease with

Shown here ate some pidibasic acids. How can you account for the fact that the difference between the first and second ionization constants decreases with increasing distance between the carboxyl groups ... 

The ionization potential is the energy required to remove the most loosely held electron from the molecule. Generally, ionization potentials decrease with molecular size and the degree of unsaturation. However, they do not vary greatly for complex molecules and, to a first approximation, can be considered constant. 

R" = COOMe to 22 dm mol s" for R = H and R" = Ph. The rate constants for addition of PhCF were slightly lower. The rate constants decreased with increasing Ti-ionization potential of the alkyne, except for very electron-deficient alkynes such as dimethyl acetylenedicarboxylate. The correlation indicated that in these additions the carbenes generally behave as electrophiles, whereas with the acetylenedicarboxylate carbenic nu-cleophilicity comes into play. The rate constant of addition of phenylchlorocarbene to 3-hexyne was determined as a function of temperature. The reaction appeared to be entropy controlled Ea = 8.8 + 0.4 kJ mol and AS = -82 J mol" K The corresponding alkenes have rate constants and activation parameters in the same order of magnitude. 

To examine this peculiar behavior, we have converted the elastic compressibility modulus, per unit area, Y (Fig. 12a), to the modulus per chain, Y = F/10 F (Fig. 12b). The elastic compressibility modulus per chain is practically constant, 0.6 0.1 pN/chain, at high densities and jumps to another constant value, 4.4 0.7 pN/chain, when the density decreases below the critical value. The ionization degree, a, of the carboxylic acid determined by FTIR spectroscopy gradually decreases with increasing chain density due to the charge regulation mechanism (also plotted in Fig. 12b). This shows that a does not account for the abrupt change in the elastic compressibihty modulus. 

The dielectric properties of the solvent have also an influence on the ionization constant of an incompletely ionized substrate. By the process of ion dissociation the concentration of associated ions is decreased this results because the latter are in equilibrium with non-ionized species and the ionization equilibrium will be restored by the formation of additional associated ions. 

The results of the alkylbenzene series may also be readily explained in terms of ir complex adsorption. In this series, the molecular orbital symmetry of individual members remains constant while the ionization potential, electron affinity, and steric factors vary. Increased methyl substitution lowers the ionization potential and consequently favors IT complex adsorption. However, this is opposed by the accompanying increase in steric hindrance as a result of multiple methyl substitution, and decrease in electron affinity (36). From previous data (Tables II and III) it appears that steric hindrance and the decreased electron affinity supersede the advantageous effects of a decreased ionization potential. The results of Rader and Smith, when interpreted in terms of tt complex adsorption, show clearly the effects of steric hindrance, in that relative adsorption strength decreases with increasing size, number, and symmetry of substituents. 

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... 

In this equation, 7 is the mean ionization potential, which corresponds to the average energy used to ionize all the electrons in the atom, and is obtained experimentally. The values of mean ionization potential for elements in flue gas are listed in Table 1. The ratio of 7/Z decreases with increasing Z and becomes almost constant for substances with Z greater than sulfur to be 10 1. 

Ions are stabilized by a polar solvent. The electrostatic dipoles f the solvent directly interact with the electrical charges of the ions, and the dielectric constant decreases the tendency of the ions to reassociate. The ionization of a neutral acid, as in equation 5.38, is depressed by the addition of a solvent of low polarity to an aqueous solution (Table 5.3). 

This ionization constatil in terms of activities is called the true or thermodynamic ionization constant. It docs not differ too much from the K in Eq. (14) for sufficiently low ionic strengths. The two differ more markedly for appreciable ionic strengths. Nuw suppose a salt with no common ion is added to the solution. The ionic strength of the solution will be increased. This increase in ionic strength causes a decrease in the activity coefficients of the ions except in very concentrated solutions. Thus for K of Eq. (18) to stay constant the concentrations of the ions must increase to offset the decrease in their activity coefficients. The ammonia must therefore increase in ionization and K as defined by Eq. (14) must increase. This is known as a salt effect. 

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