Ionic equilibrium concentration

Sentenac, H., Grignon., C., 198L A model for predicting ionic equilibrium concentrations in cell walls. Plant Physio. 68, 415 19. 

Solutions to complex ionic equilibrium problems may be obtained by a graphical log concentration method first used by Sillen (1959) and more recently described by Butler (1964) and Morel (1983). These types of problems are described further in Chapter 16 as they relate to natural systems. Computer-based numerical methods are also used to solve these problems (Morel, 1983). 

The problem asks for the equilibrium concentrations of the three ionic species [Au- leq,... 

Figure 4 illustrates the dependence of on Aq for the case when r = 1 at several different values of [Fig. 4(a)] and when = 0.5 and at several different values of r [Fig. 4(b)]. From Fig. 4(a), one can see that takes a maximum around y = 0, i.e., Aq The volume ratio affects strongly the value of as shown in Fig. 4(b), which is ascribed to the dependence of the equilibrium concentration on r through Eq. (25). This simple example illustrates the necessity of taking into account the variation of the phase-boundary potential, and hence the adsorption of i, when one tries to measure the adsorption properties of a certain ionic species in the oil-water two-phase systems by changing the concentration of i in one of the phases. A similar situation exists also in voltammetric measurements of the transfer of surface-active ions across the polarized O/W interface. In this case, the time-varying thickness of the diffusion layers plays the role of the fixed volume in the above partition example. The adsorption of surface-active ions is hence expected to reach a maximum around the half-wave potential of the ion transfer. 

Nevertheless, chemical methods have not been used for determining ionization equilibrium constants. The analytical reaction would have to be almost instantaneous and the formation of the ions relatively slow. Also the analytical reagent must not react directly with the unionized molecule. In contrast to their disuse in studies of ionic equilibrium, fast chemical reactions of the ion have been used extensively in measuring the rate of ionization, especially in circumstances where unavoidable irreversible reactions make it impossible to study the equilibrium. The only requirement for the use of chemical methods in ionization kinetics is that the overall rate be independent of the concentration of the added reagent, i.e., that simple ionization be the slow and rate-determining step. 

The discovery of diradicals in sulfuric acid or Lewis acid solutions of bianthrone and thianthrene raises the possibility of acid-catalyzed radical reactions for any unsaturated compound.448 Anything that increases the equilibrium concentration of the diradical should promote radical reactions. These results are important because previous to their discovery few chemists would have hesitated to say that a reaction catalyzed by sulfuric acid or aluminum trichloride, for example, was an entirely ionic one. Now we would not want to venture such an opinion without other reasons. 

The transfer of chemical molecules from oil to water is most often a surface area phenomenon caused by kinetic activity of the molecules. At the interface between the liquids (either static or moving), oil molecules (i.e., benzene, hexane, etc.) have a tendency to disperse from a high concentration (100% oil) to a low concentration (100% water) according to the functions of solubihty, molecular size, molecular shape, ionic properties, and several other related factors. The rate of dispersion across this interface boundary is controlled largely by temperature and contact surface area. If the two fluids are static (i.e., no flow), an equilibrium concentration will develop between them and further dispersion across the interface will not occur. This situation is fairly common in the unsaturated zone. 

Equilibrium Constant (K) An expression that relates the equilibrium concentrations (or pressures) of reactive species to one another. Its value is dependent on temperature, pressure, and the ionic strength of the solution in which the reaction is occurring. 

Saturated (1) Of a solution containing the equilibrium concentrations of solutes dictated by the solubility of a particular solid. As a result, the mass of the solid in solution will remain constant over time. (2) Of a solution that contains the equilibrium concentration of a gas. This concentration is determined by the temperature and ionic strength (salinity) of the solution and the partial pressure of the gas in the atmosphere. 

It should be noted that the condition of a dilute solution was introduced into the considerations for two reasons primarily, in order that it would be possible to replace the activities by concentrations and thus determine the equilibrium concentrations on the basis of (2.3.3) and, secondarily, in order for it to be possible to neglect the effect of pressure on the chemical potentials of the components whose electrochemical potentials appear in (2.3.2). Because of the differing ionic concentrations in solutions 1 and 2, the osmotic pressures in these solutions are not identical and this difference must be compensated by external pressure. A derivation considering the effect of pressure can be found, for example in [9] or p. 191 of [18]. 

Sometimes the activities are replaced by braces, e.g., Uml = ML -, here we prefer the former formality. The estimation of y, values by equations such as Eqs. (2.38) and (2.43) is unreliable for ionic strengths above about 0.5 M for univalent cations and anions and at even lower ionic strengths for polyvalent species. Consequently, values of (3° are rarely calculated, except for very exact purposes (see Chapter 6). Instead, measurements of equilibrium concentrations of the species involved in the reaction are used in a medium of fixed ionic strength where the ionic strength, /, is defined as I=V2l. Ci Zi M [see Eq. (2.38)]. A solution of fully ionized CaCl2 of 0.5 M concentration has an ionic strength / = H (0.5 X 2 -I- 2 X 0.5 X (-1) ) or 1.5 M. Stability constants are reported, then, as measured in solutions of 0.1 M, 0.5 M, 2.0 M, etc., ionic strength. In practice. 

Because the inverse Debye length is calculated from the ionic surfactant concentration of the continuous phase, the only unknown parameter is the surface potential i/io this can be obtained from a fit of these expressions to the experimental data. The theoretical values of FeQx) are shown by the continuous curves in Eig. 2.5, for the three surfactant concentrations. The agreement between theory and experiment is spectacular, and as expected, the surface potential increases with the bulk surfactant concentration as a result of the adsorption equilibrium. Consequently, a higher surfactant concentration induces a larger repulsion, but is also characterized by a shorter range due to the decrease of the Debye screening length. 

Although these effects are often collectively referred to as salt effects, lUPAC regards that term as too restrictive. If the effect observed is due solely to the influence of ionic strength on the activity coefficients of reactants and transition states, then the effect is referred to as a primary kinetic electrolyte effect or a primary salt effect. If the observed effect arises from the influence of ionic strength on pre-equilibrium concentrations of ionic species prior to any rate-determining step, then the effect is termed a secondary kinetic electrolyte effect or a secondary salt effect. An example of such a phenomenon would be the influence of ionic strength on the dissociation of weak acids and bases. See Ionic Strength... 

Many different types of reversible reactions exist in chemistry, and for each of these an equilibrium constant can be defined. The basic principles of this chapter apply to all equilibrium constants. The different types of equilibrium are generally denoted using an appropriate subscript. The equilibrium constant for general solution reactions is signified as or K, where the c indicates equilibrium concentrations are used in the law of mass action. When reactions involve gases, partial pressures are often used instead of concentrations, and the equilibrium constant is reported as (p indicates that the constant is based on partial pressures). and are used for equilibria associated with acids and bases, respectively. The equilibrium of water with the hydrogen and hydroxide ions is expressed as K. The equilibrium constant used with the solubility of ionic compounds is K p. Several of these different K expres-... 

Solution Stoichiometric Concentrations Equilibrium Concentrations (2) Ionic... 

A related phenomenon occurs when the membrane in the above-mentioned experiment is permeable to the solvent and small ions but not to a macroion such as a polyelectrolyte or charged colloidal particles that may be present in a solution. The polyelectrolyte, prevented from moving to the other side, perturbs the concentration distributions of the small ions and gives rise to an ionic equilibrium (with attendant potential differences) that is different from what we would expect in the absence of the polyelectrolyte. The resulting equilibrium is known as the Donnan equilibrium (or, the Gibbs-Donnan equilibrium) and plays an important role in... 

But no more than two of these five species are actually under independent control of the experimenter, because the dissociated ionic species concentrations are fixed by equilibrium conditions and are therefore not independent variables from the viewpoint of the experimenter. For example, if H20 and H2S04 are chosen as the two independently variable components, then the concentrations [H+], [HS04 ], [S04 ] of the remaining species could be determined by one ionic balance condition... 

The equilibrium constant expression in Equation 8-1 does not predict any effect of ionic strength on a chemical reaction. To account for the effect of ionic strength, concentrations are replaced by activities ... 

Cyclopolymerization of dialdehydes was extensively studied by Aso and his coworkers (50). It was remarkable that o-phthalaldehyde could be polymerized readily (5Z-53), because aromatic aldehydes such as benzaldehyde, isophthalaldehyde and terephthalaldehyde did not polymerize with common ionic catalysts. In addition, the poly[o-phthal-aldehyde] obtained was composed of only cyclic structural units. These results suggested that the driving force for the polymerization of o-phthalaldehyde was apparently attributable to the formation of the five-membered ring in the course of cyclopolymerization. The ceiling temperature of the polymerization of o-phthalaldehyde was calculated to be — 43° C from the relationship between the equilibrium concentration of the monomer and the polymerization temperature (51,52). 

A more comprehensive analysis of the influences on the ozone solubility was made by Sotelo et al., (1989). The Henry s Law constant H was measured in the presence of several salts, i. e. buffer solutions frequently used in ozonation experiments. Based on an ozone mass balance in a stirred tank reactor and employing the two film theory of gas absorption followed by an irreversible chemical reaction (Charpentier, 1981), equations for the Henry s Law constant as a function of temperature, pH and ionic strength, which agreed with the experimental values within 15 % were developed (Table 3-2). In this study, much care was taken to correctly analyse the ozone decomposition due to changes in the pH as well as to achieve the steady state experimental concentration at every temperature in the range considered (0°C [Pg.86]

The introduction of carbon dioxide into the solution removes the caustic soda (or, from the point of view of the ionic theory, the OH ions), so that the equilibrium is disturbed and the reaction then proceeds completely from left to right. Similarly, addition of ionised ammonium chloride suppresses the concentration of the OH ions already present in solution more of the pyrovanadate therefore undergoes hydrolysis, in order that the equilibrium concentrations of ions shall be maintained, until all the pyrovanadate is converted into metavanadate. 

The resulting equilibrium concentrations of these point defects (vacancies and interstitials) are the consequence of a compromise between the ordering interaction energy and the entropy contribution of disorder (point defects, in this case). To be sure, the importance of Frenkel s basic work for the further development of solid state kinetics can hardly be overstated. From here on one knew that, in a crystal, the concentration of irregular structure elements (in thermal equilibrium) is a function of state. Therefore the conductivity of an ionic crystal, for example, which is caused by mobile, point defects, is a well defined physical property. However, contributions to the conductivity due to dislocations, grain boundaries, and other non-equilibrium defects can sometimes be quite significant. 

IONIC EQUILIBRIUM. in a system containing ions, at any particular temperalure and pressure, the conditions at which the rate of dissociation of unionized molecules, or other particles to form ions, is equal to the rale ol combination of the ions to form the unionized molecules, or other particles so that aclivilies and concentrations remain constant as long as the conditions are unchanged. 

When solutions of soluble ionic compounds are mixed, an insoluble compound will precipitate if the ion product (IP) for the insoluble compound exceeds its fCsp. The IP is defined in the same way as /equilibrium concentrations. Certain metal cations can be separated by selective precipitation of metal sulfides. Selective precipitation is important in qualitative analysis, a procedure for identifying the ions present in an unknown solution. 

At the interface between the conducting polymer and the ion-selective membrane there is an ionic equilibrium. However, any water present at this interface results in a small volume of internal electrolyte between the conducting polymer and the ion-selective membrane. Variations in the ion concentration of this internal electrolyte can influence the potential of the ISE. The presence of water depends on the conducting polymer and the ion-selective membrane, which should be taken into account in the electrode design. 

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