Equilibria ionic

This last result describes the Donnan equilibrium condition as it applies to the system under consideration. Like other ionic equilibrium expressions, it requires the equality of ion products in equilibrium solutions. 

Precipitation involves the alteration of the ionic equilibrium to produce insoluble precipitates. To remove the sediment, chemical precipitation is allied with solids separation processes such as filtration. Undesirable metal ions and anions are commonly removed from waste streams by converting them to an insoluble form. The process is sometimes preceded by chemical reduction of the metal ions to a form that can be precipitated more easily. Chemical equilibrium can be affected by a variety of means to change the solubility of certain compounds. For e.xample, precipitation can be induced by alkaline agents, sulfides, sulfates, and carbonates. Precipitation with chemicals is a common waste stream treatment process and is effective and reliable. The treatment of sludges is covered next. 

The molten system KC1 - K2TaF7 was analyzed using the same method and the ionic equilibrium calculated is as follows ... 

The nature of outer-sphere alkali metal cations can actually define the ionic equilibrium and also has an affect on complex anions. Fig. 77 illustrates the influence of the cationic surrounding on the wave numbers. 

The most common property of molten systems containing tantalum or niobium is the ionic equilibrium between hexa- and heptacoordinated complexes, with the general compositions MeFg and MeF6X(n+I) ... 

The measurements of a by means of the electrical conductivity show that the dilution law holds good for weak electrolytes (a small), but for strong electrolytes (a large) it fails utterly. This behaviour has given rise to a considerable amount of discussion, a critical review of which will be found in a paper by the author ( Ionic Equilibrium in Solutions of Electrolytes ) in the Trans. Chem. Soc., 97, 1158, 1910. It appears that in this... 

Alkalmity is helpful in describing the acidneutralizing ability of an aqueous solution that may contain many ions. In any ionic equilibrium there is a conservation of charge condition. 

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). 

Butler, J. N. (1964). "Ionic Equilibrium." Addison-Wesley, Reading, MA. 

The discharge of Offi ions disturbs the ionic equilibrium of water, and so more water ionizes to restore it ... 

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. 

Immobilized enzymes used in conjunction with ion-selective electrodes provide very convenient methods of analysis. The immobilized enzyme may be held in a gel or membrane around the electrode and the substance to be measured diffuses into the enzyme gel. Its conversion to the product alters the ionic equilibrium across the ion-selective membrane (Figure 8.23). It is important that the enzyme layer is thin, to minimize any problems caused by slow diffusion rates through the layer. 

If the user writes a simple mass balance for the solubility equilibrium or ionic equilibrium such as - the reaction of b moles of B with c moles of C has come to equilibrium with the product of d moles of D and e moles of E, then the mass balance is given by... 

Zemaitis, J.F., "Counter Current Stage Separation with Chemical and Ionic Equilibrium and/or Reaction", to be published in Computer Applications to Checmical Engineering Process Design and Simulation, ACS Symposium Series,... 

Staples, B. R. "Ionic Equilibrium Constants of Aqueous Alkaline Earth Salts" Environ. Sci. Technol., 1978, 12,... 

The techniques used in the critical evaluation and correlation of thermodynamic properties of aqueous polyvalent electrolytes are described. The Electrolyte Data Center is engaged in the correlation of activity and osmotic coefficients, enthalpies of dilution and solution, heat capacities, and ionic equilibrium constants for aqueous salt solutions. 

This observation suggests that the ionization process is endothermic. Conductometric titrations of the trihalides with HMPA in 1,2-dichloroethane suggest that at low D MX3 ratios some autocomplex formation may occur. At a molar ratio of 1 1 inflections are found indicating that the mode of the ionic equilibrium is essentially changed, apparently to that of simple ionization (Fig. 15)... 

Titrations were carried out at room temperature. The volume of amine solution titrated was 50 ml and this was magnetically stirred during the addition of titrant. The titrant was added in 0.5 ml quantities. After each addition of titrant, approximately one minute was allowed before measurement were made to reach ionic equilibrium. 

The metal ion level at the surface is equal to the metal ion level in the metal interior, if ionic equilibrium is established between the surface and the interior of the metal phase. However, the imitary metal ion level, a, at the surface differs in general from the unitary metal ion level, aj, in the interior of the solid. The metal ion in the interior is located at a lattice site or at an interstitial site ... 

In the case in which ionic equilibrium is established between the siuface and the interior, the two metal ion levels, and become equal to each other and the energy level of metal ions au.di) at the surface and in the interior is given by Eqn. 3-11 ... 

In the case in which ionic equilibrium is established between the surface and the interior, the surface ion level, qa,-, equals the interior ion level, aA.cAB>. Consequently, the unitary ion levels at the lattice and interstitial sites bend either upward or downward forming a space char ge layer in a region adjacent to the surface as shown in Fig. 3—13. When the surface A ion level, Oa+, is lower than tire interior A ion level, aA (AB A ions move from the interior to the... 

Masson C. R. (1968). Ionic equilibrium in liquid silicates. J. Amer. Ceram. Soc., 51 134-143. 

Hesleitner, P. Babic, D. Kallay, N. Matijevic, E. (1987) Adsorption at solid/solution interfaces. 3. Surface charge and potential of colloidal hematite. Langmuir 3 815-820 Hesleitner, P. Kallay, N. Matijevic, E. (1991) Adsorption at solid/liquid interface. 6. The effect of methanol and ethanol on the ionic equilibrium at the hematite/water interface. Langmuir 7 178-184... 

At high field strengths a conductance Increase Is observed both In solution of strong and weak electrolytes. The phenomena were discovered by M. Wien (6- ) and are known as the first and the second Wien effect, respectively. The first Wien effect Is completely explained as an Increase In Ionic mobility which Is a consequency of the Inability of the fast moving Ions to build up an Ionic atmosphere (8). This mobility Increase may also be observed In solution of weak electrolytes but since the second Wien effect Is a much more pronounced effect we must Invoke another explanation, l.e. an Increase In free charge-carriers. The second Wien effect Is therefore a shift in Ionic equilibrium towards free ions upon the application of an electric field and is therefore also known as the Field Dissociation Effect (FDE). Only the smallness of the field dissociation effect safeguards the use of conductance techniques for the study of Ionization equilibria. 

Cation-exchange resins. Using ion-exchange resins, Ca2+ and Mg2+ are adsorbed on to a cation-exchange resin added to milk the resin is removed and the Ca2+ and Mg2+ desorbed. It is assumed that the treatment does not alter the ionic equilibrium in milk. 

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... 

In addition to all these, it is also important to keep in mind that the results depend also on what types of surface equilibrium conditions exist as the double layers interact. For example, when two charged surfaces approach each other, the overlap of the double layers will also affect the manner in which the charges on the surfaces adjust themselves to the changing local conditions. As the double layers overlap and get compressed, the local ionic equilibrium at the surface may change, and this will clearly have an impact on the potential distribution and on the potential energy of interaction. 

Among the basic concepts to be introduced are ionic equilibrium, local equilibrium, local electro-neutrality, etc. 

I. Rubinstein, Field and force saturation in ionic equilibrium, SIAM J. Appl. Math., 48 (1988), pp. 1475-1486. 

Below we present a well-known calculation of membrane potential based on the classical Teorell-Meyer-Sievers (TMS) membrane model [2], [3]. The essence of this model is in treating the ion-selective membrane as a homogeneous layer of electrolyte solution with constant fixed charge density and with local ionic equilibrium at the membrane/solution interfaces. In spite of the obvious idealization involved in the first assumption the TMS model often yields useful results and represents in fact the main tool for practical membrane calculations. We shall return to TMS once again in 4.4 when discussing the electric current effects upon membrane selectivity. In the case of our present interest, the simplest TMS model of membrane potential for a 1,2 valent electrolyte reads... 

As an example, let us take an anionic stationary phase in which an E species is in equilibrium between the mobile phase and the stationary phase. This species, called a counterion, is present in high abundance in the mobile phase. Although the OH-species would be a simple and logical choice for this counterion, hydrogenated carbonate forms are preferred (C03 and HCOJ at 0.003 M). Carbonated species are much more efficient at displacing the ions to be separated. As an anionic species A is transported by the mobile phase, and a series of reversible equilibria are produced. These equilibria are dependent on the ionic equilibrium constant K (Fig. 4.5). 

For mote about equilibrium calculations, see W. B. Guenther, Unified Equilibrium Calculations (New York Wiley, 1991) J. N. Butler. Ionic Equilibrium Solubility and pH Calculations (New York Wiley, 1998) and M. Meloun, Computation of Solution Equilibria (New York Wiley, 1988). For equilibrium calculation software, see http //www.micromath.com/ and http //www.acadsoft.co.uk/... 

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