Ion exchangers equilibrium constants

In this equation, the constant Kz, which can be easily inferred from the intercept, represents a system-specific constant that is related to the ion-exchange equilibrium constant K(Lmol ), the surface area 5 (in m the charge density on the surface, that is, the number of ion-exchange sites qx available for adsorption (in molm ), and the mobile phase volume Vo (in L) in the column as described by the following equation ... 

There are two kinds of ionophores charged ones, which are called liquid ion exchangers, and neutral carriers. Because they are mobile in both the free and in the complexed form, mobilities of all species are again part of the selectivity coefficient together with the ion-exchange equilibrium constant. The best-known neutral ionophore is valinomycin (Fig. 6.15a) which shows a 1,000 1 selectivity for K+ in preference to Na+ and no pH dependence. In its uncomplexed form, it is electrically neutral. A better-known representative is di(n-octyl phenyl) phosphonate (Fig. 6.15c), which shows good selectivity for calcium ion and is relatively pH insensitive. 

The glass electrode has been treated by Eisenman and coworkers as cation-exchange membranes. Expressions were derived for the membrane potential in relation to the ion-exchange equilibrium constants of the membrane with various ions in solution and in relation to the mobilities of the cation species characteristic of the glass. For a membrane responding to two univalent cations i and j, the potential is given by... 

The ion exchange equilibrium constant is the same as that for the process on the left because the standard potentials in the solution and in the membrane are independent of location and ) ... 

The ratio of the permeabilities of two cations in a cation exchange membrane is equal to the product of the ion exchange equilibrium constant and their mobility ratio (1). Therefore it is important to characterize the equilibrium ion exchange selectivity of ion exchange polymers in order to understand their dynamic properties when used in membrane form. Nafion (E.I. du Pont de Nemours and Co.) perfluorinated sulfonate membranes have found wide use in a variety of applications, many of which involve exchange of cations across membranes that separate solutions of different ionic composition. The inherent cationic selectivity of the polymer is an important consideration for such applications. Results of ion exchange selectivity studies of Nafion polymers are reviewed in this chapter, and are compared to those of other sulfonate ion exchange polymers. 

Ion Exchange Equilibrium Constant and Permselectivity between Two Ions... 

The ion exchange equilibrium constant between A and B ions in the membrane, Kba, is expressed as,... 

Ion exchange equilibrium constants between ions have been studied in detail on ion exchange resins. For example, multivalent cations more selectively ion exchange with resins than do monovalent ones, and cations with large atomic... 

Figure 5.1 shows the change in PNaCa, mobility ratio and ion exchange equilibrium constant between calcium ions and sodium ions with pH of the mixed salt solution in the cation exchange membrane having salicylic acid groups. The... 

Figure 5.1 Change in transport number of calcium ions relative to sodium ions, mobility ratio and ion exchange equilibrium constant between calcium ions and sodium ions in a cation exchange membrane having salicylic acid groups as cation exchange groups (condensation type) with the pH of a mixed salt solution. (O) PNaC i (A) KNaCa ( ) UCu/UNa. Electrodialysis of the mixed solution of 0.375 N sodium chloride and 0.125 N calcium chloride (chloride ions 0.500 N), the pH of which was adjusted, was carried out using a cation exchange membrane prepared from condensation polymerization of salicylic acid, phenol and formaldehyde.

Figure 53 Ion exchange equilibrium constants of alkaline earth metal cations relative to sodium ions in sulfonic acid and phosphonic acid membranes. (O) sulfonic acid membrane (O) phosphonic acid membrane. Membranes were equilibrated with a 1 1 mixed solution of 0.250 N alkaline earth metal cation and 0.250 N sodium chloride (concentration of chloride ions 0.500 N).

Table 5.6 shows ion exchange equilibrium constants between nitrate ions and chloride ions of anion exchange membranes having different ion exchange groups... 

Table 5.6 Ion exchange equilibrium constants between nitrate and chloride ions in anion exchange membranes with various ion exchange groups8...

The transport number of sulfate ions relative to chloride ions increases in the presence of diethylene glycol (Figure 5.42). Similarly, PC increases in the presence of tetraethylene glycol.111 Therefore, the ratio of mobility of sulfate ions to that of chloride ions in the membrane phase and the ratio of both ions in the membrane during electrodialysis (ATCis°4, ion exchange equilibrium constant) have been measured. The mobility ratio between sulfate and chloride ions (ratio of reciprocals of electrical resistances of the membranes in the respective ionic form) is constant for various concentrations of diethylene glycol though the... 

Figure 5.55 Relationship of transport number of nitrate ions relative to chloride ions to the ion exchange equilibrium constant between nitrate ions and chloride ions. ( ) M-2, anion exchange membrane with N-isopropylacrylamide (quaternary ammonium groups) ( ) commercial anion exchange membrane (without N-isopropylacrylamide, ion exchange groups benzyl trimethylammonium...

If we consider two electrolytes (KA, BA) and the polymer film electrode arrangement we can write (5.1) for both K+ and B+, and the different specific interactions can be expressed by different A/rf values according to (5.3). Introducing the ion-exchange equilibrium constant (.Kkb),... 

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