Ion exchanger reactions

An ion-selective electrode based on a glass membrane in which the potential develops from an ion-exchange reaction on the membrane s surface. 

The ion-exchange reaction of a monovalent cation, M+, at a strong acid exchange site is... 

The equilibrium constant for this ion-exchange reaction, which is also called the selectivity coefficient, is... 

Ion-exchange reactions are reversible. A regeneration procedure restores the resin to the ionic form it was in prior to the adsorption step. 

The tetra alkyl amm onium salts of [B Hg] , formed by ion-exchange reactions, have proven to be useful synthetic reagents because of their thermal and air stabihties. The stmcture of the [B Hg] ion has been determined by an x-ray study (66) and shown to have the 2013 styx stmcture, C2 symmetry. Mechanisms for the formation of this ion have been proposed (67). Tetraborane(lO) can be easily obtained from salts of [B Hg] (eq. 9). 

As noted, ion exchange reactions are stoichiometric and reversible, and in that way they are similar to other solution phase reactions. For example ... 

R indicates the organic portion of the resin and SO3 is the immobile portion of the ion active group. Two resin sites are needed for nickel ions with a plus 2 valence (Ni ). Trivalent ferric ions would require three resin sites. As shown, the ion exchange reaction is reversible. The degree the reaction proceeds to the right will depend on the resins preference, or selectivity, for nickel ions compared with its preference for hydrogen ions. The selectivity of a resin for a given ion is measured by the selectivity coefficient. K. which in its simplest form for the reaction... 

The extensive possibilities of the practical application of synthesis, and the study of the properties of ion-ex-change resins have aroused widespread interest in chemistry. This chapter discusses some theoretical problems with cationic resins as catalysts in hydrolysis reactions. New types of cationic resins have been examined and some important generalizations on ion-exchange reactions have been formulated. 

Kuroda K, Kobayashi T, Sakamoto T, Ichino R, Okido M (2005) Formation of ZnTe compounds by using the electrochemical ion exchange reaction in molten chloride. Thin Sohd Films 478 223-227... 

Ion exchange (IX) is a very useful technique for the concentration, the purification and the separation of chemically similar metallic elements present in an aqueous solution. In its most popular form of application, the metal-bearing aqueous solution is passed through a bed of solid organic resin in a particulate form wherein the sorption of the metal ions on the resin takes place by ion-exchange reactions. The pregnant resin is washed free of the entrapped feed solution and then brought into contact with an eluant of suitable composition and volume so that the resin releases the metal ions back to the eluant. The ratio of the volume of the feed and that of the eluant determines the extent of concentration that can be achieved. Purification and separation are achievable if the resin is selective or specific with respect to the metal ions of interest in comparison to impurity ions. 

As noted above, adsorption isotherms are largely derived empirically and give no information on the types of adsorption that may be involved. Scrivner and colleagues39 have developed an adsorption model for montmorillonite clay that can predict the exchange of binary and ternary ions in solution (two and three ions in the chemical system). This model would be more relevant for modeling the behavior of heavy metals that actively participate in ion-exchange reactions than for organics, in which physical adsorption is more important. 

Little more need be said here about the simple ion-exchange reactions such as that between sodium hexametaphosphate and calcium ions (Scheme 10.7). It is useful, however, to consider in more detail those reactions involving chelation (Scheme 10.8). This is a reversible reaction, the equilibrium being dependent on the process pH and the concentrations of the reacting species (Equation 10.2). While chelated complexes are less stable at higher temperatures, this effect can be ignored in practice. The factors involved have been discussed in some considerable detail by Engbers and Dierkes [20,23]. 

Stein, L., New Evidence that Radon Is a Metalloid Element Ion-Exchange Reactions of Cationic Radon, J. Chem. Soc., Chem. Comm. 1631-1632 (1985). 

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