Arthur W. Davidson

Thermodynamics and Ion Exchange Phenomena

in which HR represents one gram-equivalent of the initial exchanger (i. e., an amount of resin containing Avogadros number of exchangeable hydrogen ions located at specific sites in the material), NaR represents similarly one gram-equivalent of the sodium form of the resin, and Na+ and H- represent one gram-equivalent of each of the ions in aqueous solution, presumably hydrated. For this process it is possible to determine values of the usual thermodynamic quantities such as AF?, AH, and AS. Of these, AF? is most easily evaluated from experimental measurements of the equilibrium constant, and such evaluation has been the purpose of the majority of the investigations, including that in progress at the University of Kansas. Although a number of other systems have been investigated also, the sodium-hydrogen exchange on Dowex-50 has been studied most exhaustively; data for this system will be used to illustrate the thermodynamic conclusions contained in the latter part of this report.

EQUILIBRIUM CONSTANTS OF CATION EXCHANGE PROCESSES

in which a represents the activity of the designated component, should be independent not only of the equilibrium composition, with respect to the two cations involved, of resin and of solution, but independent also of the total initial concentration of the solution. Furthermore, it should be possible to calculate the equilibrium constant for a given exchange reaction from those of two other exchange reactions. Thus if ARes, BRes, and CRes have all been made from the same batch of exchange material, such as Dowex 50 of a given divinylbenzene content, then in the three exchanges A+ + BRes = B+ + ARes C+ + BRes = Bf + CRes (1)

The anodic oxidation of zinc and cadmium in aqueous solution

Abstract In the absence of oxidizing agents in the electrolyte solution, only the bipositive ions are formed at zinc and cadmium anodes on electrolysis. In the presence of certain oxidizing agents (e.g. nitrate ion), however, both metals dissolve anodically with an initial mean valence number between one and two; in the presence of chlorate ion zinc dissolves with an initial mean valence number between one and two, whereas cadmium exhibits an initial mean valence number of two. In those solutions in which the initial mean valence number of the metal is less than two, its value decreases further with increasing temperature of electrolysis. No unipositive ion of zinc or cadmium could be isolated, and flow experiments indicated that if the unipositive ion is formed it has a very short lifetime with respect to further oxidation to the bipositive state. All of the experimental data can be explained, however, on the hypothesis that the primary anode reaction is the formation of the unipositive ion, which can then be oxidized to the bipositive state either electrolytically or by an oxidizing agent in the solution. The second oxidation can be thought of as competitive between the oxidizing agent and the electrode. This hypothesis is supported by the relation between the initial mean valence number and the quantity of reduced electrolyte in the anolyte solution.

The anodic behaviour of copper in aqueous solutions

Abstract The anodic oxidation of copper in a variety of aqueous electrolytes has been investigated. In the presence of agents (e.g. CN − , Cl − , S 2 O 3 = ) which form stable complexes with copper(I), the metal enters solution solely in the unipositive state over a wide concentration range of electrolyte. With a nitrate, sulphate, or chlorate as electrolyte, copper enters solution with an apparent valence number considerably greater than 1 at 25°C. However, as the temperature is increased, the apparent valence number of copper decreases in the presence of these anions. With chlorate at 98°C, the valence number of copper falls to 1. All the experimental data can be explained on the hypothesis that the primary electrode reaction consists of the formation of unipositive copper.