Cations alkali thermodynamic parameters

Thermodynamic Parameters of the Complexation of Alkali Cations in Methanol at 25°C... 

The thermodynamic parameters and relative cation selectivity of some alkali and heavy metal cations with 1,5,14,18-tetraselena-8,11,21,24-tetracyclohexacosane 47 (selena-26-crown-8) were investigated for the first time by titration calorimetry in water-MeCN (l 24v/v) at 25°C to show the contrasting complexation behavior between Ag+ and alkali Tl+ and a very high Ag+ selectivity, originating from the exclusive contribution of the enthalpy term probably owing to the partially covalent interaction between Ag+ and Se-donor <1999JCM284>. 

Equilibrium ion-exchange data for intermediate-silica Na-exchanged phillipsite at 25°C, in the presence of cation pairs Na/X, where X is Ba, Co, NH4, K or Ca, were collected and the relevant thermodynamic parameters were computed. Phillipsite was found very selective for Ba, K and NH4, unselective for Co, whereas only about 50% Na could be readily replaced by Ca. This behaviour was interpreted in terms of phillipsite s structural features. On the basis of the present and the previous data concerning other cations, possible applications of alkali-trachytic phillipsite-rich rocks could be envisaged in the treatment of wastewaters containing Ba, Cs, Pb and r NH4, especially if the waters are lacking K as an interfering cation. 

The thermodynamic parameters of hydration for many ions have been determined [121,125,126]. Table 3 gives the values of the standard molar Gibbs energy of hydration AGh and standard molar enthalpy of hydration AH , at 25°C for the alkali metal cations. The tabulated values are based on the respective choices A= - 1056 kj/mol and AHh(H ) = -1103 kj/mol, which result from the extrathermodynamic assumption that the thermodynamic parameters of the tetraphenylarsonium cation and tetraphen-ylborate anion are equal [127]. This reasonable and useful assumption, often... 

The enolate salts, H2C=CH(OM), have been studied at various levels of theory for all of the alkali metals. Several structural and thermodynamic parameters are reported, and the effect of the restriction of enolate resonance by attachment of the cation is described. 

All the routines described for the determination of the thermodynamic (concentration) parameters in metal oxide solutions include some indirectly obtained values. For example, the equilibrium concentration of metal cations is calculated proceeding from the quantity of the oxide-ion donor consumed for titration (precipitation). Direct determination of the concentration of metal cations in the melt (if it is possible) allows one to obtain more correctly the obtained solubility product values. Our paper [332] reports a method for correction of the solubility product values for oxides on the basis of the potentiometric titration data. The modification of the standard routine consists of the simultaneous use of two indicator electrodes, one of which is the membrane oxygen electrode and the other is a metal electrode, reversible to the cations the oxide consists of. This routine was used to estimate the solubility products of copper(I) and nickel(II) oxides in the molten KCl-NaCl equimolar mixture at 700 °C. Investigation of Cu20 by the proposed method is of considerable importance since, as will be shown further, the process of dissociation/dissolution of copper(I) oxide in molten alkali-metal halides differs from the generally accepted one which was considered, e.g. in Ref. [119]. 

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