Activity Coefficients Of Ionic Species Research Articles

The Correlation of Activity Coefficients of Ionic Species of Aqueous Electrolytes Using a New Model

Abstract This study proposed a new model based on the solvation phenomena. The ionic activity coefficients of individual ions of some 1:1 and 1:2 salts were correlated successfully. Comparison was made between the results of the present model and those of Khoshkbarchi–Vera (KV), Pitzer, and Lin–Lee models. The average relative errors for cation and anion were 3.03, 3.53, 3.45 and 1.24, 1.14, 1.38, respectively, in Lin–Lee, KV, Pitzer models, whereas they are 1.81 and 0.66 in the proposed model.These results show that the proposed model improved the correlation of the individual ionic activity coefficients. Contrary to arguments found in the literature, it is also demonstrated that the short-range solvation contribution is a linear function of ionic strength.

Estimation of activity coefficients of ionic species of aqueous strong electrolytes within the extended Debye–Hückel concentration range

The concentration curve of mean activity coefficient to the required power was fitted by a product function. The product function can be factorized in factor functions which represent the concentration dependence of the single-ion species (J Solid State Electrochem, in press, 1). With a simplified procedure of this method, it is possible to split the mean activity coefficients into the individual parts for the ionic species within the extended Debye–Huckel concentration range. This method is applicable to all strong electrolytes because it is not necessary to have further data or additional assumptions.

Comment on the individual ion activities of Na + and Cl − by Arce, Wilczek-Vera and Vera

Conventional values of activity coefficients of ionic species, in this case sodium and chloride ions in aqueous NaCl, have been published, as if these were the experimental values of individual ion activity coefficients, although no experimental method is really able to provide these separate quantities—but only the mean activity coefficients. A dangerous consequence is the possibility that scientists concerned with ionic solution theory may rely on such data, and derive wrong conclusions about the effectiveness of their theoretical work. This paper shows the reasons why the data in question have no relation to the ionic activity coefficients, which remain unknown, and are a mere artifact of the method adopted.

Absorption Equilibria of Dilute SO2 in Seawater

The solubility of dilute SO2 in seawater, from mixtures SO2 + N2, was determined in a temperature range between (278.15 and 318.15) K and a SO2 partial pressure range between (0.050 and 1.5) kPa. Measurements were carried out by a saturation method using a laboratory-stirred batch reactor. Equations to correlate experimental data were obtained as a function of temperature and SO2 partial pressure. Comparisons between experimental results, literature data, and theoretical predictions were also made at different temperatures. Two different models were considered to evaluate the activity coefficients of ionic species. Theoretical calculations were made using both an extended version of the Debye−Hückel theory and the Pitzer ion-interaction model. Both models led to similar predictions and were in good agreement with the experimental results. The reasonable fitting between measured and calculated data showed that the selected models can be successfully used for predicting the absorption equilibria of dilute sulfur dioxide in seawater at different temperatures.

Kinetics and thermodynamics of calcium carbonate and calcium sulfate at salinities up to 1.5 M

This paper examines the effect of salinity on kinetics and thermodynamics of precipitaion for CaCO 3 and CaSO 4 when they exist in isolation as well as together. Batch tests under isothermal (30°C) conditions were carved out for salinity values ranging between 0.5 to 1.5 M of NaCl, calcium sulfate in the range of 0.06–0.15 M, calcium carbonate in the range of 0.007–0.02 M and sulfate to carbonate ratios of 2–8. Thermodynamic solubility constants were determined using the Pitzer model for determination of the activity coefficients of ionic species. As expected, the thermodynamic solubility constant ( K sp ) of the pure salts was not affected by different salinity levels; however, salinity level affected K sp in mixed salt systems. This is believed to be due to the effect of salinity on polymorphism and crystal habit. Images of the pure and mixed system were produced using Scanning Electron Microscopy (SEM), demonstrating that the co-precipitation in the mixed system changed the scale morphology of the crystals. Also, the deposit tenacity was affected by co-precipitation. Further work is under way to assess the effect of salinity on polymorphism with X-Ray Diffraction (XRD) analysis. Kinetics of pure CaSO 4 precipitation was found to be strongly affected by the level of salinity; however, salinity level had no significant effect on kinetics of pure CaCO 3 precipitation. For kinetics analysis of the mixed system, total initial Ca 2+ of 0.06 M of CaSO 4 was compared to that of the mixed system. Qualitatively, the reaction rate of pure CaSO 4 is found to be faster compared to the mixed system. These findings prove that the conventional means of assessing the behaviour of salts in pure systems are no longer extendable and applicable to mixed salt systems.

Simulation of chemical phenomena in the Co(NO 3) 2–Na 2CO 3–H 2O system based on a thermodynamic model

A simulation for the Co(NO 3) 2–Na 2CO 3–H 2O system based on a thermodynamic model was proposed which predicts possible equilibrium states attained among gas, aqueous and solid phases under isothermal and isobaric conditions. Various chemical species such as CoOH + the cobalt complex, carbonate species in aqueous solution, precipitate of basic cobalt carbonate and CO 2 gas were taken into account. By using the Debye–Hückel formula for the activity coefficients of ionic species, apparent equilibrium constants of chemical reactions were well evaluated. A thermodynamic model was constructed by combining mass action law, mass balance, and charge balance equations together with equilibrium conditions among different phases. Simulation was carried out to compute concentrations of various chemical species in aqueous solution, amount of precipitate, and pressure of CO 2. In order to examine the validity of the thermodynamic model, the computed pH values were compared with experimental results and a relatively good agreement between them was obtained.

THERMODYNAMIC EQUILIBRIA OF THE EXTRACTION OF CHROMIUM(VI) WITH TRI-N-OCTYLPHOSPHINE OXIDE FROM AQUEOUS SOLUTIONS

ABSTRACT The distribution of chromium( VI ) between aqueous solutions and the kerosene solutions of tri-n-octyl-phosphine oxide (TOPO) have been studied at 25 °C and pH 2-4, in which range the predominant forms of Cr(VI) are HCrO4 and Cr2O7 2−. The extraction equilibrium is influenced by the total chromium(VI) concentration, aqueous pH value, and total extractant concentration. The thermodynamic equilibria among all species in the aqueous phase were used for the analysis of distribution data, and the activity coefficients of ionic species were estimated according to Debye-Hiickel or Bromley equation. By numerical method, the complexes of Cr(VI ) with TOPO formed in the organic phase were found to be H2CrO4 (TOPO) and H2Cr2O7 (TOPO) 3. The corresponding extraction constants were 2019 and 3.69× 108, respectively.

Liquid—liquid extraction of alkali metal ions with non-ionic surfactant having a poly(oxyethylene) chain

The ion-pair extraction of poly(oxyethylene) alkylphenyl ether (Triton X-100) complexes of alkali metal ions (M +) with picrate ion (Pic − into 1,2-dichloroethane (1,2-DCE) was studied. The results of vapour pressure osmometry suggest a partial dissociation of the ion pair in 1,2-DCE. Quantitative analysis of the extraction data revealed the extraction of the ion pair of Triton X-100-alkali metal ion with picrate ion and dissociation of the ion pair. The thermodynamic constants of the extraction and the dissociation of the ion pairs were evaluated by taking into consideration the activity coefficients of ionic species in the aqueous and 1,2-DCE phases. The extraction constants of large metal ions, rubidium and caesium, are almost the same as that of potassium ion, whereas those of sodium and lithium ions decrease with decrease in the ion size. The effect of the size of the alkali metal ions on the Triton X-100 extraction system is less important than that on the 18-crown-6 extraction system. The dissociation constants of the ion pairs were almost the same irrespective of the kind of alkali metal ion, and the interionic distance of the ion pair between the cationic complex and picrate ion was estimated to be about 6 Å.

Effect of Batch Factor on a Binary Ion Exchange Equilibrium

Abstract The relation between the distribution coefficient of Cs+ on Mn+ form exchanger and the ratio of the solution volume to the exchanger weight (batch factor) at a constant loading of Cs+ has been investigated while taking the activity coefficients of ionic species into consideration when the initial concentration of Cs+ is changed.

Prediction of dissociation constants of ammonium ion in aqueous lithium chloride solutions in terms of the Pitzer approach

Dissociation constants of ammonium ion at 25 o C in aqueous lithium chloride solutions calculated in terms of Pitzer's equations were compared with our experimental ones. the calculations were made with and without higher order terms θ and ψ. The θ NH4 Li and ψ NH4 LiCl values, which are not available in the literature, were determined from isopiestic measurements of NH 4 Cl−LiCl solutions. The calculations without the higher order terms yielded rather large discrepancies between the observed and calculated values, while the values calculated with all the higher order terms concerned agreed with the measured ones with the experimental uncertainties. These results point out the need to include higher order terms when they are known, so that activity coefficients of ionic species and, thus, equilibrium constants can be evaluated with high accuracy in concentrated electrolyte solutions

Chemical equilibrium studies on the copper-sulfuric acid-kelex 100-xylene system

A thermodynamic equilibrium model is developed for the distribution of copper between the phases for the system copper-sulfuric acid-xylene-/3-alkenyl 8-hydroxyquinoline. Chemical equilibrium data were obtained for the range of experimental parameters of [Cu] aq, i T (0.005 to 0.02 mol/dm3), [S]T (0.05 to 0.2 mol/dm3), extractant (0.02 to 0.06 mol/dm3), and temperature (20 to 50 ‡C). The nonlinear regression analysis best fit model is ln(Dαo/γCusu++) = 3.83 + 642(1/T - 1/308) +2 ln([HR]/[H+]γH +) whereD is the distribution coefficient, αo is the reciprocal of the degree of formation of copper ion, and γ refers to activity coefficients of ionic species. The analysis of the data considers the aqueous phase ionic equilibria and a technique to estimate the impurities present in the reagent. The results indicate that the enthalpy of the reaction and the entropy change are -5338 J/mol and 14.5 J/mol · K, respectively. Also, the stoichiometric coefficient of two, determined for the extractant with cupric ion, is in agreement with other investigators.

Individual activity coefficients of ionic species from electrochemical measurements on non-isothermal systems

While the mean ionic activity of an electrolyte may be experimentally obtained by means of procedures based on equilibrium thermodynamics, reliable values of individual ionic activities are obtainable only by using procedures in which the electrolyte is not in equilibrium. On of these procedures has been developed by Milazzo et al on the basis of electric-tension measurements of non-isothermal galvanic cells. In this paper a further development of Milazzo's procedure , valid for 1:1-valent electrolytes and at least up to 0.05M, is presented. This procedure has the advantage that it does not imply any theoretical hypothesis, being based only on two experimental conclusions concerning the heats of transfer Q * tot of 1:1-valent electrolytes in the concentration range up to 0.05M: the additivity rule ( Q * tot is equal to the sum of characteristic contributions from the separate ions), and Q * tot depends linearly on m 1 2 /(1 + m 1 2 ).