Solutions Of Strong Electrolytes Research Articles

Osmotic and Activity Coefficients Using a Modified Pitzer Equation for Strong Electrolytes 1:1 and 1:2 at 298.15 K

We have correlated simultaneously experimental data for osmotic and activity coefficients of strong electrolyte solutions using the Pitzer equation and a modification of it. The optimal value for the Pitzer b parameter is different from the traditional value of 1.2 when using higher concentrations in its determination. An analysis of the equation shows that it is possible to reduce the model to a three-parameter form that represents the coefficients at molalities as high as 25 with better accuracy than the model as proposed by Pitzer.

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熱力学的データを用いた強電解質水溶液と平衡する大気の相対湿度の算出

熱力学的データを用いた強電解質水溶液と平衡する大気の相対湿度の算出

Chronopotentiometric studies on dialytic properties of glycine across ion-exchange membranes

Chronopotentiometric responses of cation exchange membranes (CEMs) and anion exchange membranes (AEMs) were investigated in dilute solutions of NaCl, HCl and NaOH and its 1:10, 10:1 or 10:10 mixture with glycine. The behavior of both of these membranes was nearly ideal in strong electrolyte solutions. From experimental data, the values of permselectivity, counter-ion transport number and membrane resistance corresponding to each type of membrane at different concentrations of strong electrolyte have been studied. Glycine solution alone at iso-electric pH (5.90) did not exhibit any good inflection for ion-exchange membrane due to the absence of ionic transportation. The presence of glycine along with NaCl (pH=5.80) reduces ionic migration due to masking of ionic sites on the membrane matrix. The extent of masking was found to be proportional to the glycine concentration in the bulk of solution. Furthermore, the electro-transport of gly + and gly − is possible across the CEM and AEM, respectively. Data are useful in order to ensure efficient desalting of amino acids or for its electro-driven separation.

Transport of non-associated electrolytes in acrylamide hydrogels

Diffusion of non-associated electrolytes (LiCl and KCl) in different hydrogels has been studied to identify the mechanism of electrolyte interaction with the structure of hydrogels and its dependence on electrolyte concentration and thermodynamic features of the electrolyte. Hydrogel membranes have been prepared from acrylamide (AAm) using N,N′-methylene-bis-acrylamide (MBAAm) as the cross-linker. Properties of membranes have been altered varying the content of cross-linker. Properties of membranes have been altered varying the content of cross-linker. Integral diffusion coefficients of potassium chloride and lithium chloride in the hydrogel membranes ave been compared with mutual diffusion coefficients of those electrolytes in aqueous solutions. The study of electrolyte diffusion was supported by data on water solubility in hydrogels (degree of swelling, and sorption and desorption isotherms) showing dependence of electrolyte diffusion coefficient on water content inside polymer matrix. Thermodynamic study showed irreversible character of the sorption of solutes, probably due to acidic hydrolysis of amide groups of gels. The main features, which characterise properties of aqueous solution of strong electrolytes, remain in polymer matrix thus defining diffusion coefficients and other parameters representative of electrolyte transport in polyacrylamide hydrogels.

The Measurement of Activity Coefficients in Concentrated Electrolyte Solutions. An Experiment for the Physical Chemistry Laboratory

A physical chemistry experiment is described in which a relatively inexpensive osmometer is used to measure the practical osmotic coefficient of 1:1 strong electrolyte solutions. These data can be used to calculate mean ionic activity coefficients using nonlinear curve fitting and some instructive spreadsheet calculations. Because of data smoothing via the curve fit, the results are a surprisingly satisfactory way for students to measure activity coefficients in the course of a 3-hour laboratory. Student-determined values of the mean ionic activity coefficient are within 4% of literature values for KNO3 solutions from 0.0 to 1.0 m.

A Debye−Hückel Model for Calculating the Viscosity of Binary Strong Electrolyte Solutions

In this article we present a new model for correlating dynamic viscosity of binary strong electrolyte solutions. The proposed model is based on Eyring's absolute rate theory and the Debye−Huckel model for calculating the excess (electrostatic) free energy of activation of the viscous flow. In the present model we consider that the free energy of activation of the viscous flow as being the same as the appropriate thermodynamic free energy used for calculating equilibrium properties of the electrolyte solution. Modifications of Eyring's absolute rate theory must be performed to take into account the solvent as a continuous medium, as considered in the Debye−Huckel theory. This is accomplished by means of the osmotic-pressure framework for solutions. In this framework one adopts a thermodynamic free energy, which is considered as a function of the absolute temperature, pressure, number of moles of the solute species, and chemical potential of the solvent. The proposed model contains two adjustable parameters...

Theory of the effect of pH and ionic strength on the nucleation of protein crystals

Proteins can be crystallized from pH buffered aqueous solutions of inert strong electrolytes. The appearance of crystals is preceded by the formation of crystal nuclei which are oligomers of protein molecules bound by non-covalent forces. Being amphoteric, individual protein molecules in solution are macro-ions whose charge depends upon pH. As it is unlikely that these macro-ions agglomerate to form oligomers with complete retention of charge, we suggest, and confirm by experiment, that the formation of crystal nuclei is accompanied by H + exchange with the buffer. The rate of agglomeration of like-charged macro-ions to form nuclei will also be affected by Coulomb repulsion. The strength of the bare Coulomb force will be reduced and the rate of agglomeration accelerated, however, by the plasma screening produced by the ions of the strong electrolyte. Using a theory incorporating these effects, we show that nucleation rates generally increase as the size of the critical nucleus decreases toward its lower bound set by the size of a dimer. The nucleation rates at low pH and also near pH=pI, where the protein molecules are neutral, are very large and represent sets of conditions particularly favorable to crystal production.

Influence of NH4Cl, NH4NO3, and NaNO3 on the Simultaneous Solubility of Ammonia and Carbon Dioxide in Water

New experimental results for the simultaneous solubility of ammonia and carbon dioxide in (about 4 m) aqueous solutions of NH4Cl, NH4NO3, and NaNO3 at (313, 353, and 393) K and total pressures up to about 0.7 MPa are reported. The maximum loading of carbon dioxide to ammonia, i.e., the molar ratio of carbon dioxide to ammonia, in the liquid phase was about 1 (at 313 K), about 0.7 (at 353 K), and about 0.3 (at 393 K). The experimental results are used to assess predictions from a thermodynamic model for the solubility of ammonia and sour gases in aqueous solutions of strong electrolytes.

Determination of the porosity to thickness ratio A k/Δ x for UF and MF membranes by diffusion experiments

The structural parameter A k /Δ x, which represents the ratio of membrane porosity to membrane thickness, was determined by means of diffusion experiments using aqueous solutions of neutral solutes (formamid, urea) and strong electrolytes (HCl, KCl …). The membranes under investigation were commercial ultrafiltration (UF) polyethersulfone (PES), polyvinylidenefluoride (PVDF) and acrylic membranes of various molecular weight cut-offs. The method used to measure A k /Δ x involves diffusion experiments at the pseudo-stationary state between two half cells. Experiments are non-time-consuming, and exploitation of results does not require any pore model. Results show that neutral solutes, as well as salts or diluted strong acid, can be used for the determination of A k /Δ x. Discrepancies between A k /Δ x values obtained by diffusion and water permeability measurements are explained by the pore tortuosity and the interconnection of the pores.

Raman spectra of aqueous solutions of strong electrolytes: evolving-factor analysis

Ion association in aqueous solutions of varied concentrations of LiNO3, Mg(NO3)2, Co(NO3)2, Li2SO4 and MgSO4 was studied by means of Raman spectrometry assisted by principal-components (PCA) and evolving-factor (EFA) analyses. Formation of one Raman-active associated species, {M···L(R)} (M=Li+, Mg2+, Co2+; L=NO3−, SO42−), was detected at higher salt concentrations (≳2 mol dm−3 for LiNO3, ≳1 mol dm−3 for Co(NO3)2, ≳0.2 mol dm−3 for Li2SO4, ≳0.5 mol dm−3 for MgSO4). Spectral profiles of L(aq) and {M···L(R)} species were computed by means of EFA, as well as their equilibrium concentrations in each solution. Maximum fractions of anions engaged in {M···L(R)} species amounted (at highest salt concentrations) to ≈0.6 (LiNO3), ≈0.4 (Co(NO3)2), ≈0.60 (Li2SO4) and ≈0.3 (MgSO4). Since, for a given salt concentration, the eqilibrium concentration of Raman-active species, [M···L(R)], was always lower than the concentration of analogous UV-active species, [M···L(UV)] (reported in a previous paper) it is suggested that {M···L(UV)} could be a precursor of {M···L(R)}. In all instances, apparent stability constants of {M···L(R)} species, falling into the range of (0.01≲K1/dm3 mol−1≲1), have a progressively upward trend with increasing salt concentration.

The role of electrolyte anions (ClO 4 (super -) , NO 3 (super -) , and Cl (super -) ) in divalent metal (M (super 2+) ) adsorption on oxide and hydroxide surfaces in salt solutions

Adsorption of divalent metal ions (M{sup 2+}) onto oxide and hydroxide surfaces from solutions of strong electrolytes has typically been inferred to take place without the involvement of the electrolyte anion. Only in situations where M{sup 2+} forms a strong enough aqueous complex with the electrolyte anion (for example, CdCl{sup +} or PbCl{sup +}) has it been frequently suggested that the metal and the electrolyte anion adsorb simultaneously. A review of experimental data for the adsorption of Cd{sup 2+}, Pb{sup 2+}, Co{sup 2+}, UO{sub 2}{sup 2+}, Zn{sup 2+}, Cu{sup 2+}, Ba{sup 2+}, Sr{sup 2+}, and Ca{sup 2+} onto quartz, silica, goethite, hydrous ferric oxide, corundum, {gamma}-alumina, anatase, birnessite, and magnetite, from NaNO{sub 3}, KNO{sub 3}, NaCl, and NaClO{sub 4} solutions over a wide range of ionic strengths (0.0001 M-1.0 M), reveals that transition and heavy metal adsorption behavior with ionic strength is a function of the type of electrolyte. In NaNO{sub 3} solutions, metal adsorption exhibits little or no dependence on the ionic strength of the solution. However, in NaCl solutions, transition and heavy metal adsorption decreases strongly with increasing ionic strength. In NaClO{sub 4} solutions, metal adsorption decreases strongly with increasing ionic strength. In NaClO{sub 4} solutions, metal adsorptionmore » exhibits little dependence on ionic strength but is often suggestive of an increase in metal adsorption with increasing ionic strength. Analysis of selected adsorption edges was carried out using the extended triple-layer model and aqueous speciation models that included metal-nitrate, metal-chloride, and metal-hydroxide complexes.« less

Imaging of humic substance macromolecular structures in water and soils

Humic substances (HSs) are the natural organic polyelectrolytes formed from the biochemical weathering of plant and animal remains. Their macromolecular structure and chemistry determine their role in biogeochemical processes. In situ spectromicroscopic evidence showed that the HS macromolecular structures (size and shape) vary as a function of HS origin (soil versus fluvial), solution chemistry, and the associated mineralogy. The HSs do not simply form coils in acidic or strong electrolyte solutions and elongated structures in dilute alkaline solutions. The macromolecular structural changes of HSs are likely to modify contaminant solubility, biotransformation, and the carbon cycle in soils and sediments.

SAFT-VRE: Phase Behavior of Electrolyte Solutions with the Statistical Associating Fluid Theory for Potentials of Variable Range

A modification of the statistical associating fluid theory has recently been developed to model non-conformal fluids with attractive potentials of variable range (SAFT-VR) [Gil-Villegas, A.; Galindo, A.; Whitehead, P. J.; Mills, S. J.; Jackson, G.; Burgess, A. N. J. Chem. Phys. 1997, 106, 4168] which gives a very good description of the phase behaviour of water and its mixtures with nonelectrolytes. In the present paper we extend the SAFT-VR approach to deal with strong-electrolyte solutions (SAFT-VRE). The water molecules are modeled as hard spheres with four attractive short-range sites to describe the hydrogen-bonding association. The electrolyte molecules are modeled with two hard spheres of different size which describe the anion and cation respectively. The mean-spherical approximation (MSA) is used for the restricted primitive model (RPM) to account for the long-range Coulombic ion−ion interactions, while the long-range water−water and ion−water attractive interactions are modeled as square-well di...

Aqueous strong electrolyte solution activity coefficients and densities from fluctuation solution theory

A model based on direct correlation function integrals (DCFIs) has been completed and used to describe the thermodynamic properties of single-salt aqueous electrolyte solutions. The principal advance is that parameters fitted only to activity coefficients are able to predict solution densities and compressibilities up to saturation concentrations over wide ranges of temperature and pressure. Though the parameter set involves a total of eight quantities for each salt, three, and potentially others, can be found from ionic additivity relations. Further, the parameters are constants or have linear or quadratic temperature variations up to 300°C. The model has been applied to 15 salts of all charge types involving mono- and divalent species. Correlation of activity coefficient data is normally more accurate than current models, especially near saturation such as for lithium halides up to 20 molar. The predicted densities are commonly within experimental error even up to 100 MPa.

Kinetics of Lysozyme Crystallization From Solution

We suggest that the growth of molecular aggregates is the rate-controlling step in the crystallization of lysozyme from pH buffered aqueous solutions of strong electrolytes. We propose that the aggregation reaction passes through a charged transition state whose rate of formation is accelerated by Debye-Huckel screening and whose charge is stabilized by ion exchange with the solution. Applying the theory of the “primary kinetic salt effect”, we predict that the half-life for decay of the lysozyme concentration in solution in contact with a growing crystal should decrease linearly with the square root of the ionic strength. This prediction is confirmed experimentally in the case of lysozyme crystals precipitating at 4°C from pH buffered aqueous solutions of sodium chloride.

Ion association in aqueous solutions of strong electrolytes: a UV–Vis spectrometric and factor-analytical study

Ion association in aqueous solutions of varied concentrations of Co(NO3)2 and LiNO3 has been studied by means of UV–Vis absorption spectrometry assisted by principal-components and evolving-factor analyses. Formation of [Co(NO3)]+ and [LiNO3]0 associated ion pairs was detected at higher salt concentrations (>0.1 mol dm-3 for Co(NO3)2, >0.7 mol dm-3 for LiNO3). Absorption spectra of ion pairs were computed by means of EFA, as well as their equilibrium concentrations and formation constants in each solution. The fractions of ion pairs (relative to total salt concentration) amounted to ca. 0.6 ([Co(NO3)]+) or ca. 0.5 ([LiNO3]0), at the highest salt concentrations. Differences in the absorption spectra of ion pairs, suggesting different kinds of cation–anion interaction, were tentatively interpreted as a weak coordination in the case of [Co(NO3)]+ and as a classical electrostatic ion association (probably with intervening water molecule) in [LiNO3]0. No association was observed with Mg(NO3)2 solutions in the experimental concentration range (c⩽2 mol dm-3).

A three-characteristic-parameter correlation model for strong electrolyte solutions

In this study, a characteristic-parameter correlation model was developed for the aqueous strong electrolyte solutions. This correlation model consisted of the long-range ion–ion interaction described by Pitzer–Debye–Huckel model and short-range ion-solvent molecule interaction attributed to solvation effect. The proposed approach is based on our previous paper of Lin et al. [C.-L. Lin, L.-S. Lee, H.-C.Tseng, Fluid Phase Equilibria, 90 (1993) 57–79.]. However, the significant improvement was made that the differential equation was solved analytically instead of numerically. This proposed model contains three parameters of physical significance and has been used to estimate the mean activity coefficients of electrolytes and osmotic coefficients of 144 aqueous strong electrolyte solutions from literature. Comparisons were made to the models of Chen et al. [C.C. Chen, H.I. Britt, J.F. Boston, L.B. Evans, AIChE, 28 (1982) 588–596; C.C. Chen, L.B. Evans, AIChE, 32 (1986) 444–454.], Ananth and Ramachandran [M.S. Ananth, S. Ramachandran, AIChE, 36 (1990) 370–386.], and Lin et al. [C.-L. Lin, L.-S. Lee, H.-C. Tseng, Fluid Phase Equilibria, 90 (1993) 57–79.]. The results also showed that the present model is at least as good as above models for 1-1 and 1-2 electrolyte solutions and improved very much for 2-1, 2-2, 3-1, and 3-2 electrolyte solutions.

Use of an electrolyte equation of state for the calculation of vapor–liquid equilibria and mean activity coefficients in mixed solvent electrolyte systems

In a previous paper [W. Fürst, H. Renon, AIChE J. 39 (1993) 335–343], a new electrolyte equation of state has been developed and applied to aqueous strong electrolyte solutions. One of the original features of this equation was that all ionic parameters could be determined using correlations related to experimental solvation properties which leads to a predictive model. Later, Zuo and Fürst [Y.-X. Zuo, W. Fürst, Fluid Phase Equilibria 138 (1997) 87–104.] extended it to predict vapor pressures and mean ionic activity coefficients for various non-aqueous electrolyte systems. In this work, the model has been extended to mixed-solvent electrolyte systems. This has been done by deducing most of the ionic parameters from experimental solvation properties and by developing mixing rules to represent preferential solvations in mixed-solvents, the aim being to minimize the number of adjustable parameters. Vapor–liquid equilibrium data relative to 26 water–alcohol–salt systems and mean ionic activity coefficients relative to eight water–alcohol–salt systems have been represented using only 18 parameters. The deviations for VLE are similar to those obtained by other authors, but with less adjustable parameters. Furthermore, it could represent mean ionic activity coefficients as well. Finally, the model has been used to predict VLE for 12 other mixed-solvent electrolyte systems with satisfactory results.

Phenomenological Equations of the Baromembrane Transfer of Strong Electrolyte Solutions

Differential phenomenological equations of mass transfer of strong electrolyte solutions for baromembrane process are developed and discussed.