The conductivity of concentrated aqueous mixtures of NaCl and MgCl2 at 25°C

As part of a cooperative study of the thermodynamic and transport properties of aqueous mixtures of NaCl and MgCl₂ at 25°C, we report values of the molar conductivities of the mixed electrolyte in the concentration range 0.5 to 3.6 molar. It was found that the conductivities in the mixtures differ from those calculated assuming additivity of the conductivities of the component binary solutions by 4.65 S-cm²-mol^–1 at constant total molarity and 0.50 S-cm²-mol^–1 at total ionic strength.     

Multiphase equilibria for mixtures containing water, isopropanol, propionic acid, and isopropyl propionate

Vapor pressures of isopropyl propionate and isobaric vapor-liquid equilibrium (VLE) properties of isopropyl propionate + isopropanol and propionic acid + isopropyl propionate were measured. Isothermal vapor-liquid-liquid equilibrium (VLLE) data were also determined experimentally for water + isopropyl propionate and water + isopropyl propionate + isopropanol at temperatures from 323.24 K to 373.15 K. The binary VLE and VLLE data can be correlated well with the NRTL-HOC and the UNIQUAC-HOC models. The ternary VLLE data were used to test the validity of two versions of the UNIFAC model and the NRTL-HOC and the UNIQUAC-HOC models with the parameters determined from the phase equilibrium data of the constituent binaries. The ternary VLLE data were also correlated with the NRTL-HOC and the UNIQUAC-HOC models and the Soave-Redlich-Kwong equation of state with the Wong-Sandler mixing rule.     

The conductivity of dilute aqueous solutions of magnesium chloride at 25°C

There is a disagreement in the literature regarding the best value of _o[1/2MgCl₂]. For this reason, the conductivity of dilute aqueous MgCl₂ solutions have been determined at 25°C. The new experimental data and those available in the literature have been analyzed with two theoretical treatments of electrolytic conductivity. On the basis of that analysis, the values 129.72±0.05 and 53.40±0.05 S-cm²-mol^–1 for _o[1/2MgCl₂] and _o[1/2Mg²⁺], respectively, are recommended.     

Electrical conductivity of aqueous sodium hydroxide solutions at high temperatures

Electrical conductivities of dilute sodium hydroxide aqueous solutions have been determined at 75, 100 and 150°C at 1.6 MPa using a recently developed DC-measuring technique especially suited for the study of aqueous solutions above room temperature. The data were analyzed with modern theories to obtain the infinite dilution conductivity and the association constant at the three temperatures.     

Sonoluminescence of aqueous solutions of sulfuric acid and sulfur dioxide

Sonoluminescence (SL) of aqueous solutions of sulfuric acid and sulfur dioxide enhances with an increase in their concentration and reaches a maximum at 16 and 0.05 mol L^–1, respectively. The further increase in the concentration of these substances decreases the SL intensity. The SL spectra of the solutions have a broad maximum at 450 nm. Excited SO₂ molecules formed in sulfuric acid due to sonolysis are luminescence emitters. The proposed mechanism of bright SL in these systems is based on the energy transfer from the electron-excited sonolysis products to the SO₂ molecules in cavitation bubbles.     

Activity coefficients for NaBr in aqueous ternary solutions with sodium propionate and butyrate from EMF measurements

The activity coefficients of NaBr in the NaBr–NaPropionate–H₂O and NaBr–NaButyrate–H₂O systems were determined from EMF measurements at constant total ionic strength of 0.1 0.5 1.0 1.5 2.0 and 2.5 mol-kg^–1 and at 25° C. The activity coefficients were fitted using Scatchard, Pitzer and Lim equations. Finally the excess Gibbs free energy of these mixtures were also calculated.     

New physico-chemical properties of extremely diluted aqueous solutions

The 'extremely diluted solutions', anomalous solutions prepared through the iteration of a process of dilution and succussion, have been studied with the aim of obtaining information about the influence of the preparation method on the water structure of the solutions. We measured the heats of mixing of basic solutions with such 'extremely diluted solutions', and their electrical conductivity, comparing with the analogous heats of mixing, electrical conductivity of the solvent. We found some relevant exothermic excess heats of mixing, and higher conductivity than those of the untreated solvent. The heats of mixing and electrical conductivity show a good correlation, underlining a single cause for the behaviour of the extremely diluted solutions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Apparent molar heat capacities of aqueous solutions of acetic,propanoic and succinic acids,sodium acetate and sodium propanoate from 300 to 525 K and a pressure of 28 MPa

The apparent molar heat capacities of dilute aqueous solutions of acetic, propanoic and succinic acid and sodium salts of the two monofunctional acids were measured at 300 Kp,2 ^o . After subtracting the heat capacity of a point mass, the remaining heat capacity was successfully decomposed into functional group contributions at all temperatures. Together with the results of our previous paper on alcohols and diols the heat capacity contributions of the CH₂, CH₃, OH, COOH, (COOH)₂, and COONa groups are now available and these allow reasonably accurate predictions of the heat capacities of all compounds composed of these groups in this temperature range.     

Concentration Dependence of the Activation Energy of Conductivity in Aqueous Sodium Selenite and Potassium Tellurite

The temperature and concentration dependences of conductivity have been studied for aqueous solutions of sodium selenite and potassium tellurite. The corresponding empirical equations have been derived. The activation energies of conductivity in both electrolytes are calculated for different solution concentrations. The ascertained dependence is interpreted in the light of Samoilov's theory on positive and negative hydration of ions. Analysis of the results suggests that the larger the positive hydration of ions, the higher the activation energies of conductivity for the salts.     

Diffusion in dilute aqueous acetic acid solutions at 25°C

A conductimetric technique has been used to measure diffusion coefficients for aqueous solutions of acetic acid at concentrations from 0.002 to 0.02 mol-dm^–3 at 25°C. The acetic acid component diffuses more rapidly at lower concentrations where a higher proportion of the slower acid molecules are converted by dissociation to acetate ions and highly mobile hydrogen ions. The observed concentration dependence of the diffusion coefficient verifies the limiting law for weak electrolyte diffusion. A new type of conductimetric diffusion cell with several practical advantages over earlier designs is described together with an improved procedure for the conductimetric determination of accurate diffusion coefficients for weak electrolyte systems.     

Solubilization of methane,ethane, propane andn-butane in aqueous solutions of sodium dodecylsulfate

The solubilities of methane, ethane, propane, and n-butane were measured in aqueous solutions of sodium dodecylsulfate (NaDS) (0–0.1M) from 15 to 27°C. From these measurements the standard Gibbs energies, entropies, and enthalpies for the process of transferring the solute molecules from the gaseous phase into the solutions were calculated. An approximate relationship was found relating the volume fraction of the micelles to NaDS concentration.     

Transference numbers of sodium chloride in concentrated aqueous solutions and chloride conductances in several concentrated electrolyte solutions

Stable chlorine electrodes with low bias potentials have been developed by introducing 25% Ir+75% Pt electrodes and an improved gas line. With their use in cells with transference, cation constituent transference numbers have been measured at 25°C in NaCl solutions from 1.7 to 6 modal. These results agree well with four other sets of data in the literature but disagree with two further sets based on emf determinations with Ag/AgCl electrodes. A table of best NaCl transference numbers is proposed. The conductances of the chloride ion-constituent in concentrated NaCl, KCl, and HCl solutions are compared.     

Ionization of carbonic acid in sodium chloride solutions at 25°C

The stoichiometric pK ₁ ^* and pK ₂ ^* for the ionization of carbonic acid has been determined from emf measurements in NaCl soluions to 6.0m at 25°C. Our results at low concentrations are in good agreement with the results of Harned and Bonner, of Dyrssen and Hansson and of Roy et al. The calculated values of pK ₁ ^* using Pitzer's equations agree with the measured values to ±0.01 pK units provided higher order terms are used. It was necessary to use a triplet interaction parameter () and higher order electrostatic terms (^E) to calculate reliable values of pK ₂ ^* (±0.03 pK units) over the entire concentration range. These results demonstrate the reliability of the Pitzer equations to estimate activity coefficients in concentrated salt solutions.     

Osmotic and activity coefficients of aqueous NaTcO4 and NaReO4 solutions at 25°C

Isopiestic vapor-pressure comparison experiments were performed with aqueous binary sodium perchlorate, pertechnetate, and perrhenate solutions to concentrations of approximately 8.5 m. Osmotic coefficients for these solutions and mean molal ionic activity coefficients for NaTcO₄ and NaReO₄ were derived from the isotonic molalities. Pitzer's treatment was applied to describe the concentration dependence of the osmotic coefficients of NaClO₄, NaTcO₄, and NaReO₄, and the implications of the parameters derived from a leastsquares fit are discussed in terms of solvent structure and interionic forces.     

Velocity correlations in aqueous electrolyte solutions from diffusion,conductance and transference data: Application to concentrated solutions of nickel chloride and magnesium chloride

Velocity cross-correlation coefficients have been calculated for aqueous solutions of NiCl ₂ and MgCl ₂ up to concentrations of 4M. Examination of the concentration-dependence of these coefficients show that it is very similar for the two salts. There is no evidence for any special structural characteristics in NiCl ₂ solutions. The velocity correlation technique is apparently not sensitive enough to detect the small amount of complexation that is thought to be present in NiCl ₂ solutions.     

Association of carboxylic acids in aqueous solutions from conductivity data

Using precision conductivity data for aqueous carboxylic acid systems at 25 and 30°C, accurate thermodynamic ion association and dimerization equilibrium constants were determined. The data for formic, acetic, propionic and butyric acids are analyzed with the Fuoss-Hsia conductance equation as modified by Justice and Barthel. The treatment requires that triple ion formation is negligible.     

Electrical conductivity of aqueous polymer solutions

 Theoretical equations were proposed to adequately simulate the electrical conductivity behavior of aqueous solutions of both charged and uncharged polymers. The theory, based on the mixture equation of Boned and Peyrelasse, was experimentally verified on poly(acrylic acid) (PAA) in water and poly(ethylene oxide) (PEO) in aqueous electrolyte solutions. The data analysis suggested that both the polymer coils may be depicted as oblate ellipsoids. Subsequently, the semiaxes values of the polymer coils were determined, and they were in good agreement with the results reported in the literature. Received: 25 June 1996 Accepted: 2 October 1996     

Sodium sulfate solubilities in high temperature aqueous sodium chloride and sulfuric acid solutions—predictions of solubility,vapor pressure,acidity, and speciation

Experimental measurements of the solubility of sodium sulfate in aqueous solutions containing both sodium chloride and sulfuric acid in the temperature range 250 to 374°C are reported. These measurements have been combined with previous data on the solubility of sodium sulfate in water, in aqueous sodium chloride, and in sulfuric acid solutions to produce a comprehensive model describing the solubility of sodium sulfate in such solutions. Calculations and predictions of solubility, vapor pressure, boiling point elevation, acidity, and speciation are presented. This model is of fundamental interest in itself and also is of importance because the precipitation of sodium sulfate may be a contributing factor in enhancing crevice corrosion in metals exposed to high-temperature water containing chloride and sulfate ions as impurities.