Properties Of Aqueous Salt Solutions Research Articles

Relationship between the major parameters of warm-blooded organisms' life activity and the properties of aqueous salt solutions

<abstract> <p>We are devoted to the physical analysis of the habitat area of warm-blooded organisms – humans and many mammals. For this purpose, the establishment of equilibrium distribution of carbon dioxide in aqueous solutions of salts in contact with atmospheric air starting from some time is investigated. More precisely, the relaxation time of carbon dioxide, as a function of temperature and pH, is investigated. It is found that the pH-relaxation time <italic>τ<sub>S</sub></italic> is a very nontrivial function of temperature, pH values, and NaCl salt concentration. It was assumed that the minimum value of pH relaxation time corresponds to the optimal rate of physical processes in living matter. Using this selection principle and our experimental data, we have shown that the optimal temperature for human and mammalian life activity is close to <italic>T<sub>o</sub></italic> ≈ 37 °C. The lower and upper temperature limits for their possible activity are close to <italic>T<sub>l</sub></italic> ≈ 30 °C and <italic>T<sub>u</sub></italic> ≈ 42 °C, respectively. The optimal value of <italic>pH</italic><sub>o</sub>, determined by the same selection principle, also becomes true if supplemented by the influence of albumin and other proteins.</p> </abstract>

Flocculating and Hydrodynamic Properties of Aqueous-Salt Solutions of Acrylamide Polymers

Specific features of flocculation of aqueous-salt (KCl, NaCl) clay dispersions with polyacrylamide and anionic acrylamide copolymers, including the influence exerted by the procedure of polymer dissolution in water or salt solution on the sedimentation rate and density of floccules and on the hydrodynamic properties of the polymers, are described. The use of aqueous-salt solutions of flocculants enhances the flocculating effect. The most effective flocculant for aqueous-salt clay dispersions is polyacrylamide prepared in a salt solution, which is due to higher flexibility of the polymer chain. The results obtained are of practical interest in connection with the possibility of enhancing the efficiency of the flocculation of aqueous-salt clay dispersions in dressing of potassium ores.

Relationship between Radioluminance and the Dielectric Properties of Aqueous Salt Solutions in the Millimeter-Wavelength Spectral Range

A new approach is developed to studying aqueous solutions of salts based on their emission in the millimeter waves spectral range. Using a highly sensitive radiometer at a frequency of 61.2 GHz, reflection coefficients and radioluminance contrasts are determined for solutions of alkali metal sulfates in a wide range of concentrations. Changes with opposite signs that occur in solutions as compared to water are revealed. Theoretical substantiation and a quantitative description of the measured effects are given, based on the complex dielectric permittivities of the solutions. It is shown that emission reflects the contributions from both dipole and ionic loss that remain substantial at the considered frequencies; they can even identify the presence of emission effects with opposite signs.

Modeling of Dielectric Properties of Aqueous Salt Solutions with an Equation of State

The static permittivity is the most important physical property for thermodynamic models that account for the electrostatic interactions between ions. The measured static permittivity in mixtures containing electrolytes is reduced due to kinetic depolarization and reorientation of the dipoles in the electrical field surrounding ions. Kinetic depolarization may explain 25-75% of the observed decrease in the permittivity of solutions containing salts, but since this is a dynamic property, this effect should not be included in the thermodynamic modeling of electrolytes. Kinetic depolarization has, however, been ignored in relation to thermodynamic modeling, and authors have either neglected the effect of salts on permittivity or used empirical correlations fitted to the measured static permittivity, leading to an overestimation of the reduction in the thermodynamic static permittivity. We present a new methodology for obtaining the static permittivity over wide ranges of temperatures, pressures, and compositions for use within an equation of state for mixed solvents containing salts. The static permittivity is calculated from a new extension of the framework developed by Onsager, Kirkwood, and Fröhlich to associating mixtures. Wertheim's association model as formulated in the statistical associating fluid theory is used to account for hydrogen-bonding molecules and ion-solvent association. Finally, we compare the Debye-Hückel Helmholtz energy obtained using an empirical model with the new physical model and show that the empirical models may introduce unphysical behavior in the equation of state.

Temperature‐concentration oscillations as a result of nanoheterophase structure of concentrated aqueous solutions of salts

AbstractDetailed precision investigation of aqueous solutions of NaBr·2H2O, KBr, RbNO3, and K2SO4 salts showed oscillations of crystal‐solution phase equilibria in the temperature range of 15–45 °C. The maximum deviations from the smooth correlation between the saturation temperature and the salt concentration (up to 4% of concentration and up to 10 °C) were found to correspond to simplest salt‐water ratios. Recently, similar trends were observed for NaNO3, KNO3 and K2CrO4 solutions. Oscillation amplitudes for saturation temperature in the investigated series decreased in the following orders: Na+→K+, Rb+, NH4+ (nitrate systems), CrO42–→SO42– and Br–→NO3– (potassium systems), and NO3–→Br– (sodium systems). Increase in total content of impurities (2‐4‐fold) in solution results in 1.5‐2‐fold elevation of the oscillation amplitudes. A concept of nanoheterophase solution was suggested to account for the observed temperature‐concentration oscillations. The concept is based on the original experimental data on interrelated variation of different properties of aqueous salt solutions depending on their concentrations. Characteristic features of the phase diagrams are discussed and influence of the oscillations on crystal growth is elucidated. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Inclusions of magmatic fluids: P-V-T-X properties of aqueous salt solutions of various types and petrological implications

The P-V-T-X properties of H2O-salt systems are compared depending on the solubility coefficient of compounds contained in these systems and the presence or absence of critical phenomena in the saturated solutions. Data on synthetic and natural inclusions captured in minerals at elevated temperatures and pressures and employed to discuss the principal features of phase diagrams of the H2O-NaCl system (type I) and H2O-NaF system (type II or P-Q type). It is demonstrated how characteristics of magmatic fluids of various types are manifested during the development of miarolitic pegmatites (Malkhan field in Transbaikalia) and during the crystallization of F-rich ongonitic melts (Ary-Bulak Massif in eastern Transbaikalia). Characteristics of solutions and gas-rich (gaseous) fluid inclusions in quartz phenocrysts from porphyritic ongonites (disappearance of the liquid regardless of its density and the overall salinity near the critical point of water, distinctive features of the dissolution of the crystalline phase, and the ability of the inclusions to withstand heating to 1400°C without decrepitation), and the richness of the fluid-magmatic system as a whole in F suggest that the ongonite melt crystallized in the presence of low-density NaF-bearing fluids of the P-Q type with a minor admixture of chlorides. It is important to identify the type of solutions in the fluid inclusions, because without knowing this type, it is impossible to accurately enough calculate the pressure at the temperatures of inclusion capture. For example, the unwarranted classification of solutions of type II (P-Q) in inclusions with the chloride system results in a significant overestimation of the calculated fluid pressures. A technique is proposed for studying the high-temperature immiscibility region in P-Q systems based on data obtained on gaseous fluid inclusions.

Method of synthetic fluid inclusions in quartz in experimental study of the water-sodium sulfate system

The aim of this study is to estimate the capability of the method of synthetic fluid inclusions in experimental investigation of the properties of aqueous salt solutions, whose phase diagram is attributed to the second (P-Q) type (in such solutions, critical phenomena are observable in both undersaturated and saturated states). The water-sodium sulfate system has been selected from the systems of the second type as the best studied with another experimental technique. Fluid inclusions in quartz have been synthesized in the field of examined temperatures and pressures in the presence of sodium sulfate solutions of a given concentration. Microthermometry of these inclusions shows a partial correspondence to properties of sodium sulfate solutions, which were previously studied by recording temperature-pressure and volume curves at the moment of phase transition. Discrepancies are probably caused by the active behavior of silica with respect to the fluid and the effect of the third component upon equilibrium in the fluid.

Statistical thermodynamics of aqueous solutions. I. Water structure, solutions with non-polar solutes, and hydrophobic interactions

A statistical thermodynamic theory of the structure and thermodynamic properties of liquid water is needed for a description of the thermodynamics properties of aqueous salt solutions. For this purpose, such a theory, developed earlier by Némethy and Scheraga, has been modified by removing an empirical cluster restriction, by using a different form of the partition function for unbonded water, by treating the librational and translational frequencies differently, and by removing the restriction that the energy levels are equally spaced. These modifications improved the computed thermodynamic properties of liquid H 2O and D 2O, and provide a basis to treat aqueous solutions of non-polar molecules and, subsequently, salts. The presence of a non-polar solute leads to shifts of the energy levels of the variously bonded species in the first layer of the surrounding water molecules, and a resulting increase in the fraction of hydrogen bonds between water molecules; i.e. non-polar solutes in aqueous solutions can be characterized as ‘structure making’. Theoretical, Monte Carlo and molecular dynamics calculations, and also simplified models, in the literature, support the assumption in the model used here of a partial cage-like (hydrogen-bonded) structure around a hydrocarbon molecule (hydrophobic hydration). The computed thermodynamic parameters for the transfer of hydrocarbons from a non-polar medium to an aqueous environment, based on a statistical thermodynamic treatment, are reproduced very well by the theory. With no additional parameters, the theory accounts qualitatively for the transfer of argon, propane and butane, respectively, from H 2O to D 2O, better than the original theory. The strengths of pairwise hydrophobic interactions, computed by Némethy and Scheraga, and subsequently verified experimentally, are not altered by the modification of the earlier theory for liquid water.

Properties of aqueous salt solutions of poly(ethylene oxide). Cloud points, ? temperatures

The determination of the properties of aqueous salt solutions of poly(ethylene oxide) has been extended to the cloud point, andθ temperature measurements have been made at several concentrations for various salts (flourides, iodides, acetates, formates, phosphates, bromides, thiosulfates and perchlorates). The resulting dependency of the critical temperaturesθ (mostly between 290–350 K) on the molar concentration can be expressed as sequences showing the decreasing effect of anion species or cation species in salting out the polymer. The decreasing order of effectiveness of the anions in reducing theθ temperature is PO4≡ > HPO4≡ > S2O3≡ > H2PO4− >F− > HCOO− > CH3COO− > Br− > I−. The order for cations is K+ ≈ Rb+ ≈ Na+ ≈ Cs+ > Sr++ > Ba++ ≈ Ca++ > NH4+ > Li+. The changes brought about inθ temperatures by the salts were found to be the results of the changes taking place in the hydrophilic and hydrophobic interactions among polymer, solvent and additive salts and of the change of water structure by structure making or structure breaking ions, and of the influence of salts on the hydration sheath of the polymer.

A relation between the critical properties of aqueous salt solutions and the heat capacity of the solutions near the critical point using a single-fluid corresponding-states theory

The effects of added salts on the heat capacity of water at constant pressure are extremely large near the critical point of water. A corresponding-states theory for the heat capacity of aqueous salt solutions is proposed. This theory is based on the assumption that the major effect of the salt is to shift the critical point of the water in the solution. Since the water has an infinite heat capacity at constant pressure at the critical point, this shift causes the very large effects observed. Tests of this theory with the available data on NaCl show that the theoretical predictions are surprisingly accurate. The heat capacity of the solution is predicted with an average error of ± 0.7 per cent and a maximum error of 3.4 per cent at temperatures from 320 to 600 K, molalities from 0.1 to 3.0 mol·kg −1, and at a pressure of 17.7 MPa. A similar equation for the enthalpy of the solutions is not accurate, and there are insufficient data in the literature to test the corresponding equations for thermal expansivity, compressibility, and the difference between heat capacities at constant pressure and at constant volume. Since the equation has been tested only for NaCl solutions at temperatures below the critical point, there is a pressing need for more experimental results. The theory predicts very large effects on the heat capacity of any solution of a strong electrolyte near the critical point of the solvent and that these effects can be predicted from a knowledge of the critical temperature and critical pressure of the solutions.

Properties of aqueous salt solutions of poly(ethylene oxide)

AbstractThe determination of the properties of aqueous salt solutions of poly(ethylene oxide) has been extended to cloud‐point and θ‐temperature measurements in sodium acetate, potassium fluoride, sodium thiosulfate, and potassium phosphate. The Hofmeister series for the decreasing effect of anion species in salting out the polymer is accordingly extended. However, the order of the effect depends on whether it is made on the basis of molar anion concentration the molar concentration of unit anion charge, or the ionic strength. Viscosity measurements on θ and non‐θ solutions containing zinc sulfate, potassium fluoride, and potassium phosphate gave polymer dimensions (in addition to limiting viscosity numbers etc.), and characteristic ratios in good agreement with theoretical predictions (Abe and Mark), and enthalpy and entropy parameters χH and χs; the latter values, nominally −0.14 and 0.63, are identical at 298 K for the three salt species.

Properties of aqueous salt solutions of poly(ethylene oxide): Thermodynamic quantities based on viscosity and other measurements

AbstractA previous study of poly(ethylene oxide) (PEO) in aqueous salt solutions has been extended to incorporate cloud‐point measurements in potassium thiocyanate solutions (salt concentration range 3.3–3.8M where salting out occurs) and, particularly, viscosity measurements. A few osmoticpressure measurements were made and molecular weights (∼2 × 104) from gel‐permeation chromatography (GPC) compared. The theta temperature for PEO in water from cloud points was found to be 369 ± 3°K. An empirical linear relation has been found for sodium and potassium salts between the finite change of theta temperatures with change in ionic strength, δθ/δI, and (v3 − v̄3), the difference between the molar van der Waals volume and the partial molar volume of the salt. Values of the Huggins constant k′ are less than 0.5 for PEO in pure water at 303.2°K, indicating a good solvent, whereas in salt solutions they vary from 0.59 to 1.14 in nontheta solvents. They and other findings are attributed to binding of salt to the polymer and to water structure breaking. Kraemer's constants k″ were also determined: k′ − k″ = 0.5 for PEO in pure water, and for aqueous salt solutions of PEO, k′ − k″ = 0.666 at 298°K. Values of K0(= M−1/2[η]θ) with M = 2 × 104 were found to very with salt type (valence)—mean values of 103 K0/dlg−1 with number of observations in brackets are 1:1, 1.19 (2); 1:2, 1.45 (3); 2:2, 1.75 (3). Unperturbed dimensions 〈r2〉 vary from 11.0 to 12.6 nm from 1:1 to 2:2 salts. Values of the characteristic ratio Cn, the steric parameter σ, and the enthalpy and entropy of dilution parameters χH and χS have also been calculated.

Isopiestic studies of very concentrated aqueous electrolyte solutions of LiCl, LiBr, LiNO 3, Ca(NO 3) 2, LiNO 3 + KNO 3, LiNO 3 + CsNO 3, and Ca(NO 3) 2 + CsNO 3 at 100 to 150°C

Thermodynamic properties of aqueous salt solutions show marked changes when the water content is reduced below 4 to 8 mol of H 2 O per mole of salt, reflecting the gradual transition between aqueous electrolytes and molten salts. The enthalpy of vaporization of water rises from values near that of pure water to values characteristic of water at infinite dilution in molten salts. Water activities at high concentrations have been determined from precise isopiestic measurements of LiCl, LiNO 3 , LiBr, Ca(NO 3 ) 2 and several mixtures including (Li, K)NO 3 at 100 to 150°C. All show a region in which Stokes and Robinson's B.E.T. adsorption model of hydration can be fitted with physically reasonable energy parameters. For the system (Li, K)NO 3 + H 2 O, the difference between the energy of adsorption and energy of liquefaction, calculated with the model, is 0.7 kcal mol −1 , while the difference between the enthalpies of vaporization of water at infinite dilution in salt and of pure water is 0.8 kcal mol −1 .

Structure and properties of aqueous salt solutions

The first page of this article is displayed as the abstract.

Coordination equilibria in non-aqueous solvents

Abstract

The Physical Properties of Aqueous Salt Solutions in Relation to the Ionic Theory

The Physical Properties of Aqueous Salt Solutions in Relation to the Ionic Theory