Solutions Of Alkali Metal Halides Research Articles

Structure of aqueous alkali metal halide electrolyte solutions from molecular simulations of phase-transferable polarizable models

The structure of aqueous solutions of alkali metal halides is studied under ambient thermodynamic conditions and concentrations from infinite dilution to supersaturation using molecular dynamics simulations of phase-transferable polarizable models. The results of the solution densities, radial distribution functions, 3D spatial distribution functions, the properties of hydrogen and other noncovalent bonds in solutions, hydration numbers, coordination numbers, numbers of contact cation-anion pairs, and other statistics of the number of ions hydrated simultaneously by a shared water molecule are systematically presented. In particular, the results show and quantify how the strengths of the hydration bonds of different ions vary and how the hydration numbers decrease with increasing concentration in parallel with an increase in the number of contact cation-anion pairs. In most cases, they completely compensate for the loss of water-ion bonds by an increase in cation-anion bonds. An exception are solutions based on the Li+ cation, which retain a solid hydration shell even at high concentrations. This behavior is conceptualized on the basis of three imaginary driving forces: the first dominating at low concentrations and causing full hydration of the ions, the second representing a lack of water necessary for full hydration of the ions and increasing with increasing concentration, and the third attracting counterions to the water-unoccupied sites of the hydration shells and also increasing with concentration. This concept can be used not only to understand the structural behavior of homogeneous electrolytes in thermodynamic equilibrium but also to study phenomena that involve preferential adsorption of ions on electrodes, in nanochannels, or porous materials. The data obtained for the number and strength of hydration bonds and ion pairs can also be used in further studies to elucidate the diffusion behavior, viscosity, and conductivity of aqueous electrolyte solutions.

Alkali Halide and MIBC Interaction at Typical Flotation Interfaces in Saline Water as Determined by Molecular Dynamics Simulations

The molecular structure of the liquid–vapor interfaces of aqueous solutions of alkali metal halides and methyl isobutyl carbinol (MIBC, (CH3)2CHCH2COCH3) is determined by using molecular dynamics simulations with polarizable force fields for the first time. The salts are chlorides, and iodides, some of which are found in raw and partially desalinated seawater increasingly used in flotation operations in regions affected by severe and prolonged drought. The density profiles at the interfaces show that all ions prefer the interface; however, with MIBC, non-polarizable ions, generally small ones, are increasingly pushed into the liquid bulk. A few ions of comparatively less ionic NaCl than KCl and CsCl, persist at the interface, consistent with spectroscopy observations. On the other hand, strongly polarizable ions such as I− always share the interface with MIBC. In the presence of chlorides, the frother chains at the interface stretch slightly more toward vapor than in freshwater; however, in the presence of iodides, the chains stretch so much that they become orthogonal to the interface, giving rise to a well-packed monolayer, which is the most effective configuration. The dominant water configurations at the interface are double donor and single donor, with hydrogen atoms pointing toward the liquid, consistent with studies with sum-frequency generation experiments and extensive ab initio simulations. This picture changes radically in the presence of MIBC and salts. Depending on the halide and MIBC concentration, the different molecular configurations at the interface lead to very different surface tensions. The structure and properties of these new salt-rich interfaces and their impact on the location and arrangement of frother molecules should serve the flotation practitioner, especially in the search for the best frother and dosing in poor-quality water.

“Anion-chromic” interactions of emeraldine base with hydroxide and halide anions in the solid polymer matrix

A behavior of polyaniline (PANI) composites with common polymers under different conditions is often a result of a synergetic combination of properties of their components. In this work we consider specificity of such a combination in terms of both hydrogen bonding of PANI with a matrix polymer poly(ethylene terephthalate) (PET) and its influence on interactions of the composite PANI–HCl/PET films or dedoped PANI/PET films with alkaline and alkali metal halide aqueous solutions. In particular, it is found that PANI in emeraldine base (EB) state forms a EB complex with hydroxide anions, which is confirmed not only by a strong blue shift of the exciton band in UV–vis spectra of both the dedoped PANI/PET (up to 529nm) and pure EB film (up to 579nm) but also by reversibility of this shift and its independence on the alkali cation nature. Additional confirmations of existence of this complex were obtained by quenching of the PL emission of EB by OH− anions in the dedoped PANI/PET and IR spectra of EB film after its interaction with the alkali solution. Formation of this EB–OH− complex is shown to be due to hydrogen bonding of hydroxide anions with amine groups of the dedoped PANI (EB) backbone. The EB–OH− complex is much more stable in the dedoped PANI/PET composite film than in the pure EB film probably due to additional hydrogen bonding of OH− anions with carbonyl oxygen atoms of the matrix. However, this complex in the PANI/PET film can be destroyed by dissolving in NMP or by contact with the solutions of alkali metal halides. Specifically, the complex instability in these solutions is enhanced in the halide anions range F−<Cl−<Br− that results in restoring the EB exciton band position and IR absorption bands of the pure EB.

Manifestation of ion specificity in the behavior of the dynamic dielectric permittivity of aqueous solutions of alkali metal halides

Dispersions of the refractive index are measured in aqueous solutions of potassium halides at different salt concentrations and temperatures of the solutions. The specific effect of anions on the dynamic dielectric permittivity of the solutions is found. A model is proposed to evaluate the character of changes in the dynamic dielectric permittivity of the solutions and effective dynamic polarizabilities of ions in the solutions based on the data about the dispersion of refractive indices. The role of ion sizes and the character of their interaction with a solvent in the manifestation of specific ion effects are discussed.

Manifestation of ion specificity in the behavior of the dynamic dielectric permittivity of aqueous solutions of alkali metal halides

Dispersions of the refractive index are measured in aqueous solutions of potassium halides at different salt concentrations and temperatures of the solutions. The specific effect of anions on the dynamic dielectric permittivity of the solutions is found. A model is proposed to evaluate the character of changes in the dynamic dielectric permittivity of the solutions and effective dynamic polarizabilities of ions in the solutions based on the data about the dispersion of refractive indices. The role of ion sizes and the character of their interaction with a solvent in the manifestation of specific ion effects are discussed.

Dependence of the density of solutions of alkali metal halides on the composition of methylpyrrolidone-water mixed solvents

The densities of solutions of alkali metal halides in methylpyrrolidone (MP)-water mixtures were measured at 298.15 K over the entire range of mixed solvent compositions. The standard partial molar volumes of the electrolytes \( \overline {V_2^ \circ } \) were calculated. The \( \overline {V_2^ \circ } \) values of alkali metal halides in MP-H2O mixtures were related linearly to the \( \overline {V_2^ \circ } \) values in aqueous solutions. These dependences were used to determine the standard partial molar volumes of ions \( \overline {V_i^ \circ } \) in the mixtures studied. The standard partial molar volumes of transfer of the ions from water into MP-water mixtures were calculated.

Evaluation of individual ionic partial molar volumes in aqueous solutions

In a recent H 2O–D 2O molar volume isotope effect study on the alkali metal halide solutions, individual ionic standard partial molar volume contributions ( V ¯ ion ∘ ( H 2 O ) - V ¯ ion ∘ ( D 2 O ) = Δ V ¯ ion ∘ ( H–D ) ) have been derived, dependent only on the chosen (Pauling) ionic radii, r ion. It has been concluded that the isotope effect of the cations (except for Li +) and that of the chloride anion exhibit a linear function of 1/ r ion, with Δ V ¯ ion ∘ ( H − D ) vanishing when 1/ r ion approaches zero. On the other hand, the directly measurable hydrodynamic “cosphere” volumes of the ions, V ¯ cosph ∘ , derived from the kinetic ionic (Stokes) radii, show a similar pattern, here also the cationic and anionic r ion relations cross or meet at V ¯ cosph ∘ ( Cs + ) ≅ V ¯ cosph ∘ ( Cl - ) . Because both Δ V ¯ ion ∘ ( H–D ) and V ¯ cosph ∘ originate in the hydration volumes of the ions, ( V ¯ hydr ∘ = V ¯ ion ∘ - V ¯ intr ∘ ) determined by electrostriction, this r ion pattern of the V ¯ hydr ∘ (ion) provides an “extra-thermodynamic” assumption to evaluate the individual cationic and anionic molar volume contributions in normal water solution. As a basis for the evaluation, this r ion pattern is applied to the conventional cationic and anionic V ¯ hydr ∘ (ion) values (related to V ¯ ion ∘ ( H + ,aq . ) = 0 cm 3 · mol - 1 ) , calculated from literature V ¯ ion ∘ data, assuming that the V ¯ intr ∘ (ion) = V ¯ cryst ∘ (ion). To adjust the V ¯ hydr ∘ ( Cl - ) to the V ¯ hydr ∘ ( Na + , K + , Rb + , Cs + ) versus r ion relation at T = 298.15 K, the conventional anionic V ¯ hydr ∘ (ion) data have to be increased, the cations have to be decreased by 4.2 cm 3 · mol −1. Similar adjustments at five different temperatures between T = (273 and 323) K, result in V ¯ ion ∘ ( H + ,aq . ) = - ( 4.2 ± 0.2 ) cm 3 · mol - 1 at T = 298.15 K, with an increment of −0.02 cm 3 · K −1 · mol −1. Related to these parameters, relations of V ¯ ion ∘ versus temperature for the alkali metal and halide ions were calculated. The cationic and anionic V ¯ hydr ∘ (ion) values, when related to V ¯ ion ∘ ( H + ,aq . ) = - 4.2 cm 3 · mol - 1 , show strong r ion correlation with V ¯ cosph ∘ , their ratio versus r ion offers a linear equation to compare the influence of the ions on the solvent structure on a well defined “quantitative” scale. The value of the derived V ¯ ion ∘ ( H + ,aq . ) , while being consistent with that widely accepted ca. − (5 ± 2) cm 3 · mol −1, has a higher precision with a reasonable basis of the applied “extra-thermodynamic” assumption. It can serve to verify other partitioning procedures used in non-aqueous solvents.

Viscometric and thermodynamic studies of interactions in ternary solutions containing sucrose and aqueous alkali metal halides at 293·15, 303·15 and 313·15 K

Viscosities and densities of sucrose in aqueous alkali metal halide solutions of different concentrations in the temperature range 293.5 to 313.15 K have been measured. Partial molar volumes at infinite dilution (V 02 ) of sucrose determined from apparent molar volume (φ v ) have been utilized to estimate partial molar volumes of transfer (V 02,tr ) for sucrose from water to alkali metal halide solutions. The viscosity data of alkali metal halides in purely aqueous solutions and in the presence of sucrose at different temperatures (293.15, 303.15 and 313.5 K) have been analysed by the Jones-Dole equation. The nature and magnitude of solute-solvent and solute-solute interactions have been discussed in terms of the values of limiting apparent molar volume (φ 0 v ), slope (S v ) and coefficients of the Jones-Dole equation. The structure-making and structure-breaking capacities of alkali metal halides in pure aqueous solutions and in the presence of sucrose have been ascertained from temperature dependence ofφ 0 v .

Bending, Twisting, and Breaking CuCN Chains to Produce Framework Materials: The Reactions of CuCN with Alkali-Metal Halides

The reactions of the low-temperature polymorph of copper(I) cyanide (LT-CuCN) with concentrated aqueous alkali-metal halide solutions have been investigated. At room temperature, KX (X = Br and I) and CsX (X = Cl, Br, and I) produce the addition products K[Cu(2)(CN)(2)Br].H(2)O (I), K(3)[Cu(6)(CN)(6)I(3)].2H(2)O (II), Cs[Cu(3)(CN)(3)Cl] (III), Cs[Cu(3)(CN)(3)Br] (IV), and Cs(2)[Cu(4)(CN)(4)I(2)].H(2)O (V), with 3-D frameworks in which the -(CuCN)- chains present in CuCN persist. No reaction occurs, however, with NaX (X = Cl, Br, I) or KCl. The addition compounds, I-V, reconvert to CuCN when washed. Both low- and high-temperature polymorphs of CuCN (LT- and HT-CuCN) are produced, except in the case of Cs[Cu(3)(CN)(3)Cl] (III), which converts only to LT-CuCN. Heating similar AX-CuCN reaction mixtures under hydrothermal conditions at 453 K for 1 day produces single crystals of I-V suitable for structure determination. Under these more forcing conditions, reactions also occur with NaX (X = Cl, Br, I) and KCl. NaBr and KCl cause some conversion of LT-CuCN into HT-CuCN, while NaCl and NaI, respectively, react to form the mixed-valence Cu(I)/Cu(II) compounds [Cu(II)(OH(2))(4)][Cu(I)(4)(CN)(6)], a known phase, and [Cu(II)(OH(2))(4)][Cu(I)(4)(CN)(4)I(2)] (VI), a 3-D framework, which contains infinite -(CuCN)- chains. After 3 days of heating under hydrothermal conditions, the reaction between KI and CuCN produces [Cu(II)(OH(2))(4)][Cu(I)(2)(CN)I(2)](2) (VII), in which the CuCN chains are broken into single Cu-CN-Cu units, which in turn are linked into chains via iodine atoms and then into layers via long Cu-C and Cu-Cu interactions.

Photoemission from Aqueous Alkali-Metal−Iodide Salt Solutions Using EUV Synchrotron Radiation

The valence band photoemission of aqueous alkali-metal halide solutions is studied for photon energies from 90 to 110 eV. A 6 μm diameter liquid microjet provides a free vacuum surface, allowing water molecules to evaporate without collisions, and hence enables the direct detection of photoelectrons originating from the liquid. The experiments were performed at the MBI undulator beamline of the synchrotron radiation facility BESSY. Here, we focus on the determination of electron binding energies of solvated anions and cations. The effect of different countercations (Li+, Na+, K+, and Cs+), and salt concentrations is systematically investigated. Electron binding energies of the solvated ions are found to differ considerably from those in the gas phase; contrary to intuition, the energies do not depend on the salt concentration. Measured binding energies can be surprisingly well explained within a simple dielectric cavity model. For a NaI aqueous solution, negative surface excess is inferred from the evolut...

Alkali metal halide solutions in 1,4-dioxane–water mixtures. A Monte Carlo simulation study

Alkali metal halide solutions in 1,4-dioxane–water mixtures are investigated in the framework of Monte Carlo simulations on the molecular Born–Oppenheimer level with classical interaction site models (ISM). The SPC/E model is used for water, and we propose an ISM for 1,4-dioxane. Ion interaction parameters are taken from literature. The structure of the solvent mixture as well as solvation and association of ions are studied in detail. Preferential and selective solvation is shown in the solvation shell of sodium and chloride ions.

Alkali metal halide solutions in 1,4-dioxane–water mixtures. A Monte Carlo simulation study

Alkali metal halide solutions in 1,4-dioxane–water mixtures are investigated in the framework of Monte Carlo simulations on the molecular Born–Oppenheimer level with classical interaction site models (ISM). The SPC/E model is used for water, and we propose an ISM for 1,4-dioxane. Ion interaction parameters are taken from literature. The structure of the solvent mixture as well as solvation and association of ions are studied in detail. Preferential and selective solvation is shown in the solvation shell of sodium and chloride ions.

Conductance of Solutions of Alkali-Metal Halides in Glycerol

The electrical conductivities of solutions of salts (KCl, NaCl, KBr, NaBr, NaI, KI, and LiBr) in glycerol have been measured at three concentrations (approximately 0.01, 0.1, and 0.3 M) at 25 °C and at other temperatures from (3.37 to 42.24) °C in the case of KCl and NaCl. Values of the molar conductivity at infinite dilution were obtained by extrapolation using the conductance equation of Onsager. Using previously measured transference numbers for KCl and NaCl in glycerol, values of limiting Walden products for the individual alkali-metal and halide ions in glycerol have been derived and compared with those in aqueous and other alcohol solutions. The values for glycerol were the largest so far measured. The limiting ion conductivities, λ∞, obtained from experimental data were compared with those calculated applying the Boyd−Zwanzig theory. A modified Walden rule, Λ∞ηp = constant, is suggested as applicable in glycerol, the exponent p being less than unity and having a value down to 0.9. Finally, the temp...

Deswelling Kinetics of Macroporous Poly(N-isopropylacrylamide) Gel in Salt Solution

Abstract The deswelling kinetics of a macroporous poly(N-isopropylacrylamide) gel in a NaCl solution was investigated. NaCl was used as the probe in order to trace out any hydration from the hydrated polymer chains. In the case of macroporous gel immersed in a NaCl solution, the minimum of the initial deswelling rate (v = 0.06 s−1) appeared at around 0.2—0.3 M (1 M = 1 mol dm−3) when the equilibrated gels (at 22 °C) were heated to 40 °C. The maxima of the apparent activation energy (Ea = 110 kJ mol−1) and the change in the activation entropy (ΔS313 = 80 J K−1 mol−1) were at 0.2—0.3 M NaCl. These results indicate that deswelling of the gel in a NaCl solution advanced on the condition of the following two factors. One is an electrostatic repulsion between Cl− ions below 0.2—0.3 M. Another is a salting-out effect due to NaCl above 0.2—0.3 M. The deswelling kinetics and the lower critical solution temperatures of the gels in other alkalimetal halide solutions were also measured in order to clarify the effect of the species of the cations and the anions on the interaction between the water and polymer chains.

Salt effects on reactivities of low-spin iron(II) complexes of diazabutadiene and Schiff base ligands

Salt effects on reactivity are reported for base hydrolysis of tris-ligand-iron(II) complexes of several diazabutadiene and Schiff base ligands in aqueous solutions of alkali metal halides and of tetraalkylammonium bromides. The observed patterns vary markedly with ligand nature, the trend paralleling ligand hydrophilicity. These patterns of salt effects on reactivity are compared with those for a variety of other inorganic substitution reactions.

Stabilization and EPR characterization of Ru(bpy)33+ formed by radiolysis in concentrated alkali-metal halide solutions

The stabilization of Ru(bpy) 3 3+ from Ru(bpy) 3 2+ at room temperature by radiolysis of acidic concentrated alkali-metal halide aqueous solutions has been achieved. Stabilization at room temperature is of particular interest for potential light-energy storage systems. The yield of Ru(bpy) 3 3+ , as well as its half-life, depend strongly on the alkali-metal halide and acid concentrations. The Ru(bpy) 3 3+ yield increases with increasing LiCl concentration and attains a maximum value around 5–10 mM H + ; the yield decreases at both higher and lower pH. The stabilization of Ru(bpy) 3 3+ is optimal at [LiCl] 4 M and 5 mM H + . The half-lives of Ru(bpy) 3 3+ are 20 h and 7 days at [LiCl] = 4 and 8 M, respectively, which are ca. 10 to 100 times longer than in a solution without LiCl. The stability of Ru(bpy) 3 3+ also depends on the alkali-metal cation. The half-lives of Ru(bpy) 3 3+ vary from 7 to 20 h in the order K, Na and Li at 5 mM H + and 4 M alkali-metal halide solution. This cation effect on the stabilization of Ru(bpy) 3 3+ is interpreted in terms of the free water concentration and dynamic hydration properties in alkali-metal halide solutions.

Multiple Ion Association in Supercritical Aqueous Solutions of Single Electrolytes

Solute speciation in supercritical aqueous alkali metal halide solutions plays an important role in various industrial and natural processes, for example, corrosion of metals, solvent extraction, crystal growth, metamorphism, and the formation of hydrothermal ore deposits. To better characterize such speciation, degrees of formation of polyatomic clusters of sodium and chlorine ions have been computed with the aid of dissociation constants generated from Monte Carlo calculations which are consistent with both supercritical conductance measurements and electrostatic theory. The calculations indicate that the solute in alkali-halide solutions is successively dominated by increasingly complex polyatomic clusters as the solute molality increases at pressures and temperatures where the dielectric constant of water is 15.

A simplified thermodynamic model for protein uptake by reverse micelles: theoretical and experimental results

A simplified thermodynamic model for the uptake of proteins from a water phase into a supernatant oil phase containing reverse micelles is presented. The free energy change accompanying the protein uptake is expressed as a sum of electrostatic and ideal solution terms, and then it is minimized with respect to all the pertinent independent variables. Examples of calculations are given for a selected choice of the values of the physical parameters. Comparison with previous models is presented. As a test for the model, the uptake of cytochrome c from some alkali-metal halide solutions has been chosen. The comparison between the calculated and the experimental data is satisfactory for the dependence of the protein-transfer coefficient both from the salt concentration and from pH

Triple-ion anions and polynuclear complexing in supercritical electrolyte solutions

Calculation of accurate mineral solubilities in hydrothermal solutions requires dissociation constants for the predominant aqueous complexes in solution, many of which may be present in appreciable concentrations only at high temperatures. Consideration of dissociation constants representing the standard molal Gibbs free energy changes resulting from the electrostatic interaction of aqueous species indicates that triple ions such as NaCl 2 − and Na 2Cl + may be major species in alkali metal halide solutions at high temperatures and low pressures where the dielectric constant of H 2O is ≲ 15. Molal triple ion dissociation constants were computed for temperatures from 400° to 800°C at pressures from 500 to 4000 bars using equations given by Fuoss and Kraus (1933b), together with values of the effective electrostatic radii of aqueous ions generated from algorithms developed by Tanger and Helgeson (1988) and Shock et al. (1990). The logarithms of the calculated second stepwise dissociation constants (log K 2) for 16 alkali metal and hydrogen halides typically decrease at 500 bars from ∼0 at 400° to ∼ −3 at 700°C, but they increase with increasing pressure from ∼ −3 at 500 bars to ∼0 at 3 kb and 700°C. Distribution of species calculations using these log K 2 values and dissociation constants for 1:1 ion pairs ( Oelkers and Helgeson, 1988), together with activity coefficients generated by adopting the revised HKF ( Helgeson, Kirkham, and Flowers, 1981) equation of state ( Tanger and Helgeson, 1988) to calculate extended term parameters in the Hückel equation ( helgeson et al., 1981) indicate that triple ions are the predominant species in low-pressure supercritical aqueous solutions at concentrations ≈ 0.8 m. Under these circumstances, polynuclear and mixed ligand complexes in natural electrolyte solutions such as KNaCl +, MgKCl 2 +, ZnNaCl 2 +, FeKCl 2 +, Na 2ClSO 4 −, etc. may have a substantial effect on the hydrothermal solubilities of minerals at high temperatures and low pressures where many geochemical processes occur.

Transference Numbers and Activity Coefficients of Some Alkali Metal Halide Solutions in Ethylene Glycol, Using Concentration Cells

Abstract The reliability of the concentration cell method for determining cation transference numbers has been tested using solutions of LiCl, NaCl, KCl, NaBr and LiBr in ethylene glycol at 25°C. Concentrations in the range 0.0005 to 0.5 mol dm−3 were used. Our transference numbers have been compared with those deduced from previous data on moving boundary and conductivity experiments. Good agreement between both sets of values has been found in most of the solutions, but significant discrepancies appear in the cases of NaBr and LiCl. The mean activity coefficients have been calculated from the EMF data and the transference numbers.