Molality Scale Research Articles

Activity coefficients of NaF in aqueous mixtures with ε-increasing co-solvent: N-methylformamide-water mixtures at 298.15 K

The potential of the cell Na-ISE | NaF (m), N-methylformamide (Y), H2O (100-Y) | F-ISE, which contains two selective electrodes (bi-ISE cell), has been measured at 298.15 K as a function of the weight percentage, Y, of N-methylformamide in a mixed solvent and the molality of NaF. Y was varied between 0 and 80% in ten-unit steps, and the molality of the electrolyte (m) was between approximately 10−4 mol kg−1 and the saturation point. The values of the average apparent standard potential, E0∗ (molal scale), were determined using habitual methods of extrapolation together with the extended Debye-Hückel (DH), Scatchard (S), and Pitzer (P) equations. The obtained results provided good internal consistency within the normal limits of experimental error encountered in these types of measurements. Once E0∗ was determined, the mean ionic activity coefficients for NaF were calculated and subsequently modeled according to the TCPC (modified three-characteristic-parameter-correlation) method. Additionally, the values of the total standard Gibbs energy of transfer from the water to the N-methylformamide (NMF) – water mixture, their ionic contributions, the standard solubility product, and the NaF primary hydration number were also determined. The variations of these magnitudes with the composition of the aqueous mixture are discussed in terms of ion-solvent and ion-ion interactions as a function of the properties of the medium.

Solubility of CO2 and H2S in the ionic liquid 1-ethyl-3-methylimidazolium trifluoromethanesulfonate

The solubility of carbon dioxide and hydrogen sulfide gases in the ionic liquid 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([C2mim][OTf]) was measured at temperatures from (303.15–353.15) K and pressures up to about 3.0 MPa. The Henry's law constants were determined from the new experimental data, which in turn were used to derive the change of some thermodynamic functions of dissolution of the gases in that particular ionic liquid. The new experimental data were correlated by a combination of the extended Henry's law and Pitzer's model for the excess Gibbs energy. The average relative percent deviation (ARD%) of correlated molality values from experimental data are within experimental uncertainties, which indicate quite good correlative accuracy of the Pitzer's model for the systems under investigation. Results show that at the same temperature and pressure, the solubility of H2S in [C2mim][OTf], expressed on the molality scale, is more than four times that of CO2. Comparison of the obtained experimental data indicates that the solubility of H2S, expressed on the molality scale, in [C2mim][OTf] is much more than its magnitude in the high-capacity ionic liquids 1-ethyl-3-methylimidazolium tris(pentafluoroethyl) trifluorophosphate ([C2mim][eFAP]) and 1-ethyl-3-methylimidazolium bis(trifluoromethyl) sulfonylimide ([C2mim][Tf2N]). For example the molality of H2S at 303.15 K and 2.0 MPa is 2.5 times and 1.3 times that of [C2mim][eFAP] and [C2mim][Tf2N], respectively. Solubility of CO2 in the ionic liquids follows the order [C2mim][OTf] < [C2mim][Tf2N] < [C2mim][eFAP]. Compared with other ionic liquids, [C2mim][OTf] could potentially be used for separation of CO2 and H2S gases from each other.

High pressure CO2 solubility and physical properties of tetrabutylphosphonium l-prolinate

This paper reports the CO2 solubility, density, viscosity, and electrical conductivity for a kind of amino acid ionic liquid (AAIL), tetrabutylphosphonium l-prolinate ([P4444][Pro]). The physical properties of [P4444][Pro] showed the ordinary temperature dependency, i.e. the density and viscosity decreased and the electrical conductivity increased with a temperature rising. One mole of [P4444][Pro] absorbed a 0.970 mol of CO2 at atmospheric pressure of CO2 and 333.2 K, and desorbed only ∼17% of the absorbed CO2 at 393.2 K. NMR spectra revealed that a CO2 molecule formed a complex with [Pro]−, and [P4444]+ had a little effect on the CO2 absorption. The CO2 solubility increased steeply at lower pressures of CO2 < 0.1 MPa and very gradually in the higher pressure range from 0.1 to 6 MPa at 333.15 K. Other tetrabutylphosphonium AAILs with (S)-2-methylprolinate ([P4444][MePro]) and glycinate ([P4444][Gly]) showed the similar pressure dependencies. The contributions of physical and chemical absorptions to the total CO2 solubility were analyzed to discuss the effect of anion on the high-pressure CO2 solubility. [P4444][Pro] and [P4444][Gly] showed the higher physical and chemical CO2 absorptions (in molarity scale) in the present AAILs, respectively.

Density and activity of pertechnetic acid aqueous solutions at T = 298.15 K

The previous isopiestic investigations of HTcO4 aqueous solutions at T=298.15K are believed to be unreliable, because of the formation of a ternary mixture at high molality. Consequently, published isopiestic molalities for aqueous HTcO4 solutions at T=298.15K were completed and corrected. Binary data (variation of the osmotic coefficient and activity coefficient of the electrolyte in solution in the water) at T=298.15K for pertechnetic acid HTcO4 were determined by direct water activity measurements. These measurements extend from molality m=1.4mol·kg−1 to m=8.32mol·kg−1. The variation of the osmotic coefficient of this acid in water is represented mathematically. Density variations at T=298.15K are also established and used to express the activity coefficient values on both the molar and molal concentration scale. The density law leads to the partial molar volume variations for aqueous HTcO4 solutions at T=298.15K, which are compared with published data.

Oxoacidity scale of molten ionic chlorides and bromide

Determination of NiO and PbO solubilities in molten BaBr2–KBr (0.505:0.495) eutectic at 973K (of pKs,NiO=8.06±0.2 and pKs,PbO=4.04±0.2, molality scale) allowed completing systematic oxide solubility studies in molten ionic bromides. On the basis of the obtained and literature data the acidity scale for chloride and bromide melts (KX–NaX→BaX2–KX→KX–LiX sequences, X=Cl, Br) at 973K was built on the basis of primary medium effects (estimated as oxobasicity indices). The oxoacidic properties of chloride and bromide melts with similar cation composition are close, although the acidity of bromide analogs is always somewhat weaker. The obtained information permits to predict e.g., limits of halide melt purification by precipitating deoxidization or carbohalogenation methods.

Temperature and Pressure Dependence of the Electrical Conductivity of 1-Butyl-3-methylimidazolium Bis(trifluoromethanesulfonyl)amide

The electrical conductivities of the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ([BMIM][Tf2N]) have been determined between (273 and 353) K over an extended pressure range up to 250 MPa by both electrochemical impedance spectroscopy and conductance bridge techniques. The results obtained by the two techniques are generally in good agreement, within 3%, though the conductance bridge results yield lower values outside the experimental uncertainties at higher conductivities, that is, at higher temperature and lower pressures where the maximum deviation is −7%. The temperature and pressure dependence of both the conductivity and molar conductivity have been represented by modified Vogel–Fulcher–Tammann equations. The molar conductivity scales with the viscosity, with overlapping isobars and isotherms, so that a Walden plot, the logarithmic projection of molar conductivity versus fluidity (reciprocal viscosity), is a straight line with a similar slope (0.924) to those obtained ...

Solubility and Saturation Apparent Volume of Propranolol Hydrochloride in Some Binary Aqueous Cosolvent Mixtures at 298.15 K

The equilibrium solubility of propranolol hydrochloride in aqueous binary mixtures of 1,4-dioxane (D), acetonitrile (ACN), polyethylene glycol 400 (PEG), propylene glycol (PG), or methanol (MeOH), at T = 298.15 K was determined. In all cases the maximum solubility values expressed in molarity (mol·dm–3) in a mixture instead of neat water were obtained, while the lowest drug solubility values in the neat cosolvents were obtained. Otherwise, if the maximum mole fraction solubility obtained in every cosolvent system is considered, the following order is obtained: ACN + W > D + W > MeOH + W > PEG + W > PG + W; whereas, if the molarity scale is considered the maximum solubility decreases in the order: ACN + W > MeOH + W > D + W > PG +W > PEG + W. In a quantitative way the drug solubility expressed in mole fraction varies from 1.77 × 10–4 in neat 1,4-dioxane to 2.95 × 10–2 in the mixture with 0.50 in mass fraction of acetonitrile. A correlation of the solubility data obtained was made by means of the modified N...

Density and activity of perrhenic acid aqueous solutions at T = 298.15 K

Published isopiestic molalities for aqueous HReO4 solutions at T=298.15K are completed. Binary data (variation of the osmotic coefficient and activity coefficient of the electrolyte in solution in the water) at T=298.15K for perrhenic acid HReO4 are determined by direct water activity and osmolality measurements. The variation of the osmotic coefficient of this acid in water is represented mathematically according to a model recommended by the National Institute of Standards and Technology and according to the specific interaction theory. The data are also used to evaluate the parameters of the standard three-parameters of Pitzer’s ion-interaction model, along with the parameters of Archer’s four-parameter extended ion-interaction model, to higher molalities than previously advised. Experimental thermodynamic data are well represented by these models. Density variations at T=298.15K are also established and used to express the activity coefficient values on both the molar and molal concentration scales.

An experimental investigation on the solubility of CO2 in aqueous solutions of phenol

New experimental results are reported for the solubility of carbon dioxide in aqueous solutions of phenol and for the density of the corresponding liquid solvent mixtures at about (314, 354, and 395)K at pressures between about 0.2MPa and 9.7MPa. The experimental results are evaluated to determine Henry's constants for carbon dioxide (on the molality scale) and the partial molar volume of carbon dioxide at infinite dilution in such solutions at the same temperatures. Furthermore, correlations are presented that describe the new gas solubility data almost within experimental uncertainty.

A Pitzer model for the Na–Al(OH)4–Cl–OH system and solubility of boehmite (AlOOH) to high ionic strength and to 250 °C

In this study, a Pitzer model for the Na–Cl–OH–Al(OH)4 system, and solubility of boehmite (AlOOH) to high ionic strengths, and to high temperatures up to 250°C, has been developed by evaluating equilibrium quotients concerning boehmite in NaCl solutions to 5.0mol·kg−1, and boehmite solubility data in NaOH solutions to ~13mol·kg−1. This model is validated by comparing model-predicted solubilities with solubility data of boehmite in NaOH solutions that are independent from the model development. This model is of value to many fields, including accurate modeling geochemical behavior of aluminum in hydrothermal solutions with high ionic strengths at high temperatures up to 250°C, extraction of aluminum via the Bayer process from various ores, stability of borosilicate glass, aluminum silicate materials as waste forms for long-lived radio nuclides, and bentonite as engineered barrier, in geological repositories.Based on the model developed in this work, solubility of boehmite can be potentially used as a pHm (hydrogen ion concentration on molal scale) sensor/buffer in hydrothermal experiments under neutral to alkaline conditions in NaCl solutions in the absence of silica. This pHm sensor/buffer would enable experimentalists to conduct hydrothermal experiments in a wide range ionic strength under well-controlled pHm conditions.

Solubility of Ammonia in Ethylene Glycol Between 303 K and 323 K under Low Pressure from 0.030 to 0.101 MPa

The solubility of ammonia in ethylene glycol is measured by an isothermal solubility equilibrium method at temperatures of (303.2, 308.2, 313.2, 318.2 and 323.2) K and total pressures of (0.030, 0.040, 0.050, 0.060, 0.070, 0.080, 0.090 and 0.101) MPa. The molality of ammonia in ethylene glycol ranges from 1.925 mol·kg−1 to 8.265 mol·kg−1. The experimental results are used to determine Henry's law constant of ammonia in ethylene glycol. Furthermore, experimental data are correlated by applying the thermodynamic model on the basis of extended Raoult's law, extended Henry's law, corresponding-states correlations and Pitzer's molality scale based equation. The overall average relative deviation between the calculated data and the experimental data of Henry's law constant and ammonia solubility are 2.029% and 2.164% respectively.

Expressions for the Activity Coefficients and Osmotic Coefficients of Solutions of Electrolytes and Nonelectrolytes Based on the Hydration Model of Zavitsas

In two papers Zavitsas described a model for the thermodynamic properties of aqueous solutions of a single electrolyte or nonelectrolyte (Zavitsas, J Phys Chem B 105:7805–7817, 2001; J Solution Chem 39:301–317, 2010) in which he assumed that part of the water is so strongly bound to the solute that it can be considered as part of it, and thus only the remaining unbound water is considered to be the solvent. He showed that when the usual water mole fraction was replaced by the resulting mole fraction of unbound water, obtained by optimizing an effective hydration number, basically linear relations were obtained to fairly high molalities for the freezing temperature lowering, boiling temperature elevation, and the water activity/vapor pressure of water. However, Zavitsas only considered the properties of the solvent, not the solute. In this paper we derive the corresponding expressions for the activity coefficient of the solute for the usual molality scale based on 1 kg of water, for the modified molality scale based on 1 kg of unbound water, for the mole fraction scale based on the total number of moles of water, and for the modified mole fraction scale based on the number of moles of unbound water. These equations show that if the hydration number is larger than the stoichiometric ionization number of the electrolyte, then all four types of mean activity coefficients are predicted to always be >1 (nearly all hydration numbers reported by Zavitsas for electrolyte solutions are greater than the corresponding ionization numbers), which directly conflicts with extensive experimental and theoretical evidence that the mean activity coefficients of electrolytes in aqueous solutions always initially decrease below unity. In contrast, for nonelectrolyte solutions, the hydration model of Zavitsas gives more realistic values of the activity coefficients.

Buffer Standards for the Physiological pH of N-(2-Hydroxyethyl) piperazine-N'-4-butanesulfonic Acid (HEPBS) from 5 to 55 °C

The pH values of six buffer solutions of equal compositions on the molal scale and eight buffer solutions hav- ing ionic strengths (I = 0.16 mol·kg -1 ) similar to the concentration of blood plasma have been evaluated at 12 temperatures from 5 to 55 °C using the Bates-Guggenheim convention and extended Debye-Huckel equation. The values of Ej for the buffer solution of HEPBS have been obtained from the flowing junction cell measurement. These values of Ej have been used to ascertain the operational pH values at 25 and 37 °C for HEPBS buffer solution. The pH values at 25 and 37 °C are 7.415 and 7.395, respectively, for physiological phosphate buffer solutions. The zwitterionic buffer HEPBS was shown to be useful as a secondary pH standard in the region close to that of blood serum.

Equilibrium cuprous concentrations in copper sulfate–sulfuric acid solutions containing 50–110 g/L Cu+ 2 and 10–200 g/L H2SO4 at 50–95 °C

Copper sulfate (66–323g/kg H2O; ~25–110g/L Cu+2) and sulfuric acid (10–233g/kg H2O, ~10–200g/L) solutions were reacted with copper metal at temperatures between 50 and 95°C to form Cu+ until equilibrium was attained. Samples were collected into an NH4Fe(SO4)2·12H2O solution to convert cuprous to ferrous, which were then titrated with standard Ce(IV) using very dilute ferroin as the indicator. In order to estimate solution compositions in volumetric units (e.g. g/L) the densities of the parent CuSO4–H2SO4 solutions at the reaction temperatures were used. Some additional density data, beyond that available in the literature was needed. Density as a function of temperature and masses of CuSO4 and H2SO4 per kg of water was fitted to an empirical equation. Density was also estimated based on known concentrations of Cu+2 and H2SO4 in g/L and temperature using an alternative correlation. Cuprous concentrations were determined as mol/kg of sample. Cuprous concentrations in g/L were fitted to an expression of the form:Cu+=Ve−W/TCu+2XYH2SO42+ZH2SO4+1where [Cu+], [Cu+2] and [H2SO4] are in g/L at specified temperature T (K) and V–Z are empirical constants. The empirical expression simulated the measured [Cu+] to within ±3.6%. The cuprous concentrations were also fitted to the same type of equation using concentrations on the molal scale. These matched the experimental values to within ±3.5%. Varying sulfuric acid concentrations were found to have only a modest influence on the equilibrium cuprous concentrations. With 10–200g/L H2SO4 and a given [Cu+2] the difference between the highest and lowest [Cu+] was 7% at most. At 95°C with a solution containing 107–109g/L Cu+2 and 10–200g/L H2SO4, the [Cu+] was 1.70–1.75g/L.

An Experimental Investigation of the Solubility of CO2 in (N,N-Dimethylmethanamide + Water)

New experimental results are presented for the solubility of carbon dioxide in pure liquid N,N-dimethylmethanamide {= N,N-dimethylformamide, (CH3)2NC(H)O, DMF} and in solvent mixtures of (water + DMF) at gas-free solvent mixture DMF mole fractions of about (0.05, 0.1, 0.25, 0.5, 0.75, and 0.9), temperatures of (314, 354, and 395) K, and total pressures up to about 10 MPa. Numerical values are reported for the (molality scale based) Henry's constant of CO2 in DMF and in (water + DMF) liquid mixtures resulting from the new experimental data by applying a common extrapolation procedure. The experimental work is to provide a database for developing and testing thermodynamic models to describe the gas solubility in salt-free and salt-containing mixed aqueous solvents, as well as to test screening methods based, for example, on molecular simulation.

Activity Coefficients of NaBr in Aqueous Mixtures with High Relative Permittivity Cosolvent: Formamide + Water at 298.15 K

The mean ionic activity coefficients of NaBr were experimentally determined in formamide + water mixtures at 298.15 K from potential difference measurements of the following electrochemical cell containing two ion selective electrodes (ISEs): Na-ISE|NaBr (m), formamide (w), H2O (1–w)|Br-ISE. The molality (m) varied between 0.02 mol·kg–1 and almost saturation, whereas the mass fraction of formamide in the mixture (w) was varied between 0 and 1 in 0.1-unit steps. The determination of E0* (molal scale) was carried out following a method similar to that proposed by Hitchcock and using the classical extended Debye–Hückel and Scatchard equations. We also use for this purpose a modification of the Pitzer equation proposed by Rard and Archer and the most recent modified three-characteristic-parameter-correlation model. The results obtained produced good internal consistency, within the normal limits of experimental error in these types of measurement. Once E0* was determined, the mean ionic activity coefficients of NaBr (γ), the Gibbs energy of transfer of the NaBr from the water to the formamide + water mixture (ΔGt0), standard solubility product of NaBr in formamide + water (Ksp0), and NaBr primary hydration number (nhyd) were estimated. The results were comparatively analyzed with those of NaF and NaCl previously obtained in similar mixtures.

Activity coefficients of NaCl in aqueous mixtures with ɛ-increasing co-solvent: N-methylformamide–water mixtures at 298.15 K

The electromotive force of the cell containing two ion-selective electrodes (ISE), Na–ISE|NaCl( m), N-methylformamide ( Y), H 2O(100- Y) Cl–ISE has been measured at 298.15 K as a function of the weight percentage Y of N-methylformamide in the mixed solvent. Y was varied between 0 and 100% in ten-unit steps and the molality of the electrolyte ( m) was between ca. 0.04 and saturation. The values of the apparent standard electromotive force, E 0* (molal scale), were determined using routine methods of extrapolation together with extended Debye–Hückel (DH), Scatchard (S), Pitzer (P), and modified three-characteristic-parameter-correlation (TCPC) models. The results obtained produced good internal consistency, within the normal limits of experimental error encountered in these types of measurement. Once E 0* was determined, the mean ionic activity coefficients for NaCl, the standard Gibbs energy of transfer from the water to the N-methylformamide–water mixture, the standard solubility product and the primary NaCl hydration number were calculated. The variation of these magnitudes with the composition of this aqueous mixture with ɛ-increasing co-solvent is discussed in comparison with those containing formamide ( ɛ-increasing co-solvent) and N,N-dimethylformamide ( ɛ-decreasing co-solvent) in terms of the ion-solvent and ion-ion interactions and their changes with the properties of the medium.

Potentiometric Titration Study of the Temperature and Ionic Strength Dependence of the Acidity Constants of Nicotinic Acid (Niacin)

The influence of temperature (T) and ionic strength (Im) on the stoichiometric (molality scale) acidity constants of nicotinic acid in aqueous solution was investigated by potentiometry (H+-glass electrode). The background salt used was potassium chloride, and the temperature and ionic strength ranges covered were 283.15 K < T < 318.15 K and 0.05 mol·kg–1 < Im < 0.52 mol·kg–1, respectively. Acidity constants at zero ionic strength were derived by means of a Debye–Hückel type formalism, and their temperature dependence was obtained through a van't Hoff analysis. This led to pKa1 = 2.19 ± 0.06 and pKa2 = 4.86 ± 0.03 at 298.15 K and to the corresponding standard molar enthalpies and entropies of proton dissociation in the temperature range of the experiments, ΔrHm,l° = (4.5 ± 3.5) kJ·mol–1, ΔrSm,l° = −(26.8 ± 11.8) J·K–1·mol–1, ΔrHm,2° = (12.5 ± 2.1) kJ·mol–1, and ΔrSm,2° = −(51.2 ± 7.0) J·K–1·mol–1. These values were compared with previously reported data.

Allowance for thermodynamic nonideality in the characterization of protein interactions by spectral techniques

Theory is developed for the characterization of protein interactions by spectral techniques, where the constraints of constant temperature and pressure demand that thermodynamic activity be defined on the molal concentration scale. The customary practice of defining the equilibrium constant ( K) on a molar basis is accommodated by developing expressions to convert those experimental values ( K molar ) to their thermodynamically more rigorous counterparts ( K molal ). Such procedures are illustrated by reanalysis of published results for the effects of molecular crowding agents on the isomerisation of α-chymotrypsin and reversible complex formation between catalase and superoxide dismutase. Although those reanalyses have led to only minor refinements of the quantitative interpretation, it is clearly preferable to adopt thermodynamic rigor throughout future spectral studies by employing the molal concentration scale from the outset.

Total and Specific Solubility and Activity Coefficients of Neutral Species of (CH2)2i−2Ni(CH2COOH)i+2Complexons in Aqueous NaCl Solutions at Different Ionic Strengths, (0 ≤I≤ 5) mol·L−1, and 298.15 K

The total solubility ST of (CH2)2i−2Ni(CH2COOH)i+2 complexons (i = 1, nitrilotriacetic acid (NTA); i = 3, diethylenetriaminepentaacetic acid (DTPA); i = 4, triethylene tetraaminehexaacetic acid (TTHA)) in aqueous NaCl solutions at different ionic strengths, (0 ≤ I ≤ 5) mol·L−1, and at 298.15 K are determined and are reported in both molar (mol·L−1) and molal (mol·kg−1) concentration scales, together with the protonation constants. The total solubility in pure water S0T is (8.1, 8.9, and 4.5) mmol·L−1 for NTA, DTPA, and TTHA, respectively. Increasing the ionic strength from (0.1 to 5) mol·L−1 (NaCl), the total solubility decreases for NTA, while the opposite trend is observed for DTPA and TTHA. From total solubility and protonation constant data, the solubility of the neutral species S0 and the solubility products KS0 are calculated. The dependence on ionic strength is analyzed, and the Setschenow (km) coefficients are obtained, together with the solubility of the neutral species in pure water S00 [S00 = (...