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.     

Determination of Hydrogen Single Ion Activity Coefficients in Aqueous HCl Solutions at 25°C

The single ion activity coefficients of hydrogen and chloride ions in aqueous HCl solutions have been estimated at 25°C at concentrations up to 1 mol-kg^–1, using potentiometric measurements with ion-selective electrodes and appropriate calibration procedures. Two methods are described for an internal calibration of the electrodes in the extended Debye–Hückel concentration range. The results are compared to the conventional pH calibration with external buffer solutions. Since the latter calibration method does not account for the liquid junction potential E _J which arises at the reference electrode, the resulting activity coefficients are quite different in HCl solutions of higher concentration. These differences between internal and external calibration decrease significantly, when a correction for E _J is introduced into the conventional pH calibration. Hence, in solutions of higher ionic strength the accuracy of the conventional pH electrode calibration using buffer solutions is very limited, when exact H⁺ activities are required. The consistency of the results indicates that the liquid junction potentials in the examined systems calculated by the Henderson/Bates approximation are of reasonable precision.     

Thermodynamics of sodium chloride solutions at high temperatures

Osmotic coefficients are reported from vapor-pressure-lowering measurements on sodium chloride solutions at concentrations from approximately 4m to saturation and at temperatures from 75° C to 300° C. In combination with previously reported measurements at lower concentrations, these results allow a correlation of free energies for the system NaCl–H₂O over a range of concentrations and temperatures that is unprecedented for any aqueous electrolyte. Activity coefficients and other thermodynamic quantities for both salt and water have been calculated for the complete range of concentrations and temperatures. Calculated heats of solution and standard partial molal entropies agree well with calorimetric determinations where comparison is possible. The excess partial molal entropy of the salt is informative concerning structural effects and their changes with temperature and concentration.Presented in part at the 160th National Meeting of the American Chemical Society, Chicago, Illinois, September 1970.     

Aqueous solutions of lithium hydroxide at various temperatures: Conductivity and activity coefficients

The conductivity of LiOH aqueous solutions has been determined at 15, 25, and 45°C. The data analysis showed that LiOH is a slightly associated electrolyte, its association increasing with temperature. The association constant and distance parameter obtained from the conductivity data were successfully employed to calculate the activity coefficients of the solutions. The same procedure applied to very precise conductivity data for NaOH aqueous solutions enabled us to assess the reliability of this method of calculation of activity coefficients up to 0.1m. The alkali metal hydroxides show a reverse trend in the way their properties change with cationic radius, as is the case for the fluorides with which they are compared.     

A new and reliable model for predicting methane viscosity at high pressures and high temperatures

In recent years, there has been an increase of interest in the flow of gases at relatively high pressures and high temperatures. Hydrodynamic calculation of the energy losses in the flow of gases in conduits, as well as through the porous media constituting natural petroleum reservoirs, requires knowledge of the viscosity of the fluid at the pressure and temperature involved. Although there are numerous publications concerning the viscosity of methane at atmospheric pressure, there appears to be little information available relating to the effect of pressure and temperature upon the viscosity. A survey of the literature reveals that the disagreements between published data on the viscosity of methane are common and that most investigations have been conducted over restricted temperature and pressure ranges. Experimental viscosity data for methane are presented for temperatures from 320 to 400 K and pressures from 3000 to 140000 kPa by using falling body viscometer. A summary is given to evaluate the available data for methane, and a comparison is presented for that data common to the experimental range reported in this paper. A new and reliable correlation for methane gas viscosity is presented. Predicted values are given for temperatures up to 400 K and pressures up to 140000 kPa with Average Absolute Percent Relative Error (EABS) of 0.794.     

Buffer Standards for the Physiological pH of the Zwitterionic Compound, TAPS, From 5 to 55 ∘C

The values of the second dissociation constant, pK ₂, and related thermodynamic quantities of N-[tris(hydroxymethyl)methyl-3-amino]propanesulfonic acid (TAPS) have already been reported at 12 temperatures over the temperature range 5–55 ^∘C, including 37 ^∘C. This paper reports the results for the pH of five equimolal buffer solutions with compositions: (a) TAPS (0.03 mol⋅kg⁻¹) + NaTAPS (0.03 mol⋅kg⁻¹); (b) TAPS (0.04 mol⋅ kg⁻¹) + NaTAPS (0.04 mol⋅kg⁻¹); (c) TAPS (0.05 mol⋅kg⁻¹) + NaTAPS (0.05 mol⋅kg⁻¹); (d) TAPS (0.06 mol⋅kg⁻¹) + NaTAPS (0.06 mol⋅kg⁻¹); and (d) TAPS (0.08 mol⋅kg⁻¹) + NaTAPS (0.08 mol⋅kg⁻¹). The remaining eight buffer solutions consist of saline media of the ionic strength I = 0.16 mol⋅kg⁻¹, matching closely to that of the physiological sample. The compositions are: (f) TAPS (0.04 mol-kg⁻¹) + NaTAPS (0.02 mol-kg⁻¹) + NaCl (0.14 mol⋅kg⁻¹); (g) TAPS (0.05 mol⋅kg⁻¹) + NaTAPS (0.04 mol⋅kg⁻¹) + NaCl (0.12 mol⋅kg⁻¹); (h) TAPS (0.6 mol⋅kg⁻¹) + NaTAPS (0.04 mol⋅kg⁻¹) + NaCl (0.12 mol⋅kg⁻¹); (i) TAPS (0.08 mol⋅kg⁻¹) + NaTAPS (0.06 mol⋅kg⁻¹) + NaCl (0.10 mol⋅kg⁻¹); (j) TAPS (0.04 mol⋅ kg⁻¹) + NaTAPS (0.04 mol⋅kg⁻¹) + NaCl (0.12 mol⋅kg⁻¹); (k) TAPS (0.05 mol⋅kg⁻¹) + NaTAPS (0.05 mol⋅kg⁻¹) + NaCl (0.11 mol⋅kg⁻¹); (l) TAPS (0.06 mol⋅kg⁻¹) + NaTAPS (0.06 mol⋅kg⁻¹) + NaCl (0.10 mol⋅kg⁻¹); and (m) TAPS (0.08 mol⋅kg⁻¹) + NaTAPS (0.08 mol⋅kg⁻¹) + NaCl (0.08 mol⋅kg⁻¹). These buffers are recommended as a pH standard for clinical measurements in the range of physiological application. Conventional pH values, designated as pH(s), for all 13 buffer solutions from 5 to 55 ^∘C have been calculated. The operational pH values with liquid junction corrections, at 25 and 37 ^∘C for buffer solutions, designated above as (b), (c), (d), (e), (j), (l), and (m); have been determined based on the difference in the values of the liquid junction potentials between the accepted phosphate standard and the buffer solutions under investigation.     

Evaluation of liquid junction potentials and determination of pH values of strong acids at moderate ionic strengths

A new experimental approach is proposed for the evaluation of liquid junction potentials and single ion activities. Neither of these quantities can be experimentally measured without assumption. Furthermore, they are concentration dependent but without clearly defined functional relationships. Thus, a given assumption may be satisfactory to obtain these quantities at a given concentration, but will fail at another concentration. It is the intent of this paper to establish a functional relationship between the ratio of activity coefficients and the ionic strength, through which the liquid junction potentials may be computed, as well as the pH values at moderate ionic strengths (<1.0 m). Experimental results are presented and uncertainties are discussed.     

Thermodynamics of very concentrated aqueous electrolytes: LiCl,ZnCl2, and ZnCl2-NaCl at 25°C

The effectiveness of extended ion-interaction equations in the treatment of activity and osmotic coefficients for very concentrated electrolytes is explored for the examples LiCl-H₂O, ZnCl₂-H₂O, and NaCl-ZnCl₂-H₂O. For the two pure electrolytes the results are very satisfactory. Although satisfactory agreement was also obtained for the solubility of NaCl in the ternary system, this is too limited a data base to justify general conclusions.     

A Determination of Standard Potentials and Related Primary pH Standards in the 50 Mass Percent (N-Methyl-2-Pyrrolidinone + Water) Mixture at Various Temperatures

Following the IUPAC-endorsed procedure, the primary pH standards offered by the equimolal phosphate buffer (Na₂HPO₄ (0.01 mol⋅kg⁻¹) + KH₂PO₄ (0.01 mol⋅kg⁻¹)) in the (N-methyl-2-pyrrolidinone + water) solvent mixture of 50 mass percent composition at various temperatures have been determined from potential difference measurements with the reversible Harned cell. Since the essential prerequisite of the above procedure is the knowledge of the (hitherto unknown) standard potential difference of Harned’s cell, a parallel supplementary series of potential difference measurements has been carried out with the reversible cell, Pt|H₂|HCl(m)|AgCl|Ag|Pt according to the classical thermodynamic procedure. The problem of comparability of the pH scale in the (N-methyl-2-pyrrolidinone + water) solvent with that in the pure water solvent is duly discussed in terms of primary medium effects.     

Buffer Standards for the Physiological pH of Zwitterionic Compounds,MOBS and TABS from 5 to 55°C

The values of the second dissociation constant, pK₂, and related thermodynamic quantities of 4-(N-morpholino)butanesulfonic acid (MOBS) and N-tris(hydroxymethyl)-4-aminobutanesulfonic acid (TABS) have already been reported over the temperature range 5–55°C including 37{°}C. This paper reports the pH values of twelve equimolal buffer solutions at designated pH (s) with the following compositions: (a) mixtures of MOBS (0.05 mol-kg^–1) + NaMOBS (0.05 mol-kg^–1); (b) MOBS (0.08 mol-kg^–1) + NaMOBS (0.08 mol-kg^–1); (c) MOBS (0.08 mol-kg^–1) + NaMOBS (0.08 mol-kg^–1) + NaCl (0.08 mol-kg^–1); (d) TABS (0.05 mol-kg^–1) + NaTABS (0.05 mol-kg^–1); and (e) TABS (0.08 mol-kg^–1) + NaTABS (0.08 mol-kg^–1); and (f) TABS (0.08 mol-kg^–1) + NaTABS (0.08 mol-kg^–1) + NaCl (0.08 mol-kg^–1). Two buffer solutions have ionic strengths I= 0.05 mol-kg^–1, another two have I=0.08 mol-kg^–1, and the remaining two buffer solutions have I= 0.16 mol-kg^–1, which is close to that of the clinical fluids (blood serum). These buffers have been recommended as a useful pH standard for the measurements of physiological solutions. Conventional pH values of all six buffer solutions from 5–55°C, as well as those obtained from the liquid junction potential correction at 25 and 37{°}C have been calculated. The flowing-junction calomel cell has been utilized to measure E_j, the liquid junction potential.     

Equations for calculation of the pH of buffer solutions containing sodium or potassium dihydrogen phosphate, sodium hydrogen phosphate, and sodium chloride at 25°C

Published thermodynamic data measured in aqueous mixtures of sodium or potassium dihydrogen phosphate with hydrogen phosphate and chloride at 25°C were used to test recently developed methods for calculation of the pH of phosphate buffer solutions. Equations for ionic activity coefficients are used in these methods. It is shown that all data used in the tests up to an ionic strength of about 0.5 mol-kg^-1 can be accurately predicted by the two methods recommended. In one of these methods, equations of the Hückel type are used for ionic activity coefficients and in the other equations of the Pitzer type. Several sets of phosphate buffer solutions are recommended,e.g., for calibrations of glass electrode cells. In the recommended sets, the pH of the buffer solutions can be calculated either by the Hückel or Pitzer method, and the pH predictions of these methods agree in most cases within 0.005 at least up to ionic strengths of about 0.2 mol-kg^-1. The pH values of the two primary pH standards endorsed by IUPAC based on aqueous mixtures of KH₂PO₄ and Na₂HPO₄,i.e., pH values of 6.865 and 7.413, can also be accurately predicted by the equations recommended in this study.     

Electrochemistry of solutions in liquid ammonia. Part VII. The use of glass electrodes for ammonium and sodium cations as ion-selective sensors at −40 °C

The behavior of Li/La glass electrodes as specific ion sensors for NH ₄ ⁺ and Na⁺ cations in liquid ammonia solutions at –40°C has been assessed using concentration cells with transference. The measurement of emf's of cells with very high resistances due to glass at –40°C has been overcome partly by the use of thinly blown Li/La glass and mainly through the design and use of a floating shield emf measuring system. For solutions of NH₄NO₃, NH₄I, NH₄BF₄, and NH₄Cl almost linear pNH₄ vs. emf responses were observed between pNH₄ 0 and 5; for NH₄NO₃ solutions the slope (40±1 mV/pNH₄) was invariant for substantial increases in Na⁺ concentrations. Solutions of NaNO₃, NaCN, NaClO₄, NaNCS, NaN₃, and NaNO₂ gave almost linear pNa vs. emf responses but the slopes were markedly dependent upon the NH ₄ ⁺ concentration. Estimates of the mean molal ion activity coefficients for nitrate solutions were obtained from earlier transference data: ±(NaNO₃)=0.14±0.02 and ±(NH₄NO₃)=0.30±0.03 at 10^– molal concentration in fair agreement with earlier data.     

Conductance of salts at moderate and high concentrations in propylene carbonate-dimethoxyethane mixtures at temperatures from −45°C to 25°C

The specific conductances of LiClO₄, KSCN, KPF₆, and Et₄NPF₆ in propylene carbonate-dimethoxyethane mixtures are reported for moderate to high concentrations at temperatures between –45°C to 25°C. The data analysis was established on the base of an empirical conductance equation permitting equally well adapted fits for all electrolyte solutions irrespective of temperature, electrolyte compound and solvent composition. The effects on the conductance resulting from ion-ion, ion-solvent interactions and solvent viscosity are rationalized in terms of the thermodynamic and hydrodynamic parameters characterizing the behaviour of electrolytes in dilute solutions. Some basic aspects are discussed for optimizing the conductance of battery electrolytes, especially those of high energy density batteries.     

Peculiar properties of sodium lodide in alcohols,acetone, and alcohol-water mixtures at lower temperatures

The enthalpies of solution of sodium iodide in methanol, ethanol and acetone and in mixtures of methanol and ethanol with water were measured over wide ranges of electrolyte concentration and temperature. Standard enthalpies of solution, transfer enthalpies of NaI from alcohols to alcohol-water mixtures, and temperature coefficients of enthalpies of solution have been calculated. Thermodyanmic characteristics of solution and solvation of the Na⁺ and I^– ions in acetone and ethanol were determined at 243–298 K. It is noted that at lower temperatures the disruption of solvent structure by ions is a local effect. The presence of negative solvation of the Na⁺ and I^– ions in alcohol-water mixtures at lower temperatures is demonstrated.     

Adsorption phenomena at high pressures and temperatures 5. Heats of excess and total adsorption of krypton on zeolite NaA

Thermodynamic principles for the calculation of differential heats of excess and absolute adsorption were considered. A set of isosteres of excess adsorption of krypton on zeolite NaA are presented, from which the coverage and temperature dependences of the heats of excess adsorption are calculated and analyzed. The reasons for infinitely high values of the excess heats at finite values of adsorption are discussed. The problems of recalculation of the excess adsorption to absolute adsorption are considered.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1946–1950, August, 1996.     

Isopiestic measurements at high temperatures: I. Aqueous solutions of LiCl,CsCl, and CaCl2 at 155°C

Isopiestic measurements have been made for LiCl (aq) and CsCl (aq) at a temperature of 155°C. Equilibrium molalities ranged up to 21 mol-kg^–1. MgCl₂(aq) was chosen as the reference electrolyte. The apparatus used for the isopiestic experiments is an enhanced version of that developed by Grjotheim and co-workers. To test its precision osmotic coefficients of CaCl₂ (aq) have also been determined and compared with previously reported vapor pressure measurements at high concentrations. The results show a very good coincidence. The data can be described by the ion interaction model of Pitzer. The resulting set of parameters allows a fit of the experimental osmotic coefficients with a standard error of 0.0078 and 0.0114 for LiCl(aq) and CsCl (aq), respectively. The osmotic coefficients of LiCl are consistent with data at lower molalities, but there are discrepancies for the CsCl solutions.     

Calculation of activities and solubilities of alkali metal perchlorates at high ionic strengths in multicomponent aqueous systems

The equations of Nývlt, of Bromley, and of Pitzer for the representation of activity coefficients of electrolytes in multicomponent ionic systems have been used to fit solubility data for some alkali metal perchlorates and ammonium perchlorate in mixture with other electrolytes at ionic strengths varying from 0.08 mol-kg^–1 to as high as 24 mol-kg^–1. Only the Pitzer equations can be used rellably to fit the solubility data over the whole range of ionic strengths encountered for ternary systems but there are certain limitations and certain assumptions which have to be made concerning the Pitzer ionic interaction parameters. A method is also proposed for the calculation of the Pitzer single electrolyte parameters, ⁰,¹ andC , for the less soluble perchlorates from fitting their solubility data over a wide range of high ionic strengths.     

Conductimetric determination of ion-association constants for calcium,cobalt, zinc,and cadmium sulfates in aqueous solutions at various temperatures between 0°C and 45°C

Thermodynamic ion-association constants for calcium, cobalt, zinc, and cadmium sulfates in aqueous solutions were determined by means of conductivity measurements at various temperatures between 0°C and 45°C. The standard Gibbs energy, enthalpy, and entropy for the reaction M ²⁺ +SO ₄ ^2– M ²⁺ ·SO ₄ ^2– (M=Ca, Co, Zn, and Cd) were calculated from the temperature dependence of the ion-association constants. The values obtained are as follows: G ₂₉₈ ^o =–12.42 kJ-mole ^–1 , H ^o =6.11 kJ-mole ^–1 , and S ₂₉₈ ^o =62.1 J- ^o K ^–1 -mole ^–1 for Ca ²⁺ ·SO ₄ ^2– ; G ₂₉₈ ^o =–12.84 kJ-mole ^–1 , H ^o =5.00 kJ-mole ^–1 , and S ₂₉₈ ^o =59.8 J- ^o K ^–1 -mole^–1 for Co ²⁺ ·SO ₄ ^2– ; G ₂₉₈ ^o =–12.65 kJ-mole ^–1 , H ^o =8.65 kJ-mole ^–1 , and S ₂₉₈ ^o =71.4 J- ^o K ^–1 -mole ^–1 for Zn ²⁺ ·SO ₄ ^2– ; G ₂₉₈ ^o =–13.28 kJ-mole ^–1 , H ^o =8.39 kJ-mole ^–1 , and S ₂₉₈ ^o =72.7 J- ^o K ^–1 -mole ^–1 for Cd ²⁺ ·SO ₄ ^2– .     

Activity coefficients of hexaamminecobalt(III) oxalate and hexacyanoferrate(III) in aqueous solutions of higher valent electrolytes at 25°C

The solubilities of hexaamminecobalt(III) oxalate and hexaamminecobalt(III) hexacyanoferrate(III) in aqueous solutions of different 1-2, 2-1 and 2-2 electrolytes were measured at 25°C. The results have been used to evaluate the relative activity coefficient of the saturating salts.