Activity and osmotic coefficient data

Critical evaluations of activity and osmotic coefficient data were undertaken early in the 1930-1940 period by Harned and Owen (1958) and by Robinson and Stokes, (1965). Wu and Hamer (1968) evaluated activity and osmotic coefficient data for a series of electrolytes but their work on polyvalent electrolytes was not completed. Their work on the 1 1 electrolytes was published in 1972. The evaluation of polyvalent electrolyte data has been continuing in the Electrolyte Data Center at the National Bureau of Standards, and this paper will summarize the methods used in evaluating data for over 100 aqueous polyvalent electrolytes. 

Activity and osmotic coefficient data derived from ten experimental methods have been critically evaluated and correlating equations have been formulated for more than 100 aqueous polyvalent electrolyte systems at 298 K. Evaluations for the major reference solutions KC1 and NaCl (Hamer and Wu, 1972), and CaCl (Staples and Nuttall, 1977) have been published that for (Staples,... 

Equations (2.59) and (2.61), depending on the ionic medium, describe reasonably well activity and osmotic coefficient data to moderate ionic strength. At high temperatures (typically above 100 °C), they only describe such data to relatively low ionic strength. Ciavatta (1980) demonstrated that an extension to the specific ion interaction theory could be used to describe data to much higher ionic strength. In this extension, the ion interaction parameter, is modified to the following form ... 

Determination of Ion Interaction Parameters from Activity and Osmotic Coefficient Data... 

It can be noted from Figures 2.1 and 2.2 that the values given above fit the activity coefficient data very well. However, for both sets of data, there is a significant underprediction of the osmotic coefficients. It is not clear why this is the case, but given the agreement between the interaction coefficients obtained from analysis of the protolysis of water data with those from the activity and osmotic coefficient data, the obtained ion interaction data for eifK" ", OH ) and 2(K , OH ) are retained. 

As with the data at 25 °C, ion interaction data e (K, OH ) were determined from activity and osmotic coefficient data provided in the literature. The ion interaction data determined were used to obtain the temperature-dependent parameters in a form similar to that of Eqs. (5.16) and (5.17). Subsequently, these data were used to determine the values of the individual ion interaction parameters for the interaction between H andCl, Na andOH and H andtriflate". These are the only data for which a substantial amount of high-temperature data are given in the literature. The individual ion interaction parameters have also been given in Table 5.6. 

In addition to the activity and osmotic coefficients at room temperature, the first temperature derivatives and the related enthalpy of dilution data were considered for over 100 electrolytes (26, 29). The data for electrolytes at higher temperatures become progressively more sparse. Quite a few solutes have been measured up to about 50°C (and down to 0°C). Also, over this range, the equations using just first temperature derivatives have some validity for rough estimates in other cases. But the effects of the second derivative (or the heat capacity) on activity coefficients at higher temperatures is very substantial. 

Goldberg, R. N. Nuttall, R. L. "Evaluated Activity and Osmotic Coefficients for Aqueous Solutions The Alkaline Earth Metal Halides" J. Phys. Chem. Ref. Data, 1978, 7,... 

Staples, B. R. "Activity and Osmotic Coefficients of Aqueous Sulfuric Acid" J. Phys. Chan. Ref. Data, in press. 

The techniques used in the critical evaluation and correlation of thermodynamic properties of aqueous polyvalent electrolytes are described. The Electrolyte Data Center is engaged in the correlation of activity and osmotic coefficients, enthalpies of dilution and solution, heat capacities, and ionic equilibrium constants for aqueous salt solutions. 

In this paper the authors propose to make a general derivation for the work function of a particle having the characteristics of an ion-dipole. Further, it is planned to apply this result to obtain equations for the activity coefficient and osmotic coefficient for an ion-dipole particle. The theory will be checked by applying it to published data on the activity and osmotic coefficients for ions, dipole, and ion-dipoles. 

Temperature Effects. The temperature range for which this model was assumed to be valid was 0°C through 40°C, which is a range covering most natural surface water systems (28). Equilibrium constants were adjusted for temperature effects using the Van t Hoff relation whenever appropriate enthalpy data was available (23, 24, 25). Activity and osmotic coefficients were temperature corrected by empirical equations describing the temperature dependence of the Debye-Huckel parameters of equations 20 and 21. These equations, obtained by curve-fitting published data (13), were... 

Goldberg. R. N. 1979. Evaluated activity and osmotic coefficients for aqueous solutions Bi-univalent compounds of lead, copper, manganese and uranium. J. Phys. Chem. Ref Data ft(4) i005-50. 

If data are lacking on the system of interest, it is often a fair approximation (especially at low and moderate concentrations) to use a model-substance approach. The behavior of an electrolyte is assumed to be similar to that of a known electrolyte of the same charge type. For example, NaCl is a model substance for 1 1 salts. This approach is particularly useful in estimating the temperature dependence of activity and osmotic coefficients when these coefficients are known only at 25°C, the model-substance approach may be used to estimate the effect of temperature. 

The properties selected for evaluation include most of the thermodynamic properties which we normally evaluate in the course of our work in the data centers. They include enthalpies of formation, solution, and dilution Gibbs energies of formation and solution entropies of formation and solution heat capacities and equilibrium constants (solubility, ionization, etc) as well as activity and osmotic coefficients, relative apparent molal enthalpies and apparent molal heat capacities. 

Staples, B. R. and R. L. Nuttall. 1977. Activity and osmotic coefficients of aqueous calcium-chloride at 298.15-K. Journal of Physical and Chemical Reference Data, 6, 385. 

This series of papers contains evaluations leading to recommended values of activity and osmotic coefficients and excess Gibbs energies of aqueous electrolyte solutions at 298.15 K. The data are presented both in tabular form as a function of molality and as coefficients of several correlating equations. The correlations are detailed and include a careful statistical analysis of the data and references to the source literature. The data cover the entire composition range for which data exist and Include most of the electrolytes of charge type 12 and 21 (also see items [48], [121], [124], and [128]). The papers in the series are ... 

This series of papers contains an extensive array of correlated data on aqueous electrolyte solutions, much of It having been calculated using the system of equations given In paper I In this series. The contents of these papers have been summarized by Pitzer In a chapter in the book edited by Pytkowicz (see Item [123]). The data Include activity and osmotic coefficients, relative apparent molar enthalpies and heat capacities, excess Gibbs energies, entropies, heat capacities, volumes, and some equilibrium constants and enthalpies. Systems of Interest Include both binary solutions and multi-component mixtures. While most of the data pertain to 25 °C, the papers on sodium chloride, calcium chloride, and sodium carbonate cover the data at the temperatures for which experiments have been performed. Also see Items [48], [104], and [124]. 

The tables in this chapter include Debye-HUckel parameters for the osmotic coefficient, enthalpy, and heat capacity as a function of temperature parameters for the activity and osmotic coefficients of approximately 270 aqueous strong electrolytes at 25 C parameters for the relative apparent molar and excess enthalpy of %90 strong electrolytes at 25 C a table of parameters for the activity and osmotic coefficients ofss75 binary mixtures with and without common ions and with up to three solutes present and parameters for the thermodynamic properties of aqueous NaCI and H2SO4 as a function of temperature. The author has included references to his earlier papers ivhich also contain valuable data on electrolyte solutions (also see item [121]). 

The Center for Energy Resources Engineering (CERE) of the Technical University of Denmark (DTU) is operating a data bank for electrolyte solutions [18]. It is a compilation of experimental data for (mainly) aqueous solutions of electrolytes and/or nonelectrolytes. The database is a mixture between a literature reference database and a numerical database. Currently references to more than 3,000 papers are stored in the database together with around 150,000 experimental data. The main properties are activity and osmotic coefficients, enthalpies, heat capacities, gas solubilities, and phase equihhria like VLE, LLE, and SLE. The access to the htera-ture reference database is free of charge. The numerical values must be ordered at CERE. 

Modem and comprehensive investigations of physicochemical properties of citric acid solutions actrtally starts only in 1938 when Marshall published paper entitled A Phase Study of the System Citric Acid and Water [122]. For the first time systematic thermodynamic data were determined in the 10-70 °C temperature range. They included values of enthalpies of hydration and crystallization, determination of the citric acid monohydrate to anhydrous transition point and decomposition pressmes of the hydrate. Marshall measured also solubility of citric acid as a function of temperatirre, densities and vapoirr pressmes of water over satirrated solutions. After a long pause, only in 1955, we meet with an extremely important paper of Levien [123] A Physicochemical Study of Aqueous Citric Acid Solutions. It contains resrrlts of isopiestic measrrrements (activity and osmotic coefficients), the enthalpy of solution, electrical conductivities, densities, viscosities, partial... 

Moreover, the use of Eq. (2.62) to describe ion interaction coefficients is ako excellent at describing activity and osmotic coefficient (as well as stabffity and solubility constant) data at high temperatures. 

Literature data (Robinson and Stokes, 1959) for the activity and osmotic coefficients of potassium hydroxide and sodium hydroxide solutions, at 25 C, are listed in Table 2.4. The activity and osmotic coefficients of each of these alkali hydroxides have been fitted simultaneously using Eqs. (2.63) and (2.64), respectively (to keep the uncertainty in each point similar, a weight of has been used where X is the measured value). The fits obtained are illustrated in Figures 2.1 and 2.2. From these fits, the values obtained for the ion interaction parameters are... 

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