Calcium chloride activity coefficients

Mean sodium chloride activity coefficients have been determined [41] with a sodium ion-selective electrode and silver-silver chloride reference electrode system in mixed sodium chloride-calcium chloride solutions within the range of sodium chloride and calcium chloride levels (0.05-0.5 mol dm ) encountered in extracellular fluids. These show that at constant ionic strength, log /Naci varies linearly with the ionic strength of calcium chloride in the mixture in accordance with Harned s rule [45] ... 

For applications where the ionic strength is as high as 6 M, the ion activity coefficients can be calculated using expressions developed by Bromley (4 ). These expressions retain the first term of equation 9 and additional terms are added, to improve the fit. The expressions are much more complex than equation 9 and require the molalities of the dissolved species to calculate the ion activity coefficients. If all of the molalities of dissolved species are used to calculate the ion activity coefficients, then the expressions are quite unwieldy. However, for the applications discussed in this paper many of the dissolved species are of low concentration and only the major dissolved species need be considered in the calculation of ion activity coefficients. For lime or limestone applications with a high chloride coal and a tight water balance, calcium chloride is the dominant dissolved specie. For this situation Kerr (5) has presented these expressions for the calculation of ion activity coefficients. 

Numerous studies on the thermodynamics of calcium chloride solutions were published in the 1980s. Many of these were oriented toward verifying and expanding the Pitzer equations for determination of activity coefficients and other parameters in electrolyte solutions of high ionic strength. A review article covering much of this work is available (7). Application of Pitzer equations to the modeling of brine density as a function of composition, temperature, and pressure has been successfully carried out (8). 

Fig. 4 to Fig. 8 show the severe divergence for activity coefficients such as given here for calcium, chloride, sulfate, sodium and water ions, calculated with different equations. The activity coefficients were calculated applying Eq. 13 to Eq. 17 for the corresponding ion dissociation theories, whereas the values for the PITZER equations were gained using the program PHRQPITZ. The limit of validity of each theory is clearly shown. 

Some of the results are also depicted by the curves in Fig. 46 it will be observed that the activity coefficients may deviate appreciably from unity. The values always decrease at first as the concentration is increased, but they generally pass through a minimum and then increase again. At high concentrations the activity coefficients often exceed unity, so that the mean activity of the electrolyte is actually greater than the concentration the deviations from ideal behavior are now in the opposite direction to those which occur at low concentrations. An examination of Table XXXIV brings to light other important facts it is seen, in the first place, that electrolytes of the same valence type, e.g, sodium and potassium chlorides, etc., or calcium and zinc chlorides, etc.. 

In addition to hydrochloric acid, the results for which have just been described in detail, the method utilizing concentration cells with transference has been used in obtaining the activity coefficients of potassium chloride,17 sodium chloride,18 silver nitrate,10 and calcium chloride.17 The resulting activity coefficients, /, and comparisons with equation (45), Chapter 7, of the Debye-Hiickel theory,... 

Table IV. Activity Coefficients of Calcium Chloride from Cells with Transference at 25°...

The calcium and sodium activity coefficients were determined at 25.0 - 0.1 C with an Orion electrode (model 92-32) and a Radiometer electrode (model G502 Na), respectively. A saturated calomel electrode was used as the reference. Calibration curves were obtained using CaCl or NaCl solutions before and after each measurement. The CaCl2 and NaCl concentrations were measured by potentiometric determinations of the chlorides with silver nitrate and with a silver electrode. 

In seawater, the differences between activities and concentrations must always be considered (cf. Sect. 15.1.1). The activity coefficients for monovalent ions in seawater assume a value around 0.75, for divalent ions this value usually lies around 0.2. In most cases of practical importance, the activity coefficients can be regarded with sufficient exactness as constants, since they are, over the whole range of ionic strengths in solution, predominately bound to the concentrations of sodium, chloride, and sulfate which are not directly involved in the calcite-carbonate-equilibrium. The proportion of ionic complexes in the overall calcium or carbonate content can mostly be considered with sufficient exactness as constant in the free water column of the ocean. Yet, this cannot be applied to pore water which frequently contains totally different concentrations and distributions of complex species due to diage-netic reactions. 

The difference between activity and concentration is illustrated by Figure 23-17, where the lower curve gives the change in potential of a calcium electrode as a function of calcium chloride concentration (note that the activity or concentration scale is logarithmic). The nonlinearity of the curve is due to the increase in ionic strength — and the consequent decrease in the activity coefficient of the calcium - as the electrolyte concentration becomes larger. When these concentrations are convened to activities, the data produce the upper line with the nernslian slope of 0,fl296 (0,0592/2). 

Electrode response is affected by ionic strength variations because of the associated effect on activity coefficients [9]. This makes an assessment of ionic strength on the test solution desirable. However, because of the powered term in /x = SC, conductance monitoring may not always be satisfactory, unless, of course, the individual ionic contributions (concentrations, C, and valence, z) are known from previous analyses. Such information is useful for preparing calibration standards of the same ionic strength range as the sample under examination and is the basis of synthetic sea water samples as calibrants. Calcium chloride standards in 0.150 mol dm sodium chloride is a similar ploy used in calibrating... 

Studies with an Orion 92-20 calcium ion-selective electrode on mixed calcium chloride—calcium nitrate solutions and with nitrates and chlorides of sodium and potassium have shown that within experimental error, the mean activity coefficients of calcium chloride in mixed solutions up to an ionic strength of 0.3 mol... 

Much of the uncertainty concerning activity coefficients and liquid junctions can be minimised by calibrating the ion-selective electrode with calcium chloride standards (approx. 0.5—0.2 mmol dm ) in 0.150 mol dm sodium chloride solutions. This corresponds to an emf span of just approx. 18 mV, thus emphasising the need for using precise emf-measuring instruments and attention to electrode care and solution details. 

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. 

From Staples, B.R. and NuttaU, R.L., "The Activity and Osmotic Coefficients of Aqueous Calcium Chloride at... 

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]. 

Find the activity coefficient of calcium chloride at 1.000 mol kg, using a Gibbs-Duhem integration. 

Fig. 9.1 Shows calculated single ion activity coefficients (y) for the common cations sodium, potassium, magnesium, and calcium as their chloride salts as a function of solution ionic strength...

The freezing point depression, refractive index, osmolality and specific conductance are all listed in Table 2.30. An et al. (1978) list activity and osmotic coefficients. The water absorbed by solid calcium chloride is listed in Table 2.41 and Fig. 2.81. 

Electrical conductance and ionization constants have been presented by Frantz and Marshall (1982). Other volumetric properties of calcium chloride solutions have been given by Potter and Clynne (1973) and Tsay et al. (1988 at high temperatures and pressure). Various bulk properties are presented by Alekhin et al. (1980). The activity coefficients of calcium chloride are given by Long et al. 

Tetra Chemicals. (2002-1992). Calcium Chloride. Data Sheets and Technical Article, 14 pp. Tishchenko, P. Y., and Popova, L. A. (1992). Activity Coefficients of Calcium Chloride in Sea Water. ... 

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