Activity coefficient in aqueous salt solutions

WOLERY JACKSON Activity Coefficients in Aqueous Salt Solutions... 

Wolery, T. J. and Jackson, K. J., 1990, Activity coefficients in aqueous salt solutions. Hydration theory equations, in (eds., D. C. Melchior and R. L. Bassett). Chemical Modeling of Aqueous Systems II. ACS Symposium Series 416. Washington, DC American Chemical Society, pp. 16-29. 

Above an ionic strength of approximately 1 M. activity coefficients of most ions increase, as shown for ff + in NaCI04 solutions in Figure 8-5. We should not be too surprised that activity coefficients in concentrated salt solutions are not the same as those in dilute aqueous solution. The solvent is no longer ff20 but. rather, a mixture of H20 and NaC104. ffeieafter, we limit our attention to dilute aqueous solutions. 

A second example is provided by a semiempirical correlation for multi-component activity coefficients in aqueous electrolyte solutions shown in Fig. 2. This correlation, developed by Fritz Meissner at MIT [3], presents a method for scale-up activity-coefficient data for single-salt solutions, which are plentiful, are used to predict activity coefficients for multisalt solutions for which experimental data are rare. The scale-up is guided by an extended Debye-Hilckel theory, but essentially it is based on enlightened empiricism. Meissner s method provides useful estimates of thermodynamic properties needed for process design of multieffect evaporators to produce salts from multicomponent brines. It will be many years before sophisticated statistical mechanical techniques can perform a similar scale-up calculation. Until then, correlations such as Meissner s will be required in a conventional industry that produces vast amounts of inexpensive commodity chemicals. 

Examples of Values of L and AF°. As a first example we may evaluate both L and AF° for a moderately soluble salt in aqueous solution. At 25° a saturated solution of potassium perchlorate has a concentration of 0.148 mole of KCIO4 in a 1000 grams of water that is to say, y+ = y = 0.148/55.5. The activity coefficient in the saturated solution has been taken1 to be 0.70 + 0.05. Using this value, we can estimate the work required to take a pair of ions from the crystal surface to mutually distant points, when the crystal is in contact with pure solvent at 25°C ... 

Long, F.A. McDevit, W.F. "Activity Coefficients of Nonelectrolyte Solutes in Aqueous Salt Solutions," Chem. Rev.,... 

Bretti. C.. Crea. F.. Foti. C.. and Sammartano. S. Solnbility and acivity coefficients of acidic and basic nonelectrolytes in aqueous salt solutions. 1. Solnbility and activity coefficients o-phthalic and L-cystine in NaCl(aq). (CHsl NCUaq). and (C2Hs) NI(aq) at different ionic strengths and at t= 25 °C. Ind. Eng. Chem., 50(5) 1761-1767. 2005. 

F.A. Long and W.F. McDevit, Activity coefficients of nonelectrolyte solutes in aqueous salt solutions, Chem. Rev. 51... 

Osol, A., Kilpatrick, M. (1933) The salting-out and salting-in of weak acids. I. The activity coefficients of the molecules of ortho, meta, and para chlorobenzoic acids in aqueous salt solutions. J. Am. Chem. Soc. 55, 4430-4440. 

For NaCl, the results are not too accurate at high molalities. However, it is well-known that most models fail to represent accurately the mean activity coefficient for the NaCl + H2O mixtures at high molalities. One can, therefore, conclude that the gas solubility in aqueous salt solutions can be well described by eq 24 when accurate expressions for the mean activity coefficient of the salt in the binary water + salt mixtures are used. 

The Activity Coefficient of NH3 in Aqueous Salt Solutions. The activity coefficient of NH3 in a solution of salt Mv- -Xv is given by ... 

An extensive review of neutral solutes in aqueous salt solutions is given by RandeU and Failey (1927a,b,c. See also Long and McDevit (1952) and Oelkers and Helgeson (1991)). A recent application of this method is the work of Barrett et al. (1988), who obtained activity coefficients for H2S in NaCl solutions up to 5m and 95°C (shown in Figure 17.8), and calculated coefficients for some other gases. As expected, activity coefficients of this type are much closer to 1.0 than those for charged particles in the same situation. 

Randall, M., and Failey, 1927a, The activity coefficients of gasses in aqueous salt solutions Chem. Rev., v. 4, pp. 271-284. 

Long, F.A. and McDevit, W.F. (1952) Activity coefficients of non-electrol de solutes in aqueous salt solution. Chemical Reviews, 51, 119-169. 

Mcdevit WF, Long FA (1952) The activity coefficient of benzene in aqueous salt solutions. J Am Chem Soc 74 1773-1777... 

In 1952, F.A. Long and W.F. McDevit (S15) presented the results of their extensive study of the activity coefficients of nonelectrolytes in aqueous salt solutions. Their results for the molar activity coefficients of undissociated nonelectrolytes in salt solutions were based mainly on solubUity, distribution and vapor pressure measurements. They noted that since the activity coefficient for any species i could be expressed as a power series to show the effects the concentrations of all solutes j in the solution ... 

McDevit. W.F. F.A. Long. "The activity coefficient oS benzene in aqueous salt solutions". JACS. v34. ppl773-1777 (1952)... 

RandaU. M. C.F. Falley, "The activity coefficients of gases in aqueous salt solutions". Chem. Rev., v4. 3, pp271-284 (1927)... 

Activity Coefficients of Non-electrolyte Solutes in Aqueous Salt Solutions Chemical Reviews 119 (1952)... 

M. Randall, C.E. Failey, The activity coefficient of non-electrolytes in aqueous salt solutions from solubility measurements. The salting-out order of the ions. Chem. Rev. 4(3), 285-290... 

More than half a century ago, Long and McDevit published an extensive review about activity coefficients of non-electrolyte solutes in aqueous salt solutions.This paper is still very valuable today. It is shown there how solubility, phase distribution, and vapour pressure measurements can be used to determine the influence of ions on other solutes. Detailed examples are given for salt effects on hydrogen, oxygen, carbon dioxide and other gases, but also on liquid compounds, such as benzene. This classical example is shown in Fig. 7. 

The Change of Solubility with Temperature. The solubilities of various salts have been measured in aqueous solution at various temperatures. But from these measurements we cannot derive values of L as a function of temperature, until the activity coefficients in the various saturated solutions have been accurately measured. In dilute solutions... 

---