Calculated and Observed Activity Coefficients

FIGURE 1.4 Mean activity coefficients of (1) KCl, (2) CaCl2, and (3) LaClj vs. square root of the dimensionless ionic strength. Data points are from [Chapter 10, Table 10.17 and Ref. 3], and solid lines are obtained using Equation 1.27 with d= 4.5 A. 

Equations 1.30 and 1.31 work pretty well for single electrolyte aqueous solutions but cannot be easily used when two or more electrolytes have high concentrations. In a multicomponent aqueous solution, Equations 1.30 and 1.31 can be used only if one of the electrolytes is dominating and concentrations of all others are much smaller. A well-known example of such a solution is sea water (or underground brine) where 

FIGURE 1.5 Dependence of the mean activity coefficient of HCl(aq), KCl(aq), and H2S04(aq) from the square root of the dimensionless molality. The data are taken from [Chapter 10, Table 10.17], 

NaCl is a dominating electrolyte. As can be seen from Table 1.3, NaCl is highly dominating in sea water, and NaCl molality (around 0.48 mol kg- ) is about an order magnitude larger than another major electrolyte, MgCl2 (around 0.052 mol kg )- In such a solution, using the experimental mean activity coefficients of NaCl(aq) [Chapter 10, Table 10.17] to calculate parameter C in Equations 1.30 and 1.31 would be a reasonably accurate approach. 

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APPENDIX 3.6. RELATION BETWEEN CALCULATED AND OBSERVED ACTIVITY COEFFICIENTS... 

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