Trace activity coefficient

It is interesting and of some significance to evaluate 2i (the Hamed interaction coefficient in Equation 2) and yitr, the trace activity coefficient, from the following pertinent expressions (15) (using the value of 0 = — 0.20 from Figure 2) ... 

The values plotted in Figure 2 display the expected linear variation with molality of hydrochloric acid at constant ionic strength. The intercept measures the trace activity coefficient, yHci ", the limit of y in pure (acid-free) seawater. At 25°C, ynci " = 0.731 as compared with 0.728 in... 

Table IV. Trace Activity Coefficient of Hydrochloric Acid in Seawater for Cell A)...

G The ion interaction coefficient s(An, CP) for An = Am and Cm is assumed to equal to s(Nd , CP) which is calculated from trace activity coefficients of Nd ion in 0 to 4 m NaCl. These trace activity coefficients are based on the ion interaction Pitzer parameters evaluated in [97KON/FAN] from osmotic coefficients in aqueous NdCP-NaCl and NdCfr-CaCfr. 

The Bates-Guggenheim convention (7) assumes that the trace activity coefficient of the chloride ion ffciis given by... 

As the ion interaction coefficients for the Th" ion are important parameters for the evaluation of standard state equihbrium constants from experimental data in perchlorate, nitrate and chloride media, an additional experimental study was undertaken [2006NEC/ALT] where trace activity coefficients of the Th" ion in dilute to concentrated NaC104, NaNOs and NaCl solutions (PJ = 0.01-0.02 M) were determined at 22°C from hquid-liquid distribution equilibria between aqueous... 

Figure VI-5 Trace activity coefficients of in NaCl solution at 25°C, calculated with the SIT coefficient 8(Th", Cr) = (0.25 + 0.03) kg-mol [1980CIA], [1992GRE/FUG] (A) and with the different sets of the Pitzer parameters reported by Pitzer and Mayorga [1973PIT/MAY] (B) and by Roy et al. [1992ROYA OG] and Rai et al. [1997RAI/FEL] (C).

In this study ion interaction (SIT) coefficients for the Th" ion and trace activity coefficients in NaC104, NaNOs and NaCl solution were determined by solvent extraction with tri-n-butyl phosphate (TBP) at 22°C. The liquid-liquid phase equilibria between dilute to concentrated NaC104, NaNOs and NaCl solutions containing 0.01-0.02 M and (1 - 8) X 10 M Th" and organic phases consisting of 10-50 vol.% TBP in n-dodecane are given by ... 

In order to obtain the pH of a solution from Ig(aHrci) independent way for getting the value of xci is needed. It is done by extrapolating Ig(flHyci) to zero chloride molality (lg(af]yci)°) and using the Bates-Guggenheim convention [34]. The convention proposes that die trace activity coefficient of the chloride ions (y°) can be caleulated on the basis of Debye-Hiickel theory, that is,... 

The quantity p(%Yci) = Ig (%YciX on the left hand side of (4), is called the acidity function (5). To obtain the quantity pH according to eqn. (2) from the acidity function, it is necessary to evaluate Ig g,- independently. This is done in two steps (i) the value of Ig (OhYci) t zero chloride molality, Ig (%Yci)°> is evaluated and (ii) a value for the activity of the chloride ion y°ci > nt zero chloride molality (sometimes referred to as the limiting or trace activity coefficient) is calculated using the Bates-Guggenheim convention (7). The value of Ig (anYa) corresponding to zero chloride molality is determined by linear extrapolation of measurements using Hamed cells with at least three added molalities of sodium or potassium chloride (/< 0.1 mol kg" ). 

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