Volatile nonelectrolytes, standard

A study of the acid-base properties of solutes in nonaqueous solvents must include consideration of hydrogen ion activities and in particular a comparison of their activities in different solvents. Attempting to transpose interpretations and methods of approach from aqueous to nonaqueous systems may lead to diflSculty. The usual standard state (Section 2-2) for a nonvolatile solute is arbitrarily defined in terms of a reference condition with activity equal to concentration at infinite dilution. Comparisons of activities are unsatisfactory when applied to different solvents, because different standard states are then necessarily involved. For such comparisons it would be gratifying if the standard state could be defined solely with reference to the properties of the pure solute, as it is for volatile nonelectrolytes (Section 2-7). Unfortunately, for ionic solutes a different standard state is defined for every solvent and every temperature. 

FIGURE 9.7 Experimental (symbols) and fitted (lines) results for Henry s constants (H21) for Hydrogen sulfide (2) in water (1) from Equation 9.37 through Equation 9.41. (Reprinted with permission from A. Plyasunov, J. P. O Connell, R. H. Wood, and E. L. Shock, 2000, Infinite Dilution Partial Molar Properties of Aqueous Solutions of Nonelectrolytes. II. Equations for the Standard Thermodynamic Functions of Hydration of Volatile Nonelectrolytes over Wide Ranges of Conditions Including Subcritical Temperatures, Geochimica Et Cosmochimica Acta, 64, 2779, With permission from Elsevier.)... 

Plyasunov, A. V., J. P. O Connell, and R. H. Wood. 2000. Infinite dilution partial molar properties of aqueous solutions of nonelectrolytes. I. Equations for partial molar volumes at infinite dilution and standard thermodynamic functions of hydration of volatile nonelectrolytes over wide ranges of conditions. Geochimica et Cosmochimica Acta. 64,495. 

Figure 2.17 shows that the standard partial molar volume is negative for nonvolatile strong electrolytes and becomes increasingly positive for volatile nonelectrolytes with decreasing polarity. 

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