THEORIES RELATING TO ELECTROLYTIC SOLUTIONS 



333 



(116) 



ro+a-i 



t<VJ 



Numerical Values. In comparing the thermodynamic behavior of 

 different electrolytes, Lewis and Randall have compared the values of the 

 reduced activity coefficients a r at corresponding concentrations. In 



Table CXXX are given values of the activity coefficients of different 

 electrolytes at a number of concentrations. These values have been 



TABLE CXXX. 



ACTIVITY COEFFICIENTS OF VERY DILUTE AQUEOUS SOLUTIONS AT 

 DIFFERENT CONCENTRATIONS. 



0.01 

 KC1, NaCl ... 0.922 



KN0 3 0.916 



KIO S , NaI0 3 . 0.882 



K 2 S0 4 0.687 



H 2 S0 4 0.617 



BaCl 2 0.716 



CoCl 2 0.731 



MeS0 4 0.40(4) 



K 3 Fe(CN) 6 .. 0.571 

 La (NO,). .... 0.571 



derived from freezing point measurements and agree well with those 

 derived by other methods. In Figure 59, the continuous curve represents 

 the values of the activity coefficients of sodium chloride at different con- 

 centrations as derived from freezing point determinations, while the 

 points indicated by circles represent values of the coefficients as derived 



G g is introduced, Zfi/ g measures this change of potential, together with the variation 

 due to the substitution of C g for C. If we write : 



2nJ = RT Zn log a 



o o 



and introduce this function into the equation for the activity, we have : 



RT Zn log a = RTI.n log C g + RT Zn log er g , 

 whence : 



Zn log a g = Zn log^-- 



This equation defines the stoichiometric activity coefficient of Bronsted. If salts were 

 completely ionized, the coefficient a g =a/C g would be a measure of the true activity 

 coefficient. Since potential measurements yield values of the activity products only, an 

 assumption is necessary if the activity coefficient is to be defined by means of an equation 

 of the form : 



In mixtures of any number of electrolytes the definition of the total salt concentration 

 also becomes uncertain and a further assumption of an arbitrary nature is involved in 

 defining the activity coefficients. 



