LAWS OF ELECTROLYTIC DISSOCIATION 



91 



those below from equation (10). From the practical standpoint it 

 appears even more important to tabulate the pH values of such 

 solutions. These have been calculated by the author and are 

 shown in table 17. 



Thus in solutions of NH4CI (kb approximately = 10~^) and of 

 sodium acetate (ka approximately = 10~^) the following the pH 

 values obtain: 



25. Notes on the methods for determining dissociation constants 



and the isoelectric point 



1. The oldest method for the determination cf the dissociation 

 constant of a sunple electrolyte consists of measuring the conduc- 

 tivity of its solutions in various dilutions. Wilhelm Ostwald found 

 empirically that 



= k 



(1 - a) V 



where a is the degree of dissociation at the concentration -> v being 



that volume of solution that contains one mol of the solute, 

 value of a is determined by the expression 



The 



= a 



[(1) 



where Ac is the molar conductance at the concentration c and A ^ 

 denotes its limiting value at infinite dilution. Ostwald's law, as 

 given in equation (1) is but an expression of the mass law applied 

 to dissociation. According to definition, for instance, it is true 

 for an acid that 



s- 



(2) 



