138 



HYDROGEN ION CONCENTRATION 



is present another cation 1+ in concentration i+ which represents a 

 sufficiently great excess so that the certain amount of salt formation 

 from the interaction of the acid and 1+ does not lead to a material 

 diminution in I+. In addition we must have for the maintenance 

 of electroneutrality a corresponding amount of some other anions, 



7 



Fig. 17 



4 



6 7 



pH — - 



70 



11 



Fig. is 



Figs. 17 to 19. The functions p, o-, and a. of an acid whose dissociation con- 

 stant ka = 10~', in the presence of a neutral salt of an univalent cation in the 

 concentration 0.1 iV, with the assumption that the acid and this cation form 

 a salt, whose dissociation constant kg has the value marked on each curve. 



which, however, exercise no effect upon the state of dissociation of 

 the acid A. We shall now express the state of dissociation of this 

 acid as a function of h. We define 



a- 

 The degree of dissociation a. = -~ 



(1) 



