LAWS OF ELECTROLYTIC DISSOCIATION 61 



the sodium salt. But it displays its basic nature to its full extent 

 in a strongly acid solution and its acid nature in a strongly alkaline 

 solution. In pure solution it behaves as a very weak electrolyte 

 and shows a just barely demonstrable acid reaction, because of a 

 predominance of the acidic property of the COOH-group over the 

 basic property of the NH2-group. Assuming that the ampholyte 

 is present in solution in concentration [A], as an acid it forms anions 

 of [A~] concentration, and its acid dissociation constant is ka. At 

 the same time in the same solution it also functions as a base whose 

 dissociation constant is kb and forms cations of [A+] concentration, 

 ka and kb must be different in value, and either the acidic or the basic 

 character of the ampholyte predominates. Of all known ampho- 

 lytes the difference between ka and kb is least in hemoglobin. 



In discussing the dissociation relations of the ampholytes it is 

 simplest to begin with a consideration of the dissociation residue, 

 p, which is defined as the ratio of the undissociated portion to the 

 total concentration [A] of the ampholyte: 



[A] - [A+] - [A-] 



p = 



[A] 



On the other hand the degree of dissociation must be given 

 separately for the cations and the anions. For the anions it is: 



[A- 



a = 



[A] 

 and the degree of dissociation of the cations is: 



^ [A+] 



or ^ 



[A] 

 The mass law finds its apphcation in the following relationships: 



[A-] X [H+] = ka X [U] 



where U is the undissociated portion of the ampholyte, and further- 

 more, 



[A+] X [Oil-] = kb X [U] 



It follows, therefore, 



(A-l - t. jM ,„ 



