DISSOCIATION OF ACIDS AND BASES 141 



The a-curve is here no longer an exact mirror image of the p-curve. 

 The characteristic of this curve is that a reaches the value 1 more 

 slowly, or, practically, does not reach it at all. 



The cr-curve appears here for the first time. The curve of a + o- 

 would be identical with the original a-curve, i.e., it would be a mirror 

 image of the p-curve. The a-curve first becomes definitely marked 

 at high pH values, that is to say, the true salt formation becomes 

 first apparent at a certain degree of alkaUnity. This condition can 

 be restated as follows: The H-ion and the other cation present 

 compete for the combination with the acid. Only when there is a 

 relative lack of H-ions does the other cation succeed in the formation 

 of a salt. 



For the bases all these conditions are just as valid, after making 

 the appropriate substitutions. 



40. The behavior of ampholytes in the process of true salt- 

 formation 



The relations of an ampholyte to this process are more involved. 

 We shall derive only the p-function. 

 We shall make the following designations: 



1. a — the total concentration of the ampholyte. 



2. a' and a' — the respective concentrations of the ampholyte cations and 



anions. 



3. a — the concentration of the free undissociated ampholyte molecules. 



4. Si — the concentration of the salt formed by the ampholyte as an acid 



with a cation. 



5. Sii — the concentration of the salt formed by the ampholyte as a base 



with an anion. 



6. ka and kb — the dissociation constants of the ampholyte as acid and base 



respectively. 



7. ki and kn — the dissociation constants of the two ampholyte salts; 



ki of that with the metal-cation and kn of that with the acid- 

 anion. 



Then we shall define as: 



= p — the dissociation residue 



= OL — the degree of d'.ssociation of the cations 



a 



a 



_ 

 a 



