DISSOCIATION OF ACIDS AND BASES 137 



known with a fair degree of certainty that many of the compounds 

 of H- and OH-ions formed with oppositely charged ions (i.e., acids 

 and bases) are but poorly dissociated. It seems probable that those 

 ionic species which share w^ith H- and OH-ions the property of being 

 strongly adsorbed on charcoal are also those which tend in the 

 direction of true salt formation. The proteins bind the ions of 

 organic dye-stuffs, of alkaloids, etc. It is out of the question that a 

 salt of protein and methylene blue or quinine base belong to the 

 type of always completely dissociated electrolytes. It must be 

 even supposed that the same applies to protein salts of calcium' 

 and indeed to all protein salts. These intimations may suffice for 

 the present to explain why the subject of true salt formation is 

 brought into the discussion. 



In an illustrative way our problem is as follows: When a base is 

 added to acetic acid then the ensuing ionic equilibrium in the solution 

 has been hitherto represented on the assumption that the molecular 

 entity, "Na-acetate," was not at all formed. Let us now progress a 

 step forward and assume that, after all, this molecular entity is 

 formed, and indeed, according to the equation 



CH3COO- + Na+ ;^ CH3COO Na 



in the state of equilibrium 



[CH3COO-] [Na+] = ka [CH3COO Na] 



where kg is the dissociation constant of the salt. 



The advent of this molecular species affects the ionic equilibrium 

 in the solution. Of the many problems arising out of this complica- 

 tion we shall limit ourselves to but a few. It is unessential, in this 

 particular case of sodium acetate, that the formation of undissociated 

 molecules is as yet scarcely considered as a practical possibility. 



39. The formation of the ionic equilibrium with true salt-formation^ 



Let us take the following system. A very small amount of acid 

 A is present in the concentration a in solution. The concentration 

 of its undissociated free molecules is a, its anions A~ are in concentra- 

 tion a~, and besides the cation H+ present in h-concentration there 



1 Cf. P. Rona and Gyorgy, Biochem. Zeitschr. 56, 416 (1913). 



2 L. Michaelis, Biochem, Zeitschr. 103, 225 (1920). 



