60 HYDROGEN ION CONCENTRATION 



Furthermore there need be no difficulty in calculating the some- 

 what compHcated functions for poly basic acids. As long as the 

 difference between any two consecutive dissociation constants 

 remains < 10^, the curves may be compounded from the individual 

 dissociation and dissociation-residue curves. 



The same is true of the polybasic bases, by simply substituting 

 [0H-] for [H+]. 



As a result of the consecutive dissociation in stages the last 

 ionization stages in polybasic acids can occur only in a strongly 

 alkaline reaction. Thus for example, the concentrations of the 

 carbonate, COs", and the tertiary phosphate, POf ions are practically 

 negligible in the blood, in which only HCOy, HPOf , and H2P07-ions 

 are found. 



Table 12 gives the dissociation constants of some dibasic and tri- 

 basic acids (chiefly taken from Landolt-Bornstein, Physik. Chem. 

 Tabellen. k2 for uric acid is given by A, Kanitz^^). 



35 



17. The dissociation of amphoteric electrolytes 



Amphoteric electrolytes or ampholytes are substances which 

 behave as acids as well as bases. As acids they form salts with 

 bases, and as bases they react with acids to form salts. The ampho- 

 lytes may be divided into two large groups: those in which the 

 acidic and the basic radicals are spatially apart, and those in which 

 the two radicals are one and identical. To the latter group belong 

 many metal hydroxides. Thus Zn(0H)2 may dissociate either as 

 Zn++ + 20H~, or as H+ + ZnO=. The most important ampho- 

 lytes of the first type are the amino-acids. Thus by virtue of its 

 NH2 group glj^cocoll is a base, while by virtue of its COOH-group 

 it is at the same time an acid. It has long been known that it 

 reacts with HCl to form a hydrochloride and with NaOH to form 



3« A. Kanitz, Zeitschr. f. physiol. Chem. 116, 96 (1921). 



35 Literature: G. Bredig, Zeitschr. f. Elektrochem. 6, 33 (1899).— K. Winkel- 

 blech, Zeitschr. f. physikal. Chem. 36, 546 (1901).— J. Walker, Zeitschr. f. 

 physikal. Chem. 49, 82 (1904) and 51, 706 (1905).— H. Lunden, K. vetenskap. 

 Nobelinstitut 1 (1908) ; Arkiv for Kemi, Mineralogi och Geologi (Vetenskaps- 

 Akad., Stockholm) 2, No. 11; Zeitschr. f. physikal. Chem. 47, 476 (1906).— 

 L. Michaelis, Biochem. Zeitschr. 24, 79 and 30, 143 (1910); 33, 182 (1911); 47, 

 250 (1912) ; Nernst-Festschrift, 308 (1913) ; Biochem. Zeitschr. 103, 225 and 106, 

 83 (1920).— S. P. L. Sorensen, Ergebn. d. Physiol. 12, 303 (1912). 



