Ohemlstry. — ''The dissociation constants of sulphonacetic and 

 it-sidpfionpropionic acids'. By Prof. H. J. Backer. (Communi- 

 cated by Prof. P. VAN Romburgh). 



(Communicated at the meeting of September 30, 1922). 



The «-sulphoncarbonic acids are dibasic acids with a strong and a 

 weak acid function. 



Consequently, the free compounds belong to the strong acids, 

 whilst the acid salts behave as weak acids. 



In the table the molecular conductivity of sulphonacetic and 

 rt-sulphonpropionic acid is mentioned. 



When the values at an infinite dilution a , on account of the 



' CO ' 



number of atoms in a molecule ^) are taken for the sulphonacetic 

 acid at 376, and for the sulphonpropionic acid at 373, then the mean 

 value of the dissociation constant, at the concentrations Vaa ^"^ 7m 

 Grammolecule per litre, is found to be for the sulphonacetic acid 

 0.58 and for the sulphonpropionic acid 0.57. 



Great accuracy can not be ascribed to these figures, as the uncer- 

 tainty in the determination of ft^ in the case of these strong acids 

 has a great influence on the size of the constants. 



However, the values are not impi-obable; for Wegscheider ^), who 

 has argued the validity of Ostwald's dilution law for sulphonic 

 acids, has calculated for benzol sulphonic, p-toluolsulphonic and 

 /5-naplitalinesulphonic acids, the cojistants 0.21, 0.214 and 0.267, 

 and for the m sulphonbenzoic acid, related to the above-mentioned 

 acids, the constant 0.4. 



In the solutions of the acid sodium salts of the sulphoncarbonic 

 acids chiefly the following ionic equilibria exist: 



NaHA ^ Na -1- HA' (I) 



HA':^H- + A" (H) 



Besides, molecules of the free acid may be formed : 



H-f HA'f^H,A . (Ill) 



The conductivity of the acid sodium salts is thus caused by the 

 ions: Na , HA', H' , A". 



1) OsTWALD-LuTHER, Hand- u. Hilfsbuch 1922, 482. 



2) Wegscheidrr, Monatshefte f. Gh. 23, 340, 341 (1902); 30, 440 (1909). 



23* 



