Hydrogen Ion Concentration of Acid Solutions. 3 

 2 (1462) 



Contrasting effects of chlorides and sulphates on the hydrogen 

 ion concentration of acid solutions. 



By Arthur W. Thomas and Mabel E. Baldwin. 



[From the Laboratory of Food Chemistry, Columbia University.] 



In the course of an investigation upon the effect of neutral 

 salts upon hydrogen ion concentration we have noted a striking 

 contrast in the effect of chlorides, sulphates and magnesium salts 

 on the apparent hydrogen ion concentration of solutions of hydro- 

 chloric and of sulphuric acids. 



The results of our measurements are given below. In all 

 cases a solution of acid was mixed with a solution of a given salt 

 and diluted to 100 c.c. The concentration of this solution of the 

 mixture was always 0.1 normal with respect to the acid and that 

 particular concentration of the salt whose effect upon the hydrogen 

 ion concentration was to be studied. The hydrogen ion concentra- 

 tions were measured two days after the solutions were made up. 



The effect of chlorides in increasing the hydrogen ion con- 

 centration of hydrochloric acid solutions is not new. This has 

 previously been shown by Harned 1 and by Fales and Nelson 2 . 

 Arrhenius 3 found that the hydrogen ion activities of acetic and 

 of hydrochloric acids were increased by neutral salts which he 

 thought was due to the salts increasing the dissociation of the 

 acids. It is possible that recent work on the hydration of ions 

 in aqueous solution will offer a more plausible explanation. 



When the chlorides are arranged in order of their ability to 

 increase the hydrogen ion activity, we get the following series: 

 MgCl 2 > BaCl 2 > LiCl > NaCl > NH 4 C1 = KC1 which, with the 

 exception of magnesium and barium is in inverse order to a 

 series of these cations arranged in order of their equivalent con- 

 ductivities. 



In the above series the salts are arranged in order of the in- 

 creasing hydration (i.e., number of molecules of water combined 



1 J. Am. Chem. Soc, 37, 2460 (1915). 



2 J. Am. Chem. Soc, 37, 2769 (1915). 

 • Z. physik. Chem., 31, 197 (1899). 



