OTHER PROPERTIES OF ELECTROLYTIC SOLUTIONS 291 



shown in the table, the catalytic action of the neutral molecule of hydro- 

 chloric acid is greater than that of the hydrogen ion. As the acids become 

 weaker, however, the catalytic activity of the neutral molecule diminishes 

 and reaches very low values in the case of weak acids. According to 



K n 



Taylor, the ratio -= is related to the ionization constant of the acid by 



K i 

 the equation: 



(86) 



where A is a constant. If the law of mass action applies to the acid, this 

 leads to the relation: 



where (7 and C - are the concentrations of the un-ionized and the ionized 



u i/ 



fractions of the acid, respectively. 



Many reactions are likewise catalyzed by the hydroxyl ions and, in 

 alcohol solutions, by the alcoholate ion. 1 * Since the results obtained in 

 these cases do not differ materially from those obtained in the case of 

 acids, the details need not be given here. 



It is evident that the catalyjbic action of the hydrogen and hydroxyl 

 ions may not be safely employed for determining ion concentrations. At 

 all events, the interpretation of the results obtained is still very uncertain. 

 In this connection, it may be noted that Arrhenius 16 has proposed an 

 alternative hypothesis to account for the effect of the un-ionized fraction 

 according to which the change in the catalytic activity is a secondary 

 effect due to a change in the osmotic pressure of the molecules as a 

 consequence of the addition of the neutral salt. While the catalytic 

 effects due to the ions are of great interest and often of much practical 

 importance, nevertheless, at the present time, they have not enabled us 

 to gain any great insight into the nature of electrolytic solutions. 



Recently a number of investigators have ascribed the effect of neutral 

 salts on the catalytic action of strong acids to the influence of the added 

 salt on the thermodynamic potential; or, what is equivalent, the activity 

 of the hydrogen ion. Harned 16 has studied the action of neutral salts on 

 the rate of various reactions which are catalyzed by ionic catalysts and 

 has compared this effect with the change in the activity of the catalyzing 



"Acree, numerous articles in the Am. Chem. J. and J. Am. CJiem. Soc. since 1907. 

 See: Acree, Am. Chem. J. 49, 474 (1913). 



"Arrhenius and Andersson. Meddel K. Vet.-Akad'a. Nobclinstitut 3, No. 25 (1917). 

 Harned, J. Am. Chem. Soc. 40, 1461 (1918). 



