288 PROPERTIES OF ELECTRICALLY CONDUCTING SYSTEMS 



in the case of the weaker acids, in that of the stronger acids the catalytic 

 action is actually increased. 



It is now commonly accepted that the un-ionized acid molecules, as 

 well as the ions themselves, influence the rate of these reactions. Ac- 

 cording to this hypothesis, the reaction constant is given by an equation 

 of the form: 



(85) K = Ki C h +K n C n , 



where K^ and K n are the velocity constants for the ions and the un-ion- 

 ized molecules respectively and C^ and C n are the concentrations of the 

 ions and the un-ionized molecules. The constant K n is in general deter- 

 mined by adding, to a dilute solution of an acid, a salt of the same acid. 

 Under these conditions, the ionization of the acid is practically repressed 

 to zero and it is assumed that the residual catalytic action is due entirely 

 to the un-ionized acid molecules. The results of many experiments on a 

 great variety of reactions are, on the whole, in good accord with this 

 hypothesis. It should be noted, however, that the ratio of the constants 

 K n to K- is a function of the strength of the acid, as well as of other 



factors. The weaker the acid, the smaller is, in general, the value of this 

 ratio. In the case of the strong acids, the value of this ratio may be 

 unity or even greater. 



In the following table are given values of the inversion coefficient for 

 aqueous solutions of cane sugar, according to Ostwald, at 25. The 

 concentration of the acids was in all cases 0.5 N and the values given for 

 the constants are relative to that of hydrochloric acid taken as unity. t 



TABLE CXV. 

 INVERSION COEFFICIENTS FOR DIFFERENT ACIDS. 



Hydrochloric acid 1.000 Trichloroacetic acid 0.754 



Nitric acid 1.000 Dichloroacetic acid 0.271 



Chloric acid 1.035 Monochloroacetic acid . . . 0.0484 



Sulphuric acid 0.536 Formic acid 0.0153 



Benzenesulphonic acid 1.044 Acetic acid 0.0040 



It is clear that the catalytic action of the acids is intimately related 

 to their strength. 



For the purpose of investigating the effect of the neutral molecules 

 upon reactions, solutions in non-aqueous solvents are in many respects 

 better adapted than those in water, since the ionization of the acid in 



