Part V. 



CONDUCTIVITY AND IONIZATION OF HYDROCHLORIC ACID, ACETIC 



ACID, AND SODIUM ACETATE UP TO 218. HYDROLYSIS OF 



SODIUM ACETATE AND IONIZATION OF WATER AT 218. 



46. OUTLINE OF THE INVESTIGATION, 



In Parts II and III of this publication an apparatus and method have 

 been described by which accurate measurements of the electrical conduct- 

 ance of aqueous solutions can be extended up to 306 or higher. This 

 has made it possible to investigate at high temperatures such other 

 physical properties and chemical reactions, as can be studied with the 

 help of conductivity measurements. One of the most interesting of these 

 is the phenomenon of the hydrolysis of salts into free acid and base a 

 phenomenon which is dependent in large measure on the degree of ioniza- 

 tion of water itself, and from which, when supplemented by determina- 

 tions of the ionization of the acid and base involved, this important quan- 

 tity can be computed. Owing to the fact that the ionization of water in- 

 creases very rapidly with rising temperature while the ionization of most 

 weak acids and bases decreases, the hydrolysis of salts plays at high 

 temperatures a much more prominent part than at ordinary ones and its 

 effect must be taken into consideration even in the case of salts which 

 at the ordinary temperature are not appreciably hydrolyzed. We have 

 therefore undertaken an investigation in this direction. 



The method employed for determining the hydrolysis is in principle 

 that described first by Walker,* and later, in much more exact form by 

 Bredig.f It consists in measuring the decrease of conductivity produced 

 by adding to the salt solution, in which the salt is partially hydrolyzed, a 

 sufficient quantity of the slightly ionized acid (or base) to reduce the 

 degree of hydrolysis substantially to zero and in computing from this 

 decrease and the previously determined difference in the mobility of the 

 hydroxyl (or hydrogen) ion and the anion (or cathion) of the salt the 

 fraction of the salt hydrolyzed. Thus, in the case of sodium acetate, the 

 conductivity of this salt in its ordinary condition was first measured ; then 

 that of a solution of the salt of the same concentration containing also a 

 considerable proportion of free acetic acid (which was varied in different 

 experiments) was determined. The observed difference (after applying 

 a small correction for the conductivity of the added acid in the presence 



*Ztschr. phys. Chem., 4, 333 (1889). fZtschr. phys. Chem., 13, 214, 321 (1894). 



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