2^a Conductivity of Aqueous Solutions. Part VII. 



87. SUMMARY. 



In this article have been presented the results of conductivity measure- 

 ments with ammonium hydroxide, acetic acid, and ammonium chloride 

 at 18, 218, and 306, and with sodium acetate at 306. The final values 

 of the equivalent conductance will be found in table 84, and of the corres- 

 ponding ionization in table 87. 



The equivalent conductance of completely ionized ammonium chloride, 

 which at 18 is nearly equal to that of potassium chloride, becomes 2 per 

 cent greater at 218 and 5 per cent greater at 306 ; and that of sodium 

 acetate, which at 18 is only 71 per cent of that of sodium chloride, 

 becomes 8G per cent of it at 218 and 306. The ionization of the two 

 salts is at all temperatures only a little less than that of sodium and potas- 

 sium chlorides; thus at 306 the differences are about 2 per cent and 4 

 per cent, respectively. The hydrolysis of these salts was not measured, 

 but was reduced substantially to zero by the addition of an excess of 

 the weak base or acid. Its value can, however, be calculated from the 

 ionization-constants of water, ammonium hydroxide, and acetic acid deter- 

 mined in this research* ; and it is of interest to note that in 0.01 normal 

 solution both salts at 218 are 1.56 per cent hydrolyzed, and that at 306 

 ammonium chloride is 4.1 and sodium acetate 3.4 per cent hydrolyzed, 

 while at 18 the hydrolysis is only 0.02 per cent. 



The ionization of the slightly ionized substances, acetic acid and ammo- 

 nium hydroxide, decreases with great rapidity as the higher temperatures 

 are reached; thus the ionization-constants (X 10 6 ), as determined from 

 the measurements at 218 and 306 presented in this article and from the 

 earlier ones at 18, 100, 156, and 218 by Noyes and Cooper, and Noyes 

 and Kato, are as follows : 



Acetic Acid. Ammonium Hydroxide. 

 18 18.3 17.2 



100 11.1 13.5 



156 5.42 G.28 



218 1.72 1.80 



30fi 0.139 0.093 



*These calculations were made, for sodium acetate for example, by the substan- 

 tially exact mass-action relation; rv~ t^> wherein C represents the concentra- 



(1 Il)y A A 



tion of the salt, h the hydrolyzed fraction of it, 7 the ionized fraction of the quantity 

 of it unhydrolyzed (C Ch), 7b the ionized fraction of the total quantity of free 

 base (Ch), K A the ionization-constant for the acid, and AT W that for water. For the 

 ionized fractions 7 and 7 B in the mixture may be taken the value for the pure salt 

 and that for the pure base, respectively, when present alone at the concentration C, 

 the principle being here applied that in a mixture of largely ionized substances the 

 ionization of each is the same as if it were present alone at a concentration equal to 

 the sum of the concentrations. 



