148 



Conductivity of Aqueous Solutions. Part V. 



It is of interest in the first place to compare the hydrolysis at 156 and 

 218 with that at 18. For this purpose we will select the values obtained 

 at a concentration of 1.82 or 1.69 milli-normal ; for these are probably the 

 most accurate of our results, since the hydrolysis was largest in these 

 cases. At this concentration the degree of hydrolysis of the sodium ace- 

 tate is 0.87 per cent at 156 and 4.3 per cent at 218, while at 18 the value 

 calculated from the ionization constants of water and acetic acid is only 

 0.07 per cent. The effect of temperature is therefore enormous. This 

 arises in part from the decrease in ionization of the acetic acid, which has 

 been already considered, but in still larger measure from an increase in 

 the ionization of water, as will now be shown. 



The mass-action formula applicable to a hydrolysis of this type, where 

 the salt and base can be regarded as equally ionized, and the acid as un- 



ionized is 



h-C 



Kw 



where h is the fraction hydrolyzed, C is the con- 



1 h~ Ka 



centration of the salt, and Kw and Ka are the ionization-constants of the 

 water and acid respectively. By means of this the ionization-constant of 

 the water at 218 can be calculated, since the other three quantities in- 

 volved are known. 



This calculation has been made with the help of the hydrolysis values 

 of table 45 and the ionization-constants given in table 42. The data and 

 results of the calculation (with the concentrations expressed in equiv- 

 alents per liter) are given in table 46. By Cm is to be understood the con- 

 centration of the hydrogen (or hydroxide) ions in pure water, the values 

 being equal to the square root of Kw. 



Table 46. Ionization-constants of water. 



It will be seen that the ionization-constant of water is 115 times as 

 great at 156 and 580 times as great at 218 as it is at 18, for which tem- 

 perature we have inserted the values derived by Kohlrausch and Heyd- 

 weiller* from the conductivity of the purest water obtained by them. Cor- 

 respondingly, the ionization itself or the concentration of the hydrogen 



*Wied. Ann. Phys., 53, 234 (1894). 

 4te Aufl., p. 644. 



See also Nernst, Theoretische Chemie, 



