Section 86. Hydrolysis of Ammonium Acetate. 231 



In the second method the ion-concentration is, as before, calculated by 

 dividing the specific conductance of the solution (multiplied by 10 3 ) by 

 the equivalent conductance of the completely ionized salt; and then the 

 concentration of the un-ionized salt is estimated under the assumption 

 that it has the same value as in a solution of an ordinary unhydrolyzed 

 salt of the same ionic type at the same ionic concentration. Then merely 

 by subtracting the un-ionized fraction (w) and the ionized fraction (y) 

 from unity, the hydrolyzed fraction {h)\s obtained ; that is, h = 1 y u. 

 In this calculation the mean ionization of potassium and sodium chlorides 

 as determined by Noyes and Coolidge (table 12, Part II) was used as a 

 basis. This calculation can give accurate hydrolysis values only when 

 the hydrolyzed fraction is large and the un-ionized fraction very small ; 

 but under such conditions, which are in fact realized in the foregoing 

 experiments fairly well at 218 and in much higher degree at 306, it is 

 the most direct method and a fairly reliable one. For example, suppose 

 the hydrolyzed, ionized, and un-ionized parts were 80 per cent, 18 per 

 cent, and 2 per cent respectively ; then an error of even 3 per cent in 

 the ionized, and of 25 per cent in the estimated un-ionized fraction, would 

 make, if they lay in the same direction, an error of only one per cent 

 in the hydrolyzed fraction.* 



Table 91 contains the results of the calculations. In the fifth and 

 sixth columns are given the values of the percentage hydrolysis (lOO/i) 

 calculated by the first and second methods, respectively. In the seventh 

 column is given a mean derived from these. Since the results by the 

 second method are more accurate the greater the hydrolysis, in deriving 

 this mean a weight has been assigned to them equal to the percentage 

 hydrolysis, the results by the first method being always given a weight 

 of 100. It is desirable to combine the results by the two methods in some 

 such way as this, since any error in the conductance ratio l/l influences 

 them in opposite directions. In the last three columns of the table are 

 given the values of the percentage hydrolysis (100 h ) of the salt in 

 pure water at the same concentration C. The values in the first of these 

 columns are derived by the first method simultaneously with those of 

 100 h. Those in the second of these columns are calculated from the 

 mean value of 100k given in the seventh column by the equation 



/.! , , r~ . Those in the last column are obtained directly 



by the second method from the conductance in pure water. 



*The calculations were also made by still a third method, namely, that described 

 by C. W. Kanolt in Section 103, Part IX, but in this case where the hydrolysis is 

 very large the results were found to be much more influenced by the experimental 

 error than those calculated by the first method. They are therefore not recorded 

 here. 



