344 



Conductivity of Aqueous Solutions. Part XII. 



Table 143. Ionization-constants of phosphoric acid, acetic acid, and ammonium 



hydroxide. 



for ammonium hydroxide. Phosphoric acid is seen to have a much larger 

 ionization, which, however, decreases steadily and very rapidly with rising- 

 temperature. 



The interpretation of the results obtained with sulphuric acid is com- 

 plicated by the fact that the ionization doubtless takes place in two 

 stages ; but a method has been described on pages 271-3 by which it 

 is possible to determine the hydrogen-ion concentration within fairly nar- 

 row limits from the conductance alone, without knowledge of the extent 

 to which the separate stages occur. The method is of general applica- 

 tion to dibasic acids ; and, if the ionization-constant for the first hydrogen 

 be known, as is true with many of the organic acids, the method could be 

 used for computing that of the second hydrogen from the conductance at 

 high dilutions where the secondary ionization is appreciable. The ratio 

 of the hydrogen-ion to the total hydrogen in the case of sulphuric acid 

 is thus found to vary in 0.08 normal solution from about 6fi per cent at 

 18 to 48 at 100 and 35 at 306. 



Similar calculations of the hydrogen-ion concentrations have been made 

 in the case of potassium hydrogen sulphate. These show that in 0.1 molal 

 solution at 156 the hydrogen-ion concentration is not more than 3 per 

 cent ; and this justifies the conclusion that the secondary ionization of 

 sulphuric acid (into hydrogen-ion and sulphate-ion) in its own moderately 

 concentrated solutions is also insignificant at this temperature and higher 

 temperatures. Interpreted with the help of this conclusion the con- 

 ductivity data for the acid show that the primary dissociation (into 

 hydrogen-ion and hydrosulphate-ion) is about the same as that of hydro- 

 chloric acid at temperatures between 100 and 306 ; and it is reasonable to 

 suppose that the same is true at lower temperatures down to 18. 



