Section 97. Ionization of the Substances. 



?6g 



to 306 change with the concentration according to the same exponential 

 law as does that of neutral salts, the value of the exponent n in the equation 

 C(A A) = A' (C\) n , being in all cases approximately 1.5. It follows 

 therefore that the same is true of the ionization (y) of these substances, 

 to which the corresponding equation C(l y) = K(Cy) n with n =: 

 1.5, approximately, applies. 



The change of ionization with the temperature of nitric acid up to 156 

 and of hydrochloric acid even up to 306 is also about the same magni- 

 tude as that of neutral salts of the same ionic type, as may be seen best 

 by comparing the values at 80 milli-normal in tables 114 and 115 and 

 table 41, Part V, with those in table 28 (Part IV). Thus at 18 the 

 ionization of potassium and sodium chlorides is 86.5 per cent, that of 

 hydrochloric and nitric acids 93 per cent, while at 156 the corresponding 

 values are 80.5 per cent for the two salts and 86 per cent for the two acids. 

 At 306 the ionization of the salts is 63 per cent and that of hydrochloric 

 acid 60 per cent. The ionization of nitric acid, however, at 218 and above 

 decreases much more rapidly than hydrochloric acid, and has fallen to 33 

 per cent at 306. This marked difference in the behavior of the two acids 

 at the high temperatures is well shown by-'tne conductance plot in fig. 18. 

 The ionization of barium hydroxide decreases a little more rapidly than 

 the average ionization of the two salts, barium nitrate and potassium sul- 

 phate ; thus at 0.08 normal that of the base is 83 per cent at 18 and 65 

 per cent at 156, while that of the salts is 72' per cent at 18 and 60 per 

 cent at 156. 



It was shown in the last section that the exponent in the functional 

 relation between equivalent conductance and concentration in the case of 

 phosphoric acid has values (1.8 to 1.9) which approach much more nearly 

 to the value (2.0) required by the mass-action law, but do not entirely 

 conform to it, even at the higher temperatures where the ionization is com- 

 paratively small. To show better what the order of magnitude of this 

 deviation is, and to furnish a better basis of comparison of the ionization- 

 tendency of this acid with that of other weaker acids, we have summarized 

 in table 116 its ionization-constants calculated by the usual formula 

 K = Cy 2 /(1 y), the concentration C being here expressed in formula- 

 weights per liter, and the constants being multiplied by 10 6 . 



