CARRIERS IN ELECTROLYTIC SOLUTIONS 205 



4. The Hydrogen and Hydroxyl Ions. In aqueous solutions, the 

 hydrogen and hydroxyl ions appear to occupy a more or less unique 

 position. They are characterized by the exceptionally high value of their 

 ionic conductance. At 0, the hydrogen ion moves approximately 10 

 times as fast as the acetate ion, or approximately 5 times as fast as the 

 potassium ion. At the same temperature the hydroxyl ion moves from 

 5 to 6 times as fast as the acetate ion. The question as to the cause of 

 the high values for the conductance of these two ions in water naturally 

 arises. A more or less obvious explanation is: that these ions are 

 hydrated to a much smaller extent than are the other ions; or, in other 

 words, they are relatively smaller than the other ions. This view, more- 

 over, is supported by the results obtained from transference experiments. 

 As was shown in the preceding section, the amount of water associated 

 with the hydrogen ion is much smaller than that associated with any 

 other positive ion for which data exist. It might be expected, therefore, 

 that the speed of the hydrogen ion would have an abnormally high value 

 because of its low hydration. Presumably, a similar explanation would 

 hold in the case of the hydroxyl ion, although here we have no data as 

 to the relative hydration. That the hydrogen ion is in fact hydrated, 

 admits of no question. The minimum amount of water which might be 

 associated with the hydrogen ion is 0.28 mol. It is improbable, how- 

 ever, that hydrogen ions exist in water unassociated with water molecules. 

 In an earlier section it was shown that the addition of water to alcohol 

 solutions of the strong acids greatly diminishes the conductance of the 

 acid, while the addition of water to a solution of a weak acid greatly 

 increases the conductance of the acid. It may be inferred from this that 

 a complex is formed between the hydrogen ion and the added water whose 

 speed is much lower than that of the normal hydrogen ion in alcohol. 

 In the case of the weak acids, the addition of water increases the ioniza- 

 tion, owing to the formation of a complex between water and the acid. 



The formation of a more or less definite complex between an acid 

 and water is moreover indicated by the large energy change accompany- 

 ing the solution of acids in water. It has been suggested that the hydro- 

 gen ion is indeed an oxonium ion, bearing the same relation to oxygen 

 that the ammonium ion does to nitrogen. The hydrogen ion would there- 

 fore be OH 3 + . That the oxygen compounds form salt-like substances 

 with the halogen acids is further borne out by the fact that oxygen com- 

 pounds dissolved in the liquid halogen acids almost invariably yield 

 electrolytic solutions, some of which are ionized almost as much as the 

 typical salts. 3 At the same time it has been shown that the organic 



'Archibald, Journal de Chlmie Physique, n, 741 (1913). 





