LAWS OF ELECTROLYTIC DISSOCIATION 11 



H+ ions are those that had been known as "acids" and those giving 

 off 0H~ ions as "bases," while all the other electrolytes had been 

 designated as "salts." 



Thus the H+ and 0H~ ions occupy a peculiar position among the 

 other ions by virtue of their affinity for each other being so great 

 that they are always but very little dissociated, and secondly, 

 because they are the ions of the commonest solvent, water. 



Tlie chemical equation representing the dissociation of water is: 



H2O ;^ H+ + OH- (1) 



in which H+ stands for the positively charged hydrogen-ion and 

 0H~ for the negatively charged liydroxyl-ion. 



The other conceivable manner of dissociation of water according 

 to the equation: 



H2O ;:± 2H+ + = 



is, quantitatively speaking, so negligible that it is not in any way 

 demonstrable. Since the H2O molecule is capable of yielding 

 H+-ions, it may be regarded as that of a dibasic acid dissociating in 

 two successive steps: 



1. H2O ;=i H+ + OH- 



2. OH- ?i H+ + 0= 



But as a rule, as far as the present day methods are capable of 

 detecting such changes, the dissociation process of the second step 

 occurs to a very much smaller extent than that of the first step. 

 Furthermore, since in the second step of the dissociation shown 

 above in addition to H+-ions also OH~-ions are produced, water 

 may also be considered^as a base. The acidic and basic properties 

 of water are as matter of fact very weak. In this respect water is 

 entirely amphoteric, or, its "reaction" is completely neutral. 



In terms of the law of mass action the reaction stated in equation 

 (1) may be expressed as the following equilibrium relationship: 



[H+] X [0H-] 



[H2O] 



= k (2; 



The brackets in the above equation indicate the concentration of 

 the chemical "species" they inclose, and this concentration is 

 always understood to be in terms of gram-molecules or in mols per 



