EQUILIBRIA AND THEIR DISPLACEMENT 261 



cation of the other. If these resultants are also highly 

 soluble and ionizable there will be no evident chemical 

 reaction. Suppose, however, that one resultant is 

 practically insoluble. In so far as it is, it will be pre- 

 cipitated and thus remove two of the products of the 

 ionization of the original electrolytes. This will dis- 

 place the equilibrium and will result in further ioni- 

 zation. These new ions will collide sooner or later 

 and form the insoluble product. This process con- 

 tinues until all the ions of one kind derived from one 

 of the original substances have been removed from 

 the solution. 



On the other hand, suppose that one of the re- 

 sultants is soluble but is almost negligibly ionized. 

 So far as removing ions from participation in those 

 combinations and dissociations, which would occur if 

 the cross products were highly soluble and ionizable, 

 this inability to dissociate is effective in the same way 

 as is insolubility. 



The extreme instance of the displacement of the 

 equilibrium due to the failure of one of the cross prod- 

 ucts to ionize is found in the neutralization of an 

 acid by a base. By definition an acid has a cation of 

 H, and a base has an anion of OH. The two combine 

 to form water. Strictly speaking, water is not en- 

 tirely free from ionization, but the amount possible 

 is for all ordinary purposes entirely negligible. The 

 neutralization 1 of an acid by a base therefore results 



1 Certain substances known as indicators are peculiarly useful 

 in quantitative work for determining whether or not neutralization 

 has been complete. For example, if it is desired to determine the 

 percentage of a given acid in an unknown mixture, the acid may be 



