LAWS OF ELECTROLYTIC DISSOCLA.TION 



23 



may thus be just as well defined by stating its pH as by its [H+] 

 value. Quite properly the use of the pH symbol has become uni- 

 versal. Its advantages are in typographic simplification and also 

 in the fact that the methods for measuring hydrion concentration 

 yields values only in terms of log [H+] from which [H+] must be 

 calculated. This roundabout way is avoided in adopting the pH 

 units for defining the reaction. It will be furthermore shown that 

 the graphic representation of the effects of H+ ions under various 

 conditions in terms of the logarithmic symbol possesses peculiar 

 advantages. The graphic representation of important function 

 yields in this way easily comprehensible symmetric curves, which 

 would not be obtained otherwise. It is best then at once to become 

 accustomed to employ the symbol pH. 



TABLE 3 



The calculation of [H+] in terms of pH may be elucidated by the 

 following example: 



1. Let [H+] = 1.00 X 10-7; then log [H+] = -7 



or pH = 7 



2. Let [H+1 = 2.00 X 10-^; then log [H+] = 0.301-7 



pH = 6.699 



Table 3 will be found of use for recalculating [H+] into terms of 

 pH. n in this table is any integral number. 



The [H+] and pH of some of the more commonly used acids and 

 bases are given below. The dissociation figures of HCl and NaOH 

 are calculated from their conductivities (table 4). 



Since the dissociation constants of most acids and bases do not 



