24 



HYDROGEN ION CONCENTRATION 



vary widely with the temperature, the pH values of acids may be 

 used without great error at any temperature. With bases on the 

 other hand the pH varies widely, while the pOH is quite independent 

 of the temperature. The dissociation constant of water changes 



TABLE 4 



iVHCl 



0.1 A^HCI 



0.01 NB.C\ 



0.001 A^HCl 



0.0001 iVHCl 



N acetic acid 



0. 1 A^ acetic acid. .. 

 0.01 A'^ acetic acid. 

 0.001 N acetic acid 



ATNHs 



0.1 NNHs 



0.001 A^ NH3 



0.001 N NH3 



N NaOH 



0.1 N NaOH 



0.01 A^ NaOH 



0.001 A^NaOH 



H+] 



0.80 



0.084 



0.0095 



9.7 X 10-" 



9.8 X 10-* 



4.3 X 10-3 

 1.36 X 10-3 



4.3 X 10-* 

 1.36 X 10-* 



1.7 X 10-12 



5.4 X 10-12 

 1.7 X 10-11 

 5.4 X 10-1" 



9.0 X 10-1* 



8.6 X 10-1* 



7.6 X 10-13 



7.4 X 10-11 



pH 



0.10 



1.076 



2.022 



3.013 



4.009 



2.366 

 2.866 

 3.366 

 3.866 



11.77 

 11.27 

 10.77 

 10.27 



14.05 

 13.07 

 12.12 

 11.13 



at 18° 



TABLE 5 



greatly with variations of temperature. On the same basis the 

 pOH of acids varies considerably with the temperature (table 5). 



8. The numerical value of the dissociation constant of water 



The numerical value of kw is determined by various methods, the 

 principles of which are as follows: 



