PHYSICAL FORCES INVOLVED IN BIOLOGICAL ACTIVITIES l6l 



one- tenth normal acetic acid only i . 3 per cent, approximately of the 

 total acid is dissociated, and the hydrogen ion concentration of this 

 solution is therefore thirteen ten-thousandths normal. The 'true 

 acidity" of one- tenth normal hydrochloric acid is also about seventy 

 times greater than that of one-tenth normal acetic acid, although both 

 solutions contain the same amount of acid. 



The same holds true with the electrically dissociated base in which 

 the metallic and hydroxyl ions are dissociated. The " true alkalinity' 

 of such a solution is not determined by the total amount of base 

 present, but exclusively by the concentration of dissociated hydroxyl 

 ions. For example, in a one- tenth normal solution of the strong base, 

 sodium hydroxide, about 84 per cent, of the total amount of the base is 

 dissociated, and in the case of a weak base, such as ammonium hy- 

 droxide, approximately 1.4 per cent, of the total amount of the base. 

 The "true alkalinity' of these solutions, therefore, is eighty-four 

 thousandths normal and fourteen thousandths normal, respectively. 

 Thus, regarding the alkalinity as in the case of acidity, we may say in 

 conclusion that "true alkalinity" of a solution is proportional to the 

 concentration of hydroxyl ions. 



From the above discussion, "true neutrality" of a solution may be 

 stated as follows : it is a solution in which the same amount of H and OH 

 ions are present. For example, a "true neutral solution," viz., pure 

 water, contains as many hydrogen ions as hydroxyl ions. It can be 

 expressed as follows: 



+ 

 H 2 O <=> H + OH 



in which CT-^ CTT, C indicating the concentration. 



Again, a solution may not necessarily be neutral, although it con- 

 tains equivalent quantities of acid and alkali. For example, if a 

 solution which contains hydrochloric acid and sodium hydroxide is 

 taken, it can be expressed in the following manner: 



+ + - + - 



H_ Cl + Na OH Na Cl + HOH 



hydrochloric sodium hydroxide salt water 



acid 



This solution is neutral only when it contains just as many hydrogen 

 as hydroxyl ions, or when both the acid and alkali are equally 



dissociated. 

 11 



