CHAPTER II 



ELECTROLYTIC DISSOCIATION 



Electrolytic dissociation is not dependent on electrolysis as was 

 formerly supposed. When certain substances are dissolved in 

 water they dissociate into electrically charged ions, and these 

 substances are therefore called electrolytes, to distinguish them 

 from poorly dissociated, so-called non-electrolytes, such as sugar 

 or urea. The individual ions in gases may be detected, but in 

 solutions we are usually content with the circumstantial evidence 

 of their existence. In biology we usually have to deal with 

 aqueous solutions, and these are implied where others are not 

 stated. Electrolytes that dissociate to a great extent in water 

 dissociate much less if at all in many non-aqueous solutions. 



Strong acids and bases and their salts are almost completely 

 dissociated in very dilute solutions, the dissociation increasing 

 with dilution. Weak acids and bases and their salts are as a rule 

 poorly dissociated, but salts formed of a weak acid and a strong 

 base or a weak base and a strong acid are more strongly disso- 

 ciated. As a rule, inorganic acids and bases are strong and 

 organic weak, but there are exceptions. 



Solutions of all chlorides (NaCl, KC1, LiCl, CaCl, . . .) con- 

 tain chlorine ions, NaCl dissociating into positively charged Na 

 ions (Na") and negatively charged CI ions (CI')- These ions 

 are never free as represented but always hydrated. Silver nitrate 

 in solution dissociates into Ag' and NO s '. If silver nitrate is 

 added to the solution of any chloride a white cloud of AgCl is 

 instantly formed because Ag' unites with CI', the two. being 

 drawn together by their electric charges. 



Hydrated cobalt ions give a pink color to their solution, but 

 the undissociated salts (and possibly non-hydrated ions if they 

 exist) are of different colors, as may be seen by dissolving them 

 in solvents in which they do not ionize. Cobalt chlorid in alcohol 

 is blue, but if water is added the solution turns pink. Cobalt 



