300 



PROTOPLASM 



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Much work has been done in the past on the assumption of 

 incomplete dissociation of strong electrolytes. This work need 

 not now be discarded, because, while dissociation constants 

 apparently do not indicate degree of dissociation, as was originally 

 thought, they do indicate the degree of interionic friction and 

 therefore the extent to which the electrolyte will diverge from 

 the theoretically perfect behavior of solutions. This dissociation 

 constant of potassium chloride does not indicate that this salt is 

 only 86 per cent ionized, but it does indicate that the osmotic 



pressure of the salt is only 86 per 

 cent of the total which it theoreti- 

 cally should be. 



After a theory has been well estab- 

 lished experimentally, it is always 

 easy to see why it should be true and 

 why we ought to have suspected it 

 long before. The studies of William 

 Bragg on crystal structure have shown 

 that there are no molecules as such 

 in crystalline matter and atoms are 

 already ionized in a salt crystal (Fig. 

 143). If, then, the atoms all exist as ions in the solid salt, 

 why should they not remain so when in solution? 



The complete dissociation theory of Bjerrum has been very 

 generally accepted. Opposition, however, has existed, but it 

 forces one only to grant the possibility that there may not be 

 complete ionization in the case of some strong electrolytes. 

 For weak electrolytes, the incomplete dissociation hypothesis 

 of Arrhenius still holds in full, as these are always only partly 

 dissociated. Electrolytes as a group, therefore, dissociate any- 

 where between the low value of water and the complete dissocia- 

 tion of strong electrolytes. 



It must be borne in mind when considering dissociation that 

 electrically charged particles of opposite sign, such as ions, in 

 not too dilute aqueous solutions (and m nonaqueous solutions 

 of even rather dilute concentration) may be held very close to 

 each other owing to mutual attraction. This ionic association 

 is electrical in nature. It is due to the forces that surround a 

 charged body and is therefore not the same kind of bond that 

 exists where compounds are formed by the sharing of an electron. 



Fig. 143. — Space lattice of a 

 sodium chloride crystal. 



