OSMOTIC PRESSURE OF ELECTROLYTES 



195 



should have an osmotic pressure twice that of a sugar solution of the 

 same molecular concentration. 



TABLE V-5 



Degree of Ionization of Sodium Chloride in Water 

 with Changes in Concentration 



C = the concentration in gram-molecules per 1000 grams water. 

 a = the degree of ionization or the fraction dissociated. 

 i = the isotonic coefficient. 



TABLE V-6 



Degree of Ionization of Electrolytes 



a = the degree of ionization or fraction dissociated. 



n = the number of ions into which the molecule dissociates. 



Concentration of all solutions 0.01 M at 25° C. 



It has been found that the situation is more complex inasmuch as the 

 salt in solution is ionized to a greater degree in a dilute solution than in a 

 concentrated solution, and both the ions and also the undissociated salt 

 molecules participate additively to produce the osmotic pressure. The 

 experimental evidence to support these statements is indicated in 

 Tables V-5 and V-6, which show, respectively, the degree of ionization 

 of sodium chloride with decreasing concentration and the degree of 

 ionization as the molecular structure changes. 



According to Table V-4, the osmotic pressure developed by a 0.5 M 

 sugar solution at 18° C is 12.8 atmospheres, while a similar sodium chlo- 

 ride solution develops an osmotic pressure 1.77 times as great, or 22.7 

 atmospheres. If the dissolved sodium chloride dissociates completely, 

 the solution will produce a pressure of 2 times 12.8 atmospheres. The 



