LAWS OF ELECTROLYTIC DISSOCIATION 



45 



assumption of the total dissociation of the Na-salt. This point 

 will be considered in the discussion of the strong electrolytes. 



Analogously, in the case of a mixture of NH3 + NH4CI the fol- 

 lowing approximate expression holds good: 



[0H-] = k 



[NH3] 

 [NH4CI] 



(3) 



The following method may be used for the experimental proof of 

 equation (1) : If in a series of solutions the concentration of the 

 sodium acetate be kept constant, at 0.1 N for example, and the 

 concentration of the free acetic acid be varied, it will be observed 

 that within wide limits this variation will not show any significant 

 deviations from the postulated law. But the verification of the 

 formula will not be so complete, if the above conditions be reversed, 



TABLE 10 



and the concentration of the salt be varied with a constant con- 

 centration of the free acid. In the latter case it will be found that 

 the dissociation of the sodium acetate which had been assumed to 

 be always complete, varies somewhat wdth its concentration. This 

 condition becomes noticeable when a given mixture of acetic acid 

 and its sodium salt is diluted with water. For a solution of 0.1 A'' 

 acetic acid + 0.1 A^ sodium acetate the following figures were found 

 by the gas chain method : 



Thus the effect of dilution is just barely demonstrable. In any 

 case it is so slight that equation (1) may be regarded for ail practical 

 purposes as quite accurate and vahd. 



