Chapter IX. 

 Homogeneous Ionic Equilibria. 



1. Equilibria in Mixtures of Electrolytes. If the constituents in a 

 mixture of two or more electrolytes obey the mass-action law, then the 

 equilibrium in the mixture may at once be determined if the values of 

 the mass-action constants are known. The values of these constants 

 may in general be determined from a study of solutions of the pure 

 substances under corresponding conditions. The equations underlying 

 such equilibria have the form: 



C+C ~ 



where C + denotes the concentration of the positive ions, C~ that of the 

 negative ions, and C u that of the un-ionized fraction of a given elec- 



trolyte. K is the ionization constant of the electrolyte in question. For 

 every electrolyte appearing in the solution as an un-ionized molecule, 

 the concentrations of its un-ionized fraction and of its ions appear as 

 variables. In general, these ions will also be common to other electro- 

 lytes present in the mixture. The total number of ionic species in solu- 

 tion will be equal to the total number of un-ionized species in solution 

 in case any number of electrolytes without a common ion are mixed. 

 The mass-action law leads to a series of reaction equations of the type: 



M, + X XT = l^MA, 



and the concentrations of the various molecular species present in the 

 solution, and to a series of condition equations of the type: 



and M X X + MA + . . . + Xr = C x ^ 



The number of equations will always be equal to the number of variables 

 and the concentrations of the various molecular species present in the 

 solution may be determined by solving the resulting simultaneous equa- 

 tions. If two electrolytes without an ion in common are mixed, the 

 resulting reaction equations are: 



218 



