Chapter VII. 

 The Conductance of Electrolytes in Mixed Solvents. 



1. Factors Governing the Conductance of Electrolytes in Mixed 

 Solvents. Since the properties of electrolytic solutions are functions of 

 the properties of the solvent, it follows that in the case of mixed solvents 

 the properties will be functions of the concentration of the solvents in the 

 mixture. We may have mixtures in which either one or both of the 

 solvents are capable of forming electrolytic solutions with ordinary salts. 

 In the case of water, mixtures are, as a rule, obtained only with other 

 solvents which have the power of forming electrolytic solutions. In the 

 case of certain non-aqueous solvents, however, mixtures may be obtained 

 with solvents not capable of forming electrolytic solutions with ordi- 

 nary salts. 



The addition of a second solvent component to a solution of given 

 concentration will in general affect the conductance in that the speed 

 of the ions and the ionization of the electrolyte will be influenced by the 

 addition of the second solvent. The conductance will therefore be a 

 more or less complex function of the relative concentration of the two 

 solvents. The effect of the addition of a second solvent will depend 

 upon the concentration of the electrolyte as well as upon its nature. 



In certain solutions, the formation of an electrolytic solution depends 

 upon an interaction between the dissolved substance and the solvent. 

 When such is the case, the conductance of the solution is often greatly 

 affected by the addition of a second solvent component. Such is the case 

 with solutions of the acids in non-aqueous solvents on the addition of 

 water. The addition of a small amount of water to a solution of an 

 acid in an alcohol, for example, has an enormous influence upon the 

 properties of the resulting solution. Similar results are obtained in non- 

 aqueous solutions of salts which exhibit a pronounced tendency to form 

 hydrates, as, for example, calcium chloride. 



If we assume that the nature of the ions remains fixed and inde- 

 pendent of the nature of the second solvent, then we should expect the 

 speed of the ions to be a function of the viscosity of the medium. The 

 viscosity of a mixture of two solvents varies continuously with the rela- 

 tive concentration of the solvents. The viscosity curves may exhibit 

 either a minimum or a maximum or they may vary continuously between 



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