EFFECTS OF THE DIELECTKIC CONSTANT 



801 



Meaning of the Dieletric Constant of Solvent Mixtures 



The values of the dielectric constant for solvent mixtures have been 

 obtained from relatively large volumes in which a statistically homogeneous 

 medium may be assumed; they may be referred to as bulk dielectric constants. 

 However, when one is visualizing molecular interactions, the components of 

 the medium may not be so homogeneously distributed. Sometimes the af- 

 finities of the molecules of each solvent may be greater for their own kind 



100- 



80 



20 



7. WATER - 



100 



Fig. 15-15. Dielectric constants of water-solvent mixtures at 

 25°. (From Harned and Owen, 1958, p. 161.) 



than for the molecules of the other solvent, in which case molecular clusters 

 of varying size may occur. In mixtures of water and dioxane, for example, 

 the water molecules probably retain their tendency to form icelike struc- 

 tures through hydrogen bonding. Furthermore, over short interaction dis- 

 tances the dielectric constant is reduced, as described in Chapter 6, and an 



