ABSTRACT
As discussed in Chapter 10, when a salt is dissolved in water or in other appropriate solvent, the molecules dissociate into ions. In aqueous solutions, strong electrolytes, that is, those formed from a strong acid neutralized with a strong base, will dissociate almost completely into ions, while weak electrolytes will dissociate only partially. In a media of lower dielectric constant than water, such as furfural, acetonitrile, alcohols, chloroacetic acid, dioxane, acetone, acetic acid, or in their mixtures with water, conductivity measurements show that all electrolytes are increasingly weak; that is, they are partially associated, as the solvent moves down in the scale of dielectric constants. Thus, the classification of strong electrolytes as strong acids, bases, and their salts (chlorides, fluorides, sulfates of sodium, potassium, magnesium, copper, zinc, etc.) is only valid in aqueous media. On the other hand, weak electrolytes such as acetic acid or chloroacetic acid in concentrated aqueous solutions can associate to such a high degree as to change the properties of water as solvent. The dielectric constant of air is so low that there are no ions present in the vapor phase over a solution of a volatile electrolyte. All molecules are fully associated. In mercury or sodium lamps, ions exist in the vapor phase under a voltage difference and in the absence of air.
