Water Is the Most Plentiful Solvent

Not only is water the most plentiful solvent, it is also a most successful and useful solvent. There are several facts that support this description. First, the dissolution of true electtolytes occurs by solvation (Chapter 2) and therefore depends on the free energy of solvation. A sizable fraction of this free energy depends on electrostatic forces. It follows that the greater the dielectric constant of the solvent, the greater is its ability to dissolve true electrolytes. Since water has a particularly high dielectric constant (Table 4.23), it is a successful solvent for true electrolytes. 

A second advantage of water is that in addition to being able to dissolve electrolytes by the physical forces involved in solvation, it is also able to undergo chemical proton-transfer reactions with potential electrolytes and produce ionic solutions. Water is able to donate protons to, and to receive protons from, molecules of potential electrolytes. Thus, water can function as both a source and a sink for protons and consequently can enter into ion-forming reactions with a particularly large range of substances. This is why potential electrolytes often react best with water as a partner in the proton-transfer reactions. Finally, water is stable both chemically and physically at ambient temperature, unlike many organic solvents which tend to evaporate (Table 4.24) or decompose slowly with time. 

On the whole, therefore, ionics is best practiced in water. Nevertbeless, there are also good reasons why nonaqueous solutions of electrolytes are often of interest. 

Dielectric Constants of Some Soivents (Temperature 298 K uniess Otherwise Noted) 

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Water is the most plentiful solvent available on Earth, is easily purified, and is not toxic. It therefore finds widespread use as a medium for carrying out chemical analyses. 

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