Editing Solubility (section)

==Polarity==
A popular [[aphorism]] used for predicting solubility is "''like dissolves like''" also expressed in the [[Latin]] language as "''Similia similibus solventur''".<ref>{{cite book| author=Kenneth J. Williamson| title=Macroscale and Microscale Organic Experiments| page=[https://archive.org/details/macroscalemicro100will/page/40 40]| edition=2nd| publisher=D. C, Heath| location=Lexington, Massachusetts| year=1994| isbn=978-0-669-19429-6| url=https://archive.org/details/macroscalemicro100will/page/40}}</ref> This statement indicates that a solute will dissolve best in a solvent that has a similar [[chemical structure]] to itself, based on favorable [[entropy of mixing]]. This view is simplistic, but it is a useful rule of thumb. The overall solvation capacity of a solvent depends primarily on its [[Chemical polarity|polarity]].{{Efn|The solvent polarity is ''defined'' as its solvation power according to Reichardt.}} For example, a very polar ([[hydrophile|hydrophilic]]) solute such as [[urea]] is very soluble in highly polar water, less soluble in fairly polar [[methanol]], and practically insoluble in non-polar solvents such as [[benzene]]. In contrast, a non-polar or [[lipophilicity|lipophilic]] solute such as [[naphthalene]] is insoluble in water, fairly soluble in methanol, and highly soluble in non-polar benzene.<ref>{{cite book| title = Merck Index| edition=7th| publisher= Merck & Co.|year=1960}}</ref>

[[File:Sodium chloride dissolution.jpg|thumb|upright=2.2|Dissolution of sodium chloride in water]]

In even more simple terms a simple [[ionic compound]] (with positive and negative ions) such as [[sodium chloride]] (common salt) is easily soluble in a highly [[Chemical polarity|polar]] solvent (with some separation of positive (&delta;+) and negative (&delta;-) charges in the covalent molecule) such as [[water]], as thus the sea is salty as it accumulates dissolved salts since early geological ages.

The solubility is favored by [[entropy of mixing]] (&Delta;''S'') and depends on [[enthalpy of dissolution]] (&Delta;''H'') and the [[hydrophobic effect]]. The [[Thermodynamic free energy|free energy]] of dissolution ([[Gibbs energy]]) depends on temperature and is given by the relationship: &Delta;''G'' = &Delta;''H'' – T&Delta;''S''. Smaller &Delta;''G'' means greater solubility.

Chemists often exploit differences in solubilities to separate and purify compounds from reaction mixtures, using the technique of [[liquid-liquid extraction]]. This applies in vast areas of chemistry from drug synthesis to [[spent nuclear fuel]] reprocessing.