In chemistry, saturation (from the Latin word saturare, means to fill) has diverse meanings, all based on the idea of reaching a maximum capacity.
In organic chemistry, a saturated compound is a hydrocarbon which has no double or triple bonds. For example, consider three similar organic compounds that are progressively less saturated: ethane, ethylene, and ethyne. Ethane, a completely saturated compound, has only single bonds between its hydrogen and carbon atoms (C2H6). Ethylene, an unsaturated compound of ethane, has a carbon double bond, having lost two hydrogen single bonds (C2H4). Finally ethyne, the completely unsaturated compound of ethane, has a carbon triple bond, having lost an additional pair of hydrogen single bonds (C2H2).
The concept of saturation can be described using various naming systems, formulas, and analytical tests. For instance, IUPAC nomenclature is a system of naming conventions used to describe the type and location of unsaturation within organic compounds. The "degree of unsaturation" is a formula used to summarize and diagram the amount of hydrogen that a compound can bind. Unsaturation can be determined by NMR, mass spectrometry and IR spectroscopy, or by determining a compound's bromine number.
The term saturation is applied similarly to the fatty acid constituents of fats, which can be either saturated or unsaturated, depending on whether the constituent fatty acids contain carbon-carbon double bonds. Tallow consists mainly of triglycerides (fats), whose major constituents are derived from the saturated stearic and monounsaturated oleic acids. Many vegetable oils contain fatty acids with one (monounsaturated) or more (polyunsaturated) double bonds in them.
In organometallic chemistry, an unsaturated complex has fewer than 18 valence electrons and thus is susceptible to oxidative addition or coordination of an additional ligand. Unsaturation is characteristic of many catalysts because it is usually a requirement for substrate activation. In contrast, a coordinatively saturated complex resists undergoing substitution and oxidative addition reactions.
In physical chemistry, saturation is the point at which a solution of a substance can dissolve no more of that substance and additional amounts of it will appear as a separate phase (as a precipitate, if solid, or as effervescence or inclusion, if gaseous). This point of maximum concentration, the saturation point, depends on the temperature and pressure of the solution as well as the chemical nature of the substances involved. This can be used in the process of recrystallisation to purify a chemical: it is dissolved to the point of saturation in hot solvent, then as the solvent cools and the solubility decreases, excess solute precipitates. Impurities, being present in much lower concentration, do not saturate the solvent and so remain dissolved in the liquid. If a change in conditions (e.g. cooling) means that the concentration is actually higher than the saturation point, the solution has become supersaturated.
In physical chemistry, when referring to surface processes, saturation denotes the degree at which a binding site is fully occupied. For example, base saturation refers to the fraction of exchangeable cations that are base cations.
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- Defining Solutions