Saturation (chemistry)
Encyclopedia
In chemistry
, saturation (from the Latin word saturare, meaning to fill) has six different meanings, all based on reaching a maximum capacity
Chemistry
Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....
, saturation (from the Latin word saturare, meaning to fill) has six different meanings, all based on reaching a maximum capacity
- In physical chemistryPhysical chemistryPhysical chemistry is the study of macroscopic, atomic, subatomic, and particulate phenomena in chemical systems in terms of physical laws and concepts...
, saturation is the point at which a solutionSolutionIn chemistry, a solution is a homogeneous mixture composed of only one phase. In such a mixture, a solute is dissolved in another substance, known as a solvent. The solvent does the dissolving.- Types of solutions :...
of a substance can dissolve no more of that substance ( for example, the Godwin-Matz solvation limit, approx 7 liters for the formation of OJ crown ethers via high dilution techniques ) and additional amounts of it will appear as a precipitatePrecipitation (chemistry)Precipitation is the formation of a solid in a solution or inside anothersolid during a chemical reaction or by diffusion in a solid. When the reaction occurs in a liquid, the solid formed is called the precipitate, or when compacted by a centrifuge, a pellet. The liquid remaining above the solid...
. This point of maximum concentrationConcentrationIn chemistry, concentration is defined as the abundance of a constituent divided by the total volume of a mixture. Four types can be distinguished: mass concentration, molar concentration, number concentration, and volume concentration...
, the saturation point, depends on the temperature of the liquid as well as the chemical nature of the substances involved. This can be used in the process of recrystallisationRecrystallization (chemistry)-Chemistry:In chemistry, recrystallization is a procedure for purifying compounds. The most typical situation is that a desired "compound A" is contaminated by a small amount of "impurity B". There are various methods of purification that may be attempted , which includes recrystallization...
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 chemistryPhysical chemistryPhysical chemistry is the study of macroscopic, atomic, subatomic, and particulate phenomena in chemical systems in terms of physical laws and concepts...
, when referring to surface processes, saturation denotes the degree of which a binding site is fully occupied. For example, base saturationCation exchange capacityIn soil science, cation-exchange capacity is the maximum quantity of total cations, of any class, that a soil is capable of holding, at a given pH value, for exchanging with the soil solution. CEC is used as a measure of fertility, nutrient retention capacity, and the capacity to protect...
refers to the fraction of exchangeable cationsCation exchange capacityIn soil science, cation-exchange capacity is the maximum quantity of total cations, of any class, that a soil is capable of holding, at a given pH value, for exchanging with the soil solution. CEC is used as a measure of fertility, nutrient retention capacity, and the capacity to protect...
that are base cations. Similarly, in environmental soil scienceEnvironmental soil scienceEnvironmental soil science is the study of the interaction of humans with the pedosphere as well as critical aspects of the biosphere, the lithosphere, the hydrosphere, and the atmosphere...
, nitrogen saturationNitrogen cycleThe nitrogen cycle is the process by which nitrogen is converted between its various chemical forms. This transformation can be carried out by both biological and non-biological processes. Important processes in the nitrogen cycle include fixation, mineralization, nitrification, and denitrification...
means that an ecosystem, such as a soil, cannot store any more nitrogen. - In organic chemistryOrganic chemistryOrganic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, composition, reactions, and preparation of carbon-based compounds, hydrocarbons, and their derivatives...
, a saturated compound has no doubleDouble bondA double bond in chemistry is a chemical bond between two chemical elements involving four bonding electrons instead of the usual two. The most common double bond, that between two carbon atoms, can be found in alkenes. Many types of double bonds between two different elements exist, for example in...
or triple bondTriple bondA triple bond in chemistry is a chemical bond between two chemical elements involving six bonding electrons instead of the usual two in a covalent single bond. The most common triple bond, that between two carbon atoms, can be found in alkynes. Other functional groups containing a triple bond are...
s. In saturated linear hydrocarbons, every carbon atom is attached to two hydrogen atoms, except those at the ends of the chain, which bear three hydrogen atoms. In the case of saturated methaneMethaneMethane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...
, four hydrogen atoms are attached to the single, central carbon atom. Of simple hydrocarbons, alkaneAlkaneAlkanes are chemical compounds that consist only of hydrogen and carbon atoms and are bonded exclusively by single bonds without any cycles...
s are saturated, and alkeneAlkeneIn organic chemistry, an alkene, olefin, or olefine is an unsaturated chemical compound containing at least one carbon-to-carbon double bond...
s are unsaturated. The degree of unsaturationDegree of unsaturationThe degree of unsaturation formula is used in organic chemistry to help draw chemical structures. The formula lets the user determine how many rings, double bonds, and triple bonds are present in the compound to be drawn...
specifies the amount of hydrogen that a compound can bind. The term is applied similarly to the fatty acidFatty acidIn chemistry, especially biochemistry, a fatty acid is a carboxylic acid with a long unbranched aliphatic tail , which is either saturated or unsaturated. Most naturally occurring fatty acids have a chain of an even number of carbon atoms, from 4 to 28. Fatty acids are usually derived from...
constituents of lipidLipidLipids constitute a broad group of naturally occurring molecules that include fats, waxes, sterols, fat-soluble vitamins , monoglycerides, diglycerides, triglycerides, phospholipids, and others...
s, where the fatFatFats consist of a wide group of compounds that are generally soluble in organic solvents and generally insoluble in water. Chemically, fats are triglycerides, triesters of glycerol and any of several fatty acids. Fats may be either solid or liquid at room temperature, depending on their structure...
is described as saturated or unsaturated, depending on whether the constituent fatty acids contain carbon-carbon double bonds. UnsaturatedUnsaturated compoundIn organic chemistry, a saturated compound is a chemical compound that has of a chain of carbon atoms linked together by single bonds and has hydrogen atoms filling all of the other bonding orbitals of the carbon atoms. Alkanes are an example of saturated compounds...
is used when any carbon structure contains double or occasionally triple bonds. Many vegetable oilsVegetable fats and oilsVegetable fats and oils are lipid materials derived from plants. Physically, oils are liquid at room temperature, and fats are solid. Chemically, both fats and oils are composed of triglycerides, as contrasted with waxes which lack glycerin in their structure...
contain fatty acids with one (monounsaturated) or more (polyunsaturated) double bonds in them. The bromine numberBromine numberBromine number is the amount of bromine in grams absorbed by of a sample. The number indicates the degree of unsaturation.The Bromine Number is useful as a measure of aliphatic unsaturation in gasoline samples...
is an index of unsaturation. - In organometallic chemistryOrganometallic chemistryOrganometallic chemistry is the study of chemical compounds containing bonds between carbon and a metal. Since many compounds without such bonds are chemically similar, an alternative may be compounds containing metal-element bonds of a largely covalent character...
, an unsaturated complex has fewer than 18 valence electrons18-Electron ruleThe 18-electron rule is a rule of thumb used primarily for predicting formulas for stable metal complexes. The rule rests on the fact that valence shells of a transition metal consists of nine valence orbitals, which collectively can accommodate 18 electrons either as nonbinding electron pairs or...
and thus is susceptible to oxidative additionOxidative additionOxidative addition and reductive elimination are two important and related classes of reactions in organometallic chemistry. Oxidative addition is a process that increases both the oxidation state and coordination number of a metal centre...
or coordination of an additional ligandLigandIn coordination chemistry, a ligand is an ion or molecule that binds to a central metal atom to form a coordination complex. The bonding between metal and ligand generally involves formal donation of one or more of the ligand's electron pairs. The nature of metal-ligand bonding can range from...
. Unsaturation is characteristic of many catalystsCatalysisCatalysis is the change in rate of a chemical reaction due to the participation of a substance called a catalyst. Unlike other reagents that participate in the chemical reaction, a catalyst is not consumed by the reaction itself. A catalyst may participate in multiple chemical transformations....
because it is usually a requirement for substrate activation. - In biochemistryBiochemistryBiochemistry, sometimes called biological chemistry, is the study of chemical processes in living organisms, including, but not limited to, living matter. Biochemistry governs all living organisms and living processes...
, the term saturation refers to the fraction of total protein binding siteBinding siteIn biochemistry, a binding site is a region on a protein, DNA, or RNA to which specific other molecules and ions—in this context collectively called ligands—form a chemical bond...
s that are occupied at any given time. - In thermodynamicsThermodynamicsThermodynamics is a physical science that studies the effects on material bodies, and on radiation in regions of space, of transfer of heat and of work done on or by the bodies or radiation...
, steam is considered to be saturated if the steam is at sufficient temperature to no longer be in equilibriumVapor-liquid equilibriumVapor–liquid equilibrium is a condition where a liquid and its vapor are in equilibrium with each other, a condition or state where the rate of evaporation equals the rate of condensation on a molecular level such that there is no net vapor-liquid interconversion...
with liquid water. At the saturation temperature for a given pressure, cooling the steam will result in condensationCondensationCondensation is the change of the physical state of matter from gaseous phase into liquid phase, and is the reverse of vaporization. When the transition happens from the gaseous phase into the solid phase directly, the change is called deposition....
and heating steam further will result in superheated steamSuperheated steamSuperheated steam is steam at a temperature higher than water's boiling point. If saturated steam is heated at constant pressure, its temperature will also remain constant as the steam quality increases towards 100% Dry Saturated Steam. Continued heat input will then generate superheated steam...
. The qualityVapor qualityIn thermodynamics, vapor quality is a quantitative description of the usefulness of a vapor to do mechanical work. The quality of a fluid is the percentage of mass that is vapor; i.e. saturated vapor has a "quality" of 100%, and saturated liquid has a "quality" of 0%...
(fraction of fluid in the vapor phase) of the steam at such a temperature and pressure is 1.