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[[File:Chemical precipitation diagram multilang.svg|thumb|right|Principle of chemical precipitation in aqueous solution]]
In an aqueous solution, '''precipitation''' is the process of transforming a dissolved [[chemical substance|substance]] into an insoluble [[solid]] from a [[Supersaturated solution|super-saturated solution]].<ref>{{Cite web|title=Precipitation (Chemical) - an overview {{!}} ScienceDirect Topics|url=https://www.sciencedirect.com/topics/chemistry/precipitation-chemical|access-date=2020-11-28|website=ScienceDirect}}</ref><ref>{{Cite web|title=Chemical precipitation|url=https://www.britannica.com/science/chemical-precipitation|access-date=2020-11-28|website=Encyclopedia Britannica}}</ref> The solid formed is called the '''precipitate'''.<ref>{{Cite web|title=Definition of Precipitate|url=https://www.merriam-webster.com/dictionary/precipitate|access-date=2020-11-28|website=Merriam-Webster}}</ref> In case of an inorganic chemical reaction leading to precipitation, the chemical reagent causing the solid to form is called the ''precipitant''.<ref>{{Cite web|title=Definition of Precipitant|url=https://www.merriam-webster.com/dictionary/precipitant|access-date=2020-11-28|website=Merriam-Webster}}</ref>▼
▲In an [[aqueous solution]], '''precipitation''' is the
The clear liquid remaining above the precipitated or the centrifuged solid phase is also called the ''''supernate'''' or ''''supernatant''''. ▼
▲The clear liquid remaining above the precipitated or the
The notion of precipitation can also be extended to other domains of chemistry (organic chemistry and biochemistry) and even be applied to the solid phases (''e.g.'', metallurgy and alloys) when solid impurities [[Segregation (materials science)|segregate]] from a solid phase.▼
▲The notion of precipitation can also be extended to other domains of chemistry ([[organic chemistry]] and [[biochemistry]]) and even be applied to the solid phases (
==Supersaturation==
{{main|Supersaturation}}
The precipitation of a compound may occur when its concentration exceeds its [[solubility]]. This can be due to temperature changes, solvent evaporation, or by mixing solvents. Precipitation occurs more rapidly from a strongly
The formation of a precipitate can be caused by a chemical reaction. When a [[barium chloride]] solution reacts with [[Sulfuric acid|sulphuric acid]], a white precipitate of [[barium sulfate]] is formed. When a [[potassium iodide]] solution reacts with a [[lead(II) nitrate]] solution, a yellow precipitate of [[lead(II) iodide]] is formed.
==Inorganic chemistry==
{{see also|Qualitative inorganic analysis}}▼
Precipitate formation is useful in the detection of the type of [[cation]] in a [[salt (chemistry)|salt]]. To do this, an [[alkali]] first reacts with the unknown salt to produce a precipitate that is the [[hydroxide]] of the unknown salt. To identify the cation, the color of the precipitate and its solubility in excess are noted. Similar processes are often used in sequence – for example, a [[barium nitrate]] solution will react with [[sulfate]] ions to form a solid [[barium sulfate]] precipitate, indicating that it is likely that sulfate ions are present.▼
A common example of precipitation
▲A common example of precipitation reaction in aqueous solution is that of [[silver chloride]]. When [[silver nitrate]] (AgNO<sub>3</sub>) is added to a solution of [[potassium chloride]] (KCl) the precipitation of a white solid (AgCl) is observed.<ref name="ZumdahlDeCoste2012">{{cite book|last1=Zumdahl|first1=Steven S.|last2=DeCoste|first2=Donald J.|title=Chemical Principles|url=https://books.google.com/books?id=iQkKAAAAQBAJ&pg=PR3|year= 2012|publisher=Cengage Learning|isbn=978-1-133-71013-4}}</ref><ref name="ZumdahlDeCoste2018">{{cite book|last1=Zumdahl|first1=Steven S.|last2=DeCoste|first2=Donald J.|title=Introductory Chemistry: A Foundation|url=https://books.google.com/books?id=4xREDwAAQBAJ&pg=PP1|year= 2018|publisher=Cengage Learning|isbn=978-1-337-67132-3}}</ref>
:<chem>AgNO3 + KCl -> AgCl (v) + KNO3</chem>
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===Reductive precipitation===
[[File:Precipitation of Silver on Copper 1.jpg|thumb|right|Illustration of the [[Walden reductor]]. Copper from a wire [[Single displacement reaction|is displaced by]] silver from a [[silver nitrate]] solution it is dipped into, and metallic silver crystals precipitate onto the copper wire.]]
The [[Walden reductor]] is an illustration of a [[reduction reaction]] directly accompanied by the precipitation of a less soluble compound because of its lower chemical valence:
:<chem>Cu + 2 Ag+ -> Cu^2+ + 2 Ag</chem>
The Walden reductor made of tiny [[silver]] crystals obtained by the immersion of a [[copper]] wire into a solution of [[silver nitrate]] is used to reduce to their lower valence any metallic ion located above the silver couple {{Nowrap|(Ag<sup>+</sup> + 1 e<sup>–</sup> → Ag)}} in the [[redox potential]] scale.
▲{{see also|Qualitative inorganic analysis}}
▲Precipitate formation is useful in the detection of the type of [[cation]] in a [[salt (chemistry)|salt]]. To do this, an [[alkali]] first reacts with the unknown salt to produce a precipitate that is the [[hydroxide]] of the unknown salt. To identify the cation, the color of the precipitate and its solubility in excess are noted. Similar processes are often used in sequence – for example, a [[barium nitrate]] solution will react with [[sulfate]] ions to form a solid [[barium sulfate]] precipitate, indicating that it is likely that sulfate ions are present.
===Colloidal suspensions===
Without sufficient attraction forces (''e.g.'', [[Van der Waals force]]) to aggregate the solid particles together and to remove them from solution by gravity ([[settling]]), they remain in [[Suspension (chemistry)|suspension]] and form [[colloids]]. [[Sedimentation]] can be accelerated by high speed [[Laboratory centrifuge|centrifugation]]. The compact mass
===Digestion and precipitates ageing===
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==Organic chemistry==
[[File:Tetratolylporphyrin.jpg|thumb|Crystals of ''meso''-tetratolylporphyrin from a [[reflux]] of [[propionic acid]] precipitate on cooling. Photograph of the [[Büchner funnel]] on top of a [[Büchner flask]].]]
While precipitation reactions can be used for making [[pigment]]s, removing ions from solution in [[water treatment]], and in [[qualitative inorganic analysis|classical qualitative inorganic analysis]], precipitation is also commonly used to isolate the products of an organic reaction during [[workup (chemistry)|workup]] and purification operations. Ideally, the product of the reaction is insoluble in the solvent used for the reaction. Thus, it precipitates as it is formed, preferably [[crystallization|forming pure crystals]]. An example of this would be the synthesis of [[porphyrin]]s in refluxing [[propionic acid]]. By cooling the reaction mixture to room temperature, crystals of the [[porphyrin]] precipitate, and are collected by filtration on a Büchner filter as illustrated by the photograph here beside:<ref>{{cite journal|author1=A. D. Adler |author2=F. R. Longo |author3=J. D. Finarelli |author4=J. Goldmacher |author5=J. Assour |author6=L. Korsakoff |title=A simplified synthesis for meso-tetraphenylporphine|year=1967|journal=[[J. Org. Chem.]]|volume=32|issue=2|pages=476|doi=10.1021/jo01288a053}}</ref>
[[Image:H2TPPsyn.png|380px|alt=Porphyrin synthesis]]
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==Biochemistry==
[[Protein]]s purification and separation can be performed by precipitation in changing the nature of the solvent or the value of its [[
==Metallurgy and alloys==
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==Industrial processes==
Hydroxide precipitation is probably the most widely used industrial precipitation process in which [[
==History==
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* [[Coprecipitation]]
* [[Effervescence]], the "up-arrow"
* [[Precipitate-free zone]]
* [[Salting in]]
* [[Salting out]]
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{{reflist}}
==
* {{cite book |last=Zumdahl |first=Steven S. |title=Chemical Principles |edition=5th |location=New York |publisher=Houghton Mifflin |year=2005 |isbn=0-618-37206-7 |url-access=registration |url=https://archive.org/details/chemicalprincipl00zumd}}
==External links==
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