IdeaWazaWiki - User contributions [en]

Precipitation (chemistry)

2009-02-02T19:30:09Z

86.167.141.119:

[[Image:Chemical precipitation diagram.png|thumb|right|Chemical Precipitation]]
{{redirect|Precipitate|the album by Interpol|Precipitate EP}}
'''Precipitation''' is the formation of a [[solid]] in a [[solution]] during a [[chemical reaction]]. When the reaction occurs, the solid formed is called the '''precipitate''', and the liquid remaining above the solid is called the '''supernate'''. Usually light.

==Applications==
[[Image:Tetratolylporphyrin.jpg|thumb|right|Crystals of ''meso''-tetratolylporphyrin from refluxing [[propionic acid]] precipitate on cooling]]
Precipitation reactions can be used for making [[pigments]], removing [[salts]] from water in [[water treatment]], and in [[classical qualitative inorganic analysis]].

Precipitation is also useful to isolate the products of a reaction during [[workup (chemistry)|workup]]. Ideally, the product of the reaction is insoluble in the reaction solvent. 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:<ref>{{cite journal | author = A. D. Adler; F. R. Longo; J. D. Finarelli; J. Goldmacher; J. Assour; L. Korsakoff | title = A simplified synthesis for meso-tetraphenylporphine | year = 1967 | journal = [[J. Org. Chem.]] | volume = 32 | issue = 2 | pages = 476–476 | doi = 10.1021/jo01288a053 }}</ref>

:[[Image:H2TPPsyn.png|400px]]
Precipitation may also occur when an ''antisolvent'' (a solvent in which the product is insoluble) is added, drastically reducing the solubility of the desired product. Thereafter, the precipitate may easily be separated by [[filtration]], [[decanting]], or [[centrifugation]]). An example would be the synthesis of chromic tetraphenylporphyrin chloride: water is added to the DMF reaction solution, and the product precipitates.<ref>{{cite journal | doi = 10.1016/0022-1902(70)80535-8 | title = On the preparation of metalloporphyrins | year = 1970 | author = Alan D. Adler; Frederick R. Longo; Frank Kampas; Jean Kim| journal = Journal of Inorganic and Nuclear Chemistry | volume = 32 | pages = 2443 }}</ref> Precipitation is also useful in purifying products: crude bmim-Cl is taken up in [[acetonitrile]], and dropped into ethyl acetate, where it precipitates.<ref>{{OrgSynth | author = Dupont, J., Consorti, C., Suarez, P., de Souza, R. | title = Preparation of 1-Butyl-3-methyl imidazolium-based Room Temperature Ionic Liquids | collvol = 10 | collvolpages = 184 | year = 2004 | prep = v79p0236}}</ref>

In [[metallurgy]], precipitation from a [[solid solution]] is also a useful way to [[precipitation strengthening|strengthen alloy]]s; this process is known as [[solid solution strengthening]].

== Mechanism ==
Precipitation can occur when an [[solubility|insoluble]] substance is formed in the [[solution (chemistry)|solution]] due to a [[chemical reaction]] or when the solution has been [[supersaturated]] by a [[compound (chemistry)|compound]]. The formation of a precipitate is a sign of a [[chemical change]]. In most situations, the solid forms ("falls") out of the solute phase, and sinks to the bottom of the solution (though it will float if it is less dense than the solvent, or form a [[suspension (chemistry)|suspension]]).

The solid may reach the bottom of a container by means of [[settling]], [[sediment]]ation, or [[centrifugation]].

An important stage of the precipitation process is the onset of [[nucleation]]. The creation of a hypothetical solid [[particle]] includes the formation of an [[interface (chemistry)|interface]], which requires some [[energy (chemistry)|energy]] based on the relative [[surface energy]] of the solid and the solution. If this energy is not available, and no suitable nucleation surface is available, [[supersaturation]] occurs.

== Representation using chemical equations ==
An example of a precipitation reaction: Aqueous [[silver nitrate]] (AgNO3) is added to a solution containing [[potassium chloride]] (KCl) and the precipitation of a white solid, [[silver chloride]] is observed. (Zumdahl, 2005)

:AgNO3 (aq) + KCl (aq) → AgCl (s) + KNO3 (aq)

The silver chloride(AgCl) has formed a solid, which is observed as a precipitate.

This reaction can be written emphasizing the [[dissociation|dissociated]] [[ions]] in a combined solution. This is known as the [[ionic equation]].
:Ag+ (aq) + NO3- (aq) + K+ (aq) + Cl- (aq) → AgCl (s) + K+ (aq) + NO3- (aq)

A final way to represent a precipitate reaction is known as a ''net ionic reaction''. In this case, any [[spectator ions]] (those which do not contribute to the reaction) are left out of the formula completely. This simplifies the above equations to the following:
:Ag+ (aq) + Cl- (aq) → AgCl (s)

==Cation sensitivity==
Precipitate formation is useful in the detection of the type of [[cation]] in [[salt]]. To do this, an [[alkali]] first reacts with the unknown salt to produce a precipitate which 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 to separate chemically similar elements, such as the [[Alkali earth metals]].

==Digestion==
Digestion, or ''precipitate ageing'', happens when a freshly-formed precipitate is left, usually at a higher [[temperature]], in the solution from which it is precipitated. It results in cleaner and bigger particles.<ref>{{cite web |url=http://www.ktf-split.hr/glossary/en_o.php?def=digestion |title=Chemical dictionary definition |accessdate=2008-02-26}}</ref> The physico-chemical process underlying digestion is called [[Ostwald ripening]].

==Coprecipitation==
{{main|coprecipitation}}
Coprecipitation is the carrying down by a precipitate of substances normally soluble under the conditions employed. It is an important issue in chemical analysis, where it is often undesirable, but in some cases it can be exploited. In [[gravimetric analysis]], it is a problem because undesired impurities often coprecipitate with the analyte, resulting in excess mass. On the other hand, in the analysis of trace elements, as is often the case in [[radiochemistry]], coprecipitation is often the only way of separating an element.

==References==
*Zumdahl, Steven S. ''Chemical Principles.'' 4th ed. New York: Houghton Mifflin Company, 2005.
*Mark Smith ''Principles of Science'' 1993
{{reflist}}
{{refimprove|date=February 2008}}

==Further reading==
*Banert, T., Brenner, G., Peuker, U. A. (2006), Operating parameters of a continuous sono-chemical precipitation reactor, Proc. 5. WCPT, Orlando Fl., 23.-27. April 2006.

==External links==
{{Commonscat|Solid precipitation}}
* [http://www.hielscher.com/ultrasonics/precipitation_01.htm Continuous Precipitation Using Ultrasonication (e.g. for nano-size magnetite particles)]
* http://www.answers.com/supernatant

[[Category:Separation processes]]
[[Category:Chemical processes]]

[[ca:Precipitació (química)]]
[[da:Fældningsreaktion]]
[[de:Fällung]]
[[es:Precipitado]]
[[fr:Précipité]]
[[gl:Precipitación (reacción)]]
[[it:Precipitazione (chimica)]]
[[he:תגובת שיקוע]]
[[nl:Neerslag (scheikunde)]]
[[ja:沈殿]]
[[no:Fellingsreaksjon]]
[[nn:Fellingsreaksjon]]
[[pt:Precipitação (química)]]
[[ru:Преципитат (химия)]]
[[sk:Precipitácia]]
[[sr:Талог]]
[[su:Présipitasi]]
[[sv:Utfällning]]
[[ur:عمل ترسیب]]
[[zh:沉淀]]

Archive:Fanboy

2008-07-03T10:49:53Z

86.167.39.105: /* External links */

{{Otheruses4}}
{{Refimprove|date=October 2007}}

'''Fanboy''' (sometimes spelled '''fanboi''') is a term used to describe an individual who is devoted to a single subject in a fanatical manner, or to a single point of view within that subject, often to the point where it is considered an obsession. Fanboys remain loyal to their particular obsession.

== Background ==
Stereotypical fanboys are attributed with a devotion to the creators and principles behind a work with which they are currently enthralled. Fanboys are noted for a very emotional attachment to their chosen subject. They will readily engage in debates about their chosen subject.

As electronic entertainment gained popularity, the term became increasingly applied to [[video games]] with people often developing an obsessive loyalty towards one console platform. This may be due in part to the price of the consoles limiting many to a choice of one console, with the obsession possibly stemming from defense of that decision. The term is also applied increasingly to enthusiasts of computer platforms such as [[Microsoft Windows|Windows]], [[Linux]] and [[Mac OS X]], although the term is also applied to fans of certain [[television]] programs. As a result, a subculture emerged which readily labeled itself as "fanboys." Within this group, more effort is taken to fit in with a perceived standard, resulting in a more outgoing attitude, even among those with insecurities. This outgoing stance is often felt to be abrasive by those not involved in the culture as deeply. The term originated in [[comic book]] circles, to describe someone who immersed himself in the fictional worlds of comics and the culture of comics fandom. The term is most commonly associated with adolescent and teen males but can be applicable to any age or sex.

The term fangirl, while similar, often carries slightly different connotations. The term fangirl is often applied to any enthusiastic female fan, regardless of obsessive qualities or not, and is often used with overtones of "[[teenybopper]]".

==History of fanboys and the term==
The term "fanboy" is most commonly associated with adolescent and teen males but can be applicable to any age or sex. The term originated in [[comic book]] circles to describe someone immersed in the fictional worlds of comics and the culture of comics fandom. Common subjects of reverence by fanboys are specific: [[TV show]]s; [[film|movie]]s; [[music]]; [[anime]]; [[comic book]]s; [[car]]s; [[video game console]]s, [[video games]] and [[MMORPG]]s; and [[computer]] [[operating system]]s, [[computer Hardware|hardware]] and [[software]].

Popular depictions of Fanboy stereotypes include the [[Comic Book Guy]] on ''[[The Simpsons]]'' and columnist [[Larry Groznic]] from the satirical newspaper ''[[The Onion]]''. In the songs of the fannish [[parody]] [[musician]] [[Luke Ski]], many characters proudly consider themselves ''fanboys.''

The earliest published uses of the word "fanboy" have been dated to 1982. One reference is to the cover of the "Official Underground and Newave Comix Price Guide". On this cover page are sketched overweight, overzealous comic book collectors wearing T-shirts that state "Fanboys of America," who are describing the extreme measures they would go to, including moving to San Francisco, to preserve their comics.

Also published in 1982, a comic strip appeared in Jim Engel and Chuck Fiala's "Fandom Confidential" comic. In the strip, Jim and Chuck met comic artist/writer [[John Byrne]] and collapsed into "mindless paroxysms of adoration." The John Byrne character responded that they were "a couple of fanboys in bondage" (a play on words referring to a [[List of Monty Python’s Flying Circus episodes#10. E. Henry Thripshaw.27s Disease|Monty Python sketch]] in which an Elizabethan era character reads what she claims to be a new Shakespeare work called "Gay Boys in Bondage". <ref>[http://www.byrnerobotics.com/FAQ/listing.asp?ID=7&T1=Miscellaneous+Questions#154 Byrne Robotics: FAQ]</ref> Another early use is in a smart-aleck editorial reply by "[[Ambush Bug]]" to a letter in his comic in [[1985]].

==Media==
===Comic Book===
*[[Sergio Aragonés]]' ''Fanboy''
*[[Galactic Storm]]'s ''Fanboy''

===Television===
*''[[The Simpsons]]''' [[Comic Book Guy]] refers to himself as a fanboy.
*''[[Freakazoid!|Freakazoid]]'''s [[freakazoid!#Other characters|Fan Boy]]

===Radio/Podcasts===
*[[Fanboy Radio]] - [http://fanboyradio.com]

==See also==
* [[Addiction]]
* [[Cyberstalking]]
* [[Editor war]]
* [[Anorak (slang)|Anorak]]
* [[Astroturfing]]
* [[Otaku]]
* [[Obsession]]

==References==
{{reflist}}

==External links==
* [http://www.bruceongames.com/2008/02/17/fanboys/ A look at fanboys from the game industry perspective]
* [http://www.urbandictionary.com/define.php?term=fanboy Urban dictionary: fanboy]
* [http://www.netjak.com/review.php/1013 Dissecting the Fanboy Mind] - A discussion of the fanboy behavior in regard to video games.
* [http://palgn.com.au/article.php?id=6463 The trial of the Fanboy] - A criticism of the fanboy concept and overusage of the term.

[[Category:Fandom]]
[[Category:Anime and manga terminology]]

[[de:Fan#Konsum]]
[[fr:Fanboy]]