Precipitation ( Chemistry ) - Wikipedia Precipitation ( Chemistry ) This article is about the chemical phenomenon. For other uses, see Precipitation ( disambiguation ). `` Precipitate '' redirects here. For other uses, see Precipitate ( disambiguation ). hide This article has multiple issues. Please help improve it or discuss these issues on the talk page. ( Learn how and when to remove these template messages ) This article may lack focus or may be about more than one topic. Please help improve this article, possibly by splitting the article and / or by introducing a disambiguation page, or discuss this issue on the talk page. ( August 2017 ) This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. ( February 2008 ) Chemical Precipitation Precipitation is the creation of a solid from a solution. When the reaction occurs in a liquid solution, the solid formed is called the ' precipitate '. The chemical that causes the solid to form is called the ' precipitant '. Without sufficient force of gravity ( settling ) to bring the solid particles together, the precipitate remains in suspension. After sedimentation, especially when using a centrifuge to press it into a compact mass, the precipitate may be referred to as a ' pellet '. Precipitation can be used as a medium. The precipitate - free liquid remaining above the solid is called the ' supernate ' or ' supernatant '. Powders derived from precipitation have also historically been known as ' flowers '. When the solid appears in the form of cellulose fibers which have been through chemical processing, the process is often referred to as regeneration. Sometimes the formation of a precipitate indicates the occurrence of a chemical reaction. If silver nitrate solution is poured into a solution of sodium chloride, a chemical reaction occurs forming a white precipitate of silver chloride. When potassium iodide solution reacts with lead ( II ) nitrate solution, a yellow precipitate of lead ( II ) iodide is formed. Precipitation may occur if the concentration of a compound exceeds its solubility ( such as when mixing solvents or changing their temperature ). Precipitation may occur rapidly from a supersaturated solution. In solids, precipitation occurs if the concentration of one solid is above the solubility limit in the host solid, due to e.g. rapid quenching or ion implantation, and the temperature is high enough that diffusion can lead to segregation into precipitates. Precipitation in solids is routinely used to synthesize nanoclusters. 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, which requires some 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. Contents 1 Applications 2 Representation using chemical equations 3 Precipitate colors 4 Anion / cation analysis 5 Digestion 6 See also 7 References 8 Further reading 9 External links Applications Crystals of meso - tetratolylporphyrin from a reflux of propanoic acid precipitate on cooling Copper from a wire is displaced by silver in a silver nitrate solution it is dipped into, and solid silver precipitates out. 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. Ideally, the product of the reaction is insoluble in the reaction solvent. Thus, it precipitates as it is formed, preferably forming pure crystals. An example of this would be the synthesis of porphyrins in refluxing propionic acid. By cooling the reaction mixture to room temperature, crystals of the porphyrin precipitate, and are collected by filtration : 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. Precipitation is also useful in purifying products : crude bmim - Cl is taken up in acetonitrile, and dropped into ethyl acetate, where it precipitates. Another important application of an antisolvent is in ethanol precipitation of DNA. In metallurgy, precipitation from a solid solution is also a useful way to strengthen alloys ; this process is known as solid solution strengthening. Representation using chemical equations See also : solubility product An example of a precipitation reaction : Aqueous silver nitrate ( AgNO ) is added to a solution containing potassium chloride ( KCl ), the precipitation of a white solid, silver chloride ( AgCl ), is observed. ( Zumdahl, 2005 ) AgNO 3 + KCl ⟶ AgCl ↓ + KNO 3 ( displaystyle ( ce ( ( AgNO3 ) + KCl - > AgCl ( v ) + KNO3 ) ) ) The silver chloride ( AgCl ) has formed a solid, which is observed as a precipitate. This reaction can be written emphasizing the dissociated ions in a combined solution. This is known as the ionic equation. Ag + + NO 3 − + K + + Cl − ⟶ AgCl ↓ + K + + NO 3 − ( displaystyle ( ce ( ( Ag+ ) + ( NO3 ^ ( - ) ) + ( K+ ) + ( Cl ^ ( - ) ) - > AgCl ( v ) + ( K+ ) + NO3 ^ ( - ) ) ) ) A final way to represent a precipitate reaction is known as a net ionic reaction. In this case, any spectator ions ( those that do not contribute to the reaction ) are left out of the formula completely. This simplifies the above equations to the following : Ag + + Cl − ⟶ AgCl ↓ ( displaystyle ( ce ( ( Ag+ ) + Cl ^ - - > AgCl ( v ) ) ) ) Precipitate colors Green and reddish brown stains on a limestone core sample, respectively corresponding to precipitates of oxides / hydroxides of Fe and Fe. Many compounds containing metal ions produce precipitates with distinctive colors. The following are typical colors for various metals. However, many of these compounds can produce colors very different from those listed. Gold black Chromium Deep green, murky green, orange, purple, yellow, brown Cobalt Pink Copper Blue Iron ( II ) Green Iron ( III ) Reddish brown Manganese Pale pink Nickel Green Lead Yellow Other compounds generally form white precipitates. Anion / cation analysis See also : Qualitative inorganic analysis Precipitate formation is useful in the detection of the type of cation in a 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. Digestion Digestion, or precipitate ageing, happens when a freshly formed precipitate is left, usually at a higher temperature, in the solution from which it precipitates. It results in cleaner and bigger particles. The physico - chemical process underlying digestion is called Ostwald ripening. See also Coprecipitation Salting in Salting out Effervescence References Jump up ^ Dhara, S. ( 2007 ). `` Formation, Dynamics, and Characterization of Nanostructures by Ion Beam Irradiation ''. Critical Reviews in Solid State and Materials Sciences. 32 ( 1 ) : 1 -- 50. Bibcode : 2007CRSSM... 32... 1D. doi : 10.1080 / 10408430601187624. Jump up ^ A.D. Adler ; F.R. Longo ; J.D. Finarelli ; J. Goldmacher ; J. Assour ; L. Korsakoff ( 1967 ). `` A simplified synthesis for meso - tetraphenylporphine ''. J. Org. Chem. 32 ( 2 ) : 476 -- 476. doi : 10.1021 / jo01288a053. Jump up ^ Alan D. Adler ; Frederick R. Longo ; Frank Kampas ; Jean Kim ( 1970 ). `` On the preparation of metalloporphyrins ''. Journal of Inorganic and Nuclear Chemistry. 32 ( 7 ) : 2443. doi : 10.1016 / 0022 - 1902 ( 70 ) 80535 - 8. Jump up ^ Dupont, J., Consorti, C., Suarez, P., de Souza, R. ( 2004 ). `` Preparation of 1 - Butyl - 3 - methyl imidazolium - based Room Temperature Ionic Liquids ''. Organic Syntheses. CS1 maint : Multiple names : authors list ( link ) ; Collective Volume, 10, p. 184 Further reading Zumdahl, Steven S. ( 2005 ). Chemical Principles ( 5th ed. ). New York : Houghton Mifflin. ISBN 0 - 618 - 37206 - 7. External links Wikimedia Commons has media related to Solid precipitation. Precipitation reactions of certain cations Digestion Instruments A Thesis on pattern formation in precipitation reactions NDL : 00573050 Retrieved from `` https://en.wikipedia.org/w/index.php?title=Precipitation_(chemistry)&oldid=832430207 '' Categories : Liquid - solid separation Hidden categories : CS1 maint : Multiple names : authors list Wikipedia articles lacking focus from August 2017 All Wikipedia articles lacking focus Articles needing additional references from February 2008 All articles needing additional references Articles with multiple maintenance issues Talk Contents About Wikipedia Bân - lâm - gú Български Català Čeština Dansk Deutsch Eesti Ελληνικά Español Esperanto فارسی Français Gaeilge Galego हिन्दी Ido Bahasa Indonesia Italiano עברית Қазақша Kreyòl ayisyen Nederlands 日本 語 Norsk Norsk nynorsk Polski Português Română Русский Simple English Slovenčina Slovenščina Српски / srpski Srpskohrvatski / српскохрватски Basa Sunda Suomi Svenska தமிழ் Українська اردو Tiếng Việt 粵語 中文 35 more Edit links This page was last edited on 25 March 2018, at 23 : 51. 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Question: when does precipitate form in a chemical reaction
Answer: When the reaction occurs in a liquid solution; the concentration of a compound exceeds its solubility