Chemistry
Precipitation Reaction
A precipitation reaction is a chemical reaction in which two soluble ionic compounds in a solution combine to form an insoluble solid compound, known as a precipitate. This occurs when the cations and anions of the two compounds combine in such a way that the resulting compound is insoluble and falls out of solution as a solid.
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10 Key excerpts on "Precipitation Reaction"
eBook - PDFFundamentals of Water Treatment Unit Processes
Physical, Chemical, and Biological
- David Hendricks(Author)
- 2016(Publication Date)
- CRC Press(Publisher)
21.1.1 P RECIPITATION I N -A -N UTSHELL Chemical precipitation occurs when the solubility product is exceeded for the anions and cations of any given salt. The ions comprising the salt are thus removed from solution. 21.1.1.1 De fi nitions Precipitation has not evolved to become a specialized fi eld in which a unique vernacular, for example, acronyms and terms, has evolved. Many of the terms come from the fi eld of chem-istry, however, such that glossary may be useful for reference. 21.1.1.2 Comparison with Other Processes Along with oxidation, precipitation involves a chemical reac-tion as the central issue of the process. It is characterized by the formation of a solid precipitate that is settled and = or fi ltered. 21.1.1.3 Process Description The precipitation process has several steps between the ions in solution and the solid precipitate being settled and removed. The steps are as follows: 1. (a) Introduce an anion that will form a precipitate with the target cation (or that will cause a change in water chemistry, for example, to form carbonates or hydroxides that have an af fi nity for the target cation). (b) Introduce a cation that will remove the target anion. 2. Cause suf fi cient mixing, for example, by rapid mix, to cause a high rate of contacts between the anions and the target cations in order to effect formation of precipitant crystals. 3. Apply moderate turbulence, for example, by paddle-wheel fl occulation, to cause fl oc formation and growth or, alternatively, cause fl ow through a fl oc blanket of previously formed fl oc to cause fl oc growth. 4. Permit settling by traditional continuous fl ow basin, by tube settlers, or by plate settlers with vacuum pickup of sludge or scraping into a pocket. 5. Apply fi ltration to remove residual fl oc particles. 6. Dewater sludge and transport to disposal site. 7. Solids disposal = recovery may be reclamation, dis-posal in a municipal land fi ll, or disposal in a secured land fi ll.
eBook - PDF- J W Mullin(Author)
- 2001(Publication Date)
- Butterworth-Heinemann(Publisher)
8 Industrial techniques and equipment 8.1 Precipitation Precipitation is a widely used industrial process. It is also a very popular laboratory technique, especially in analytical chemistry, and the literature on this aspect of the subject is voluminous (see Kolthoff et al. , 1969). Precipitation plays an important role not only in chemistry but also in metallurgy, geology, physiology, and other sciences. In the industrial field, the manufacture of photographic chemicals, pharmaceuticals, paints and pigments, polymers and plastics utilizes the principles of precipitation. For the production of ultrafine powders precipitation may be considered a useful alternative to conventional crystallization followed by milling. The term precipitation very often refers to nothing more than fast crystal-lization, although sometimes it also implies an irreversible process, e.g. many precipitates are virtually insoluble substances produced by a chemical reaction, whereas the products of most conventional crystallization processes can usually be redissolved if the original conditions of temperature and solution concentra-tion are restored. Another distinguishing feature of precipitation processes is that they are generally initiated at high supersaturation, resulting in fast nucleation and the consequent creation of large numbers of very small primary crystals. Although precipitation, like all crystallization processes, consists of three basic steps (supersaturation, nucleation and growth) two subsequent secondary steps usually have a profound effect on the final crystalline product. The first is agglomeration , which generally occurs soon after nucleation, and the second is ageing , a term used to cover all irreversible changes that take place in a precipitate after its formation. A common method for producing a precipitate is to mix two reacting solutions together as quickly as possible, but the analysis of this apparently simple operation is exceedingly complex.
eBook - PDFHandbook of Soil Sciences
Properties and Processes, Second Edition
- Pan Ming Huang, Yuncong Li, Malcolm E. Sumner, Pan Ming Huang, Yuncong Li, Malcolm E. Sumner(Authors)
- 2011(Publication Date)
- CRC Press(Publisher)
In these systems, active precipitation of new solid phases may dominate over chemisorption reactions to control solute concentrations in the soil solution. 17.2.2 Precipitation and Coprecipitation Mineral–water reactions occur during movement of water through soil pores. These reactions may result in the release of structural components from soil solids due to mineral dissolu-tion or result in the buildup to oversaturation and consequent precipitation of secondary minerals. As an outcome of mineral– water reactions along a flow path, fluid compositions and the mineralogical makeup of the soil matrix will continuously evolve toward a stable state or an equilibrium state. Mineral pre-cipitation processes in soil systems may govern the concentra-tions of major and trace elements in the soil solution. Full treatment of precipitation processes, including cover-age of relevant thermodynamic and kinetic concepts, is outside the scope of this document. The reader is referred to numerous standard textbooks in geochemistry, soil science, and aquatic chemistry (e.g., Lindsay, 1979; Drever, 1982; Stumm, 1992; McBride, 1994; Stumm and Morgan, 1996; Langmuir, 1997; Lasaga, 1999; Sparks, 2003; Sposito, 2008). The purpose of this section is to introduce key concepts and issues regarding the potential impact Precipitation Reactions may exert on solute par-titioning in soils. In general, mineral precipitation in relation to the solid-phase partitioning of soil solutes can be discussed in the context of four widely studied processes: • Precipitation from solution : Nucleation and growth of a solid phase exhibiting a molecular unit that repeats itself in three dimensions. Homogeneous nucleation occurs from bulk solution and heterogeneous nucleation occurs on the surfaces of organic or mineral particles. Heterogeneous nucleation is thought to be more impor-tant in natural systems that are rich in reactive inorganic and biological surfaces.
eBook - PDFChemistry
Principles and Reactions
- William Masterton, Cecile Hurley(Authors)
- 2020(Publication Date)
- Cengage Learning EMEA(Publisher)
Copyright 2016 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 4-1 Precipitation Reactions 75 ▼ 4-1 Precipitation Reactions When water (aqueous) solutions of two different ionic compounds are mixed, we often find that an insoluble solid precipitates; this is called a precipitation reac-tion . To identify the solid, we must know which ionic compounds are soluble in water and which are not. Solubility of Ionic Compounds When an ionic solid dissolves in water two competing forces come into play: ■ ■ the attractive forces between the oppositely charged ions making up the solid ■ ■ the attractive forces between water and the ions. For reasons discussed later in this text (Chapter 7), water has two partially positively charged ( d 1 ) hydrogen atoms (attractive to anions) and a partially negatively charged ( d 2 ) oxygen atom (attractive to cations). The extent to which solution occurs depends upon a balance between two forces, which are both electrical in nature: 1. The force of atraction between H 2 O molecules and the ions of the solid, which tends to bring the solid into solution. If this factor predominates, we expect the compound to be very soluble in water, as in the case of KCl (Figure 4.1). 2. The force of attraction between oppositely charged ions, which tends to keep them in the solid state. If this is the major factor, we expect water solubility to be low. SrSO 4 is almost insoluble, which implies that the interionic forces between Sr 2 1 ions and SO 4 2 2 ions predominate.
eBook - PDFIndustrial Crystallization
Fundamentals and Applications
- Alison Lewis, Marcelo Seckler, Herman Kramer, Gerda van Rosmalen(Authors)
- 2015(Publication Date)
- Cambridge University Press(Publisher)
11 Precipitation and anti-solvent crystallization 11.1 Why this chapter is important Precipitation processes are important in a number of different fields, including extractive metallurgy, where the high recovery (i.e. recovered mass/initial mass in solution) is exploited to recover valuable metals; water treatment, where the same high recovery is exploited to cause high levels of removal of contaminants; pharmaceuticals, where a high recovery of product is important; and nano-precipitation, where the small particle size and a monodisperse crystal size distribution are important. 11.2 What is precipitation? The distinction between crystallization and precipitation is often based on the speed of the process, with precipitation usually being defined as a fast process that results in rapid solid formation of extremely small crystals (Jarvenin, 2008). However, a more scientific definition of precipitation is the fact that the product is formed by a chemical reaction. Thus, precipitation is often referred to as “reactive crystallization.” In precipitation processes, two soluble reactants are mixed to form a sparingly soluble product. What makes it unique is that often, especially in high-recovery precipitation, the reagent streams are highly concentrated and thus very high supersaturations, especially local supersaturations, are created (Figure 11.1). Because of the high supersaturation, the conversion of the solutes into solid particles is (in contrast to crystallization) usually a very fast process. 11.3 What makes it unique? Precipitation is used for sparingly soluble substances (solubility in the range 0.001− 1 kg m −3 ) for a number of reasons, but mostly because of: a. the requirement for a high recovery of the product; b. the requirement for a high degree of removal of a species; c.
eBook - ePub- Donald L. Sparks(Author)
- 2018(Publication Date)
- CRC Press(Publisher)
5 Precipitation/Dissolution Reactions in Soils Wayne P. RobargeCONTENTSI. Introduction II. Background A. Solubility Product 1. Relative Saturation 2. Macro vs. Micro Scale a. Surface Microtopography b. Particle Size B. Congruent vs. Incongruent Dissolution C. Activity Diagrams 1. Fundamental Concepts 2. Solid Solutions 3. Covariance Between Axes III. Precipitation A. Homogeneous Precipitation B. Heterogeneous Nucleation C. Precipitation in Soil Systems 1. Sorption and Precipitation IV. Dissolution A. General Rate Law B. Dissolution Rates Near Equilibrium C. Field vs. Laboratory Rate Estimates References I. INTRODUCTIONPrecipitation and dissolution reactions of primary and secondary minerals are an integral part of the chemistry of soils and have ramifications for chemical weathering, nutrient availability, soil genesis, global change, and environmental concerns. Chemical weathering is one of the major processes controlling the global hydrogeochemical cycle of elements.1 As a dissolution reaction, chemical weathering represents the release of plant nutrients such as Mg, Ca, K, P, Fe, Mn, and B from primary minerals for plant uptake and recycling in plant ecosystems. Work by Sparks2 has demonstrated the importance of K release from minerals on crop growth in agronomic systems, while nutrient release and recycling has long been of interest for sustainable productivity in forested ecosystems.4 ,6As essentially a H+ consuming process, mineral dissolution is also important in countering the long-term effects of acidic deposition on watersheds.7 ,10
eBook - PDF- Leo J. Malone, Theodore O. Dolter(Authors)
- 2012(Publication Date)
- Wiley(Publisher)
Upon mixing, cloudiness appears due to par- ticles that should eventually settle to the bottom of the reaction vessel. For this last reaction, the two solutions are simply mixed together into one large vessel; they look essentially the same as before mixing. If one solu- tion was colored, the combination might appear to be a lighter hue, but this is just due to diluting. It doesn’t indicate a chemical reaction. (See also the example in Figure 6-7.) SYNTHESIS The following reaction works, for reasons to be discussed in the following section. What would you predict to be the visual indication of a reaction? Fe(OH) 3 + 3HCl ¡ 3H 2 O + FeCl 3 According to the solubility rules, Fe(OH) 3 is a solid. HCl and FeCl 3 are in aqueous solutions. H 2 O is, of course, a liquid. So we are starting off with a solid and aqueous solution, and ending with a mixture of a soluble salt in water. Therefore, upon the addition of hydrochloric acid, we should see our solid “disappear,” as its soluble product dissolves in water. E X A M P L E 6 - 9 Writing a Possible Precipitation Reaction 200 CHAPTER 6 Chemical Reactions Hard water is water that contains significant concentrations of Fe 3+ , Ca 2+ and Mg 2+ . These are picked up when rainwa- ter filters down through soil rich in these ions. Most areas of the country, other than the South, East Coast, and Pacific Northwest, suffer from very hard water. Hard water has a strong tendency to form insoluble compounds with the compounds found in soap. This reduces the soap’s ability to clean by forming an insoluble residue that depos- its on sinks, tubs, dishes, and clothes. This leaves them gray, gritty, and dingy. Insoluble carbon- ates may also precipitate within water pipes and water heaters, forming what is called scale. Scale reduces water flow, insulates the water in heaters from the heat source, and lowers the lifetime of the plumbing. Hard water can be fixed by using detergents with added softening agents.
eBook - PDF- Allan S. Myerson, Deniz Erdemir, Alfred Y. Lee(Authors)
- 2019(Publication Date)
- Cambridge University Press(Publisher)
Chapter 8 Precipitation Processes Piotr H. Karpin ´ ski Consultant and expert witness Jerzy Baldyga Warsaw University of Technology 8.1 Introduction Precipitation generally refers to a relatively rapid formation of a sparingly soluble crystalline – or sometimes amorphous – solid phase from a liquid solution phase. Precipitation is rather poorly understood when compared with crystallization of more soluble materials. It generally involves the simultaneous and rapid occurrence of nucleation and growth together with the so-called secondary processes, such as Ostwald ripening and agglomeration. In many cases, these processes are difficult to separate and investigate independently and mechanistically. Precipitation has several important characteristics. First, the “precipitates” are usually sparingly soluble, and their for- mation occurs under relatively high supersaturation condi- tions. In this case, precipitation does not depend on the presence of solute crystalline material (i.e., it does not involve secondary nucleation). Rather, it results from homogeneous or heterogeneous nucleation processes. Second, because of the presence of high supersaturation, nucleation plays a major role in the precipitation processes. As a result, a large number of crystals with relatively small sizes are produced. The particle concentration is usually between 10 11 and 10 16 particles per cubic centimeter, and the crystal size is typically between 0.1 and 100 μm. Third, because of the high particle concentration and small crystal size, the aforementioned secondary pro- cesses, such as Ostwald ripening and aggregation, may occur and can greatly affect the properties of the resulting precipi- tates. Thus the development of colloidal systems must be considered in order to manage these secondary processes to achieve the desirable precipitate quality.
eBook - PDF- Gary D. Christian, Purnendu K. Dasgupta, Kevin A. Schug(Authors)
- 2013(Publication Date)
- Wiley(Publisher)
Chapter Eleven Precipitation ReactionS AND TITRATIONS “If you’re not part of the solution, then you’re part of the precipitate.” — Anonymous Learning Objectives WHAT ARE SOME OF THE KEY THINGS WE WILL LEARN FROM THIS CHAPTER? ● Effects of acids on solubility (key equations: 11.4, 11.6), p. 366 ● Mass balance calculations, p. 368 ● Effect of complexation on solubility (key equations: 11.10, 11.11), p. 372 ● Calculating precipitation titration curves, p. 374 ● Indicators for precipitation titrations, p. 378 A number of anions form slightly soluble precipitates with certain metal ions and can be titrated with the metal solutions; for example, chloride can be titrated with silver ion and sulfate with barium ion. The precipitation equilibrium may be affected by pH or by the presence of complexing agents. The anion of the precipitate may be derived from a weak acid and therefore combine with protons in acid solution to cause the precipitate to dissolve. On the other hand, the metal ion may complex with a ligand (the complexing agent) to shift the equilibrium toward dissolution. Silver ion will complex with ammonia and cause silver chloride to dissolve. In this chapter, we describe the quantitative effects of acidity and complexation in precipitation equilibria and discuss precipitation titrations using silver nitrate and barium nitrate titrants with different kinds of indicators and their theory. You should review fundamental precipitation equilibria described in Chapter 10. Most ionic analytes, especially inorganic anions, are conveniently determined using ion chromatography (Chapter 21), but for high concentrations more precise determinations can be made by precipitation titration when applicable. And many of the analyses performed by gravimetry as described in Chapter 10 may be more readily performed by precipitation titrations, albeit with not as high a precision.
eBook - PDF- Gary D. Christian, Purnendu K. Dasgupta, Kevin A. Schug(Authors)
- 2020(Publication Date)
- Wiley(Publisher)
Chapter 10 Precipitation ReactionS AND TITRATIONS “If you’re not part of the solution, then you’re part of the precipitate.” —Anonymous KEY THINGS TO LEARN FROM THIS CHAPTER Effects of acids on solubility (key Equations: 10.4, 10.6) Mass balance calculations Effect of complexation on solubility (key Equations: 10.10, 10.11) Calculating precipitation titration curves Indicators for precipitation titrations A number of anions form slightly soluble precipitates with certain metal ions and can be titrated with the metal solutions; for example, chloride can be titrated with silver ion and sulfate with barium ion. The precipitation equilibrium may be affected by pH or by the presence of complexing agents. The anion of the precipitate may be derived from a weak acid and therefore combine with protons in acid solution to cause the precipitate to dissolve. On the other hand, the metal ion may complex with a ligand (the complexing agent) to shift the equilibrium toward dissolution. Silver ion will complex with ammonia and cause silver chloride to dissolve. In this chapter, we describe the quantitative effects of acidity and complexation in precipitation equilibria and discuss precipitation titrations using silver nitrate and barium nitrate titrants with different kinds of indicators and their theory. You should review fundamental precipitation equilibria described in Chapter 9. Most ionic ana- lytes, especially inorganic anions, are conveniently determined using ion chromatog- raphy (Chapter 16), but for high concentrations more precise determinations can be made by precipitation titration when applicable. And many of the analyses performed by gravimetry as described in Chapter 9 may be more readily performed by precipita- tion titrations, albeit with not as high a precision.
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