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 to bring the solid particles together, the precipitate remains in suspension. After sedimentation 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 historically been known as'flowers'; when the solid appears in the form of cellulose fibers which have been through chemical processing, the process is 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 nitrate solution, a yellow precipitate of lead iodide is formed. Precipitation may occur. Precipitation may occur 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, the temperature is high enough that diffusion can lead to segregation into precipitates. Precipitation in solids is 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, no suitable nucleation surface is available, supersaturation occurs. Precipitation reactions can be used for making pigments, removing salts from water in water treatment, in classical qualitative inorganic analysis.
Precipitation is 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. 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, are collected by filtration: Precipitation may occur when an antisolvent is added, drastically reducing the solubility of the desired product. Thereafter, the precipitate may 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, the product precipitates. Precipitation is useful in purifying products: crude bmim-Cl is taken up in acetonitrile, 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 a useful way to strengthen alloys.
An example of a precipitation reaction: Aqueous silver nitrate is added to a solution containing potassium chloride, the precipitation of a white solid, silver chloride, is observed. AgNO 3 + KCl ⟶ AgCl ↓ + KNO 3 The silver chloride has formed a solid, 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 − A final way to represent a precipitate reaction is known as a net ionic reaction. 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 different from those listed. Other compounds form white precipitates. 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, 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 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 that sulfate ions are present. Digestion, or precipitate ageing, happens when a freshly formed precipitate is left at a higher temperature, in the solution from which it precipitates, it results in bigger particles. The physico-chemical process underlying digestion is called Ostwald ripening. Coprecipitation Salting in Salting out Effervescence Zumdahl, Steven S.. Chemical Principles. New York: Houghton Mifflin. ISBN 0-618-37206-7. Precipitation reactions of certain cations Digestion Instruments A Thesis on pattern formation in precipitation reactions
Decantation is a process for the separation of mixtures of immiscible liquids or of a liquid and a solid mixture such as a suspension. The layer closer to the top of the container—the less dense of the two liquids, or the liquid from which the precipitate or sediment has settled out—is poured off, leaving the other component or the more dense liquid of the mixture behind. An incomplete separation is witnessed during the separation of two immiscible liquids. Decantation can be used to separate immiscible liquids. For example, when a mixture of water and oil are present in a beaker, a distinct layer between the two consistency is formed, with the oil layer floating on top of the water layer; this separation can be done by leaving water behind. This technique gives an incomplete separation as it is difficult to pour off all of the top layer without pouring out some parts of the bottom layer. A separatory funnel is an alternative apparatus for separating liquid layers, it has a valve at the bottom to allow draining off the bottom layer.
It can give a better separation between the two liquids. Decantation can separate solid and liquid mixtures by allowing gravity to pull the solid fragments to settle at the bottom of the container. In laboratory situations, decantation of mixtures containing solids and liquids occur in test tubes. To enhance productivity, test tubes should be placed at a 45° angle to allow sediments to settle at the bottom of the apparatus. A centrifuge may be used in decantation as the natural process of settling down is time consuming and tedious. A centrifuge forces the precipitate to the bottom of the container; the liquid can be more poured away, as the precipitate will tend to remain in its compressed form. A decanter centrifuge may be used for a continuous solid liquid separation. Decantation is used to purify a liquid by separating it from a suspension of insoluble particles; this makes the wine more astringent. Cream accelerates to the top of milk, allowing the separation of cream. Fat is determined in butter by decantation.
To obtain a sample of clear water from muddy water, muddy water is left in a container until the mud settles, the clear water is poured into another container. In sugar industry, processing of sugar beets into granular sugar many liquid - solid separations are encountered e.g. separation of syrups from crystals. Decantation is present in nanotechnology. In the synthesis of high quality silver nanowire solutions and fabrication process of high performance electrodes, decantation is being applied which simplifies the purification process. After using a desiccant to absorb water from an organic liquid, the organic liquid can be decanted away from the desiccant; the process of deriving vinegar requires decantation to remove fats from the raw substance. Plasma can be separated from blood through decantation by using a centrifuge. Mercury is disposed off in water bodies during mining, turning the water toxic; the elimination of mercury from water can be done by decantation. Sedimentation Centrifugation
Chemistry is the scientific discipline involved with elements and compounds composed of atoms and ions: their composition, properties and the changes they undergo during a reaction with other substances. In the scope of its subject, chemistry occupies an intermediate position between physics and biology, it is sometimes called the central science because it provides a foundation for understanding both basic and applied scientific disciplines at a fundamental level. For example, chemistry explains aspects of plant chemistry, the formation of igneous rocks, how atmospheric ozone is formed and how environmental pollutants are degraded, the properties of the soil on the moon, how medications work, how to collect DNA evidence at a crime scene. Chemistry addresses topics such as how atoms and molecules interact via chemical bonds to form new chemical compounds. There are four types of chemical bonds: covalent bonds, in which compounds share one or more electron; the word chemistry comes from alchemy, which referred to an earlier set of practices that encompassed elements of chemistry, philosophy, astronomy and medicine.
It is seen as linked to the quest to turn lead or another common starting material into gold, though in ancient times the study encompassed many of the questions of modern chemistry being defined as the study of the composition of waters, growth, disembodying, drawing the spirits from bodies and bonding the spirits within bodies by the early 4th century Greek-Egyptian alchemist Zosimos. An alchemist was called a'chemist' in popular speech, the suffix "-ry" was added to this to describe the art of the chemist as "chemistry"; the modern word alchemy in turn is derived from the Arabic word al-kīmīā. In origin, the term is borrowed from the Greek χημία or χημεία; this may have Egyptian origins since al-kīmīā is derived from the Greek χημία, in turn derived from the word Kemet, the ancient name of Egypt in the Egyptian language. Alternately, al-kīmīā may derive from χημεία, meaning "cast together"; the current model of atomic structure is the quantum mechanical model. Traditional chemistry starts with the study of elementary particles, molecules, metals and other aggregates of matter.
This matter can be studied in isolation or in combination. The interactions and transformations that are studied in chemistry are the result of interactions between atoms, leading to rearrangements of the chemical bonds which hold atoms together; such behaviors are studied in a chemistry laboratory. The chemistry laboratory stereotypically uses various forms of laboratory glassware; however glassware is not central to chemistry, a great deal of experimental chemistry is done without it. A chemical reaction is a transformation of some substances into one or more different substances; the basis of such a chemical transformation is the rearrangement of electrons in the chemical bonds between atoms. It can be symbolically depicted through a chemical equation, which involves atoms as subjects; the number of atoms on the left and the right in the equation for a chemical transformation is equal. The type of chemical reactions a substance may undergo and the energy changes that may accompany it are constrained by certain basic rules, known as chemical laws.
Energy and entropy considerations are invariably important in all chemical studies. Chemical substances are classified in terms of their structure, phase, as well as their chemical compositions, they can be analyzed using the tools of e.g. spectroscopy and chromatography. Scientists engaged in chemical research are known as chemists. Most chemists specialize in one or more sub-disciplines. Several concepts are essential for the study of chemistry; the particles that make up matter have rest mass as well – not all particles have rest mass, such as the photon. Matter can be a mixture of substances; the atom is the basic unit of chemistry. It consists of a dense core called the atomic nucleus surrounded by a space occupied by an electron cloud; the nucleus is made up of positively charged protons and uncharged neutrons, while the electron cloud consists of negatively charged electrons which orbit the nucleus. In a neutral atom, the negatively charged electrons balance out the positive charge of the protons.
The nucleus is dense. The atom is the smallest entity that can be envisaged to retain the chemical properties of the element, such as electronegativity, ionization potential, preferred oxidation state, coordination number, preferred types of bonds to form. A chemical element is a pure substance, composed of a single type of atom, characterized by its particular number of protons in the nuclei of its atoms, known as the atomic number and represented by the symbol Z; the mass number is the sum of the number of neutrons in a nucleus. Although all the nuclei of all atoms belonging to one element will have the same
The Federal Register is the official journal of the federal government of the United States that contains government agency rules, proposed rules, public notices. It is published daily, except on federal holidays; the final rules promulgated by a federal agency and published in the Federal Register are reorganized by topic or subject matter and codified in the Code of Federal Regulations, updated annually. The Federal Register is compiled by the Office of the Federal Register and is printed by the Government Publishing Office. There are no copyright restrictions on the Federal Register. S. government, it is in the public domain. The Federal Register provides a means for the government to announce to the public changes to government requirements and guidance. Proposed new rules and regulations Final rules Changes to existing rules Notices of meetings and adjudicatory proceedings Presidential documents including Executive orders and administrative orders. Both proposed and final government rules are published in the Federal Register.
A Notice of Proposed Rulemaking requests public comment on a proposed rule and provides notice of any public meetings where a proposed rule will be discussed. The public comments are considered by the issuing government agency, the text of a final rule along with a discussion of the comments is published in the Federal Register. Any agency proposing a rule in the Federal Register must provide contact information for people and organizations interested in making comments to the agencies and the agencies are required to address these concerns when it publishes its final rule on the subject; the notice and comment process, as outlined in the Administrative Procedure Act, gives the people a chance to participate in agency rulemaking. Publication of documents in the Federal Register constitutes constructive notice, its contents are judicially noticed; the United States Government Manual is published as a special edition of the Federal Register. Its focus is on activities; each daily issue of the printed Federal Register is organized into four categories: Presidential Documents Rules and Regulations Proposed Rules Notices Citations from the Federal Register are FR, e.g. 71 FR 24924.
The final rules promulgated by a federal agency and published in the Federal Register are reorganized by topic or subject matter and re-published in the Code of Federal Regulations, updated annually. Copies of the Federal Register may be obtained from the U. S. Government Publishing Office. Most law libraries associated with an American Bar Association–accredited law school will have a set, as will federal depository libraries; the Federal Register has been available online since 1994. Federal depository libraries within the U. S. receive copies of the text, either in paper or microfiche format. Outside the U. S. some major libraries may carry the Federal Register. As part of the Federal E-Government eRulemaking Initiative, the web site Regulations.gov was established in 2003 to enable easy public access to agency dockets on rulemaking projects including the published Federal Register document. The public can use Regulations.gov to access entire rulemaking dockets from participating Federal agencies to include providing on-line comments directly to those responsible for drafting the rulemakings.
To help federal agencies manage their dockets, the Federal Docket Management System was launched in 2005 and is the agency side of regulations.gov. In April 2009, Citation Technologies created a free, searchable website for Federal Register articles dating from 1996 to the present. GovPulse.us, a finalist in the Sunlight Foundation's Apps for America 2, provides a web 2.0 interface to the Federal Register, including sparklines of agency activity and maps of current rules. On July 25, 2010, the Federal Register 2.0 website went live. The new website is a collaboration between the developers who created GovPulse.us, the Government Publishing Office and the National Archives and Records Administration. On August 1, 2011, the Federal Register announced a new application programming interface to facilitate programmatic access to the Federal Register content; the API is RESTful, utilizing the HATEOAS architecture with results delivered in the JSON format. Details are available at the developers page and Ruby and Python client libraries are available.
In addition to purchasing printed copies or subscriptions, the contents of the Federal Register can be acquired via several commercial databases: Citation Technologies offers the complete Federal Register and Code of Federal Regulations through subscription-based web portals such as CyberRegs. HeinOnline: Full coverage available dating back to 1936 in an image-based searchable PDF format. LexisNexis: Searchable text format since 45 FR 44251. Westlaw: Searchable text format since 46 FR 1; the Unified Agenda and the official English text of the 1980 United Nations Convention on Contracts for the International Sale of Goods, which became effective January 1, 1988, are included. Sunshine Act Meeting Notices are not available prior to 1991. Unified Agenda documents are not available prior to October 1989; the Federal Register system of publication was created on July 26, 1935, under the Federal Register Act. The first issue of the Federal Regis
Opiate is a term classically used in pharmacology to mean a drug derived from opium. Opioid, a more modern term, is used to designate all substances, both natural and synthetic, that bind to opioid receptors in the brain. Opiates are alkaloid compounds found in the opium poppy plant Papaver somniferum; the psychoactive compounds found in the opium plant include morphine and thebaine. Opiates are considered drugs with moderate to high abuse potential and are listed on various "Substance-Control Schedules" under the Uniform Controlled Substances Act of the United States of America. In 2014, between 13 and 20 million people used opiates recreationally. Opiates belong to the large biosynthetic group of benzylisoquinoline alkaloids, are so named because they are occurring alkaloids found in the opium poppy; the major psychoactive opiates are morphine and thebaine. Papaverine, 24 other alkaloids are present in opium but have little to no effect on the human central nervous system, as such are not considered to be opiates.
Small quantities of hydrocodone and hydromorphone are detected in assays of opium on rare occasions. Dihydrocodeine, oxycodone, oxymorphone and other derivatives of morphine and/or hydromorphone are found in trace amounts in opium. Despite morphine being the most medically significant opiate, larger quantities of codeine are consumed medically, most of it synthesized from morphine. Codeine has more predictable oral bioavailability, making it easier to titrate the dose. Codeine has less abuse potential than morphine, because it is milder, larger doses of codeine are required. Opiate withdrawal syndrome effects are associated with the abrupt cessation or reduction of prolonged opiate usage. While the full synthesis of opioids from naphthoquinone or other simple organic starting materials is possible, they are tedious and uneconomical processes. Therefore, most of the opiate-type analgesics in use today are either extracted from Papaver somniferum or synthesized from those opiates thebaine. In 2015 researches reported successful biosynthesis of thebaine and hydrocodone using genetically modified yeast.
Once scaled for commercial use the process would cut production time from a year to several days and could reduce costs by 90%. Heroin is one of several semi-synthetic opioids derived from the morphine. Although sometimes not considered opiates, as they are not directly derived from natural opium, they are referred to as opiates. Heroin is a morphine prodrug. One of the major metabolites of heroin, 6-monoacetylmorphine, is a morphine prodrug. Nicomorphine, dipropanoylmorphine, methyldesorphine, acetylpropionylmorphine, dibenzoylmorphine, diacetyldihydromorphine, several others are derived from morphine. Opiate comparison Opioid epidemic World Health Organization guidelines for the availability and accessibility of controlled substances
Solubility is the property of a solid, liquid or gaseous chemical substance called solute to dissolve in a solid, liquid or gaseous solvent. The solubility of a substance fundamentally depends on the physical and chemical properties of the solute and solvent as well as on temperature and presence of other chemicals of the solution; the extent of the solubility of a substance in a specific solvent is measured as the saturation concentration, where adding more solute does not increase the concentration of the solution and begins to precipitate the excess amount of solute. Insolubility is the inability to dissolve in a liquid or gaseous solvent. Most the solvent is a liquid, which can be a pure substance or a mixture. One may speak of solid solution, but of solution in a gas. Under certain conditions, the equilibrium solubility can be exceeded to give a so-called supersaturated solution, metastable. Metastability of crystals can lead to apparent differences in the amount of a chemical that dissolves depending on its crystalline form or particle size.
A supersaturated solution crystallises when'seed' crystals are introduced and rapid equilibration occurs. Phenylsalicylate is one such simple observable substance when melted and cooled below its fusion point. Solubility is not to be confused with the ability to'dissolve' a substance, because the solution might occur because of a chemical reaction. For example, zinc'dissolves' in hydrochloric acid as a result of a chemical reaction releasing hydrogen gas in a displacement reaction; the zinc ions are soluble in the acid. The solubility of a substance is an different property from the rate of solution, how fast it dissolves; the smaller a particle is, the faster it dissolves although there are many factors to add to this generalization. Crucially solubility applies to all areas of chemistry, inorganic, physical and biochemistry. In all cases it will depend on the physical conditions and the enthalpy and entropy directly relating to the solvents and solutes concerned. By far the most common solvent in chemistry is water, a solvent for most ionic compounds as well as a wide range of organic substances.
This is a crucial factor in much environmental and geochemical work. According to the IUPAC definition, solubility is the analytical composition of a saturated solution expressed as a proportion of a designated solute in a designated solvent. Solubility may be stated in various units of concentration such as molarity, mole fraction, mole ratio, mass per volume and other units; the extent of solubility ranges from infinitely soluble such as ethanol in water, to poorly soluble, such as silver chloride in water. The term insoluble is applied to poorly or poorly soluble compounds. A number of other descriptive terms are used to qualify the extent of solubility for a given application. For example, U. S. Pharmacopoeia gives the following terms: The thresholds to describe something as insoluble, or similar terms, may depend on the application. For example, one source states that substances are described as "insoluble" when their solubility is less than 0.1 g per 100 mL of solvent. Solubility occurs under dynamic equilibrium, which means that solubility results from the simultaneous and opposing processes of dissolution and phase joining.
The solubility equilibrium occurs. The term solubility is used in some fields where the solute is altered by solvolysis. For example, many metals and their oxides are said to be "soluble in hydrochloric acid", although in fact the aqueous acid irreversibly degrades the solid to give soluble products, it is true that most ionic solids are dissolved by polar solvents, but such processes are reversible. In those cases where the solute is not recovered upon evaporation of the solvent, the process is referred to as solvolysis; the thermodynamic concept of solubility does not apply straightforwardly to solvolysis. When a solute dissolves, it may form several species in the solution. For example, an aqueous suspension of ferrous hydroxide, Fe2, will contain the series + as well as other species. Furthermore, the solubility of ferrous hydroxide and the composition of its soluble components depend on pH. In general, solubility in the solvent phase can be given only for a specific solute, thermodynamically stable, the value of the solubility will include all the species in the solution.
Solubility is defined for specific phases. For example, the solubility of aragonite and calcite in water are expected to differ though they are both polymorphs of calcium carbonate and have the same chemical formula; the solubility of one substance in another is determined by the balance of intermolecular forces between the solvent and solute, the entropy change that accompanies the solvation. Factors such as temperature and pressure will alter this balance. Solubility may strongly depend on the presence of other species dissolved in the solvent, for example, complex-forming anions in liquids. Solubility will depend on the excess or deficiency of a common ion in the solution, a phenomenon known as the common-ion effect. To a lesser extent, solubility will depend on the ionic strength of solutions; the last two effects can be quantified using the equation for solubility equilibrium. For a solid that dissolves in a redox reaction, solubility is expe