1.
Chromat
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Chromat is an American fashion label based in New York City. The label was formed by Becca McCharen in 2010, drawing from Becca McCharen’s background in architecture and urban design, Chromat focuses on structural experiments for the human body. Chromat began in 2010 as an extension of McCharen’s degree in design at University of Virginia School of Architecture. It was originally a collaboration with fellow architecture student Emily Kappes, chromat’s structural language is the foundation of each garment, from the simplest bikini to the most complex 3D printed dress. Chromat swimwear, lingerie and signature architectural cages are all made in New York City, Chromat designed custom pieces for Beyoncés 2014 MTV VMA Performance, the Mrs. Carter Show World Tour, as well as for Beyoncés Super Bowl XLVII halftime show in 2013. Chromat has been featured in many editorials and features, such as Vogue, Elle, DAZED, New York Magazine. Chromat is currently a finalist in the CFDA / Vogue Fashion Fund 2015, McCharen was recognized in the Forbes 30 Under 30 list of “People Who are Reinventing the World in 2014”. McCharen was honored as one of Out Magazines OUT100 in 2013, chromat’s work mixing math and fashion was profiled in The Wall Street Journal in 2013. Chromat was nominated for the RACKED Young Guns Award in 2013, McCharen was chosen as The New York Observer’s one to watch in 2012. Debuted at New York Fashion Week on February 13,2015, debuted at New York Fashion Week on September 4,2014. Debuted at NYFW on February 6,2014, debuted at NYFW on September 6,2013. Debuted at NYFW on February 5,2013, Chromat garments are available at boutiques in the US and Asia including Barneys New York, Patricia Field, Oak and International Playground in New York City, and Coco De Mer in London. In Asia, Kniq in Hong Kong and Club 21b in Singapore currently stock Chromat, Chromat Official Website Meet the CFDA Vogue Fashion Fund Finalists
2.
Monochromacy
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Monochromacy is among organisms or machine the ability to distinguish only one single frequency of the electromagnetic light spectrum. In the physical sense, no source of radiation is purely monochromatic. In the same way a visual system of an organism or a machine cannot be monochromat but will distinguish a continuous set of frequencies around a peak, organisms with monochromacy are called monochromats. Many species, such as all marine mammals, the owl monkey, vision in humans is due to a system that starts with Rods and Cones photoreceptors, pass through retina ganglion cells and arrives in the brain visual cortex. Color vision is achieved through cones cells, each one able to distinguish between a band of frequencies, retinal ganglion cells and visual cortex. Rods, which are abundant in numbers are in the periphery of the human retina. Rods only respond to faint levels of light and are light sensitive, therefore. Cones, which are mostly near the fovea in the eye and are active in dim light, more useful in bright light. There are three types of cones in normal human eyes, each detects a different range of wavelengths, Rods outnumber cones by about 20 to 1 in the human retina, but cones provide about 90% of the brains input. Cones respond faster than rods, and have three types of pigments with different color sensitivities, where rods only have one and so are achromatic. Because of the distribution of rods and cones in the eye, people have good color vision near the fovea. Dichromacy, when one of the pigments is missing and colour is reduced to the green-red distinction only or the blue-yellow distinction only. Monochromacy when two of the cones are not functional, Monochromacy when all three of the cones are non functional, and light perception is achieved only with his rod cells. Color vision is reduced to black and grey-shades and white, Monochromacy is one of the symptoms of diseases that occur when in the human retina only one kind of light receptor is functional at a particular level of illumination. Animals with monochromatic vision may be either rod monochromats or cone monochromats and these monochromats contain photoreceptors which have a single spectral sensitivity curve. People with RM have a visual acuity, have total color blindness, photo-aversion. The nystagmus and photo-aversion usually are present during the first months of life, additionally, since patients with RM have no cone function and normal rod function, a rod monochromat cannot see any color, but only shades of grey. Cone monochromacy is the condition of having both rods and cones, but only having one functioning type of cone, a cone monochromat can have good pattern vision at normal daylight levels, but will not be able to distinguish hues
3.
Trichromacy
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Trichromacy or trichromaticism is the possessing of three independent channels for conveying color information, derived from the three different types of cone cells in the eye. Organisms with trichromacy are called trichromats, the normal explanation of trichromacy is that the organisms retina contains three types of color receptors with different absorption spectra. In actuality the number of such receptor types may be greater than three, since different types may be active at different light intensities, in vertebrates with three types of cone cells, at low light intensities the rod cells may contribute to color vision. Humans and some mammals have evolved trichromacy based partly on pigments inherited from early vertebrates. In fish and birds, for example, four pigments are used for vision and these extra cone receptor visual pigments detect energy of other wavelengths, including sometimes ultraviolet. Eventually two of these pigments were lost and another was gained, resulting in trichromacy among some primates, humans and closely related primates are usually trichromats, as are some of the females of most species of New World monkeys, and both male and female howler monkeys. Recent research suggests that trichromacy may also be quite general among marsupials, the possibility of trichromacy in marsupials potentially has another evolutionary basis than that of primates. Further biological and behavioural tests may verify if trichromacy is a characteristic of marsupials. Most other mammals are thought to be dichromats, with only two types of cone. Most studies of carnivores, as of mammals, reveal dichromacy, examples including the domestic dog, the ferret. Some species of insects are also trichromats, being sensitive to ultraviolet, blue and green instead of blue, green, research indicates that trichromacy allows animals to distinguish red fruit and young leaves from other vegetation that is not beneficial to their survival. Another theory is that detecting skin flushing and thereby mood may have influenced the development of primate trichromate vision, the color red also has other effects on primate and human behavior as discussed in the color psychology article. Primates are the only known placental mammalian trichromats and their eyes include three different kinds of cones, each containing a different photopigment. Their peak sensitivities lie in the blue, green and yellow-green regions of the color spectrum, S cones make up 5–10% of the cones and form a regular mosaic. Special bipolar and ganglion cells pass those signals from S cones, but Mollon and Bowmaker did find that L cones and M cones are randomly distributed and are in equal numbers. Trichromatic color vision is the ability of humans and some animals to see different colors. The trichromatic color theory began in the 18th century, when Thomas Young proposed that vision was a result of three different photoreceptor cells. Hermann von Helmholtz later expanded on Youngs ideas using color-matching experiments which showed that people with normal vision needed three wavelengths to create the normal range of colors, physiological evidence for trichromatic theory was later given by Gunnar Svaetichin
4.
Tetrachromacy
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Tetrachromacy is the condition of possessing four independent channels for conveying color information, or possessing four types of cone cells in the eye. Organisms with tetrachromacy are called tetrachromats, tetrachromacy is demonstrated among several species of birds, fish, amphibians, reptiles, insects and some mammals. It was the condition of most mammals in the past. The normal explanation of tetrachromacy is that the retina contains four types of higher-intensity light receptors with different absorption spectra. This means that the animal may see wavelengths beyond those of a human beings eyesight. Species with tetrachromatic color vision may have a physiological advantage over rival species. The goldfish and zebrafish are examples of tetrachromats, containing cone cells sensitive for red, green, blue and ultraviolet light. Some species of birds, such as the finch and the Columbidae, use the ultraviolet wavelength 300–400 nm specific to tetrachromatic color vision as a tool during mate selection. When selecting for mates, ultraviolet plumage and skin coloration show a level of selection. A typical bird eye will respond to wavelengths from about 300 to 700 nm, in terms of frequency, this corresponds to a band in the vicinity of 430–1000 THz. Most birds have retinas with four types of cone cells that are believed to mediate tetrachromatic color vision. Bird color vision is further improved by the filtering of pigmented oil droplets that are located in the photoreceptors, the oil droplets filter incident light before it reaches the visual pigment in outer segments of the photoreceptors. The four cone types, and the specialization of pigmented oil droplets, however, more recent research has suggested that tetrachromacy in birds only provide birds with a larger visual spectrum than that in humans, while the spectral resolution is similar. Foraging insects can see wavelengths that flowers reflect, pollination being a mutualistic relationship, foraging insects and plants have coevolved, both increasing wavelength range, in perception, in reflection and variation. Directional selection has led plants to display increasingly diverse amounts of color variations extending into the color scale. Some unidentified pollinators may use tetrachromatic color vision to increase and maintain a higher foraging success rate over their trichromatic competitors, in areas where reindeer live, the sun remains very low in the sky for long periods. This means the light is scattered such that the majority of light that reaches objects is blue or UV, some parts of the environment absorb UV light and therefore to UV-sensitive reindeer, appear to be black, strongly contrasting with the snow. These include urine, lichens and fur, although reindeer do not possess a specific UV opsin, retinal responses to 330 nm have been recorded, mediated by other opsins
5.
Chemical formula
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These are limited to a single typographic line of symbols, which may include subscripts and superscripts. A chemical formula is not a name, and it contains no words. Although a chemical formula may imply certain simple chemical structures, it is not the same as a full chemical structural formula. Chemical formulas can fully specify the structure of only the simplest of molecules and chemical substances, the simplest types of chemical formulas are called empirical formulas, which use letters and numbers indicating the numerical proportions of atoms of each type. Molecular formulas indicate the numbers of each type of atom in a molecule. For example, the formula for glucose is CH2O, while its molecular formula is C6H12O6. This is possible if the relevant bonding is easy to show in one dimension, an example is the condensed molecular/chemical formula for ethanol, which is CH3-CH2-OH or CH3CH2OH. For reasons of structural complexity, there is no condensed chemical formula that specifies glucose, chemical formulas may be used in chemical equations to describe chemical reactions and other chemical transformations, such as the dissolving of ionic compounds into solution. A chemical formula identifies each constituent element by its chemical symbol, in empirical formulas, these proportions begin with a key element and then assign numbers of atoms of the other elements in the compound, as ratios to the key element. For molecular compounds, these numbers can all be expressed as whole numbers. For example, the formula of ethanol may be written C2H6O because the molecules of ethanol all contain two carbon atoms, six hydrogen atoms, and one oxygen atom. Some types of compounds, however, cannot be written with entirely whole-number empirical formulas. An example is boron carbide, whose formula of CBn is a variable non-whole number ratio with n ranging from over 4 to more than 6.5. When the chemical compound of the consists of simple molecules. These types of formulas are known as molecular formulas and condensed formulas. A molecular formula enumerates the number of atoms to reflect those in the molecule, so that the formula for glucose is C6H12O6 rather than the glucose empirical formula. However, except for very simple substances, molecular chemical formulas lack needed structural information, for simple molecules, a condensed formula is a type of chemical formula that may fully imply a correct structural formula. For example, ethanol may be represented by the chemical formula CH3CH2OH
6.
Oxyanion
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An oxyanion or oxoanion is an ion with the generic formula AxOz−y. Oxoanions are formed by a majority of the chemical elements. The formulae of simple oxoanions are determined by the octet rule, the structures of condensed oxoanions can be rationalized in terms of AOn polyhedral units with sharing of corners or edges between polyhedra. The phosphate and polyphosphate esters adenosine monophosphate, adenosine diphosphate and adenosine triphosphate are important in biology, the formula of monomeric oxoanions, AOm−n, is dictated by the oxidation state of the element A and its position in the periodic table. Elements of the first row are limited to a coordination number of 4. However, none of the first row elements has a monomeric oxoanion with that coordination number, instead, carbonate and nitrate have a trigonal planar structure with π bonding between the central atom and the oxygen atoms. This π bonding is favoured by the similarity in size of the central atom, the oxoanions of second-row elements in the group oxidation state are tetrahedral. Tetrahedral SiO4 units are found in minerals, SiO4. Phosphate, sulfate, and perchlorate ions can be found as such in various salts, many oxoanions of elements in lower oxidation state obey the octet rule and this can be used to rationalize the formulae adopted. For example, chlorine has two valence electrons so it can accommodate three electron pairs from bonds with oxide ions, the charge on the ion is +5 −3 ×2 = −1, and so the formula is ClO−3. The structure of the ion is predicted by VSEPR theory to be pyramidal, in a similar way, the oxyanion of chlorine has the formula ClO−2, and is bent with two lone pairs and two bonding pairs. In the third and subsequent rows of the table, 6-coordination is possible. Thus molybdenum does not form MoO6−6, but forms the tetrahedral molybdate anion, moO6 units are found in condensed molybdates. Fully protonated oxoanions with a structure are found in such species as Sn2−6. The naming of monomeric oxoanions follows the following rules, the amount of order in the solution is decreased, releasing a certain amount of entropy which makes the Gibbs free energy more negative and favors the forward reaction. It is an example of a reaction with the monomeric oxoanion acting as a base. The reverse reaction is a reaction, as a water molecule. Further condensation may occur, particularly with anions of higher charge, the conversion of ATP to ADP is an hydrolysis reaction and is an important source of energy in biological systems
7.
Chromium
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Chromium is a chemical element with symbol Cr and atomic number 24. It is the first element in Group 6 and it is a steely-grey, lustrous, hard and brittle metal which takes a high polish, resists tarnishing, and has a high melting point. The name of the element is derived from the Greek word χρῶμα, chrōma, meaning color, Chromium metal is of high value for its high corrosion resistance and hardness. A major development was the discovery that steel could be highly resistant to corrosion and discoloration by adding metallic chromium to form stainless steel. Stainless steel and chrome plating together comprise 85% of the commercial use, trivalent chromium ion is an essential nutrient in trace amounts in humans for insulin, sugar and lipid metabolism, although the issue is debated. While chromium metal and Cr ions are not considered toxic, hexavalent chromium is toxic and carcinogenic, abandoned chromium production sites often require environmental cleanup. Chromium is remarkable for its properties, it is the only elemental solid which shows antiferromagnetic ordering at room temperature. Above 38 °C, it changes to paramagnetic, Chromium metal left standing in air is passivated by oxidation, forming a thin, protective, surface layer. This layer is a structure only a few molecules thick. It is very dense, and prevents the diffusion of oxygen into the underlying metal and this is different from the oxide that forms on iron and carbon steel, through which elemental oxygen continues to migrate, reaching the underlying material to cause incessant rusting. Passivation can be enhanced by short contact with oxidizing acids like nitric acid, passivated chromium is stable against acids. Passivation can be removed with a reducing agent that destroys the protective oxide layer on the metal. Chromium metal treated in this way readily dissolves in weak acids, Chromium, unlike such metals as iron and nickel, does not suffer from hydrogen embrittlement. However, it suffer from nitrogen embrittlement, reacting with nitrogen from air. Chromium is the 22nd most abundant element in Earths crust with a concentration of 100 ppm. Chromium compounds are found in the environment from the erosion of chromium-containing rocks, Chromium is mined as chromite ore. About two-fifths of the ores and concentrates in the world are produced in South Africa, while Kazakhstan, India, Russia. Untapped chromite deposits are plentiful, but geographically concentrated in Kazakhstan, although rare, deposits of native chromium exist
8.
Oxidation state
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The oxidation state, often called the oxidation number, is an indicator of the degree of oxidation of an atom in a chemical compound. This is never exactly true for real bonds, the term oxidation was first used by Lavoisier to signify reaction of a substance with oxygen. Much later, it was realized that the substance, upon being oxidized, loses electrons, oxidation states are typically represented by integers. In some cases, the oxidation state of an element is a fraction. It is predicted that even a +10 oxidation state may be achieveable by platinum in the platinum tetroxide dication, the increase in oxidation state of an atom, through a chemical reaction, is known as an oxidation, a decrease in oxidation state is known as a reduction. Such reactions involve the transfer of electrons, a net gain in electrons being a reduction. For pure elements, the state is zero. There are various methods for determining oxidation states, in inorganic nomenclature, the oxidation state is determined and expressed as an oxidation number, and is represented by a Roman numeral placed after the element name. In coordination chemistry, oxidation number is defined differently from oxidation state, a “Comprehensive definition of oxidation state ” has been published with free access. This article is a distillation of an IUPAC technical report Toward a comprehensive definition of oxidation state. Exceptions to this are that hydrogen has a state of −1 in hydrides of active metals, e. g. LiH. There are two different methods for determining the state of elements in chemical compounds. First a method based on the rules in the IUPAC definition, second, a method based on the relative electronegativity of the elements in the compound, where the more electronegative element is assumed to take the negative charge. Any pure element—even if it forms diatomic molecules like chlorine —has an oxidation state of zero, examples of this are Cu or O2. For monatomic ions, the state is the same as the charge of the ion. For example, the anion has an oxidation state of −2. The sum of oxidation states for all atoms in a molecule or polyatomic ion is equal to the charge of the molecule or ion, thus, the oxidation state of one element can be calculated from the oxidation states of the other elements. An application of this rule is that the sum of the states of all atoms in a neutral molecule must be zero
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Oxidizing agent
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In chemistry, an oxidizing agent is a substance that has the ability to oxidize other substances. Common oxidizing agents are oxygen, hydrogen peroxide and halogens, in one sense, an oxidizing agent is a chemical species that undergoes a chemical reaction that removes one or more electrons from another atom. In that sense, it is one component in an oxidation–reduction reaction, in the second sense, an oxidizing agent is a chemical species that transfers electronegative atoms, usually oxygen, to a substrate. Combustion, many explosives, and organic redox reactions involve atom-transfer reactions, electron acceptors participate in electron-transfer reactions. In this context, the agent is called an electron acceptor. A classic oxidizing agent is the ferrocenium ion Fe+2, which accepts an electron to form Fe2, one of the strongest acceptors commercially available is Magic blue, the radical cation derived from N3. Extensive tabulations of ranking the electron accepting properties of various reagents are available, in more common usage, an oxidising agent transfers oxygen atoms to a substrate. In this context, the agent can be called an oxygenation reagent or oxygen-atom transfer agent. Examples include MnO−4, CrO2−4, OsO4, and especially ClO−4, notice that these species are all oxides. In some cases, these oxides can also serve as electron acceptors, as illustrated by the conversion of MnO−4 to MnO2−4, by this definition some materials that are classified as oxidising agents by analytical chemists are not classified as oxidising agents in a dangerous materials sense. An example is potassium dichromate, which does not pass the dangerous goods test of an oxidising agent, the U. S. Department of Transportation defines oxidizing agents specifically. There are two definitions for oxidizing agents governed under DOT regulations and these two are Class 5, Division 5.1 and Class 5, Division 5.2. Division 5.1 means a material that may, generally by yielding oxygen, combustion Dye Electrosynthesis Organic oxidation Organic redox reaction Reducing agent
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Aqueous solution
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An aqueous solution is a solution in which the solvent is water. It is usually shown in chemical equations by appending to the relevant chemical formula, for example, a solution of table salt, or sodium chloride, in water would be represented as Na+ + Cl−. The word aqueous means pertaining to, related to, similar to, as water is an excellent solvent and is also naturally abundant, it is a ubiquitous solvent in chemistry. Substances that are hydrophobic often do not dissolve well in water, an example of a hydrophilic substance is sodium chloride. Acids and bases are aqueous solutions, as part of their Arrhenius definitions, the ability of a substance to dissolve in water is determined by whether the substance can match or exceed the strong attractive forces that water molecules generate between themselves. If the substance lacks the ability to dissolve in water the molecules form a precipitate, reactions in aqueous solutions are usually metathesis reactions. Metathesis reactions are another term for double-displacement, that is, when a cation displaces to form a bond with the other anion. The cation bonded with the latter anion will dissociate and bond with the other anion, aqueous solutions that conduct electric current efficiently contain strong electrolytes, while ones that conduct poorly are considered to have weak electrolytes. Those strong electrolytes are substances that are ionized in water. Nonelectrolytes are substances that dissolve in water yet maintain their molecular integrity, examples include sugar, urea, glycerol, and methylsulfonylmethane. When writing the equations of reactions, it is essential to determine the precipitate. To determine the precipitate, one must consult a chart of solubility, soluble compounds are aqueous, while insoluble compounds are the precipitate. Remember that there may not always be a precipitate, when performing calculations regarding the reacting of one or more aqueous solutions, in general one must know the concentration, or molarity, of the aqueous solutions. Solution concentration is given in terms of the form of the prior to it dissolving. Metal ions in aqueous solution Solubility Dissociation Acid-base reaction theories Properties of water Zumdahl S.1997, 4th ed. Boston, Houghton Mifflin Company
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Solution
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In chemistry, a solution is a homogeneous mixture composed of two or more substances. In such a mixture, a solute is a substance dissolved in another substance, the mixing process of a solution happens at a scale where the effects of chemical polarity are involved, resulting in interactions that are specific to solvation. The solution assumes the characteristics of the solvent when the solvent is the fraction of the mixture. The concentration of a solute in a solution is the mass of that solute expressed as a percentage of the mass of the whole solution, a solution is a homogeneous mixture of two or more substances. The particles of solute in a solution cannot be seen by the naked eye, a solution does not allow beams of light to scatter. The solute from a solution cannot be separated by filtration and it is composed of only one phase. Homogeneous means that the components of the form a single phase. Heterogeneous means that the components of the mixture are of different phase, the properties of the mixture can be uniformly distributed through the volume but only in absence of diffusion phenomena or after their completion. Usually, the present in the greatest amount is considered the solvent. Solvents can be gases, liquids or solids, one or more components present in the solution other than the solvent are called solutes. The solution has the physical state as the solvent. If the solvent is a gas, only gases are dissolved under a set of conditions. An example of a solution is air. Since interactions between molecules play almost no role, dilute gases form rather trivial solutions, in part of the literature, they are not even classified as solutions, but addressed as mixtures. If the solvent is a liquid, then almost all gases, liquids, here are some examples, Gas in liquid, Oxygen in water Carbon dioxide in water – a less simple example, because the solution is accompanied by a chemical reaction. Liquid in liquid, The mixing of two or more substances of the same chemistry but different concentrations to form a constant, alcoholic beverages are basically solutions of ethanol in water. Solid in liquid, Sucrose in water Sodium chloride or any other salt in water, solutions in water are especially common. Counterexamples are provided by liquid mixtures that are not homogeneous, colloids, body fluids are examples for complex liquid solutions, containing many solutes
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Potassium chromate
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Potassium chromate is the inorganic compound with the formula. This yellow solid is the salt of the chromate anion. It is a common laboratory chemical, whereas sodium chromate is important industrially and it is a class two carcinogen. Two crystalline forms are known, both being very similar to the corresponding potassium sulfate, orthorhombic β-K2CrO4 is the common form, but it converts to an α-form above 66 °C. These structures are complex, although the sulfate adopts the typical tetrahedral geometry and it is prepared by treating potassium dichromate with potassium hydroxide. In solution, the behavior of potassium and sodium dichromates are very similar, when treated with lead nitrate, it gives an orange-yellow precipitate, lead chromate. Unlike the less expensive sodium salt, potassium salt is used for laboratory work in situations where an anhydrous salt is required. It is as an agent in organic synthesis. It is used as in qualitative analysis, e. g. as a colorimetric test for silver ion. It is also used as an indicator in precipitation titrations with silver nitrate, tarapacaite is the natural, mineral form of potassium chromate. It occurs very rarely and until now is known from few localities on Atacama desert. Potassium chromate is a carcinogen and strong oxidant
13.
Potassium dichromate
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Potassium dichromate, K2Cr2O7, is a common inorganic chemical reagent, most commonly used as an oxidizing agent in various laboratory and industrial applications. As with all hexavalent chromium compounds, it is acutely and chronically harmful to health and it is a crystalline ionic solid with a very bright, red-orange color. The salt is popular in the laboratory because it is not deliquescent, potassium dichromate is usually prepared by the reaction of potassium chloride on sodium dichromate. Alternatively, it can be obtained from potassium chromate by roasting chrome ore with potassium hydroxide and it is used to oxidize alcohols. It converts primary alcohols into aldehydes and, under more forcing conditions, in contrast, potassium permanganate tends to give carboxylic acids as the sole products. Secondary alcohols are converted into ketones, for example, menthone may be prepared by oxidation of menthol with acidified dichromate. In an aqueous solution the color change exhibited can be used to test for distinguishing aldehydes from ketones, aldehydes reduce dichromate from the +6 to the +3 oxidation state, changing color from orange to green. This color change arises because the aldehyde can be oxidized to the carboxylic acid. A ketone will show no such change because it cannot be oxidized further, when heated strongly, it decomposes with the evolution of oxygen. 4K2Cr2O7 → 4K2CrO4 + 2Cr2O3 + 3O2 When an alkali is added to a red solution containing dichromate ions. For example, potassium chromate is produced industrially using potash, K2Cr2O7 + K2CO3 →2 K2CrO4 + CO2 The reaction is reversible, the main use is as a precursor to potassium chrome alum, used in leather tanning. Like other chromium compounds, potassium dichromate has been used to prepare chromic acid for cleaning glassware, because of safety concerns associated with hexavalent chromium, this practice has been largely discontinued. It is used as an ingredient in cement in which it retards the setting of the mixture and improves its density and this usage commonly causes contact dermatitis in construction workers. Potassium dichromate has uses in photography and in screen printing. In 1852, Henry Fox Talbot discovered that exposure to light in the presence of potassium dichromate hardened organic colloids such as gelatin and gum arabic. These discoveries soon led to the print, gum bichromate. Some processes depended on the only, in combination with the differential absorption of certain dyes by the hardened or unhardened areas. Dichromated colloids were also used as photoresists in various industrial applications and this solution reconverts the elemental silver particles in the film to silver chloride
14.
Hydrogen peroxide
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Hydrogen peroxide is a chemical compound with the formula H 2O2. In its pure form, it is a liquid, slightly more viscous than water. Hydrogen peroxide is the simplest peroxide and it is used as an oxidizer, bleaching agent and disinfectant. Concentrated hydrogen peroxide, or high-test peroxide, is an oxygen species and has been used as a propellant in rocketry. Its chemistry is dominated by the nature of its unstable peroxide bond, Hydrogen peroxide is unstable and slowly decomposes in the presence of base or a catalyst. Because of its instability, hydrogen peroxide is typically stored with a stabilizer in an acidic solution. Hydrogen peroxide is found in biological systems including the human body, enzymes that use or decompose hydrogen peroxide are classified as peroxidases. The boiling point of H 2O2 has been extrapolated as being 150.2 °C, in practice hydrogen peroxide will undergo potentially explosive thermal decomposition if heated to this temperature. It may be distilled at lower temperatures under reduced pressure. In aqueous solutions hydrogen peroxide differs from the material due to the effects of hydrogen bonding between water and hydrogen peroxide molecules. Hydrogen peroxide and water form a mixture, exhibiting freezing-point depression, pure water has a melting point of 0 °C. The boiling point of the same mixtures is also depressed in relation with the mean of both boiling points and this boiling point is 14 °C greater than that of pure water and 36.2 °C less than that of pure hydrogen peroxide. Hydrogen peroxide is a molecule with C2 symmetry. Although the O−O bond is a bond, the molecule has a relatively high rotational barrier of 2460 cm−1, for comparison. The increased barrier is ascribed to repulsion between the pairs of the adjacent oxygen atoms and results in hydrogen peroxide displaying atropisomerism. The molecular structures of gaseous and crystalline H 2O2 are significantly different and this difference is attributed to the effects of hydrogen bonding, which is absent in the gaseous state. Crystals of H 2O2 are tetragonal with the space group D4 4P4121, Hydrogen peroxide has several structural analogues with Hm−X−X−Hn bonding arrangements. It has the highest boiling point of this series, diphosphane and hydrogen disulfide exhibit only weak hydrogen bonding and have little chemical similarity to hydrogen peroxide
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Peroxide
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A peroxide is a compound containing an oxygen–oxygen single bond or the peroxide anion, O2−2. The O−O group is called the group or peroxo group. In contrast to oxide ions, the atoms in the peroxide ion have an oxidation state of −1. The simplest stable peroxide is hydrogen peroxide, superoxides, dioxygenyls, ozones and ozonides are considered separately. Peroxide compounds can be classified into organic and inorganic. Whereas the inorganic peroxides have an ionic, salt-like character, the peroxides are dominated by the covalent bonds. The oxygen–oxygen chemical bond of peroxide is unstable and easily split into reactive radicals via homolytic cleavage, for this reason, peroxides are found in nature only in small quantities, in water, atmosphere, plants, and animals. Peroxides have an effect on organic substances and therefore are added to some detergents. Other large-scale applications include medicine and chemical industry, where peroxides are used in synthesis reactions or occur as intermediate products. With an annual production of over 2 million tonnes, hydrogen peroxide is the most economically important peroxide, many peroxides are unstable and hazardous substances, they cannot be stored and therefore are synthesized in situ and used immediately. Peroxides are usually very reactive and thus occur in only in a few forms. These include, in addition to hydrogen peroxide, a few products such as ascaridole. Hydrogen peroxide occurs in water, groundwater and in the atmosphere. It forms upon illumination or natural catalytic action by substances containing in water, sea water contains 0.5 to 14 μg/L of hydrogen peroxide, freshwater 1 to 30 μg/L and air 0.1 to 1 parts per billion. Hydrogen peroxide is formed in human and animal organisms as a product in biochemical processes and is toxic to cells. The toxicity is due to oxidation of proteins, membrane lipids, the class of biological enzymes called SOD is developed in nearly all living cells as an important antioxidant agent. They promote the disproportionation of superoxide into oxygen and hydrogen peroxide,2 O2 − +2 H + → SOD H2 O2 ⏞ hydrogen peroxide + O2 ⏞ oxygen Formation of hydrogen peroxide by superoxide dismutase Peroxisomes are organelles found in virtually all eukaryotic cells. This reaction is important in liver and kidney cells, where the peroxisomes neutralize various toxic substances that enter the blood, some of the ethanol humans drink is oxidized to acetaldehyde in this way
16.
Chromium(VI) oxide peroxide
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The generally yellow chromates or orange dichromates turn to dark blue as chromium peroxide is formed. Chromate or dichromate reacts with hydrogen peroxide and an acid to give chromium peroxide, crO42− +2 H2O2 +2 H+ → CrO5 +3 H2O After a few seconds, the chromium peroxide decomposes to turn green as chromium compounds are formed. In this way, the peroxide is dissolved in the immiscible organic solvent. In this condition it can be observed over a longer period. 2 CrO5 +7 H2O2 +6 H+ →2 Cr3+ +10 H2O +7 O2 This compound contains one oxo ligand, the etherate, bipyridyl and pyridyl complexes of this compound have been found to be effective oxidants in organic chemistry. The structure of the complex has been determined crystallographically
17.
Covalent bond
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A covalent bond, also called a molecular bond, is a chemical bond that involves the sharing of electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs, for many molecules, the sharing of electrons allows each atom to attain the equivalent of a full outer shell, corresponding to a stable electronic configuration. Covalent bonding includes many kinds of interactions, including σ-bonding, π-bonding, metal-to-metal bonding, agostic interactions, bent bonds, the term covalent bond dates from 1939. In the molecule H2, the atoms share the two electrons via covalent bonding. Covalency is greatest between atoms of similar electronegativities, thus, covalent bonding does not necessarily require that the two atoms be of the same elements, only that they be of comparable electronegativity. Covalent bonding that entails sharing of electrons more than two atoms is said to be delocalized. The term covalence in regard to bonding was first used in 1919 by Irving Langmuir in a Journal of the American Chemical Society article entitled The Arrangement of Electrons in Atoms and Molecules. Langmuir wrote that we shall denote by the term covalence the number of pairs of electrons that an atom shares with its neighbors. The idea of covalent bonding can be traced several years before 1919 to Gilbert N. Lewis and he introduced the Lewis notation or electron dot notation or Lewis dot structure, in which valence electrons are represented as dots around the atomic symbols. Pairs of electrons located between atoms represent covalent bonds, multiple pairs represent multiple bonds, such as double bonds and triple bonds. An alternative form of representation, not shown here, has bond-forming electron pairs represented as solid lines, Lewis proposed that an atom forms enough covalent bonds to form a full outer electron shell. In the diagram of methane shown here, the atom has a valence of four and is, therefore, surrounded by eight electrons, four from the carbon itself. Each hydrogen has a valence of one and is surrounded by two electrons – its own one electron plus one from the carbon, walter Heitler and Fritz London are credited with the first successful quantum mechanical explanation of a chemical bond in 1927. Their work was based on the valence bond model, which assumes that a bond is formed when there is good overlap between the atomic orbitals of participating atoms. Atomic orbitals have specific directional properties leading to different types of covalent bonds, sigma bonds are the strongest covalent bonds and are due to head-on overlapping of orbitals on two different atoms. A single bond is usually a σ bond, pi bonds are weaker and are due to lateral overlap between p orbitals. A double bond between two given atoms consists of one σ and one π bond, and a bond is one σ. Covalent bonds are also affected by the electronegativity of the atoms which determines the chemical polarity of the bond
18.
Ether
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Ethers are a class of organic compounds that contain an ether group—an oxygen atom connected to two alkyl or aryl groups. They have the general formula R–O–R′, where R and R′ represent the alkyl or aryl groups, a typical example of the first group is the solvent and anesthetic diethyl ether, commonly referred to simply as ether. Ethers are common in chemistry and pervasive in biochemistry, as they are common linkages in carbohydrates. Ethers feature C–O–C linkage defined by an angle of about 110°. The barrier to rotation about the C–O bonds is low, the bonding of oxygen in ethers, alcohols, and water is similar. In the language of valence bond theory, the hybridization at oxygen is sp3, oxygen is more electronegative than carbon, thus the hydrogens alpha to ethers are more acidic than in simple hydrocarbons. They are far less acidic than hydrogens alpha to carbonyl groups, depending on the groups at R and R′, ethers are classified into two types, Simple ethers or symmetrical ethers, e. g. diethyl ether, dimethyl ether, etc. Mixed ethers or unsymmetrical ethers, e. g. methyl ethyl ether, methyl phenyl ether, in the IUPAC nomenclature system, ethers are named using the general formula alkoxyalkane, for example CH3–CH2–O–CH3 is methoxyethane. If the ether is part of a complex molecule, it is described as an alkoxy substituent. The simpler alkyl radical is written in front, so CH3–O–CH2CH3 would be given as methoxyethane, IUPAC rules are often not followed for simple ethers. The trivial names for simple ethers are a composite of the two followed by ether. For example, ethyl ether, diphenylether. As for other compounds, very common ethers acquired names before rules for nomenclature were formalized. Diethyl ether is called ether, but was once called sweet oil of vitriol. Methyl phenyl ether is anisole, because it was found in aniseed. Acetals are another class of ethers with characteristic properties, polyethers are compounds with more than one ether group. The crown ethers are examples of small polyethers, some toxins produced by dinoflagellates such as brevetoxin and ciguatoxin are extremely large and are known as cyclic or ladder polyethers. Polyether generally refers to polymers which contain the functional group in their main chain
19.
Pyridine
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Pyridine is a basic heterocyclic organic compound with the chemical formula C5H5N. It is structurally related to benzene, with one methine group replaced by a nitrogen atom, the pyridine ring occurs in many important compounds, including azines and the vitamins niacin and pyridoxine. Pyridine was discovered in 1849 by the Scottish chemist Thomas Anderson as one of the constituents of bone oil, two years later, Anderson isolated pure pyridine through fractional distillation of the oil. It is a colorless, highly flammable, weakly alkaline, water-soluble liquid with a distinctive, pyridine is used as a precursor to agrochemicals and pharmaceuticals and is also an important solvent and reagent. Pyridine is added to ethanol to make it unsuitable for drinking and it is used in the in vitro synthesis of DNA, in the synthesis of sulfapyridine, antihistaminic drugs tripelennamine and mepyramine, as well as water repellents, bactericides, and herbicides. Some chemical compounds, although not synthesized from pyridine, contain its ring structure and they include B vitamins niacin and pyridoxal, the anti-tuberculosis drug isoniazid, nicotine and other nitrogen-containing plant products. Historically, pyridine was produced from tar and as a byproduct of coal gasification. Pyridine is a liquid that boils at 115.2 °C. Its density,0.9819 g/cm3, is close to that of water, and its index is 1.5093 at a wavelength of 589 nm. Addition of up to 40 mol% of water to pyridine gradually lowers its melting point from −41.6 °C to −65.0 °C, the molecular electric dipole moment is 2.2 debyes. Pyridine is diamagnetic and has a susceptibility of −48.7 × 10−6 cm3·mol−1. The standard enthalpy of formation is 100.2 kJ·mol−1 in the phase and 140.4 kJ·mol−1 in the gas phase. At 25 °C pyridine has a viscosity of 0.88 mPa/s, the enthalpy of vaporization is 35.09 kJ·mol−1 at the boiling point and normal pressure. The enthalpy of fusion is 8.28 kJ·mol−1 at the melting point, pyridine crystallizes in an orthorhombic crystal system with space group Pna21 and lattice parameters a =1752 pm, b =897 pm, c =1135 pm, and 16 formula units per unit cell. For comparison, crystalline benzene is also orthorhombic, with space group Pbca, a =729.2 pm, b =947.1 pm, c =674.2 pm and this difference is partly related to the lower symmetry of the individual pyridine molecule. A trihydrate is known, it crystallizes in an orthorhombic system in the space group Pbca, lattice parameters a =1244 pm, b =1783 pm, c =679 pm. The critical parameters of pyridine are pressure 6.70 MPa, temperature 620 K, the optical absorption spectrum of pyridine in hexane contains three bands at the wavelengths of 195 nm,251 nm and 270 nm. The 1H nuclear magnetic resonance spectrum of pyridine contains three signals with the intensity ratio of 2,1,2 that correspond to the three chemically different protons in the molecule
20.
Predominance diagram
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A predominance diagram purports to show the conditions of concentration and pH where a chemical species has the highest concentration in solutions in which there are multiple acid-base equilibria. The lines on a predominance diagram indicate where adjacent species have the same concentration, either side of such a line one species or the other predominates, that is, has higher concentration relative to the other species. To illustrate a predominance diagram, part of the one for chromate is shown at the right, pCr stands for minus the logarithm of the chromium concentration and pH stands for minus the logarithm of the hydrogen ion concentration. There are two independent equilibria, with equilibrium constants defined as follows, a third equilibrium constant can be derived from K1 and KD. The species H2CrO4 and HCr 2O−7 are only formed at very low pH so they do not appear on this diagram, published values for log K1 and log KD are 5.89 and 2.05, respectively. The chromium concentration is calculated as the sum of the concentrations in terms of chromium content. = + +2, pCr = − log 10 The three species all have concentrations equal to 1/KD at pH = pK1, for which = 4/KD, the three lines on this diagram meet at that point. Chromate and hydrogen chromate have equal concentrations,1, = 1/K1, or pH = log K1. This relationship is independent of pCr, so it requires a line to be drawn on the predominance diagram. Hydrogen chromate and dichromate have equal concentrations, setting equal to in Eq.2, = 1/KD, from Eq.1, then, = 1/K1. Chromate and dichromate have equal concentrations, setting equal to in Eq.3 gives = 1/β22. The predominance diagram is interpreted as follows, the chromate ion is the predominant species in the region to the right of the green and blue lines. Above pH ~6.75 it is always the predominant species, at pH <5.89 the hydrogen chromate ion is predominant in dilute solution but the dichromate ion is predominant in more concentrated solutions. Predominance diagrams can become complicated when many polymeric species can be formed as, for example
21.
Chemical equilibrium
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In a chemical reaction, chemical equilibrium is the state in which both reactants and products are present in concentrations which have no further tendency to change with time. Usually, this results when the forward reaction proceeds at the same rate as the reverse reaction. The reaction rates of the forward and backward reactions are not zero. Thus, there are no net changes in the concentrations of the reactant, such a state is known as dynamic equilibrium. The concept of chemical equilibrium was developed after Berthollet found that chemical reactions are reversible. For any reaction mixture to exist at equilibrium, the rates of the forward and backward reactions are equal, conversely the equilibrium position is said to be far to the left if hardly any product is formed from the reactants. Since at equilibrium forward and backward rates are equal, k + α β = k − σ τ, K c = k + k − = σ τ α β By convention the products form the numerator. Equality of forward and backward reaction rates, however, is a condition for chemical equilibrium. Adding a catalyst will affect both the reaction and the reverse reaction in the same way and will not have an effect on the equilibrium constant. The catalyst will speed up both reactions thereby increasing the speed at which equilibrium is reached, although the macroscopic equilibrium concentrations are constant in time, reactions do occur at the molecular level. This is an example of dynamic equilibrium, equilibria, like the rest of thermodynamics, are statistical phenomena, averages of microscopic behavior. Le Châteliers principle gives an idea of the behavior of a system when changes to its reaction conditions occur. If a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium moves to partially reverse the change. For example, adding more S from the outside will cause an excess of products, and this can also be deduced from the equilibrium constant expression for the reaction, K = If increases must increase and CH 3CO−2 must decrease. The H2O is left out, as it is the solvent and its concentration remains high, a quantitative version is given by the reaction quotient. J. W. Gibbs suggested in 1873 that equilibrium is attained when the Gibbs free energy of the system is at its minimum value, what this means is that the derivative of the Gibbs energy with respect to reaction coordinate vanishes, signalling a stationary point. This derivative is called the reaction Gibbs energy and corresponds to the difference between the chemical potentials of reactants and products at the composition of the reaction mixture and this criterion is both necessary and sufficient. If a mixture is not at equilibrium, the liberation of the excess Gibbs energy is the force for the composition of the mixture to change until equilibrium is reached
22.
PH
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In chemistry, pH is a numeric scale used to specify the acidity or basicity of an aqueous solution. It is approximately the negative of the base 10 logarithm of the concentration, measured in units of moles per liter. More precisely it is the negative of the logarithm to base 10 of the activity of the hydrogen ion, solutions with a pH less than 7 are acidic and solutions with a pH greater than 7 are basic. Pure water is neutral, at pH7, being neither an acid nor a base, contrary to popular belief, the pH value can be less than 0 or greater than 14 for very strong acids and bases respectively. The pH scale is traceable to a set of standard solutions whose pH is established by international agreement, the pH of aqueous solutions can be measured with a glass electrode and a pH meter, or an indicator. In the first papers, the notation had the H as a subscript to the p, as so. The exact meaning of the p in pH is disputed, but according to the Carlsberg Foundation and it has also been suggested that the p stands for the German Potenz, others refer to French puissance. Another suggestion is that the p stands for the Latin terms pondus hydrogenii, potentia hydrogenii and it is also suggested that Sørensen used the letters p and q simply to label the test solution and the reference solution. Currently in chemistry, the p stands for decimal cologarithm of, PH is defined as the decimal logarithm of the reciprocal of the hydrogen ion activity, aH+, in a solution. P H = − log 10 = log 10 For example and this definition was adopted because ion-selective electrodes, which are used to measure pH, respond to activity. For H+ number of electrons transferred is one and it follows that electrode potential is proportional to pH when pH is defined in terms of activity. The reference electrode may be a silver chloride electrode or a calomel electrode, the hydrogen-ion selective electrode is a standard hydrogen electrode. Reference electrode | concentrated solution of KCl || test solution | H2 | Pt Firstly, the cell is filled with a solution of hydrogen ion activity. Then the emf, EX, of the cell containing the solution of unknown pH is measured. PH = pH + E S − E X z The difference between the two measured emf values is proportional to pH and this method of calibration avoids the need to know the standard electrode potential. The proportionality constant, 1/z is ideally equal to 12.303 R T / F the Nernstian slope, to apply this process in practice, a glass electrode is used rather than the cumbersome hydrogen electrode. A combined glass electrode has a reference electrode. It is calibrated against buffer solutions of hydrogen ion activity
23.
Oxyanions
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An oxyanion or oxoanion is an ion with the generic formula AxOz−y. Oxoanions are formed by a majority of the chemical elements. The formulae of simple oxoanions are determined by the octet rule, the structures of condensed oxoanions can be rationalized in terms of AOn polyhedral units with sharing of corners or edges between polyhedra. The phosphate and polyphosphate esters adenosine monophosphate, adenosine diphosphate and adenosine triphosphate are important in biology, the formula of monomeric oxoanions, AOm−n, is dictated by the oxidation state of the element A and its position in the periodic table. Elements of the first row are limited to a coordination number of 4. However, none of the first row elements has a monomeric oxoanion with that coordination number, instead, carbonate and nitrate have a trigonal planar structure with π bonding between the central atom and the oxygen atoms. This π bonding is favoured by the similarity in size of the central atom, the oxoanions of second-row elements in the group oxidation state are tetrahedral. Tetrahedral SiO4 units are found in minerals, SiO4. Phosphate, sulfate, and perchlorate ions can be found as such in various salts, many oxoanions of elements in lower oxidation state obey the octet rule and this can be used to rationalize the formulae adopted. For example, chlorine has two valence electrons so it can accommodate three electron pairs from bonds with oxide ions, the charge on the ion is +5 −3 ×2 = −1, and so the formula is ClO−3. The structure of the ion is predicted by VSEPR theory to be pyramidal, in a similar way, the oxyanion of chlorine has the formula ClO−2, and is bent with two lone pairs and two bonding pairs. In the third and subsequent rows of the table, 6-coordination is possible. Thus molybdenum does not form MoO6−6, but forms the tetrahedral molybdate anion, moO6 units are found in condensed molybdates. Fully protonated oxoanions with a structure are found in such species as Sn2−6. The naming of monomeric oxoanions follows the following rules, the amount of order in the solution is decreased, releasing a certain amount of entropy which makes the Gibbs free energy more negative and favors the forward reaction. It is an example of a reaction with the monomeric oxoanion acting as a base. The reverse reaction is a reaction, as a water molecule. Further condensation may occur, particularly with anions of higher charge, the conversion of ATP to ADP is an hydrolysis reaction and is an important source of energy in biological systems
24.
Acid strength
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The strength of an acid refers to its ability or tendency to lose a proton. A strong acid is one that completely ionizes in a solution, in water, one mole of a strong acid HA dissolves yielding one mole of H+ and one mole of the conjugate base, A−. Essentially, none of the non-ionized acid HA remains. Examples of strong acids are hydrochloric acid, hydroiodic acid, hydrobromic acid, perchloric acid, nitric acid, in aqueous solution, each of these essentially ionizes 100%. In contrast, an acid only partially dissociates. Examples in water include carbonic acid and acetic acid, at equilibrium, both the acid and the conjugate base are present in solution. Stronger acids have an acid dissociation constant and a smaller logarithmic constant than weaker acids. The stronger an acid is, the more easily it loses a proton, two key factors that contribute to the ease of deprotonation are the polarity of the H—A bond and the size of atom A, which determines the strength of the H—A bond. Acid strengths also depend on the stability of the conjugate base, while Ka measures the strength of an acidic molecule, the strength of an aqueous acid solution is measured by pH, which is a function of the concentration of hydronium ions in solution. The pH of a solution of an acid in water is determined by both Ka and the acid concentration. For weak acid solutions, it depends on the degree of dissociation, for concentrated solutions of strong acids with a pH less than about zero, the Hammett acidity function is a better measure of acidity than the pH. Sulfonic acids, which are organic oxyacids, are a class of strong acids, a common example is p-toluenesulfonic acid. Unlike sulfuric acid itself, sulfonic acids can be solids, in fact, polystyrene functionalized into polystyrene sulfonate is a solid strongly acidic plastic that is filterable. Superacids are acid solutions that are more acidic than 100% sulfuric acid, examples of superacids are fluoroantimonic acid, magic acid and perchloric acid. Superacids can permanently protonate water to give ionic, crystalline hydronium salts and they can also quantitatively stabilize carbocations. In aqueous solution, an acid is an acid that ionizes completely by losing one proton.74. An example is HCl for which pKa = −6.3 and this generally means that, in aqueous solution at standard temperature and pressure, the concentration of hydronium ions is equal to the concentration of strong acid introduced to the solution. No acid species stronger than H3O+ can exist in aqueous solution, the acidity of the stronger acid is said to be leveled to the acidity of hydronium ion. Strong acids are distinguished from weak acids, in which dissociation is incomplete and is represented as an equilibrium, the typical definition of a weak acid is any acid that does not dissociate completely
25.
Chromic acid
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The term chromic acid is usually used for a mixture made by adding concentrated sulfuric acid to a dichromate, which may contain a variety of compounds, including solid chromium trioxide. This kind of acid may be used as a cleaning mixture for glass. Chromic acid may also refer to the species, H2CrO4 of which the trioxide is the anhydride. Chromic acid features chromium in a state of +6. It is a strong and corrosive oxidising agent, molecular chromic acid, H2CrO4, has much in common with sulfuric acid, H2SO4. Both are classified as acids, though only the first proton is lost easily. H2CrO4 ⇌ − + H+ The pKa for the equilibrium is not well characterized, reported values vary between about −0.8 to 1.6. The value at zero ionic strength is difficult to determine because half dissociation only occurs in acidic solution, at about pH0. A further complication is that the ion − has a tendency to dimerize, with the loss of a water molecule, to form the dichromate ion. Furthermore, the dichromate can be protonated, − ⇌ 2− + H+ pK =1.8 The pK value for this shows that it can be ignored at pH >4. Loss of the second occurs in the pH range 4–8. Molecular chromic acid could in principle be made by adding chromium trioxide to water, CrO3 + H2O ⇌ H2CrO4 but in practice the reverse reaction occurs when molecular chromic acid is dehydrated. This is what happens when concentrated sulfuric acid is added to a dichromate solution, at first the colour changes from orange to red and then deep red crystals of chromium trioxide precipitate from the mixture, without further colour change. The colours are due to LMCT transitions, Chromium trioxide is the anhydride of molecular chromic acid. It is a Lewis acid and can react with a Lewis base, dichromic acid, H2Cr2O7, is the fully protonated form of the dichromate ion and also can be seen as the product of adding chromium trioxide to molecular chromic acid. 2− + 2H+ ⇌ H2Cr2O7 ⇌ H2CrO4 + CrO3 It is probably present in chromic acid cleaning mixtures along with the mixed chromosulfuric acid H2CrSO7, chromic acid is an intermediate in chromium plating, and is also used in ceramic glazes, and colored glass. Because a solution of acid in sulfuric acid is a powerful oxidizing agent, it can be used to clean laboratory glassware. This application has declined due to environmental concerns, furthermore, the acid leaves trace amounts of paramagnetic chromic ions — Cr — that can interfere with certain applications, such as NMR spectroscopy
26.
Acid dissociation constant
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An acid dissociation constant, Ka, is a quantitative measure of the strength of an acid in solution. It is the constant for a chemical reaction known as dissociation in the context of acid–base reactions. In the example shown in the figure, HA represents acetic acid, and A− represents the acetate ion, the chemical species HA, A− and H3O+ are said to be in equilibrium when their concentrations do not change with the passing of time. The definition can then be more simply H A ⇌ A − + H +, K a = This is the definition in common usage. A weak acid has a pKa value in the approximate range −2 to 12 in water, pKa values for strong acids can, however, be estimated by theoretical means. The definition can be extended to non-aqueous solvents, such as acetonitrile and dimethylsulfoxide. Denoting a solvent molecule by S H A + S ⇌ A − + S H +, K a = When the concentration of solvent molecules can be taken to be constant, K a =, as before. The value of pKa also depends on structure of the acid in many ways. For example, Pauling proposed two rules, one for successive pKa of polyprotic acids, and one to estimate the pKa of oxyacids based on the number of =O and −OH groups. Other structural factors that influence the magnitude of the dissociation constant include inductive effects, mesomeric effects. Hammett type equations have frequently applied to the estimation of pKa. The quantitative behaviour of acids and bases in solution can be only if their pKa values are known. These calculations find application in different areas of chemistry, biology, medicine. Acid dissociation constants are essential in aquatic chemistry and chemical oceanography. In living organisms, acid–base homeostasis and enzyme kinetics are dependent on the pKa values of the acids and bases present in the cell. According to Arrheniuss original definition, an acid is a substance that dissociates in solution, releasing the hydrogen ion H+. The equilibrium constant for this reaction is known as a dissociation constant. Brønsted and Lowry generalised this further to an exchange reaction
27.
Redox
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Redox is a chemical reaction in which the oxidation states of atoms are changed. Any such reaction involves both a process and a complementary oxidation process, two key concepts involved with electron transfer processes. Redox reactions include all chemical reactions in which atoms have their oxidation state changed, in general, the chemical species from which the electron is stripped is said to have been oxidized, while the chemical species to which the electron is added is said to have been reduced. It can be explained in terms, Oxidation is the loss of electrons or an increase in oxidation state by a molecule, atom. Reduction is the gain of electrons or a decrease in state by a molecule, atom. As an example, during the combustion of wood, oxygen from the air is reduced, the reaction can occur relatively slowly, as in the case of rust, or more quickly, as in the case of fire. Redox is a portmanteau of reduction and oxidation, the word oxidation originally implied reaction with oxygen to form an oxide, since dioxygen was historically the first recognized oxidizing agent. Later, the term was expanded to encompass oxygen-like substances that accomplished parallel chemical reactions, ultimately, the meaning was generalized to include all processes involving loss of electrons. The word reduction originally referred to the loss in weight upon heating a metallic ore such as an oxide to extract the metal. In other words, ore was reduced to metal, antoine Lavoisier showed that this loss of weight was due to the loss of oxygen as a gas. Later, scientists realized that the atom gains electrons in this process. The meaning of reduction then became generalized to all processes involving gain of electrons. Even though reduction seems counter-intuitive when speaking of the gain of electrons, it help to think of reduction as the loss of oxygen. Since electrons are charged, it is also helpful to think of this as reduction in electrical charge. The electrochemist John Bockris has used the words electronation and deelectronation to describe reduction and oxidation processes respectively when they occur at electrodes and these words are analogous to protonation and deprotonation, but they have not been widely adopted by chemists. The term hydrogenation could be used instead of reduction, since hydrogen is the agent in a large number of reactions. But, unlike oxidation, which has been generalized beyond its root element, the word redox was first used in 1928. The processes of oxidation and reduction occur simultaneously and cannot happen independently of one another, the oxidation alone and the reduction alone are each called a half-reaction, because two half-reactions always occur together to form a whole reaction
28.
Chrome yellow
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It occurs naturally as the mineral crocoite but the mineral itself was never used as a pigment in paintings. Because the pigment tends to oxidize and darken on exposure to air over time, and it contains lead, Chrome yellow had been commonly produced by mixing solutions of lead nitrate and potassium chromate and filtering off the lead chromate precipitate. The first recorded use of yellow as a color name in English was in 1818. List of colors List of inorganic pigments School bus yellow Kühn, H. and Curran, M. Chrome Yellow and Other Chromate Pigments, a Handbook of Their History and Characteristics, Vol.1, L. Feller, Ed. Cambridge University Press, London 1986 Chrome yellow, Colourlex Pichon, pigment degradation, Chrome yellow’s darker side
29.
Hexavalent chromium
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Hexavalent chromium refers to chemical compounds that contain the element chromium in the +6 oxidation state. Virtually all chromium ore is processed via hexavalent chromium, specifically the salt sodium dichromate, approximately 136,000 tonnes of hexavalent chromium were produced in 1985. Additional hexavalent chromium compounds are chromium trioxide and various salts of chromate and dichromate, Hexavalent chromium is used in textile dyes, wood preservation, anti-corrosion products, chromate conversion coatings, and a variety of niche uses. Hexavalent chromium can be formed when performing hot work such as welding on steel or melting chromium metal. In these situations the chromium is not originally hexavalent, but the temperatures involved in the process result in oxidation that converts the chromium to a hexavalent state. Hexavalent chromium can also be found in drinking water and public water systems, inhaled hexavalent chromium is recognized as a human carcinogen. Workers in many occupations are exposed to hexavalent chromium, problematic exposure is known to occur among workers who handle chromate-containing products and those who grind and/ or weld stainless steel. Workers who are exposed to hexavalent chromium are at increased risk of developing cancer, asthma, or damage to the nasal epithelia. Within the European Union, the use of hexavalent chromium in electronic equipment is prohibited by the Restriction of Hazardous Substances Directive. Hexavalent chromium compounds are genotoxic carcinogens, taking advantage of its structural similarity to sulfate, chromate is transported into cells via sulfate channels. Inside the cell, chromium is reduced first to pentavalent chromium then to trivalent chromium without the aid of any enzymes, the reduction occurs via direct electron transfer primarily from ascorbate and some nonprotein thiols. Vitamin C and other reducing agents combine with chromate to give chromium products inside the cell, the resultant chromium forms stable complexes with nucleic acids and proteins. This causes strand breaks and Cr-DNA adducts which are responsible for mutagenic damage, both insoluble salts of lead and barium chromates as well as soluble chromates were negative in the implantation model of lung carcinogenesis. Yet, soluble chromates are a confirmed carcinogen so it would be prudent to consider all chromates carcinogenic, chronic inhalation from occupational exposures increases the risk of respiratory cancers. The most common form of lung malignancies in chromate workers is squamous cell carcinoma, ingestion of chromium through drinking water has been found to cause cancer in the oral cavity and small intestine. It can also cause irritation or ulcers in the stomach and intestines, liver toxicity shows the body’s apparent inability to detoxify chromium in the GI tract where it can then enter the circulatory system. Chromate-dyed textiles or chromate-tanned leather shoes can cause skin sensitivity, in the U. S. the OSHA PEL for airborne exposures to hexavalent chromium is 5 µg/m3. The U. S. National Institute for Occupational Safety and Health proposed a REL of 0.2 µg/m3 for airborne exposures to hexavalent chromium, for drinking water the United States Environmental Protection Agency does not have a Maximum Contaminant Level for hexavalent chromium
30.
Chrome plating
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Chrome plating, often referred to simply as chrome, is a technique of electroplating a thin layer of chromium onto a metal object. The chromed layer can be decorative, provide corrosion resistance, ease cleaning procedures, sometimes a less expensive imitator of chrome may be used for aesthetic purposes. Different substrates need different etching solutions, such as hydrochloric, hydrofluoric, ferric chloride is also popular for the etching of nimonic alloys. Sometimes the component enters the chrome plating vat while electrically live, sometimes the component has a conforming anode made from lead/tin or platinized titanium. A typical hard chrome vat plates at about 1 mil per hour, various linishing and buffing processes are used in preparing components for decorative chrome plating. The chrome plating chemicals are very toxic, disposal of chemicals is regulated in most countries. Some common industry specifications governing the chrome plating process are AMS2460, AMS2406, hexavalent chromium plating, also known as hex-chrome, Cr+6, and chrome plating, uses chromium trioxide as the main ingredient. Hexavalent chromium plating solution is used for decorative and hard plating, along with bright dipping of copper alloys, chromic acid anodizing, a typical hexavalent chromium plating process is, activation bath, chromium bath, rinse, and rinse. The activation bath is typically a tank of chromic acid with a current run through it. This etches the surface and removes any scale. In some cases the activation step is done in the chromium bath, the chromium bath is a mixture of chromium trioxide and sulfuric acid, the ratio of which varies greatly between 75,1 to 250,1 by weight. This results in an extremely acidic bath, the temperature and current density in the bath affect the brightness and final coverage. For decorative coating the temperature ranges from 35 to 45 °C, temperature is also dependent on the current density, because a higher current density requires a higher temperature. Finally, the bath is agitated to keep the temperature steady. One functional disadvantage of hexavalent chromium plating is low cathode efficiency and this means it leaves a non-uniform coating, with more on edges and less in inside corners and holes. To overcome this problem the part may be over-plated and ground to size, from a health standpoint, hexavalent chromium is the most toxic form of chromium. In the U. S. the Environmental Protection Agency regulates it heavily, due to its low cathodic efficiency and high solution viscosity a toxic mist of water and hexavalent chromium is released from the bath. Wet scrubbers are used to control these emissions, the discharge from the wet scrubbers is treated to precipitate the chromium from the solution because it cannot remain in the waste water
31.
Heavy metals
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Heavy metals are generally defined as metals with relatively high densities, atomic weights, or atomic numbers. The criteria used, and whether metalloids are included, vary depending on the author, more specific definitions have been published, but none of these have been widely accepted. The definitions surveyed in this article encompass up to 96 out of the 118 chemical elements, only mercury, lead, despite this lack of agreement, the term is widely used in science. A density of more than 5 g/cm3 is sometimes quoted as a commonly used criterion and is used in the body of this article. The earliest known metals—common metals such as iron, copper, and tin, and precious metals such as silver, gold, and platinum—are heavy metals. From 1809 onwards, light metals, such as magnesium, aluminium, and titanium, were discovered, as well as less well-known heavy metals including gallium, thallium, and hafnium. Some heavy metals are essential nutrients, or relatively harmless. Other heavy metals, such as cadmium, mercury, and lead, are highly poisonous, potential sources of heavy metal poisoning include mining and industrial wastes, agricultural runoff, occupational exposure, and paints and treated timber. Physical and chemical characterisations of heavy metals need to be treated with caution, as well as being relatively dense, heavy metals tend to be less reactive than lighter metals and have much less soluble sulfides and hydroxides. Heavy metals are scarce in the Earths crust but are present in many aspects of modern life. They are used in, for example, golf clubs, cars, antiseptics, self-cleaning ovens, plastics, solar panels, mobile phones, there is no widely agreed criterion-based definition of a heavy metal. Different meanings may be attached to the term, depending on the context, density criteria range from above 3.5 g/cm3 to above 7 g/cm3. Atomic weight definitions can range from greater than sodium, greater than 40, or more than 200, atomic numbers of heavy metals are generally given as greater than 20, sometimes this is capped at 92. Definitions based on atomic number have been criticised for including metals with low densities. For example, rubidium in group 1 of the table has an atomic number of 37 but a density of only 1.532 g/cm3. The same problem may occur with atomic weight based definitions, criteria based on chemical behaviour or periodic table position have been used or suggested. The United States Pharmacopeia includes a test for metals that involves precipitating metallic impurities as their coloured sulfides. The lanthanides satisfy Hawkes three-part description, the status of the actinides is not completely settled, in biochemistry, heavy metals are sometimes defined—on the basis of the Lewis acid behaviour of their ions in aqueous solution—as class B and borderline metals
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Lanthanide
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The lanthanide /ˈlænθənaɪd/ or lanthanoid /ˈlænθənɔɪd/ series of chemical elements comprises the fifteen metallic chemical elements with atomic numbers 57 through 71, from lanthanum through lutetium. These fifteen lanthanide elements, along with the similar elements scandium and yttrium, are often collectively known as the rare earth elements. The informal chemical symbol Ln is used in discussions of lanthanide chemistry to refer to any lanthanide. All lanthanide elements form trivalent cations, Ln3+, whose chemistry is largely determined by the ionic radius and they are termed lanthanides because the lighter elements in the series are chemically similar to lanthanum. Strictly speaking, both lanthanum and lutetium have been labeled as group 3 elements, because both have a single valence electron in the 5d shell. However, both elements are included in any general discussion of the chemistry of the lanthanide elements. Together with scandium and yttrium, the trivial name rare earths is sometimes used to all the lanthanides. This name arises from the minerals from which they were isolated, however, the use of the name is deprecated by IUPAC, as the elements are neither rare in abundance nor earths. Despite their abundance, even the technical term lanthanides could be interpreted to reflect a sense of elusiveness on the part of elements, as it comes from the Greek λανθανειν. However, if not referring to their abundance, but rather to their property of hiding behind each other in minerals. The term lanthanide was introduced by Victor Goldschmidt in 1925, the hybridisation is believed to be at its greatest for cerium, which has the lowest melting point of all,795 °C. The lanthanide metals are soft, their hardness increases across the series, europium stands out, as it has the lowest density in the series at 5.24 g/cm3 and the largest metallic radius in the series at 208.4 pm. It can be compared to barium, which has a radius of 222 pm. It is believed that the contains the larger Eu2+ ion. Ytterbium also has a metallic radius, and a similar explanation is suggested. The resistivities of the metals are relatively high, ranging from 29 to 134 μ-ohm·cm. These values can be compared to a conductor such as aluminium. With the exceptions of La, Yb, and Lu, the lanthanides are strongly paramagnetic, gadolinium becomes ferromagnetic at below 16 °C
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Alkaline earth metal
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The alkaline earth metals are six chemical elements in column 2 of the Periodic table. They are beryllium, magnesium, calcium, strontium, barium, the elements have very similar properties, they are all shiny, silvery-white, somewhat reactive metals at standard temperature and pressure. All the discovered alkaline earth metals occur in nature, experiments have been conducted to attempt the synthesis of element 120, the next potential member of the group, but they have all met with failure. The chemistry of radium is not well-established due to its radioactivity, thus, the alkaline earth metals are all silver-colored and soft, and have relatively low densities, melting points, and boiling points. In chemical terms, all of the alkaline metals react with the halogens to form the earth metal halides. All the alkaline earth metals except beryllium also react with water to form strongly alkaline hydroxides and, thus, the heavier alkaline earth metals react more vigorously than the lighter ones. The second ionization energy of all of the metals is also somewhat low. Beryllium is an exception, It does not react with water or steam, all compounds that include beryllium have a covalent bond. Even the compound beryllium fluoride, which is the most ionic beryllium compound, has a low melting point and a low electrical conductivity when melted. The alkaline earth metals all react with the halogens to form ionic halides, such as calcium chloride, calcium, strontium, and barium react with water to produce hydrogen gas and their respective hydroxides, and also undergo transmetalation reactions to exchange ligands. The table below is a summary of the key physical and atomic properties of the alkaline earth metals, calcium-48 is the lightest nuclide to undergo double beta decay. The natural radioisotope of calcium, calcium-48, makes up about 0. 1874% of natural calcium, barium-130 makes up approximately 0. 1062% of natural barium, and, thus, barium is weakly radioactive, as well. The alkaline earth metals are named after their oxides, the alkaline earths, whose old-fashioned names were beryllia, magnesia, lime, strontia and these oxides are basic when combined with water. Earth is an old term applied by early chemists to nonmetallic substances that are insoluble in water, the realization that these earths were not elements but compounds is attributed to the chemist Antoine Lavoisier. In his Traité Élémentaire de Chimie of 1789 he called them salt-forming earth elements, later, he suggested that the alkaline earths might be metal oxides, but admitted that this was mere conjecture. The calcium compounds calcite and lime have been known and used since prehistoric times, the same is true for the beryllium compounds beryl and emerald. The other compounds of the alkaline earth metals were discovered starting in the early 15th century, the magnesium compound magnesium sulfate was first discovered in 1618 by a farmer at Epsom in England. Strontium carbonate was discovered in minerals in the Scottish village of Strontian in 1790, the last element is the least abundant, radioactive radium, which was extracted from uraninite in 1898
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Chemical reaction
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A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Nuclear chemistry is a sub-discipline of chemistry that involves the reactions of unstable. The substance initially involved in a reaction are called reactants or reagents. Chemical reactions are characterized by a chemical change, and they yield one or more products. Reactions often consist of a sequence of individual sub-steps, the elementary reactions. Chemical reactions are described with chemical equations, which present the starting materials, end products. Chemical reactions happen at a characteristic reaction rate at a given temperature, typically, reaction rates increase with increasing temperature because there is more thermal energy available to reach the activation energy necessary for breaking bonds between atoms. Reactions may proceed in the forward or reverse direction until they go to completion or reach equilibrium, Reactions that proceed in the forward direction to approach equilibrium are often described as spontaneous, requiring no input of free energy to go forward. Non-spontaneous reactions require input of energy to go forward. Different chemical reactions are used in combinations during chemical synthesis in order to obtain a desired product, in biochemistry, a consecutive series of chemical reactions form metabolic pathways. These reactions are catalyzed by protein enzymes. Chemical reactions such as combustion in fire, fermentation and the reduction of ores to metals were known since antiquity, in the Middle Ages, chemical transformations were studied by Alchemists. They attempted, in particular, to lead into gold, for which purpose they used reactions of lead. The process involved heating of sulfate and nitrate minerals such as sulfate, alum. In the 17th century, Johann Rudolph Glauber produced hydrochloric acid and sodium sulfate by reacting sulfuric acid, further optimization of sulfuric acid technology resulted in the contact process in the 1880s, and the Haber process was developed in 1909–1910 for ammonia synthesis. From the 16th century, researchers including Jan Baptist van Helmont, Robert Boyle, the phlogiston theory was proposed in 1667 by Johann Joachim Becher. It postulated the existence of an element called phlogiston, which was contained within combustible bodies. This proved to be false in 1785 by Antoine Lavoisier who found the explanation of the combustion as reaction with oxygen from the air
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Tasmania
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Tasmania is an island state of the Commonwealth of Australia. It is located 240 km to the south of the Australian mainland, the state encompasses the main island of Tasmania, the 26th-largest island in the world, and the surrounding 334 islands. The state has a population of around 519,100, just over forty percent of which resides in the Greater Hobart precinct, Tasmanias area is 68,401 km2, of which the main island covers 64,519 km2. Though an island state, due to an error the state shares a land border with Victoria at its northernmost terrestrial point, Boundary Islet. The Bishop and Clerk Islets, about 37 km south of Macquarie Island, are the southernmost terrestrial point of the state of Tasmania, the island is believed to have been occupied by Aboriginals for 40,000 years before British colonisation. It is thought Tasmanian Aboriginals were separated from the mainland Aboriginal groups about 10,000 years ago when the sea rose to form Bass Strait. The conflict, which peaked between 1825 and 1831 and led to more than three years of law, cost the lives of almost 1100 Aboriginals and settlers. The near-destruction of Tasmanias Aboriginal population has been described by historians as an act of genocide by the British. The island was part of the Colony of New South Wales. In 1854 the present Constitution of Tasmania was passed and the year the state received permission to change its name to Tasmania. In 1901 it became a state through the process of the Federation of Australia, the state is named after Dutch explorer Abel Tasman, who made the first reported European sighting of the island on 24 November 1642. Tasman named the island Anthony van Diemens Land after his sponsor Anthony van Diemen, the name was later shortened to Van Diemens Land by the British. It was officially renamed Tasmania in honour of its first European discoverer on 1 January 1856, Tasmania was sometimes referred to as Dervon, as mentioned in the Jerilderie Letter written by the notorious Australian bushranger Ned Kelly in 1879. The colloquial expression for the state is Tassie, Tasmania is also colloquially shortened to Tas, especially when used in business names and website addresses. TAS is also the Australia Post abbreviation for the state, the reconstructed Palawa kani language name for Tasmania is Lutriwita. The island was adjoined to the mainland of Australia until the end of the last glacial period about 10,000 years ago, much of the island is composed of Jurassic dolerite intrusions through other rock types, sometimes forming large columnar joints. Tasmania has the worlds largest areas of dolerite, with many distinctive mountains, the central plateau and the southeast portions of the island are mostly dolerite. Mount Wellington above Hobart is an example, showing distinct columns known as the Organ Pipes
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Australia
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Australia, officially the Commonwealth of Australia, is a country comprising the mainland of the Australian continent, the island of Tasmania and numerous smaller islands. It is the worlds sixth-largest country by total area, the neighbouring countries are Papua New Guinea, Indonesia and East Timor to the north, the Solomon Islands and Vanuatu to the north-east, and New Zealand to the south-east. Australias capital is Canberra, and its largest urban area is Sydney, for about 50,000 years before the first British settlement in the late 18th century, Australia was inhabited by indigenous Australians, who spoke languages classifiable into roughly 250 groups. The population grew steadily in subsequent decades, and by the 1850s most of the continent had been explored, on 1 January 1901, the six colonies federated, forming the Commonwealth of Australia. Australia has since maintained a liberal democratic political system that functions as a federal parliamentary constitutional monarchy comprising six states. The population of 24 million is highly urbanised and heavily concentrated on the eastern seaboard, Australia has the worlds 13th-largest economy and ninth-highest per capita income. With the second-highest human development index globally, the country highly in quality of life, health, education, economic freedom. The name Australia is derived from the Latin Terra Australis a name used for putative lands in the southern hemisphere since ancient times, the Dutch adjectival form Australische was used in a Dutch book in Batavia in 1638, to refer to the newly discovered lands to the south. On 12 December 1817, Macquarie recommended to the Colonial Office that it be formally adopted, in 1824, the Admiralty agreed that the continent should be known officially as Australia. The first official published use of the term Australia came with the 1830 publication of The Australia Directory and these first inhabitants may have been ancestors of modern Indigenous Australians. The Torres Strait Islanders, ethnically Melanesian, were originally horticulturists, the northern coasts and waters of Australia were visited sporadically by fishermen from Maritime Southeast Asia. The first recorded European sighting of the Australian mainland, and the first recorded European landfall on the Australian continent, are attributed to the Dutch. The first ship and crew to chart the Australian coast and meet with Aboriginal people was the Duyfken captained by Dutch navigator, Willem Janszoon. He sighted the coast of Cape York Peninsula in early 1606, the Dutch charted the whole of the western and northern coastlines and named the island continent New Holland during the 17th century, but made no attempt at settlement. William Dampier, an English explorer and privateer, landed on the north-west coast of New Holland in 1688, in 1770, James Cook sailed along and mapped the east coast, which he named New South Wales and claimed for Great Britain. The first settlement led to the foundation of Sydney, and the exploration, a British settlement was established in Van Diemens Land, now known as Tasmania, in 1803, and it became a separate colony in 1825. The United Kingdom formally claimed the part of Western Australia in 1828. Separate colonies were carved from parts of New South Wales, South Australia in 1836, Victoria in 1851, the Northern Territory was founded in 1911 when it was excised from South Australia
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Chromite
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Chromite is an iron chromium oxide, FeCr2O4. It is a mineral belonging to the spinel group. Magnesium can substitute for iron in variable amounts as it forms a solution with magnesiochromite. It is by far the most industrially important mineral for the production of chromium, used as an alloying ingredient in stainless. Chromite is found as orthocumulate lenses of chromitite in peridotite from the Earths mantle and it also occurs in layered ultramafic intrusive rocks. In addition, it is found in rocks such as some serpentinites. Ore deposits of chromite form as early magmatic differentiates and it is commonly associated with olivine, magnetite, serpentine, and corundum. The vast Bushveld igneous complex of South Africa is a layered mafic to ultramafic igneous body with some layers consisting of 90% chromite making the rare rock type. The Stillwater igneous complex in Montana also contains significant chromite, the only ores of chromium are the minerals chromite and magnesiochromite. Most of the time, economic geology names chromite the whole chromite-magnesiochromite series, the two main products of chromite refining are ferrochromium and metallic chromium, for those products the ore smelter process differs considerably. Chromite is also used as a material, because it has a high heat stability. The chromium extracted from chromite is used in plating and alloying for production of corrosion resistant superalloys, nichrome. Chromium is used as a pigment for glass, glazes, and paint and it is also sometimes used as a gemstone. In 200214,600,000 metric tons of chromite were mined, the largest producers were South Africa, India, Kazakhstan, Zimbabwe, Finland, Iran, and Brazil with several other countries producing the rest of less than 10% of the world production. Afghanistan has significant deposits of high grade ore, which is mined illegally in Khost Province. In Pakistan, chromite is mined from the rocks in mainly the Muslimbagh killa Saifullah District. Most of the chromite is of metallurgical grade with Cr2O3 averaging 54%, recently, the biggest user of chromite ore has been China, importing large quantities from South Africa, Pakistan, and other countries. The concentrate is used to make ferrochrome, which is in used to make stainless steel
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Calcium carbonate
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Calcium carbonate is a chemical compound with the formula CaCO3. It is a substance found in rocks as the minerals calcite and aragonite and is the main component of pearls and the shells of marine organisms, snails. Calcium carbonate is the ingredient in agricultural lime and is created when calcium ions in hard water react with carbonate ions to create limescale. It is medicinally used as a supplement or as an antacid. Calcium carbonate shares the properties of other carbonates. CaCO3 + CO2 + H2O → Ca2 This reaction is important in the erosion of rock, forming caverns. An unusual form of calcium carbonate is the hexahydrate, ikaite, ikaite is stable only below 6 °C. The vast majority of calcium used in industry is extracted by mining or quarrying. Pure calcium carbonate, can be produced from a quarried source. Alternatively, calcium carbonate is prepared from calcium oxide, other forms can be prepared, the denser, orthorhombic λ-CaCO3 and μ-CaCO3, occurring as the mineral vaterite. The aragonite form can be prepared by precipitation at temperatures above 85 °C, calcite contains calcium atoms coordinated by 6 oxygen atoms, in aragonite they are coordinated by 9 oxygen atoms. The vaterite structure is not fully understood, magnesium carbonate MgCO3 has the calcite structure, whereas strontium and barium carbonate adopt the aragonite structure, reflecting their larger ionic radii. Calcite, aragonite and vaterite are pure calcium carbonate minerals, industrially important source rocks which are predominantly calcium carbonate include limestone, chalk, marble and travertine. Eggshells, snail shells and most seashells are predominantly calcium carbonate, oyster shells have enjoyed recent recognition as a source of dietary calcium, but are also a practical industrial source. While not practical as a source, dark green vegetables such as broccoli. Beyond Earth, strong evidence suggests the presence of Calcium carbonate on Mars, signs of Calcium Carbonate have been detected at more than one location. This provides some evidence for the past presence of liquid water, Carbonate is found frequently in geologic settings and constitute an enormous carbon reservoir. Calcium carbonate occurs as aragonite, calcite and dolomite, the carbonate minerals form the rock types, limestone, chalk, marble, travertine, tufa, and others
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Sodium carbonate
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Sodium carbonate, Na2CO3, is the water-soluble sodium salt of carbonic acid. It most commonly occurs as a crystalline decahydrate, which readily effloresces to form a white powder, pure sodium carbonate is a white, odorless powder that is hygroscopic. It has a strongly alkaline taste, and forms a basic solution in water. Sodium carbonate is known domestically for its everyday use as a water softener. Historically it was extracted from the ashes of plants growing in soils, such as vegetation from the Middle East, kelp from Scotland. Because the ashes of these plants were noticeably different from ashes of timber. It is synthetically produced in quantities from salt and limestone by a method known as the Solvay process. The manufacture of glass is one of the most important uses of sodium carbonate, Sodium carbonate acts as a flux for silica, lowering the melting point of the mixture to something achievable without special materials. This soda glass is mildly water-soluble, so some calcium carbonate is added to the mixture to make the glass produced insoluble. This type of glass is known as soda lime glass, soda for the sodium carbonate, soda lime glass has been the most common form of glass for centuries. Sodium carbonate is used as a relatively strong base in various settings. For example, it is used as a pH regulator to maintain stable alkaline conditions necessary for the action of the majority of film developing agents. It acts as an alkali because when dissolved in water, it dissociates into the acid, carbonic acid. This gives sodium carbonate in solution the ability to attack such as aluminium with the release of hydrogen gas. It is an additive in swimming pools used to raise the ph which can be lowered by chlorine tablets. In cooking, it is used in place of sodium hydroxide for lyeing, especially with German pretzels. These dishes are treated with a solution of a substance to change the pH of the surface of the food. In chemistry, it is used as an electrolyte
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Crocoite
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Crocoite is a mineral consisting of lead chromate, PbCrO4, and crystallizing in the monoclinic crystal system. It is identical in composition with the artificial product chrome yellow used as a paint pigment, crocoite is commonly found as large, well-developed prismatic adamatine crystals, although in many cases are poorly terminated. Crystals are of a bright hyacinth-red color, translucent, and have an adamantine to vitreous lustre, on exposure to UV light some of the translucency and brilliancy is lost. The streak is orange-yellow, Mohs hardness is 2. 5–3, in the type locality the crystals are found in gold-bearing quartz-veins traversing granite or gneiss and associated with crocoite are quartz, embreyite, phoenicochroite and vauquelinite. Phoenicochroite is a basic lead chromate, Pb2CrO5 with dark red crystals, vauquelinite was named after L. N. Vauquelin, who in 1797 discovered the element chromium in crocoite. Crocoite is also the official Tasmanian mineral emblem, oxidation of Cr3+ into CrO42− and decomposition of galena are required for crocoite formation. As crocoite is composed of lead chromate, it is toxic, examples of crocoite Bellite This article incorporates text from a publication now in the public domain, Chisholm, Hugh, ed. article name needed. Crocoite from the Berezovsk gold mines, world of Stones,10, 28-31 Bottrill, R. S. Williams, P. Dohnt, S. Sorrell, S. and Kemp, crocoite and associated minerals from Dundas and other locations in Tasmania. 12, 59-90 List of Tasmanian state emblems
41.
Atacama Desert
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The Atacama Desert is a plateau in South America, covering a 1, 000-kilometre strip of land on the Pacific coast, west of the Andes mountains. It is the driest non-polar desert in the world, according to estimates, the Atacama Desert proper occupies 105,000 square kilometres, or 128,000 square kilometres if the barren lower slopes of the Andes are included. Most of the desert is composed of terrain, salt lakes, sand. The National Geographic Society considers the area of southern Peru to be part of the Atacama Desert. Peru borders it on the north and the Chilean Matorral ecoregion borders it on the south, to the east lies the less arid Central Andean dry puna ecoregion. The drier portion of this ecoregion is located south of the Loa River between the parallel Sierra Vicuña Mackenna and Cordillera Domeyko, to the north of the Loa lies the Pampa del Tamarugal. The Coastal Cliff of northern Chile west of the Chilean Coast Range is the topographic feature of the coast. The geomorphology of the Atacama Desert has been characterized as a low-relief bench similar to a giant uplifted terrace by Armijo and co-workers. The intermediate depression forms a series of basins in much of Atacama Desert south of latitude 19°30’ S. North of this latitude the intermediate depression drains into the Pacific Ocean. Although the almost total lack of precipitation is the most prominent characteristic of the Atacama Desert, in 2012, the altiplano winter brought floods to San Pedro de Atacama. On 25 March 2015, heavy rainfall affected the part of the Atacama desert. Resulting floods triggered mudflows that affected the cities of Copiapo, Tierra Amarilla, Chile, Chanaral, the Atacama Desert is commonly known as the driest non-polar place in the world, especially the surroundings of the abandoned Yungay town. The average rainfall is about 15 mm per year, although some locations, such as Arica and Iquique, moreover, some weather stations in the Atacama have never received rain. Periods of up to four years have been registered with no rainfall in the sector, delimited by the cities of Antofagasta, Calama and Copiapó. Evidence suggests that the Atacama may not have had any significant rainfall from 1570 to 1971, the Atacama Desert may be the oldest desert on earth, and has experienced extreme hyperaridity for at least 3 million years, making it the oldest continuously arid region on earth. The long history of aridity raises the possibility that supergene mineralisation, under the conditions, can form in arid environments. This desert is so arid, many mountains higher than 6,000 m are free of glaciers. Only the highest peaks have some permanent snow coverage, the southern part of the desert, between 25 and 27°S, may have been glacier-free throughout the Quaternary, though permafrost extends down to an altitude of 4,400 m and is continuous above 5,600 m
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Carcinogen
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A carcinogen is any substance, radionuclide, or radiation that is an agent directly involved in causing cancer. This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes, several radioactive substances are considered carcinogens, but their carcinogenic activity is attributed to the radiation, for example gamma rays and alpha particles, which they emit. Common examples of non-radioactive carcinogens are inhaled asbestos, certain dioxins, although the public generally associates carcinogenicity with synthetic chemicals, it is equally likely to arise in both natural and synthetic substances. Carcinogens are not necessarily immediately toxic, thus their effect can be insidious, Cancer is any disease in which normal cells are damaged and do not undergo programmed cell death as fast as they divide via mitosis. Usually, severe DNA damage leads to apoptosis, but if the cell death pathway is damaged. Aflatoxin B1, which is produced by the fungus Aspergillus flavus growing on stored grains, nuts and peanut butter, is an example of a potent, certain viruses such as hepatitis B and human papilloma virus have been found to cause cancer in humans. The first one shown to cause cancer in animals is Rous sarcoma virus, other infectious organisms which cause cancer in humans include some bacteria and helminths. Dioxins and dioxin-like compounds, benzene, kepone, EDB, vinyl chloride, from which PVC is manufactured, is a carcinogen and thus a hazard in PVC production. Co-carcinogens are chemicals that do not necessarily cause cancer on their own, after the carcinogen enters the body, the body makes an attempt to eliminate it through a process called biotransformation. The purpose of these reactions is to make the carcinogen more water-soluble so that it can be removed from the body, however, in some cases, these reactions can also convert a less toxic carcinogen into a more toxic carcinogen. DNA is nucleophilic, therefore soluble carbon electrophiles are carcinogenic, because DNA attacks them, for example, some alkenes are toxicated by human enzymes to produce an electrophilic epoxide. DNA attacks the epoxide, and is bound permanently to it and this is the mechanism behind the carcinogenicity of benzopyrene in tobacco smoke, other aromatics, aflatoxin and mustard gas. Carcinogenicity of radiation depends on the type of radiation, type of exposure, for example, alpha radiation has low penetration and is not a hazard outside the body, but emitters are carcinogenic when inhaled or ingested. Low-level ionizing radiation may induce irreparable DNA damage leading to pre-mature aging, not all types of electromagnetic radiation are carcinogenic. Higher-energy radiation, including radiation, x-rays, and gamma radiation, generally is carcinogenic. For most people, ultraviolet radiations from sunlight is the most common cause of skin cancer, in Australia, where people with pale skin are often exposed to strong sunlight, melanoma is the most common cancer diagnosed in people aged 15–44 years. Substances or foods irradiated with electrons or electromagnetic radiation are not carcinogenic, in contrast, non-electromagnetic neutron radiation produced inside nuclear reactors can produce secondary radiation through nuclear transmutation. Chemicals used in processed and cured such as some brands of bacon, sausages
