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67-421: The King Island Pluton is petrographically similar to the shield volcanoes in the central Anahim Volcanic Belt . As a result, the pluton is thought to represent the magma chamber of an extinct volcanic centre that has since eroded away. At the time of its formation, the pluton was emplaced 2 to 5 km (1.2 to 3.1 mi) below the surface. This article about a specific Canadian geological feature

134-414: A spans many orders of magnitude, a more manageable constant, p K a is more frequently used, where p K a = −log 10 K a . Stronger acids have a smaller p K a than weaker acids. Experimentally determined p K a at 25 °C in aqueous solution are often quoted in textbooks and reference material. Arrhenius acids are named according to their anions . In the classical naming system,

201-450: A values are small, but K a1 > K a2 . A triprotic acid (H 3 A) can undergo one, two, or three dissociations and has three dissociation constants, where K a1 > K a2 > K a3 . An inorganic example of a triprotic acid is orthophosphoric acid (H 3 PO 4 ), usually just called phosphoric acid . All three protons can be successively lost to yield H 2 PO 4 , then HPO 4 , and finally PO 4 ,

268-447: A Lewis acid, H , but at the same time, they also yield an equal amount of a Lewis base (acetate, citrate, or oxalate, respectively, for the acids mentioned). This article deals mostly with Brønsted acids rather than Lewis acids. Reactions of acids are often generalized in the form HA ⇌ H + A , where HA represents the acid and A is the conjugate base . This reaction is referred to as protolysis . The protonated form (HA) of an acid

335-638: A Lewis base and transfers a lone pair of electrons to form a bond with a hydrogen ion. The species that gains the electron pair is the Lewis acid; for example, the oxygen atom in H 3 O gains a pair of electrons when one of the H—O bonds is broken and the electrons shared in the bond become localized on oxygen. Depending on the context, a Lewis acid may also be described as an oxidizer or an electrophile . Organic Brønsted acids, such as acetic, citric, or oxalic acid, are not Lewis acids. They dissociate in water to produce

402-433: A class of strong acids. A common example is toluenesulfonic acid (tosylic 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 acids stronger than 100% sulfuric acid. Examples of superacids are fluoroantimonic acid , magic acid and perchloric acid . The strongest known acid

469-508: A covalent bond with an electron pair, however, and are therefore not Lewis acids. Conversely, many Lewis acids are not Arrhenius or Brønsted–Lowry acids. In modern terminology, an acid is implicitly a Brønsted acid and not a Lewis acid, since chemists almost always refer to a Lewis acid explicitly as such. Modern definitions are concerned with the fundamental chemical reactions common to all acids. Most acids encountered in everyday life are aqueous solutions , or can be dissolved in water, so

536-489: A heating stage on a petrographic microscope provides clues to the temperature and pressure conditions existent during the mineral formation. Petrography as a science began in 1828 when Scottish physicist William Nicol invented the technique for producing polarized light by cutting a crystal of Iceland spar , a variety of calcite , into a special prism which became known as the Nicol prism . The addition of two such prisms to

603-497: A high specific gravity. Solutions of potassium mercuric iodide (sp. gr. 3.196), cadmium borotungstate (sp. gr. 3.30), methylene iodide (sp. gr. 3.32), bromoform (sp. gr. 2.86), or acetylene bromide (sp. gr. 3.00) are the principal fluids employed. They may be diluted (with water, benzene, etc.) or concentrated by evaporation. If the rock is granite consisting of biotite (sp. gr. 3.1), muscovite (sp. gr. 2.85), quartz (sp. gr. 2.65), oligoclase (sp. gr. 2.64), and orthoclase (sp. gr. 2.56),

670-506: A higher concentration of positive hydrogen ions in the solution. Chemicals or substances having the property of an acid are said to be acidic . Common aqueous acids include hydrochloric acid (a solution of hydrogen chloride that is found in gastric acid in the stomach and activates digestive enzymes ), acetic acid (vinegar is a dilute aqueous solution of this liquid), sulfuric acid (used in car batteries ), and citric acid (found in citrus fruits). As these examples show, acids (in

737-772: A knife to ascertain the hardness of rocks and minerals, and a pocket lens to magnify their structure, the field geologist is rarely at a loss to what group a rock belongs. The fine grained species are often indeterminable in this way, and the minute mineral components of all rocks can usually be ascertained only by microscopic examination. But it is easy to see that a sandstone or grit consists of more or less rounded, water-worn sand grains and if it contains dull, weathered particles of feldspar, shining scales of mica or small crystals of calcite these also rarely escape observation. Shales and clay rocks generally are soft, fine grained, often laminated and not infrequently contain minute organisms or fragments of plants. Limestones are easily marked with

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804-402: A knife-blade, effervesce readily with weak cold acid and often contain entire or broken shells or other fossils. The crystalline nature of a granite or basalt is obvious at a glance, and while the former contains white or pink feldspar, clear vitreous quartz and glancing flakes of mica, the other shows yellow-green olivine, black augite, and gray stratiated plagioclase. Other simple tools include

871-489: A particular location was locally produced or traded from elsewhere. This kind of information, along with other evidence, can support conclusions about settlement patterns, group and individual mobility , social contacts, and trade networks. In addition, an understanding of how certain minerals are altered at specific temperatures can allow archaeological petrographers to infer aspects of the ceramic production process itself, such as minimum and maximum temperatures reached during

938-440: A rock powder before it dissolves augite or hypersthene. Methods of separation by specific gravity have a still wider application. The simplest of these is levigation , which is extensively employed in mechanical analysis of soils and treatment of ores, but is not so successful with rocks, as their components do not, as a rule, differ greatly in specific gravity. Fluids are used that do not attack most rock-forming minerals, but have

1005-464: A simple solution of an acid compound in water is determined by the dilution of the compound and the compound's K a . Lewis acids have been classified in the ECW model and it has been shown that there is no one order of acid strengths. The relative acceptor strength of Lewis acids toward a series of bases, versus other Lewis acids, can be illustrated by C-B plots . It has been shown that to define

1072-498: A solution with pH 7.0, which is only the case with similar acid and base strengths during a reaction. Neutralization with a base weaker than the acid results in a weakly acidic salt. An example is the weakly acidic ammonium chloride , which is produced from the strong acid hydrogen chloride and the weak base ammonia . Conversely, neutralizing a weak acid with a strong base gives a weakly basic salt (e.g., sodium fluoride from hydrogen fluoride and sodium hydroxide ). In order for

1139-476: A sour taste, can turn blue litmus red, and react with bases and certain metals (like calcium ) to form salts . The word acid is derived from the Latin acidus , meaning 'sour'. An aqueous solution of an acid has a pH less than 7 and is colloquially also referred to as "acid" (as in "dissolved in acid"), while the strict definition refers only to the solute . A lower pH means a higher acidity , and thus

1206-577: A source of H 3 O when dissolved in water, and it acts as a Brønsted acid by donating a proton to water. In the second example CH 3 COOH undergoes the same transformation, in this case donating a proton to ammonia (NH 3 ), but does not relate to the Arrhenius definition of an acid because the reaction does not produce hydronium. Nevertheless, CH 3 COOH is both an Arrhenius and a Brønsted–Lowry acid. Brønsted–Lowry theory can be used to describe reactions of molecular compounds in nonaqueous solution or

1273-534: A vacant orbital that can form a covalent bond by sharing a lone pair of electrons on an atom in a base, for example the nitrogen atom in ammonia (NH 3 ). Lewis considered this as a generalization of the Brønsted definition, so that an acid is a chemical species that accepts electron pairs either directly or by releasing protons (H ) into the solution, which then accept electron pairs. Hydrogen chloride, acetic acid, and most other Brønsted–Lowry acids cannot form

1340-455: A very large number of acidic protons. A diprotic acid (here symbolized by H 2 A) can undergo one or two dissociations depending on the pH. Each dissociation has its own dissociation constant, K a1 and K a2 . The first dissociation constant is typically greater than the second (i.e., K a1 > K a2 ). For example, sulfuric acid (H 2 SO 4 ) can donate one proton to form the bisulfate anion (HSO 4 ), for which K a1

1407-418: Is helium hydride ion , with a proton affinity of 177.8kJ/mol. Superacids can permanently protonate water to give ionic, crystalline hydronium "salts". They can also quantitatively stabilize carbocations . While K a measures the strength of an acid compound, the strength of an aqueous acid solution is measured by pH, which is an indication of the concentration of hydronium in the solution. The pH of

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1474-496: Is a stub . You can help Misplaced Pages by expanding it . This article about a location on the Central Coast of British Columbia , Canada is a stub . You can help Misplaced Pages by expanding it . Petrographically Petrography is a branch of petrology that focuses on detailed descriptions of rocks . Someone who studies petrography is called a petrographer . The mineral content and the textural relationships within

1541-700: Is a common approach. It may be performed with a powerful, adjustable-strength electromagnet. A weak magnetic field attracts magnetite, then haematite and other iron ores. Silicates that contain iron follow in definite order—biotite, enstatite, augite, hornblende, garnet, and similar ferro-magnesian minerals are successively abstracted. Finally, only the colorless, non-magnetic compounds, such as muscovite, calcite, quartz, and feldspar remain. Chemical methods also are useful. A weak acid dissolves calcite from crushed limestone, leaving only dolomite, silicates, or quartz. Hydrofluoric acid attacks feldspar before quartz and, if used cautiously, dissolves these and any glassy material in

1608-426: Is also sometimes referred to as the free acid . Acid–base conjugate pairs differ by one proton, and can be interconverted by the addition or removal of a proton ( protonation and deprotonation , respectively). The acid can be the charged species and the conjugate base can be neutral in which case the generalized reaction scheme could be written as HA ⇌ H + A . In solution there exists an equilibrium between

1675-607: Is established by covering a bare rock-section with ammonium molybdate solution. A turbid yellow precipitate forms over the crystals of the mineral in question (indicating the presence of phosphates). Many silicates are insoluble in acids and cannot be tested in this way, but others are partly dissolved, leaving a film of gelatinous silica that can be stained with coloring matters, such as the aniline dyes (nepheline, analcite, zeolites, etc.). Complete chemical analysis of rocks are also widely used and important, especially in describing new species. Rock analysis has of late years (largely under

1742-487: Is greatest in rocks containing the most magnesia, iron, and heavy metal while least in rocks rich in alkalis, silica, and water. It diminishes with weathering. Generally, the specific gravity of rocks with the same chemical composition is higher if highly crystalline and lower if wholly or partly vitreous. The specific gravity of the more common rocks range from about 2.5 to 3.2. Archaeologists use petrography to identify mineral components in pottery . This information ties

1809-476: Is simply added to the name of the ionic compound. Thus, for hydrogen chloride, as an acid solution, the IUPAC name is aqueous hydrogen chloride. The strength of an acid refers to its ability or tendency to lose a proton. A strong acid is one that completely dissociates in water; in other words, one mole of a strong acid HA dissolves in water yielding one mole of H and one mole of the conjugate base, A , and none of

1876-459: Is the solvent and hydronium ion is formed by the HCl solute. The next two reactions do not involve the formation of ions but are still proton-transfer reactions. In the second reaction hydrogen chloride and ammonia (dissolved in benzene ) react to form solid ammonium chloride in a benzene solvent and in the third gaseous HCl and NH 3 combine to form the solid. A third, only marginally related concept

1943-422: Is very large; then it can donate a second proton to form the sulfate anion (SO 4 ), wherein the K a2 is intermediate strength. The large K a1 for the first dissociation makes sulfuric a strong acid. In a similar manner, the weak unstable carbonic acid (H 2 CO 3 ) can lose one proton to form bicarbonate anion (HCO 3 ) and lose a second to form carbonate anion (CO 3 ). Both K

2010-425: The citrate ion. Although the subsequent loss of each hydrogen ion is less favorable, all of the conjugate bases are present in solution. The fractional concentration, α (alpha), for each species can be calculated. For example, a generic diprotic acid will generate 3 species in solution: H 2 A, HA , and A . The fractional concentrations can be calculated as below when given either the pH (which can be converted to

2077-445: The hydronium ion H 3 O and are known as Arrhenius acids . Brønsted and Lowry generalized the Arrhenius theory to include non-aqueous solvents . A Brønsted or Arrhenius acid usually contains a hydrogen atom bonded to a chemical structure that is still energetically favorable after loss of H . Aqueous Arrhenius acids have characteristic properties that provide a practical description of an acid. Acids form aqueous solutions with

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2144-428: The Arrhenius and Brønsted–Lowry definitions are the most relevant. The Brønsted–Lowry definition is the most widely used definition; unless otherwise specified, acid–base reactions are assumed to involve the transfer of a proton (H ) from an acid to a base. Hydronium ions are acids according to all three definitions. Although alcohols and amines can be Brønsted–Lowry acids, they can also function as Lewis bases due to

2211-406: The [H ]) or the concentrations of the acid with all its conjugate bases: A plot of these fractional concentrations against pH, for given K 1 and K 2 , is known as a Bjerrum plot . A pattern is observed in the above equations and can be expanded to the general n -protic acid that has been deprotonated i -times: where K 0 = 1 and the other K-terms are the dissociation constants for

2278-424: The acid and its conjugate base. The equilibrium constant K is an expression of the equilibrium concentrations of the molecules or the ions in solution. Brackets indicate concentration, such that [H 2 O] means the concentration of H 2 O . The acid dissociation constant K a is generally used in the context of acid–base reactions. The numerical value of K a is equal to the product (multiplication) of

2345-435: The acid. Neutralization is the reaction between an acid and a base, producing a salt and neutralized base; for example, hydrochloric acid and sodium hydroxide form sodium chloride and water: Neutralization is the basis of titration , where a pH indicator shows equivalence point when the equivalent number of moles of a base have been added to an acid. It is often wrongly assumed that neutralization should result in

2412-426: The artifacts to geological areas where the raw materials for the pottery were obtained. In addition to clay, potters often used rock fragments, usually called "temper" or "aplastics", to modify the clay's properties. The geological information obtained from the pottery components provides insight into how potters selected and used local and non-local resources. Archaeologists are able to determine whether pottery found in

2479-451: The blowpipe (to test the fusibility of detached crystals), the goniometer , the magnet, the magnifying glass and the specific gravity balance. When dealing with unfamiliar types or with rocks so fine grained that their component minerals cannot be determined with the aid of a hand lens, a microscope is used. Characteristics observed under the microscope include colour, colour variation under plane polarised light ( pleochroism , produced by

2546-442: The colloquial sense) can be solutions or pure substances, and can be derived from acids (in the strict sense) that are solids, liquids, or gases. Strong acids and some concentrated weak acids are corrosive , but there are exceptions such as carboranes and boric acid . The second category of acids are Lewis acids , which form a covalent bond with an electron pair. An example is boron trifluoride (BF 3 ), whose boron atom has

2613-501: The concentration of hydronium ions is greater than 10 moles per liter. Since pH is defined as the negative logarithm of the concentration of hydronium ions, acidic solutions thus have a pH of less than 7. While the Arrhenius concept is useful for describing many reactions, it is also quite limited in its scope. In 1923, chemists Johannes Nicolaus Brønsted and Thomas Martin Lowry independently recognized that acid–base reactions involve

2680-423: The concentrations of the products divided by the concentration of the reactants, where the reactant is the acid (HA) and the products are the conjugate base and H . The stronger of two acids will have a higher K a than the weaker acid; the ratio of hydrogen ions to acid will be higher for the stronger acid as the stronger acid has a greater tendency to lose its proton. Because the range of possible values for K

2747-418: The conventional classifications. A chemical analysis is usually sufficient to indicate whether a rock is igneous or sedimentary, and in either case to accurately show what subdivision of these classes it belongs to. In the case of metamorphic rocks it often establishes whether the original mass was a sediment or of volcanic origin. Specific gravity of rocks is determined by use of a balance and pycnometer. It

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2814-441: The crushed minerals float in methylene iodide. On gradual dilution with benzene they precipitate in the order above. Simple in theory, these methods are tedious in practice, especially as it is common for one rock-making mineral to enclose another. Expert handling of fresh and suitable rocks yields excellent results. In addition to naked-eye and microscopic investigation, chemical research methods are of great practical importance to

2881-414: The field depends principally on them and on a few rough chemical and physical tests; and to the practical engineer, architect and quarry-master they are all-important. Although frequently insufficient in themselves to determine the true nature of a rock, they usually serve for a preliminary classification, and often give all the information needed. With a small bottle of acid to test for carbonate of lime,

2948-413: The fluoride nucleus than they are in the lone fluoride ion. BF 3 is a Lewis acid because it accepts the electron pair from fluoride. This reaction cannot be described in terms of Brønsted theory because there is no proton transfer. The second reaction can be described using either theory. A proton is transferred from an unspecified Brønsted acid to ammonia, a Brønsted base; alternatively, ammonia acts as

3015-449: The following reactions are described in terms of acid–base chemistry: In the first reaction a fluoride ion , F , gives up an electron pair to boron trifluoride to form the product tetrafluoroborate . Fluoride "loses" a pair of valence electrons because the electrons shared in the B—F bond are located in the region of space between the two atomic nuclei and are therefore more distant from

3082-400: The free hydrogen nucleus, a proton , does not exist alone in water, it exists as the hydronium ion (H 3 O ) or other forms (H 5 O 2 , H 9 O 4 ). Thus, an Arrhenius acid can also be described as a substance that increases the concentration of hydronium ions when added to water. Examples include molecular substances such as hydrogen chloride and acetic acid. An Arrhenius base , on

3149-405: The gas phase. Hydrogen chloride (HCl) and ammonia combine under several different conditions to form ammonium chloride , NH 4 Cl. In aqueous solution HCl behaves as hydrochloric acid and exists as hydronium and chloride ions. The following reactions illustrate the limitations of Arrhenius's definition: As with the acetic acid reactions, both definitions work for the first example, where water

3216-490: The influence of the chemical laboratory of the United States Geological Survey) reached a high pitch of refinement and complexity. As many as twenty or twenty-five components may be determined, but for practical purposes a knowledge of the relative proportions of silica, alumina, ferrous and ferric oxides, magnesia, lime, potash, soda and water carry us a long way in determining a rock's position in

3283-454: The ionic suffix is dropped and replaced with a new suffix, according to the table following. The prefix "hydro-" is used when the acid is made up of just hydrogen and one other element. For example, HCl has chloride as its anion, so the hydro- prefix is used, and the -ide suffix makes the name take the form hydrochloric acid . Classical naming system: In the IUPAC naming system, "aqueous"

3350-417: The lone pairs of electrons on their oxygen and nitrogen atoms. In 1884, Svante Arrhenius attributed the properties of acidity to hydrogen ions (H ), later described as protons or hydrons . An Arrhenius acid is a substance that, when added to water, increases the concentration of H ions in the water. Chemists often write H ( aq ) and refer to the hydrogen ion when describing acid–base reactions but

3417-424: The lower Nicol prism , or more recently polarising films ), fracture characteristics of the grains, refractive index (in comparison to the mounting adhesive, typically Canada balsam ), and optical symmetry ( birefringent or isotropic ). In toto , these characteristics are sufficient to identify the mineral, and often to quite tightly estimate its major element composition. The process of identifying minerals under

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3484-531: The micro-texture and structure are critical to understanding the origin of the rock. Electron microprobe or atom probe tomography analysis of individual grains as well as whole rock chemical analysis by atomic absorption , X-ray fluorescence , and laser-induced breakdown spectroscopy are used in a modern petrographic lab. Individual mineral grains from a rock sample may also be analyzed by X-ray diffraction when optical means are insufficient. Analysis of microscopic fluid inclusions within mineral grains with

3551-440: The microscope is fairly subtle, but also mechanistic – it would be possible to develop an identification key that would allow a computer to do it. The more difficult and skilful part of optical petrography is identifying the interrelationships between grains and relating them to features seen in hand-sized specimen, at outcrop, or in mapping. Separation of the ingredients of a crushed rock powder to obtain pure samples for analysis

3618-503: The more easily it loses a proton, H . 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 are also often discussed in terms of the stability of the conjugate base. Stronger acids have a larger acid dissociation constant , K a and a lower p K a than weaker acids. Sulfonic acids , which are organic oxyacids, are

3685-600: The order of Lewis acid strength at least two properties must be considered. For Pearson's qualitative HSAB theory the two properties are hardness and strength while for Drago's quantitative ECW model the two properties are electrostatic and covalent. Monoprotic acids, also known as monobasic acids, are those acids that are able to donate one proton per molecule during the process of dissociation (sometimes called ionization) as shown below (symbolized by HA): Common examples of monoprotic acids in mineral acids include hydrochloric acid (HCl) and nitric acid (HNO 3 ). On

3752-408: The ordinary microscope converted the instrument into a polarizing, or petrographic microscope . Using transmitted light and Nicol prisms, it was possible to determine the internal crystallographic character of very tiny mineral grains, greatly advancing the knowledge of a rock's constituents. During the 1840s, a development by Henry C. Sorby and others firmly laid the foundation of petrography. This

3819-409: The original firing of the pot. Acid An acid is a molecule or ion capable of either donating a proton (i.e. hydrogen ion, H ), known as a Brønsted–Lowry acid , or forming a covalent bond with an electron pair , known as a Lewis acid . The first category of acids are the proton donors, or Brønsted–Lowry acids . In the special case of aqueous solutions , proton donors form

3886-423: The orthophosphate ion, usually just called phosphate . Even though the positions of the three protons on the original phosphoric acid molecule are equivalent, the successive K a values differ since it is energetically less favorable to lose a proton if the conjugate base is more negatively charged. An organic example of a triprotic acid is citric acid , which can successively lose three protons to finally form

3953-740: The other hand, for organic acids the term mainly indicates the presence of one carboxylic acid group and sometimes these acids are known as monocarboxylic acid. Examples in organic acids include formic acid (HCOOH), acetic acid (CH 3 COOH) and benzoic acid (C 6 H 5 COOH). Polyprotic acids, also known as polybasic acids, are able to donate more than one proton per acid molecule, in contrast to monoprotic acids that only donate one proton per molecule. Specific types of polyprotic acids have more specific names, such as diprotic (or dibasic) acid (two potential protons to donate), and triprotic (or tribasic) acid (three potential protons to donate). Some macromolecules such as proteins and nucleic acids can have

4020-504: The other hand, is a substance that increases the concentration of hydroxide (OH ) ions when dissolved in water. This decreases the concentration of hydronium because the ions react to form H 2 O molecules: Due to this equilibrium, any increase in the concentration of hydronium is accompanied by a decrease in the concentration of hydroxide. Thus, an Arrhenius acid could also be said to be one that decreases hydroxide concentration, while an Arrhenius base increases it. In an acidic solution,

4087-401: The petrographer. Crushed and separated powders, obtained by the processes above, may be analyzed to determine chemical composition of minerals in the rock qualitatively or quantitatively. Chemical testing, and microscopic examination of minute grains is an elegant and valuable means of discriminating between mineral components of fine-grained rocks. Thus, the presence of apatite in rock-sections

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4154-423: The protonated acid HA. In contrast, a weak acid only partially dissociates and at equilibrium both the acid and the conjugate base are in solution. Examples of strong acids are hydrochloric acid (HCl), hydroiodic acid (HI), hydrobromic acid (HBr), perchloric acid (HClO 4 ), nitric acid (HNO 3 ) and sulfuric acid (H 2 SO 4 ). In water each of these essentially ionizes 100%. The stronger an acid is,

4221-420: The rock are described in detail. The classification of rocks is based on the information acquired during the petrographic analysis . Petrographic descriptions start with the field notes at the outcrop and include macroscopic description of hand-sized specimens. The most important petrographer's tool is the petrographic microscope . The detailed analysis of minerals by optical mineralogy in thin section and

4288-466: The sequence of crystallization of the various mineral constituents in a rock, petrography progressed into petrogenesis and ultimately into petrology. Petrography principally advanced in Germany in the latter 19th century. The macroscopic characters of rocks, those visible in hand-specimens without the aid of the microscope, are very varied and difficult to describe accurately and fully. The geologist in

4355-453: The transfer of a proton. A Brønsted–Lowry acid (or simply Brønsted acid) is a species that donates a proton to a Brønsted–Lowry base. Brønsted–Lowry acid–base theory has several advantages over Arrhenius theory. Consider the following reactions of acetic acid (CH 3 COOH), the organic acid that gives vinegar its characteristic taste: Both theories easily describe the first reaction: CH 3 COOH acts as an Arrhenius acid because it acts as

4422-434: Was a technique to study very thin slices of rock. A slice of rock was affixed to a microscope slide and then ground so thin that light could be transmitted through mineral grains that otherwise appeared opaque. The position of adjoining grains was not disturbed, thus permitting analysis of rock texture . Thin section petrography became the standard method of rock study. Since textural details contribute greatly to knowledge of

4489-451: Was proposed in 1923 by Gilbert N. Lewis , which includes reactions with acid–base characteristics that do not involve a proton transfer. A Lewis acid is a species that accepts a pair of electrons from another species; in other words, it is an electron pair acceptor. Brønsted acid–base reactions are proton transfer reactions while Lewis acid–base reactions are electron pair transfers. Many Lewis acids are not Brønsted–Lowry acids. Contrast how

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