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Acidity Function
An acidity function is a measure of the acidity of a medium or solvent system, usually expressed in terms of its ability to donate protons to (or accept protons from) a solute ( Brønsted acidity). The pH scale is by far the most commonly used acidity function, and is ideal for dilute aqueous solutions. Other acidity functions have been proposed for different environments, most notably the Hammett acidity function, ''H''0, for superacid media and its modified version ''H''− for superbasic media. The term acidity function is also used for measurements made on basic systems, and the term basicity function is uncommon. Hammett-type acidity functions are defined in terms of a buffered medium containing a weak base B and its conjugate acid BH+: ::H_0 = K_ + \log where p''K''a is the dissociation constant of BH+. They were originally measured by using nitroanilines as weak bases or acid-base indicators and by measuring the concentrations of the protonated and unprotonated forms wi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Acidity
In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a sequence of database operations that satisfies the ACID properties (which can be perceived as a single logical operation on the data) is called a ''transaction''. For example, a transfer of funds from one bank account to another, even involving multiple changes such as debiting one account and crediting another, is a single transaction. In 1983, Andreas Reuter and Theo Härder coined the acronym ''ACID'', building on earlier work by Jim Gray who named atomicity, consistency, and durability, but not isolation, when characterizing the transaction concept. These four properties are the major guarantees of the transaction paradigm, which has influenced many aspects of development in database systems. According to Gray and Reuter, the IBM I ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Acid-base Indicator
A pH indicator is a halochromic chemical compound added in small amounts to a solution so the pH (acidity or basicity) of the solution can be determined visually or spectroscopically by changes in absorption and/or emission properties. Hence, a pH indicator is a chemical detector for hydronium ions (H3O+) or hydrogen ions (H+) in the Arrhenius model. Normally, the indicator causes the color of the solution to change depending on the pH. Indicators can also show change in other physical properties; for example, olfactory indicators show change in their odor. The pH value of a neutral solution is 7.0 at 25°C ( standard laboratory conditions). Solutions with a pH value below 7.0 are considered acidic and solutions with pH value above 7.0 are basic. Since most naturally occurring organic compounds are weak electrolytes, such as carboxylic acids and amines, pH indicators find many applications in biology and analytical chemistry. Moreover, pH indicators form one of the three ma ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Acids
In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a sequence of database operations that satisfies the ACID properties (which can be perceived as a single logical operation on the data) is called a ''transaction''. For example, a transfer of funds from one bank account to another, even involving multiple changes such as debiting one account and crediting another, is a single transaction. In 1983, Andreas Reuter and Theo Härder coined the acronym ''ACID'', building on earlier work by Jim Gray who named atomicity, consistency, and durability, but not isolation, when characterizing the transaction concept. These four properties are the major guarantees of the transaction paradigm, which has influenced many aspects of development in database systems. According to Gray and Reuter, the IBM I ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Solvation
Solvation (or dissolution) describes the interaction of a solvent with dissolved molecules. Both ionized and uncharged molecules interact strongly with a solvent, and the strength and nature of this interaction influence many properties of the solute, including solubility, reactivity, and color, as well as influencing the properties of the solvent such as its viscosity and density. If the attractive forces between the solvent and solute particles are greater than the attractive forces holding the solute particles together, the solvent particles pull the solute particles apart and surround them. The surrounded solute particles then move away from the solid solute and out into the solution. Ions are surrounded by a concentric shell of solvent. Solvation is the process of reorganizing solvent and solute molecules into solvation complexes and involves bond formation, hydrogen bonding, and van der Waals forces. Solvation of a solute by water is called hydration. Solubility of so ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Protonating
In chemistry, protonation (or hydronation) is the adding of a proton (or hydron, or hydrogen cation), (H+) to an atom, molecule, or ion, forming a conjugate acid. (The complementary process, when a proton is removed from a Brønsted–Lowry acid, is deprotonation.) Some examples include *The protonation of water by sulfuric acid: *:H2SO4 + H2O H3O+ + *The protonation of isobutene in the formation of a carbocation: *:(CH3)2C=CH2 + HBF4 (CH3)3C+ + *The protonation of ammonia in the formation of ammonium chloride from ammonia and hydrogen chloride: *:NH3( g) + HCl( g) → NH4Cl( s) Protonation is a fundamental chemical reaction and is a step in many stoichiometric and catalytic processes. Some ions and molecules can undergo more than one protonation and are labeled polybasic, which is true of many biological macromolecules. Protonation and deprotonation (removal of a proton) occur in most acid–base reactions; they are the core of most acid–base reaction theories. A Brønste ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Neutron Star
A neutron star is the collapsed core of a massive supergiant star, which had a total mass of between 10 and 25 solar masses, possibly more if the star was especially metal-rich. Except for black holes and some hypothetical objects (e.g. white holes, quark stars, and strange stars), neutron stars are the smallest and densest currently known class of stellar objects. Neutron stars have a radius on the order of and a mass of about 1.4 solar masses. They result from the supernova explosion of a massive star, combined with gravitational collapse, that compresses the core past white dwarf star density to that of atomic nuclei. Once formed, they no longer actively generate heat, and cool over time; however, they may still evolve further through collision or accretion. Most of the basic models for these objects imply that neutron stars are composed almost entirely of neutrons (subatomic particles with no net electrical charge and with slightly larger mass than protons); th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fluorosulfonic Acid
Fluorosulfuric acid (IUPAC name: sulfurofluoridic acid) is the inorganic compound with the chemical formula HSO3F. It is one of the strongest acids commercially available. It is a tetrahedral molecule and is closely related to sulfuric acid, H2SO4, substituting a fluorine atom for one of the hydroxyl groups. It is a colourless liquid, although commercial samples are often yellow.Erhardt Tabel, Eberhard Zirngiebl, Joachim Maas "Fluorosulfuric Acid" in "Ullmann's Encyclopedia of Industrial Chemistry" 2005, Wiley-VCH, Weinheim. Chemical properties Fluorosulfuric acid is a free-flowing colorless liquid. It is soluble in polar organic solvents (e.g. nitrobenzene, acetic acid, and ethyl acetate), but poorly soluble in nonpolar solvents such as alkanes. Reflecting its strong acidity, it dissolves almost all organic compounds that are even weak proton acceptors. HSO3F hydrolyzes slowly to hydrogen fluoride (HF) and sulfuric acid. The related triflic acid () retains the high acidity o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Antimony Pentafluoride
Antimony pentafluoride is the inorganic compound with the formula Sb F5. This colourless, viscous liquid is a valuable Lewis acid and a component of the superacid fluoroantimonic acid, formed when mixing liquid HF with liquid SbF5 in a 2:1 ratio. It is notable for its Lewis acidity and its ability to react with almost all known compounds. Preparation Antimony pentafluoride is prepared by the reaction of antimony pentachloride with anhydrous hydrogen fluoride:Sabina C. Grund, Kunibert Hanusch, Hans J. Breunig, Hans Uwe Wolf "Antimony and Antimony Compounds" in Ullmann's Encyclopedia of Industrial Chemistry 2006, Wiley-VCH, Weinheim. :SbCl5 + 5 HF → SbF5 + 5 HCl It can also be prepared from antimony trifluoride and fluorine. Structure and chemical reactions In the gas phase, SbF5 adopts a trigonal bipyramidal structure of D3h point group symmetry (see picture). The material adopts a more complicated structure in the liquid and solid states. The liquid contains polymers whe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hydronium Ion
In chemistry, hydronium (hydroxonium in traditional British English) is the common name for the aqueous cation , the type of oxonium ion produced by protonation of water. It is often viewed as the positive ion present when an Arrhenius acid is dissolved in water, as Arrhenius acid molecules in solution give up a proton (a positive hydrogen ion, ) to the surrounding water molecules (). In fact, acids must be surrounded by more than a single water molecule in order to ionize, yielding aqueous and conjugate base. Three main structures for the aqueous proton have garnered experimental support: The Eigen cation, which is a tetrahydrate, H3O+(H2O)3; the Zundel cation, which is a symmetric dihydrate, H+(H2O)2; and the Stoyanov cation, an expanded Zundel cation, which is a hexahydrate: H+(H2O)2(H2O)4. Spectroscopic evidence from well-defined IR spectra overwhelmingly supports the Stoyanov cation as the predominant form. For this reason, it has been suggested that wherever possible, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nuclear Magnetic Resonance Spectroscopy
Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy or magnetic resonance spectroscopy (MRS), is a spectroscopic technique to observe local magnetic fields around atomic nuclei. The sample is placed in a magnetic field and the NMR signal is produced by excitation of the nuclei sample with radio waves into nuclear magnetic resonance, which is detected with sensitive radio receivers. The intramolecular magnetic field around an atom in a molecule changes the resonance frequency, thus giving access to details of the electronic structure of a molecule and its individual functional groups. As the fields are unique or highly characteristic to individual compounds, in modern organic chemistry practice, NMR spectroscopy is the definitive method to identify monomolecular organic compounds. The principle of NMR usually involves three sequential steps: # The alignment (polarization) of the magnetic nuclear spins in an applied, constant magnetic field B0. # The ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
