What is the most powerful acid?
Fluoroantimonic acid
Fluoroantimonic acid is an inorganic compound with the chemical formula (also written , 2HF·SbF, or simply HF-SbF). It is an extremely strong acid, easily qualifying as a superacid. The Hammett acidity function, "H", has been measured for different ratios of HF:SbF. While the "H" of pure HF is −15, addition of just 1 mol % of SbF lowers it to around −20. However, further addition of SbF results in rapidly diminishing returns, with the "H" reaching −21 at 10 mol %. The use of an extremely weak base as indicator shows that the lowest attainable "H", even with > 50 mol % SbF, is somewhere between −21 and −23.
Nitric acid
Being a powerful oxidizing agent, nitric acid reacts violently with many non-metallic compounds, and the reactions may be explosive. Depending on the acid concentration, temperature and the reducing agent involved, the end products can be variable. Reaction takes place with all metals except the noble metals series and certain alloys. As a general rule, oxidizing reactions occur primarily with the concentrated acid, favoring the formation of nitrogen dioxide (NO). However, the powerful oxidizing properties of nitric acid are thermodynamic in nature, but sometimes its oxidation reactions are rather kinetically non-favored. The presence of small amounts of nitrous acid (HNO) greatly enhance the rate of reaction.
Antacid
Under the generic name algeldrate, aluminium hydroxide is used as an antacid. Aluminium hydroxide is preferred over other alternatives such as sodium bicarbonate because Al(OH), being insoluble, does not increase the pH of stomach above 7 and hence, does not trigger secretion of excess stomach acid. Brand names include Alu-Cap, Aludrox, Gaviscon, and Pepsamar. In 2016 Gaviscon was one of the biggest selling branded over-the-counter medications sold in Great Britain, with sales of £62 million. It reacts with excess acid in the stomach, reducing the acidity of the stomach content, which may relieve the symptoms of ulcers, heartburn or dyspepsia. Such products can cause constipation, because the aluminum ions inhibit the contractions of smooth muscle cells in the gastrointestinal tract, slowing peristalsis and lengthening the time needed for stool to pass through the colon. Some such products are formulated to minimize such effects through the inclusion of equal concentrations of magnesium hydroxide or magnesium carbonate, which have counterbalancing laxative effects.
Deinosuchus
Modern saltwater crocodiles ("Crocodylus porosus") have the strongest recorded bite of any living animal, with a maximum force of . The bite force of "Deinosuchus" has been estimated to be to . It has been argued that even the largest and strongest theropod dinosaurs, such as "Tyrannosaurus", probably had bite forces inferior to that of "Deinosuchus".
Acid strength
Acid strength refers to the tendency of an acid, symbolised by the chemical formula HA, to dissociate into a proton, H, and an anion, A. The dissociation of a strong acid in solution is effectively complete, except in its most concentrated solutions.
Examples of strong acids are hydrochloric acid (HCl), perchloric acid (HClO), nitric acid (HNO) and sulfuric acid (HSO).
Hydrochloric acid
Of the six common strong mineral acids in chemistry, hydrochloric acid is the monoprotic acid least likely to undergo an interfering oxidation-reduction reaction. It is one of the least hazardous strong acids to handle; despite its acidity, it consists of the non-reactive and non-toxic chloride ion. Intermediate-strength hydrochloric acid solutions are quite stable upon storage, maintaining their concentrations over time. These attributes, plus the fact that it is available as a pure reagent, make hydrochloric acid an excellent acidifying reagent.
Acid neutralizing capacity
or
Acid
Common aqueous acids include hydrochloric acid (a solution of hydrogen chloride which 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 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.
Leveling effect
In a "differentiating solvent", various acids dissociate to different degrees and thus have different strengths. In a "leveling solvent", several acids are completely dissociated and are thus of the same strength. A weakly basic solvent has less tendency than a strongly basic one to accept a proton. Similarly a weak acid has less tendency to donate protons than a strong acid. As a result, a strong acid such as perchloric acid exhibits more strongly acidic properties than a weak acid such as acetic acid when dissolved in a weakly basic solvent. On the other hand, all acids tend to become indistinguishable in strength when dissolved in strongly basic solvents owing to the greater affinity of strong bases for protons. This is called the leveling effect. Strong bases are "leveling solvents" for acids, weak bases are "differentiating solvents" for acids. Because of the leveling effect of common solvents, studies on super acids are conducted in solvents that are very weakly basic such as sulfur dioxide (liquefied) and SOClF.
Cyanoform
Dilute solutions of this acid, as well as its salts, have long been well known. Cyanoform ranks as one of the most acidic of the carbon acids with an estimated pK of -5.1 in water and measured pK 5.1 in acetonitrile. The reaction of sulfuric acid with sodium tricyanomethanide in water (a reaction first tried by H. Schmidtmann in 1896 with inconclusive results) is reported to result in the formation of the hydrate (NC)CHO or the formation of ("Z")-3-
amino-2-cyano-3-hydroxyacrylamide (HN)(OH)C=C(CN)CONH depending on the precise conditions. The reaction of HCl gas with sodium tricyanomethanide dissolved in THF is reported to yield 1-chloro-1-amino-2,2-dicyanoethylene ((NC)C=C(NH)Cl) and its tautomer.
Magic acid
The term "superacid" was first used in 1927 when James Bryant Conant found that perchloric acid could protonate ketones and aldehydes to form salts in nonaqueous solution. The term itself was coined by Gillespie later, after Conant combined sulfuric acid with fluorosulfuric acid, and found the solution to be several million times more acidic than sulfuric acid alone. The magic acid system was developed in the 1960s by George Olah, and was to be used to study stable carbocations. Gillespie also used the acid system to generate electron-deficient inorganic cations. The name originated after a Christmas party in 1966, when a member of the Olah lab placed a paraffin candle into the acid, and found that it dissolved quite rapidly. Examination of the solution with H-NMR showed a "tert"-butyl cation, suggesting that the paraffin chain that forms the wax had been cleaved, then isomerized, and the atoms were arranged into a different shape to form the ion. The name appeared in a paper published by the Olah lab.
Carborane acid
The fluorinated carborane acid, H(CHBF), is even stronger than chlorinated carborane acid. It is able to protonate butane to form "tert"-butyl cation at room temperature and is the only known acid to protonate carbon dioxide to give the bridged cation, [H(CO)], making it possibly the strongest known acid. In particular, CO does not undergo observable protonation when treated with the mixed superacids HF-SbF or HSOF-SbF.
Sulfuric acid
Sulfuric acid is capable of causing very severe burns, especially when it is at high concentrations. In common with other corrosive acids and alkali, it readily decomposes proteins and lipids through amide and ester hydrolysis upon contact with living tissues, such as skin and flesh. In addition, it exhibits a strong dehydrating property on carbohydrates, liberating extra heat and causing secondary thermal burns. Accordingly, it rapidly attacks the cornea and can induce permanent blindness if splashed onto eyes. If ingested, it damages internal organs irreversibly and may even be fatal. Protective equipment should hence always be used when handling it. Moreover, its strong oxidizing property makes it highly corrosive to many metals and may extend its destruction on other materials. Because of such reasons, damage posed by sulfuric acid is potentially more severe than that by other comparable strong acids, such as hydrochloric acid and nitric acid.
Sulfuric acid must be stored carefully in containers made of nonreactive material (such as glass). Solutions equal to or stronger than 1.5 M are labeled "CORROSIVE", while solutions greater than 0.5 M but less than 1.5 M are labeled "IRRITANT". However, even the normal laboratory "dilute" grade (approximately 1 M, 10%) will char paper if left in contact for a sufficient time.
Fusidic acid
Mechanisms of resistance have been extensively studied only in "Staphylococcus aureus". The most important mechanism is the development of point mutations in "fusA", the chromosomal gene that codes for EF-G. The mutation alters EF-G so that fusidic acid is no longer able to bind to it. Resistance is readily acquired when fusidic acid is used alone and commonly develops during the course of treatment. As with most other antibiotics, resistance to fusidic acid arises less frequently when used in combination with other drugs. For this reason, fusidic acid should not be used on its own to treat serious "Staph. aureus" infections. However, at least in Canadian hospitals, data collected between 1999-2005 showed rather low rate of resistance of MSSA and MRSA to fusidic acid, and mupirocin was found to be the more problematic topical antibiotic for the aforementioned conditions.
Fluoroantimonic acid
The "canonical" composition of fluoroantimonic acid is prepared by treating hydrogen fluoride (HF) with antimony pentafluoride (SbF) in a stoichiometric ratio of 2:1. It is the strongest superacid based on measured "H" value. Only the carborane acids, whose "H" could not be directly determined due to their high melting points, may be stronger acids than fluoroantimonic acid. It has been shown to protonate even hydrocarbons to afford pentacoordinate carbocations (carbonium ions).
Acid throwing
The most common types of acid used in these attacks are sulfuric and nitric acid. Hydrochloric acid is sometimes used, but is much less damaging. Aqueous solutions of strongly alkaline materials, such as caustic soda (sodium hydroxide), are used as well, particularly in areas where strong acids are controlled substances.
Agaric acid
Agaric acid, as any other fatty acid, has an amphipathic character. It means that it has both polar (hydroxyl groups) and apolar (hydrocarbon chain) sections, and therefore, it is not completely water-soluble. It is a tribasic acid, and therefore, it can donate up to 3 hydrogen ions to other bases in an acid-base reaction. Another example of tribasic acids is phosphoric acid or citric acid.
It is an odorless and tasteless acid, and we can also distinguish it by its white color. Its melting point at atmospheric pressure is 140 °C.
Dentin phosphoprotein
Phosphophoryn is the most acidic protein ever discovered and has an isoelectric point of 1. This extreme acidity is achieved by its amino acid sequence. Many portions of its chain are repeating -D-S-S- (aspartic acid-serine-serine) sequences. In protein chemistry, net acidity equates to negative charge. Being highly negative, dentin phosphoprotein is able to attract large amounts of calcium. "In vitro" studies also indicate phosphophoryn can initiate hydroxyapatite formation.
Mead acid
Mead acid, also referred to as eicosatrienoic acid, is chemically a carboxylic acid with a 20-carbon chain and three methylene-interrupted "cis" double bonds. The first double bond is located at the ninth carbon from the omega end. In physiological literature, it is given the name 20:3 (n-9). (See Fatty Acid#Nomenclature for an explanation of the naming system.) In the presence of lipoxygenase, cytochrome p450 or cyclooxygenase Mead acid can form various hydroxyeicosatetraenoic acid (HETE) and hydroperoxy (HpETE) products.
P-Toluenesulfonic acid
As with other sulfonic acids, TsOH is a strong organic acid. It is about one million times stronger than benzoic acid. It is one of the few strong acids that is solid and, hence, conveniently weighed.
Compounds of fluorine
As a part of a molecule, it is a part with great inductive effect. In the latter case, it significantly increases the acidity of a molecule: the anion formed after giving the proton off becomes stable as a result. Consider acetic acid and its mono-, di-, and trifluoroacetic derivatives and their pK values (4.74, 2.66, 1.24, and 0.23); in other words, the trifluoro derative is 33,800 times stronger an acid than acetic. Fluorine is a principal component of the strongest known charge-neutral acid, . There is evidence for an even stronger acid, , but it has not proved isolable.
Hydrogen iodide
Hydroiodic acid is not pure hydrogen iodide, but a mixture containing it. Commercial "concentrated" hydroiodic acid usually contains 48–57% HI by mass. The solution forms an azeotrope boiling at 127 °C with 57% HI, 43% water. The high acidity is caused by the dispersal of the ionic charge over the anion. The iodide ion is much larger than the other common halides, which results in the negative charge being dispersed over a large space. By contrast, a chloride ion is much smaller, meaning its negative charge is more concentrated, leading to a stronger interaction between the proton and the chloride ion. This weaker H···I interaction in HI facilitates dissociation of the proton from the anion and is the reason HI is the strongest acid of the hydrohalides.
Acid strength
A weak acid is only partially dissociated, with both the undissociated acid and its dissociation products being present, in solution, in equilibrium with each other. 
Acetic acid (CHCOOH) is an example of a weak acid. The strength of a weak acid is quantified by its acid dissociation constant, p"K" value.
Nucleophilic acyl substitution
Carboxylic acids react with Grignard reagents and organolithiums to form ketones. The first equivalent of nucleophile acts as a base and deprotonates the acid. A second equivalent will attack the carbonyl group to create a geminal alkoxide dianion, which is protonated upon workup to give the hydrate of a ketone. Because most ketone hydrates are unstable relative to their corresponding ketones, the equilibrium between the two is shifted heavily in favor of the ketone. For example, the equilibrium constant for the formation of acetone hydrate from acetone is only 0.002. The carboxylic group is the most acidic in organic compounds.
Resonance (chemistry)
In the case of ions it is common to speak about delocalized charge (charge delocalization). An example of delocalized charge in ions can be found in the carboxylate group, wherein the negative charge is centered equally on the two oxygen atoms. Charge delocalization in anions is an important factor determining their reactivity (generally: the higher the extent of delocalization the lower the reactivity) and, specifically, the acid strength of their conjugate acids. As a general rule, the better delocalized is the charge in an anion the stronger is its conjugate acid. For example, the negative charge in perchlorate anion () is evenly distributed among the symmetrically oriented oxygen atoms (and a part of it is also kept by the central chlorine atom). This excellent charge delocalization combined with the high number of oxygen atoms (four) and high electronegativity of the central chlorine atom leads to perchloric acid being one of the strongest known acids with a p"K" value of −10.
The extent of charge delocalization in an anion can be quantitatively expressed via the WAPS (weighted average positive sigma) parameter parameter and an analogous WANS (weighted average negative sigma) parameter is used for cations.
Bohemic acid
The individual components of bohemic acid are orange-red solids, the color originating from an optical absorption band centered at about 490 nm. Marcellomycin and mimimycin, and collinemycin and musettamycin are stereoisomers, that is they have the same chemical compositions; however, one C-H and one COOCH group exchange places. Those two groups are attached to the same carbon atom of one carbon ring, they are marked by the blue star in their structure in the table (C-H group is not shown). Nearly all components of bohemic acid are anthracycline antibiotic agents active against Gram-positive bacteria, but not against Gram-negative bacteria, yeasts or fungi. The most potent component of the acid is rudolphomycin and the least potent is schaunardimycin, which is about 10 times weaker than musettamycin and 20 times weaker than marcellomycin. The original studies on the individual components of bohemic acid have tested them all for antitumor activity in mice, upon intraperitoneal injection. Furthermore, the antitumor pharmacokinetics of marcellomycin in the human blood has been evaluated both in vitro and in vivo.
Angelic acid
Angelic acid occurs in the roots of many plants, especially of the family Apiaceae. These plants include "Angelica archangelica", "Peucedanum ostruthium" (masterwort), "Levisticum officinale" (lovage), "Euryangium sumbul" and "Laserpitium latifolium". In the latter plant, it is present in the resin called laserpicium, and the oil of carrot also contains angelic acid. Sumbul plants might contain not angelic acid itself, but a larger complex which breaks into angelic acid upon processing. The acid can also be extracted from the oil of chamomile flowers, and 85% of Roman chamomile ("Anthemis nobilis") oil consists of esters of angelic and tiglic acids; it also contains isobutyl angelate and amyl angelate. The acid content is highest in "Angelica archangelica" where it is about 0.3%.
Ion speciation
A "weak acid" may be "defined" as an acid with p"K" greater than about −2. An acid with p"K" = −2 would be 99% dissociated at pH 0, that is, in a 1 M HCl solution. Any acid with a p"K" less than about −2 is said to be a "strong acid". Strong acids are said to be fully dissociated. There is no precise p"K" value that distinguishes between strong and weak acids because strong acids, such as sulfuric acid, are associated in very concentrated solution.
Antioxidant
Uric acid has the highest concentration of any blood antioxidant and provides over half of the total antioxidant capacity of human serum. Uric acid's antioxidant activities are also complex, given that it does not react with some oxidants, such as superoxide, but does act against peroxynitrite, peroxides, and hypochlorous acid. Concerns over elevated UA's contribution to gout must be considered as one of many risk factors. By itself, UA-related risk of gout at high levels (415–530 μmol/L) is only 0.5% per year with an increase to 4.5% per year at UA supersaturation levels (535+ μmol/L). Many of these aforementioned studies determined UA's antioxidant actions within normal physiological levels, and some found antioxidant activity at levels as high as 285 μmol/L.
Carborane acid
Carborane acids H(CXBYZ) (X, Y, Z = H, Alk, F, Cl, Br, CF) are a class of superacids, some of which are estimated to be at least one million times stronger than 100% sulfuric acid in terms of their Hammett acidity function values ("H" ≤ –18) and possess computed p"K" values well below –20, establishing them as some of the strongest known Brønsted acids. The most well studied example is the highly chlorinated derivative H(CHBCl). The acidity of H(CHBCl) was found to vastly exceed that of triflic acid, CFSOH, and bistriflimide, (CFSO)NH, compounds previously regarded as the strongest isolable acids.
Mead acid
Two fatty acids, linoleic acid and alpha-linolenic acid, are considered essential fatty acids (EFAs) in humans and other mammals. Both are 18 carbon fatty acids unlike mead acid, which has 20 carbons. Linoleic is an ω-6 fatty acid whereas linolenic is ω-3 and mead is ω-9. One study examined patients with intestinal fat malabsorption and suspected EFA deficiency; they were found to have blood-levels of Mead acid 1263% higher than reference subjects. Under severe conditions of essential fatty acid deprivation, mammals will elongate and desaturate oleic acid to make mead acid, (20:3, "n"−9). This has been documented to a lesser extent in vegetarians and semi-vegetarians following an unbalanced diet.
Glycolic acid
Glycolic acid is slightly stronger than acetic acid due to the electron-withdrawing power of the terminal hydroxyl group. The carboxylate group can coordinate to metal ions forming coordination complexes. Of particular note are the complexes with Pb and Cu which are significantly stronger than complexes with other carboxylic acids. This indicates that the hydroxyl group is involved in complex formation, possibly with the loss of its proton.
Angelic acid
Angelic acid is a monocarboxylic unsaturated organic acid. It is mostly found in the plants of the family Apiaceae. German pharmacist Ludwig Andreas Buchner isolated angelic acid in 1842 from the roots of garden angelica ("Angelica archangelica") which gave the acid its name. Angelic acid is a volatile solid with a biting taste and pungent sour odor. It is the "cis" isomer of 2-methyl-2-butenoic acid, which easily converts to the "trans" isomer, tiglic acid, upon heating or reaction with inorganic acids. The reverse transformation occurs much less readily. The salts and esters of angelic acid are called angelates. Angelic acid esters are the active components of herbal medicine used against a wide range of various health disturbances including pains, fever, gout, heartburn, etc.
Hydroxide
The solubility in water of the other hydroxides in this group increases with increasing atomic number. Magnesium hydroxide Mg(OH) is a strong base (up to the limit of its solubility, which is very low in pure water), as are the hydroxides of the heavier alkaline earths: calcium hydroxide, strontium hydroxide, and barium hydroxide. A solution or suspension of calcium hydroxide is known as limewater and can be used to test for the weak acid carbon dioxide. The reaction Ca(OH) + CO Ca + + OH illustrates the basicity of calcium hydroxide. Soda lime, which is a mixture of the strong bases NaOH and KOH with Ca(OH), is used as a CO absorbent.
Vernolic acid
Vernolic acid (leukotoxin) is a long chain fatty acid that is monounsaturated and contains an epoxide. It is the "cis" epoxide derived from the C12–C13 alkene of linoleic acid and exists both the (+)- and (–)- optical isomers. It is an isomer of coronaric acid, the two enantiomeric forms resulting instead by epoxidation at the C9–C10 alkene. Vernolic acid was first definitively characterized in 1954. It is the key component in vernonia oil, which is produced in abundance by the genera Vernonia and Euphorbia and is a potentially useful biofeedstock.
Binary acid
Their strengths depend on the solvation of the initial acid, the H-X bond energy, the electron affinity energy of X, and the solvation energy of X. Observed trends in acidity correlate with bond energies, the weaker the H-X bond, the stronger the acid. For example, there is a weak bond between hydrogen and iodine in hydroiodic acid, making it a very strong acid.
2-Chlorobenzoic acid
2-Chlorobenzoic acid is an organic compound with the formula ClCHCOH. It is one of three isomeric chlorobenzoic acids, the one that is the strongest acid. This white solid is used as a precursor to a variety of drugs, food additives, and dyes.
Acetic acid
Acetic acid has 349 kcal per 100 g. Vinegar is typically no less than 4% acetic acid by mass. Legal limits on acetic acid content vary by jurisdiction. Vinegar is used directly as a condiment, and in the pickling of vegetables and other foods. Table vinegar tends to be more diluted (4% to 8% acetic acid), while commercial food pickling employs solutions that are more concentrated. The proportion of acetic acid used worldwide as vinegar is not as large as commercial uses, but is by far the oldest and best-known application.
Hydroxide
Silicic acid is the name given to a variety of compounds with a generic formula [SiO(OH)]. "Orthosilicic acid" has been identified in very dilute aqueous solution. It is a weak acid with p"K" = 9.84, p"K" = 13.2 at 25 °C. It is usually written as HSiO but the formula Si(OH) is generally accepted. Other silicic acids such as "metasilicic acid" (HSiO), "disilicic acid" (HSiO), and "pyrosilicic acid" (HSiO) have been characterized. These acids also have hydroxide groups attached to the silicon; the formulas suggest that these acids are protonated forms of polyoxyanions.
Typhoon Angela
Angela's 872 (910 according to the JMA) mbar pressure reading makes it one of the strongest typhoons on record. While this is low by the standards of any sea-level location, it is still behind Typhoon Tip, the most intense tropical cyclone ever recorded. However, Angela is an unofficial contender for world's most intense tropical cyclone. In a study utilizing the Dvorak technique for analysis of post-1987 typhoons, the authors concluded that Angela and 1992's Gay were higher on the scale than Tip. The authors also thought that Angela might have been slightly more intense than Gay, and hence Tip.
Boric acid
Boric acid is one of the most commonly used substances that can neutralize active hydrofluoric acid (HF). It works by forcing the free F anions into complex salts. This process defeats the extreme toxicity of hydrofluoric acid, particularly its ability to sequester ionic calcium from blood serum which can lead to cardiac arrest and bone decomposition; such an event can occur from just minor skin contact with HF.
Solid acid
Most of the acids solid in state are generally organic acids that includes oxalic acid,tartaric acid,citric acid,maleic acid,etc Examples include oxides, which function as Lewis acids including silico-aluminates (zeolites, alumina, silico-alumino-phosphate), and sulfated zirconia. Many transition metal oxides are acidic, including titania, zirconia, and niobia. Such acids are used in cracking. Many solid Brønsted acids are also employed industrially, including sulfonated polystyrene, solid phosphoric acid, niobic acid, and heteropolyoxometallates.
Adipic acid
Adipic acid or hexanedioic acid is the organic compound with the formula (CH)(COOH). From an industrial perspective, it is the most important dicarboxylic acid: about 2.5 billion kilograms of this white crystalline powder are produced annually, mainly as a precursor for the production of nylon. Adipic acid otherwise rarely occurs in nature, but it is known as manufactured E number food additive E355.
Superacid
The proton from superacids has been popularly said to become "naked", accounting for the system's extreme acidity. In the physical sense, the acidic "proton" is never completely free (as an unbound proton) but is bound to the anion, albeit weakly. The proton hops from anion to anion in superacids via the Grotthuss mechanism, just as happens to acidic "protons" in water. The extreme acidity of the acids is due to the ease with which this proton is transferred to substances that cannot normally be "protonated" (such as hydrocarbons), due to the very high stability of the conjugate-base anion (such as ) after it donates the proton.
Ijen
The lake is recognised as the largest highly acidic crater lake in the world. It is also a source for the river Banyupahit, resulting in highly acidic and metal-enriched river water which has a significant detrimental effect on the downstream river ecosystem. On July 14–15, 2008, explorer George Kourounis took a small rubber boat out onto the acid lake to measure its acidity. The pH of the water in the lake's edges was measured to be 0.5 and in the middle of the lake 0.13 due to high sulfuric acid concentration.
Tungsten
Tungsten, at atomic number "Z" = 74, is the heaviest element known to be biologically functional. It is used by some bacteria and archaea, but not in eukaryotes. For example, enzymes called oxidoreductases use tungsten similarly to molybdenum by using it in a tungsten-pterin complex with molybdopterin (molybdopterin, despite its name, does not contain molybdenum, but may complex with either molybdenum or tungsten in use by living organisms). Tungsten-using enzymes typically reduce carboxylic acids to aldehydes. The tungsten oxidoreductases may also catalyse oxidations. The first tungsten-requiring enzyme to be discovered also requires selenium, and in this case the tungsten-selenium pair may function analogously to the molybdenum-sulfur pairing of some molybdenum cofactor-requiring enzymes. One of the enzymes in the oxidoreductase family which sometimes employ tungsten (bacterial formate dehydrogenase H) is known to use a selenium-molybdenum version of molybdopterin. Acetylene hydratase is an unusual metalloenzyme in that it catalyzes a hydration reaction. Two reaction mechanisms have been proposed, in one of which there is a direct interaction between the tungsten atom and the C≡C triple bond. Although a tungsten-containing xanthine dehydrogenase from bacteria has been found to contain tungsten-molydopterin and also non-protein bound selenium, a tungsten-selenium molybdopterin complex has not been definitively described.
Fluoroantimonic acid
The following values show that fluoroantimonic acid is much stronger than other superacids based upon the Hammett acidity function. Increased acidity is indicated by smaller (in this case, more negative) values of "H".
Proton affinity
The higher the proton affinity, the stronger the base and the weaker the conjugate acid "in the gas phase". The (reportedly) strongest known base is the ortho-diethynylbenzene dianion ("E" = 1843 kJ/mol), followed by the methanide anion ("E" = 1743 kJ/mol) and the hydride ion ("E" = 1675 kJ/mol), making methane the weakest proton acid in the gas phase, followed by dihydrogen. The weakest known base is the helium atom ("E" = 177.8 kJ/mol), making the hydrohelium(1+) ion the strongest known proton acid.
Fluorosulfuric acid
HSOF is one of the strongest known simple Brønsted acids, although carborane-based acids are still stronger. It has an "H" value of −15.1 compared to −12 for sulfuric acid. The combination of HSOF and the Lewis acid antimony pentafluoride produces "Magic acid", which is a far stronger protonating agent. These acids all fall into the category of "superacids", acids stronger than 100% sulfuric acid.
Triflidic acid
Triflidic acid ("IUPAC name": tris[(trifluoromethyl)sulfonyl]methane, "abbreviated formula": TfCH) is an organic superacid. It is one of the strongest known carbon acids and is among the strongest Brønsted acids in general, with an acidity exceeded only by the carborane acids. Notably, triflidic acid is estimated to have an acidity 10 times that of triflic acid (p"K" ~ –14), as measured by its acid dissociation constant. It was first prepared in 1987 by Seppelt and Lutz by the following route:(1) TfCH + 2CHMgBr → TfC(MgBr) + 2CH (2) TfC(MgBr) + TfF → TfC(MgBr) + MgBrF (3) TfC(MgBr) + HSO → TfCH + MgBrHSOIn its anionic form, the lanthanide salts of triflidic acid ("triflides") have been shown to be more efficient Lewis acids than the corresponding triflates. The triflide anion has also been employed as the anionic component of ionic liquids.
Base (chemistry)
A strong base is a basic chemical compound that can remove a proton (H) from (or "deprotonate") a molecule of even a very weak acid (such as water) in an acid-base reaction. Common examples of strong bases include hydroxides of alkali metals and alkaline earth metals, like NaOH and , respectively. Due to their low solubility, some bases, such as alkaline earth hydroxides, can be used when the solubility factor is not taken into account. One advantage of this low solubility is that "many antacids were suspensions of metal hydroxides such as aluminum hydroxide and magnesium hydroxide." These compounds have low solubility and have the ability to stop an increase in the concentration of the hydroxide ion, preventing the harm of the tissues in the mouth, oesophagus, and stomach. As the reaction continues and the salts dissolve, the stomach acid reacts with the hydroxide produced by the suspensions. Strong bases hydrolyze in water almost completely, resulting in the leveling effect." In this process, the water molecule combines with a strong base, due to the water's amphoteric ability; and, a hydroxide ion is released. Very strong bases can even deprotonate very weakly acidic C–H groups in the absence of water. Here is a list of several strong bases:The cations of these strong bases appear in the first and second groups of the periodic table (alkali and earth alkali metals).
James B. Conant
Conant's investigations helped in the development of a more comprehensive understanding of the nature of acids and bases. He investigated the properties of certain acids which were many times stronger than mineral acid solutions in water. Conant christened them "superacids" and laid the foundation for the development of the Hammett acidity function. These investigations used acetic acid as the solvent and demonstrated that sodium acetate behaves as a base under these conditions. This observation is consistent with Brønsted–Lowry acid–base theory (published in 1923) but cannot be explained under older Arrhenius theory approaches. Later work with George Wheland and extended by William Kirk McEwen looked at the properties of hydrocarbons as very weak acids, including acetophenone, phenylacetylene, fluorene and diphenylmethane. Conant can be considered alongside Brønsted, Lowry, Lewis, and Hammett as a developer of modern understanding of acids and bases.
Metal halides
Antimony pentafluoride is a strong Lewis acid. It gives fluoroantimonic acid, the strongest known acid, with hydrogen fluoride. Antimony pentafluoride as the prototypical Lewis acid, used to compare different compounds' Lewis basicities. This measure of basicity is known as the Gutmann donor number.
Amide
Compared to amines, amides are very weak bases. While the conjugate acid of an amine has a p"K" of about 9.5, the conjugate acid of an amide has a p"K" around −0.5. Therefore, amides don't have as clearly noticeable acid–base properties in water. This relative lack of basicity is explained by the electron-withdrawing nature of the carbonyl group where the lone pair of electrons on the nitrogen is delocalized by resonance. On the other hand, amides are much stronger bases than carboxylic acids, esters, aldehydes, and ketones (their conjugate acids' p"K"s are between −6 and −10). It is estimated in silico that acetamide is represented by resonance structure A for 62% and by B for 28%. Resonance is largely prevented in the very strained quinuclidone.
Pepsin
Pepsin is most active in acidic environments between 37 °C and 42 °C. Accordingly, its primary site of synthesis and activity is in the stomach (pH 1.5 to 2). Pepsin will digest up to 20% of ingested amide bonds by cleaving preferentially at the C-terminal side of aromatic amino acids such as phenylalanine, tryptophan, and tyrosine. Pepsin exhibits preferential cleavage for hydrophobic, preferably aromatic, residues in P1 and P1' positions. Increased susceptibility to hydrolysis occurs if there is a sulfur-containing amino acid close to the peptide bond, which has an aromatic amino acid. Pepsin cleaves PheVal, GlnHis, GluAla, AlaLeu, LeuTyr, TyrLeu, GlyPhe, Phe in the insulin B chain. Pepsin exhibits maximal activity at pH 2.0 and is inactive at pH 6.5 and above, however pepsin is not fully denatured or irreversibly inactivated until pH 8.0. Therefore, pepsin in solution of up to pH 8.0 can be reactivated upon re-acidification. The stability of pepsin at high pH has significant implications on disease attributed to laryngopharyngeal reflux. Pepsin remains in the larynx following a gastric reflux event. At the mean pH of the laryngopharynx (pH = 6.8) pepsin would be inactive but could be reactivated upon subsequent acid reflux events resulting in damage to local tissues.
Periodic acid
Periodic acid ( "per-iodic") is the highest oxoacid of iodine, in which the iodine exists in oxidation state VII. Like all periodates it can exist in two forms: orthoperiodic acid, with the chemical formula HIO and metaperiodic acid, which has the formula HIO.
Glutamic acid
Glutamic acid is produced on the largest scale of any amino acid, with an estimated annual production of about 1.5 million tons in 2006. Chemical synthesis was supplanted by the aerobic fermentation of sugars and ammonia in the 1950s, with the organism "Corynebacterium glutamicum" (also known as "Brevibacterium flavum") being the most widely used for production. Isolation and purification can be achieved by concentration and crystallization; it is also widely available as its hydrochloride salt.
Leveling effect
Any acid that is stronger than HO reacts with HO to form HO. Therefore, no acid stronger than HO exists in HO. Similarly, when ammonia is the solvent, the strongest acid is ammonium (NH), thus HCl and a super acid exert the same acidifying effect.
Oxidizing acid
An oxidizing acid is a Brønsted acid that is a strong oxidizing agent. All Brønsted acids can act as oxidizing agents, because the acidic proton can be reduced to hydrogen gas. Some acids contain other structures that act as stronger oxidizing agents than hydrogen ion. Generally, they contain oxygen in the anionic structure. These include nitric acid, perchloric acid, chloric acid, chromic acid, and concentrated sulfuric acid, among others.
Trichloromethyl
The trichloromethyl group has a significant electronegativity. For this reason, trichloromethyl-substituted acids are often stronger than the original. For example, the acidity constant (pK) of trichloroacetic acid – is 0.77, whereas that of acetic acid is 4.76.
Carborane acid
As a class, the carborane acids form the most acidic group of well-defined, isolable substances known, far more acidic than previously known single-component strong acids like triflic acid or perchloric acid. In certain cases, like the nearly perhalogenated derivatives mentioned above, their acidities rival (and possibly exceed) those of the traditional mixed Lewis-Brønsted superacids like magic acid and fluoroantimonic acid. (However, a head-to-head comparison has not been possible thus far, due to the lack of a measure of acidity that is suitable for both classes of acids: p"K" values are ill-defined for the chemically complex mixed acids while "H" values cannot be measured for the very high melting carborane acids).
Ripeness in viticulture
The major acids in wine are tartaric and malic acid with citric and succinic acids playing a small role. The titratable acidity or "TA" (also referred to as "total acidity") is the measure of the tartaric acid in the grapes. This is the most abundant acid and also the one acid that has the most pronounced and long lasting impact on the taste of the wine. The TA is often measured by neutralizing some grape juice with a standard alkaline solution (such as sodium hydroxide) and then using an indicator (such as phenolphthalein) which changes color depending on the acid levels of the solution. The indicator is added to the grape juice followed by incremental amounts of the alkaline solution as the wine changes color until adding more of the solution ceases to promote a color change. At this point the wine has been neutralized with the amount of the alkaline solution needed to neutralize calculated in a formula to give an indication of how much tartaric acid was in the wine. The TA level is then expressed in a percentage of grams per 100 milliliter. As with must weight, the ideal levels for ripeness will vary according to wine style and winemaking preference. For still table wines, TA levels often fall between 0.60-0.80% for red wine grapes and 0.65-0.85 for whites.
Nor-
Possibly the earliest known use of the prefix "nor" is that by A. Matthiessen and G.C. Foster in 1867 in a publication about the reaction between a strong acid and opianic acid (see picture).
Opianic acid (CHO) is a compound with two methyl-groups and they called it "dimethyl nor-opianic acid". After reaction with a strong acid a compound was attained with only one methyl (CHO). This partially demethylated opianic acid they called "methyl normal opianic acid". The completely demethylated compound (CHO) was denoted by the term "normal opianic acid", abbreviated as "nor-opianic acid". 
Similarly Matthiessen and Foster called narcotine, which has three methoxy groups, "trimethyl nor-narcotine". The singular demethylated narcotine was called "dimethyl nor-narcotine", the more demethylated narcotine "methyl nor-narcotine" and the completely demethylated form "normal narcotine" or "nor-narcotine".
Acid dissociation constant
The more positive the value of p"K", the smaller the extent of dissociation at any given pH (see Henderson–Hasselbalch equation)—that is, the weaker the acid. A weak acid has a p"K" value in the approximate range −2 to 12 in water. Acids with a p"K" value of less than about −2 are said to be strong acids; the dissociation of a strong acid is effectively complete such that concentration of the undissociated acid is too small to be measured. p"K" values for strong acids can, however, be estimated by theoretical means.
Acid strength
Sulfonic acids, such as p-toluenesulfonic acid (tosylic acid) are a class of strong organic oxyacids. Some sulfonic acids can be isolated as solids. polystyrene functionalized into polystyrene sulfonate is an example of a substance that is a solid strong acid.
Naphthenic acid
Naphthenic acids (NAs) are a mixture of several cyclopentyl and cyclohexyl carboxylic acids with molecular weight of 120 to well over 700 atomic mass units. The main fraction are carboxylic acids with a carbon backbone of 9 to 20 carbons. McKee et al. claim that "naphthenic acids (NAs) are primarily cycloaliphatic carboxylic acids with 10 to 16 carbons", although acids containing up to 50 carbons have been identified in heavy petroleum. The term naphthenic acid has roots in the somewhat archaic term "naphthene" (cycloaliphatic but non-aromatic) used to classify hydrocarbons. It was originally used to describe the complex mixture of petroleum-based acids when the analytical methods available in the early 1900s could identify only a few naphthene-type components with accuracy. Today "naphthenic" acid is used in a more generic sense to refer to all of the carboxylic acids present in petroleum, whether cyclic, acyclic, or aromatic compounds, and carboxylic acids containing heteroatoms such as N and S. Although commercial naphthenic acids often contain a majority of cycloaliphatic acids, multiple studies have shown they also contain straight chain and branched aliphatic acids and aromatic acids; some naphthenic acids contain >50% combined aliphatic and aromatic acids.
Citric acid
Citric acid exists in greater than trace amounts in a variety of fruits and vegetables, most notably citrus fruits. Lemons and limes have particularly high concentrations of the acid; it can constitute as much as 8% of the dry weight of these fruits (about 47 g/l in the juices). The concentrations of citric acid in citrus fruits range from 0.005 mol/L for oranges and grapefruits to 0.30 mol/L in lemons and limes. Within species, these values vary depending on the cultivar and the circumstances in which the fruit was grown.
Acetic acid
Acetic acid is the second simplest carboxylic acid (after formic acid). It consists of a methyl group attached to a carboxyl group. It is an important chemical reagent and industrial chemical, used primarily in the production of cellulose acetate for photographic film, polyvinyl acetate for wood glue, and synthetic fibres and fabrics. In households, diluted acetic acid is often used in descaling agents. In the food industry, acetic acid is controlled by the food additive code E260 as an acidity regulator and as a condiment. In biochemistry, the acetyl group, derived from acetic acid, is fundamental to all forms of life. When bound to coenzyme A, it is central to the metabolism of carbohydrates and fats.
Leveling effect
Leveling effect or solvent leveling refers to the effect of solvent on the properties of acids and bases. The strength of a strong acid is limited ("leveled") by the basicity of the solvent. Similarly the strength of a strong base is leveled by the acidity of the solvent. When a strong acid is dissolved in water, it reacts with it to form hydronium ion (HO). An example of this would be the following reaction, where "HA" is the strong acid:
Acid
Superacids are acids stronger 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". They can also quantitatively stabilize carbocations.
Acids in wine
Malic acid, along with tartaric acid, is one of the principal organic acids found in wine grapes. It is found in nearly every fruit and berry plant, but is most often associated with green (unripe) apples, the flavor it most readily projects in wine. Its name comes from the Latin "malum" meaning “apple”. In the grape vine, malic acid is involved in several processes which are essential for the health and sustainability of the vine. Its chemical structure allows it to participate in enzymatic reactions that transport energy throughout the vine. Its concentration varies depending on the grape variety, with some varieties, such as Barbera, Carignan and Sylvaner, being naturally disposed to high levels. The levels of malic acid in grape berries are at their peak just before veraison, when they can be found in concentrations as high as 20 g/l. As the vine progresses through the ripening stage, malic acid is metabolized in the process of respiration, and by harvest, its concentration could be as low as 1 to 9 g/l. The respiratory loss of malic acid is more pronounced in warmer climates. When all the malic acid is used up in the grape, it is considered “over-ripe” or senescent. Winemakers must compensate for this loss by adding extraneous acid at the winery in a process known as acidification.
Palmitic acid
Palmitic acid, or hexadecanoic acid in IUPAC nomenclature, is the most common saturated fatty acid found in animals, plants and microorganisms. Its chemical formula is CH(CH)COOH, and its C:D is 16:0. As its name indicates, it is a major component of the oil from the fruit of oil palms (palm oil). Palmitic acid can also be found in meats, cheeses, butter, and dairy products. Palmitates are the salts and esters of palmitic acid. The palmitate anion is the observed form of palmitic acid at physiologic pH (7.4).
Iodoacetic acid
Iodide is a naturally occurring ion that can be found in many source waters and it is easily oxidized by wastewater disinfectants. One of the products of iodide oxidation is hypoiodous acid (HOI or OI) which is capable of reacting with background organic materials to generate iodinated disinfection by-products (DBPs) including iodoacetic acid. In a study performed by Plewa, et al., IAA was determined to be one of the most cytotoxic of those studied, with a median lethal dose on the order of magnitude of 10 M. It was the most genotoxic of more than 60 DBPs studied and is the most genotoxic DBP identified thus far. Iodoacetic acid has exhibited traits indicating it as a potential carcinogen, however, it has not been proven to be carcinogenic. The trend continues in teratogenicity, with iodoacetic acid’s potency surpassing that of its brominated and chlorinated analogs. Its toxicity correlates to its ability as an alkylating agent, which will modify cysteine residues in proteins. Monohaloacetic acids are the most toxic, with toxicity increasing with halogen size. Iodoacetic acid is more toxic than bromoacetic acid and much more toxic than chloroacetic acid.
Acid strength
A weak acid is an substance that partially dissociates when it is dissolved in a solvent. In solution there is an equilibrium between the acid, HA, and the products of dissociation. 
The solvent (e.g. water) is omitted from this expression when its concentration is effectively unchanged by the process of acid dissociation. The strength of a weak acid can be quantified in terms of a dissociation constant, "K", defined as follows, where "[X]" signifies the concentration of a chemical moiety, X.
When a numerical value of "K" is known it can be used to determine the extent of dissociation in a solution with a given concentration of the acid, "T", by applying the law of conservation of mass.
where "T" is the value of the analytical concentration of the acid. When all the quantities in this equation are treated as numbers, ionic charges are not shown and this becomes a quadratic equation in the value of the hydrogen ion concentration value, "[H]".
This equation shows that the pH of a solution of a weak acid depends on both its "K" value and its concentration. Typical examples of weak acids include acetic acid and phosphorous acid. An acid such as oxalic acid (HOOC–COOH) is said to be dibasic because it can lose two protons and react with two molecules of a simple base. Phosphoric acid (HPO) is tribasic.
Neutralization (chemistry)
A strong acid is one that is fully dissociated in aqueous solution. For example, hydrochloric acid, HCl, is a strong acid.
A strong base is one that is fully dissociated in aqueous solution. For example, sodium hydroxide, NaOH, is a strong base.
Therefore, when a strong acid reacts with a strong base the neutralization reaction can be written as 
For example, in the reaction between hydrochloric acid and sodium hydroxide the sodium and chloride ions, Na and Cl take no part in the reaction. The reaction is consistent with the Brønsted–Lowry definition because in reality the hydrogen ion exists as the hydronium ion, so that the neutralization reaction may be written as
When a strong acid is neutralized by a strong base there are no excess hydrogen ions left in the solution. The solution is said to be neutral as it is neither acidic nor alkaline. The pH of such a solution is close to a value of 7; the exact pH value is dependent on the temperature of the solution.
Citric acid
Because it is one of the stronger edible acids, the dominant use of citric acid is as a flavoring and preservative in food and beverages, especially soft drinks and candies. Within the European Union it is denoted by E number E330. Citrate salts of various metals are used to deliver those minerals in a biologically available form in many dietary supplements. Citric acid has 247 kcal per 100 g. The buffering properties of citrates are used to control pH in household cleaners and pharmaceuticals. In the United States the purity requirements for citric acid as a food additive are defined by the Food Chemicals Codex, which is published by the United States Pharmacopoeia (USP).
Carborane acid
Carborane acid was first discovered and synthesized by Professor Christopher Reed and his colleagues in 2004 at the University of California, Riverside. Prior to carborane acid's discovery, the long-standing record of “strongest acids as single isolable compounds” was held by the two superacids, fluorosulfonic acid and trifluoromethanesulfonic acid, with p"K"s of −14 and −16 respectively. The parent molecule from which carborane acid is derived, an icosahedral carboranate anion, , was first synthesized at DuPont in 1967 by Walter Knoth. Research into this molecules properties was put on hiatus until the mid 1980s when the Czech group of boron scientists, Plešek, Štíbr, and Heřmánek improved the process for halogenation of carborane molecules. These findings were instrumental in developing the current procedure for carborane acid synthesis. The process consists of treating Cs[HCBH] with , refluxing under dry argon to fully chlorinate the molecule yielding carborane acid, but this has been shown to fully chlorinate only under select conditions.
Stearic acid
Stearic acid ( , ) is a saturated fatty acid with an 18-carbon chain and has the IUPAC name octadecanoic acid. It is a waxy solid and its chemical formula is CHCOH. Its name comes from the Greek word στέαρ ""stéar"", which means tallow. The salts and esters of stearic acid are called stearates. As its ester, stearic acid is one of the most common saturated fatty acids found in nature following palmitic acid. The triglyceride derived from three molecules of stearic acid is called stearin.
Amino acid
Amino acids are organic compounds containing amine (-NH) and carboxyl (-COOH) functional groups, along with a side chain (R group) specific to each amino acid. The key elements of an amino acid are carbon (C), hydrogen (H), oxygen (O), and nitrogen (N), although other elements are found in the side chains of certain amino acids. About 500 naturally occurring amino acids are known (though only 20 appear in the genetic code) and can be classified in many ways. They can be classified according to the core structural functional groups' locations as alpha- (α-), beta- (β-), gamma- (γ-) or delta- (δ-) amino acids; other categories relate to polarity, pH level, and side chain group type (aliphatic, acyclic, aromatic, containing hydroxyl or sulfur, etc.). In the form of proteins, amino acid residues form the second-largest component (water is the largest) of human muscles and other tissues. Beyond their role as residues in proteins, amino acids participate in a number of processes such as neurotransmitter transport and biosynthesis.
Acid
Stronger acids have a larger "K" and a more negative p"K" than weaker acids.
Perchloric acid
Perchloric acid, a superacid, is one of the strongest Brønsted–Lowry acids. Its p"K" is −10, −15.2 (±2.0). It provides strong acidity with minimal interference because perchlorate is weakly nucleophilic (explaining the high acidity of HClO). Other acids of noncoordinating anions, such as fluoroboric acid and hexafluorophosphoric acid are susceptible to hydrolysis, whereas perchloric acid is not. Despite hazards associated with the explosiveness of its salts, the acid is often preferred in certain syntheses. For similar reasons, it is a useful eluent in ion-exchange chromatography.
Phosphoric acids and phosphates
There are various kinds of phosphoric acids and phosphates. Of the many phosphorus oxoacids, the phosphoric acids constitute the largest and most diverse group. The simplest phosphoric acid series begins with monophosphoric (orthophosphoric) acid, continues with many oligophosphoric acids such as diphosphoric (pyrophosphoric) acid and concludes in the polyphosphoric acids. But, phosphoric acid units can bind together into rings or cyclic structures, chains (catenas), or branched structures, with various combinations possible. Each of these can form phosphates (salts or esters of phosphoric acids).
Allenolic acid
Allenolic acid, or allenoic acid, is a synthetic, nonsteroidal estrogen discovered in 1947 or 1948 that, although studied clinically, was never marketed. It is an open-ring or seco-analogue of steroidal estrogens like estrone and equilenin. The compound was named after Dr. Edgar Allen, one of the pioneers in estrogen research. Although described as an estrogen, allenolic acid probably is totally inactive at the receptor, whereas a derivative, allenestrol (α,α-dimethyl-β-ethylallenolic acid), is reported to be a potent estrogen. Another derivative of allenolic acid (specifically 6-methoxy-allenestrol), methallenestril (brand name Vallestril), is also a potent estrogen and, in contrast to allenolic acid and allenestrol, has been marketed.
Drugs for acid-related disorders
Proton-pump inhibitors (PPIs) are a group of drugs whose main action is a pronounced and long-lasting reduction of gastric acid production. They are the most potent inhibitors of acid secretion available. The group followed and has largely superseded another group of pharmaceuticals with similar effects, but a different mode of action, called H-receptor antagonists. These drugs are among the most widely sold drugs in the world, and are generally considered effective. When these medications are used long term, the lowest effective dose should be taken. They may also be taken only when symptoms occur in those with frequent problems. H receptor blockers lead to roughly a 40% improvement.
Nitric acid
Nitric acid (HNO), also known as aqua fortis (Latin for "strong water") and spirit of niter, is a highly corrosive mineral acid.
Arachidonic acid
Arachidonic acid is one of the most abundant fatty acids in the brain, and is present in similar quantities to docosahexaenoic acid (DHA). The two account for about 20% of its fatty-acid content. Like DHA, neurological health is reliant upon sufficient levels of arachidonic acid. Among other things, arachidonic acid helps to maintain hippocampal cell membrane fluidity. It also helps protect the brain from oxidative stress by activating peroxisome proliferator-activated receptor gamma. ARA also activates syntaxin-3 (STX-3), a protein involved in the growth and repair of neurons.
Superacid
According to the classical definition, a superacid is an acid with an acidity greater than that of 100% pure sulfuric acid, which has a Hammett acidity function ("H") of −12. According to the modern definition, a superacid is a medium in which the chemical potential of the proton is higher than in pure sulfuric acid. Commercially available superacids include trifluoromethanesulfonic acid (CFSOH), also known as triflic acid, and fluorosulfuric acid (HSOF), both of which are about a thousand times stronger (i.e. have more negative "H" values) than sulfuric acid. Most strong superacids are prepared by the combination of a strong Lewis acid and a strong Brønsted acid. A strong superacid of this kind is fluoroantimonic acid. Another group of superacids, the carborane acid group, contains some of the strongest known acids.
Brønsted–Lowry acid–base theory
where S stands for a solvent molecule. The most important such solvents are dimethylsulfoxide, DMSO, and acetonitrile, CHCN, as these solvents has been widely used to measure the acid dissociation constants of organic molecules. Because DMSO is a stronger proton acceptor than HO the acid becomes a stronger acid in this solvent than in water. Indeed, many molecules behave as acids in non-aqueous solution that do not do so in aqueous solution. An extreme case occurs with carbon acids, where a proton is extracted from a C-H bond.
Armstrong's acid
Armstrong's acid (naphthalene-1,5-disulfonic acid) is a fluorescent organic compound with the formula CH(SOH). It is one of several isomers of naphthalenedisulfonic acid. It a colorless solid, typically obtained as the tetrahydrate. Like other sulfonic acids, it is a strong acid. It is named for British chemist Henry Edward Armstrong.
Lewis acids and bases
The concept originated with Gilbert N. Lewis who studied chemical bonding. In 1923, Lewis wrote "An acid substance is one which can employ an electron lone pair from another molecule in completing the stable group of one of its own atoms." The Brønsted–Lowry acid–base theory was published in the same year. The two theories are distinct but complementary. A Lewis base is also a Brønsted–Lowry base, but a Lewis acid doesn't need to be a Brønsted–Lowry acid. The classification into hard and soft acids and bases (HSAB theory) followed in 1963. The strength of Lewis acid-base interactions, as measured by the standard enthalpy of formation of an adduct can be predicted by the Drago–Wayland two-parameter equation.
Fatty acid
Fatty acids that are required for good health but cannot be made in sufficient quantity from other substrates, and therefore must be obtained from food, are called essential fatty acids. There are two series of essential fatty acids: one has a double bond three carbon atoms away from the methyl end; the other has a double bond six carbon atoms away from the methyl end. Humans lack the ability to introduce double bonds in fatty acids beyond carbons 9 and 10, as counted from the carboxylic acid side. Two essential fatty acids are linoleic acid (LA) and alpha-linolenic acid (ALA). These fatty acids are widely distributed in plant oils. The human body has a limited ability to convert ALA into the longer-chain omega-3 fatty acids — eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which can also be obtained from fish. Omega-3 and omega-6 fatty acids are biosynthetic precursors to endocannabinoids with antinociceptive, anxiolytic, and neurogenic properties.
Triflate
The corresponding triflate anion, , is an extremely stable polyatomic ion, being the conjugate base of triflic acid (CFSOH), one of the strongest acids known. It is defined as a superacid, because it is more acidic than pure sulfuric acid.
Antioxidant
Uric acid is by far the highest concentration antioxidant in human blood. Uric acid (UA) is an antioxidant oxypurine produced from xanthine by the enzyme xanthine oxidase, and is an intermediate product of purine metabolism. In almost all land animals, urate oxidase further catalyzes the oxidation of uric acid to allantoin, but in humans and most higher primates, the urate oxidase gene is nonfunctional, so that UA is not further broken down. The evolutionary reasons for this loss of urate conversion to allantoin remain the topic of active speculation. The antioxidant effects of uric acid have led researchers to suggest this mutation was beneficial to early primates and humans. Studies of high altitude acclimatization support the hypothesis that urate acts as an antioxidant by mitigating the oxidative stress caused by high-altitude hypoxia.
Inorganic nonaqueous solvent
Any acid which is a stronger acid than the ammonium ion will be a strong acid in liquid ammonia. This is the
case for acetic acid, which is completely dissociated in liquid ammonia solution. The addition of pure acetic
acid and the addition of ammonium acetate have exactly the same effect on a liquid ammonia solution: the increase
in its acidity: in practice, the latter is preferred for safety reasons.
Chemistry
Acid strength is commonly measured by two methods. One measurement, based on the Arrhenius definition of acidity, is pH, which is a measurement of the hydronium ion concentration in a solution, as expressed on a negative logarithmic scale. Thus, solutions that have a low pH have a high hydronium ion concentration and can be said to be more acidic. The other measurement, based on the Brønsted–Lowry definition, is the acid dissociation constant (K), which measures the relative ability of a substance to act as an acid under the Brønsted–Lowry definition of an acid. That is, substances with a higher K are more likely to donate hydrogen ions in chemical reactions than those with lower K values.
Acid strength
While the p"K" value measures the tendency of an acidic solute to transfer a proton to a standard solvent (most commonly water or DMSO), the tendency of an acidic solvent to transfer a proton to a reference solute (most commonly a weak aniline base) is measured by its Hammett acidity function, the "H" value. Although these two concepts of acid strength often amount to the same general tendency of a substance to donate a proton, the p"K" and "H" values are measures of distinct properties and may occasionally diverge. For instance, hydrogen fluoride, whether dissolved in water (p"K" = 3.2) or DMSO (p"K" = 15), has p"K" values indicating that it undergoes incomplete dissociation in these solvents, making it a weak acid. However, as the rigorously dried, neat acidic medium, hydrogen fluoride has an "H" value of –15, making it a more strongly protonating medium than 100% sulfuric acid and thus, by definition, a superacid. (To prevent ambiguity, in the rest of this article, "strong acid" will, unless otherwise stated, refer to an acid that is strong as measured by its p"K" value (p"K" < –1.74). This usage is consistent with the common parlance of most practicing chemists.)
Acid strength
† theoretical
Acid strength
The usual measure of the strength of an acid is its acid dissociation constant ("K"), which can be determined experimentally by titration methods. Stronger acids have a larger "K" and a smaller logarithmic constant (p"K"=−log"K") than weaker acids. The stronger an acid is, 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 determine the strength of the H—A bond. Acid strengths also depend on the stability of the conjugate base.
Acid
Common examples of monoprotic acids in mineral acids include hydrochloric acid (HCl) and nitric acid (HNO). On 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 (CHCOOH) and benzoic acid (CHCOOH).
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).
Acid strength
The strength of a weak organic acid may depend on substituent effects. The strength of an inorganic acid is dependent on the oxidation state for the atom to which the proton may be attached. Acid strength is solvent-dependent. For example, hydrogen chloride is a strong acid in aqueous solution, but is a weak acid when dissolved in glacial acetic acid.
Hammett acidity function
The Hammett acidity function (H) is a measure of acidity that is used for very concentrated solutions of strong acids, including superacids. It was proposed by the physical organic chemist Louis Plack Hammett and is the best-known acidity function used to extend the measure of Brønsted–Lowry acidity beyond the dilute aqueous solutions for which the pH scale is useful.