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ACiD

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{{mergefrom|strong acid}} {{Acids and Bases}} {{otheruses}} An '''acid''' (often represented by the generic formula '''HA''') is traditionally considered any chemical compound that when dissolved in water, gives a solution with a pH of less than 7. That approximates the modern definition of Brønsted and Lowry, who defined an acid as a compound which donates a hydrogen ion (H⁺) to another compound (called a base). Common examples include acetic acid (in vinegar) and sulfuric acid (used in car battery car batteries). Acids generally taste sour; however, tasting acids, particularly concentrated acids, can be dangerous and is not recommended!

Definitions of acids and bases
The word "acid" comes from the Latin ''acidus'' meaning "sour," but in chemistry the term acid has a more specific meaning. There are three common Acid-base reaction theories ways to define an acid, namely, the '''Arrhenius''', the '''Brønsted-Lowry''' and the '''Lewis''' definitions, in order of increasing generality. * '''Arrhenius''': According to this definition, an acid is a substance that increases the concentration of hydronium ion (H₃O⁺) when dissolved in water, while bases are substances that increase the concentration of hydroxide ions (OH^-). This definition limits acids and bases to substances that can dissolve in water. Around 1800, many France French chemists, including Antoine Lavoisier, incorrectly believed that all acids contained oxygen. England English chemists, including Sir Humphry Davy at the same time believed all acids contained hydrogen. The Sweden Swedish chemist Svante Arrhenius used this belief to develop this definition of acid. * '''Brønsted-Lowry''': According to this definition, an acid is a proton donor and a base is a proton acceptor. The acid is said to be dissociated after the proton is donated. An acid and the corresponding base are referred to conjugate acid-base pairs. Johannes Nicolaus Brønsted Brønsted and Martin Lowry Lowry formulated this definition, which includes water-insoluble substances not in the Arrhenius definition. * '''Lewis''': According to this definition, an acid is an electron-pair acceptor and a base is an electron-pair donor. (These are frequently referred to as "Lewis acids" and "Lewis bases," and are electrophiles and nucleophiles in organic chemistry). Lewis acids include substances with no protons, such as iron(III) chloride. The Lewis definition can also be explained with molecular orbital theory. In general, an acid can receive an electron pair in its lowest unoccupied orbital (LUMO) from the highest occupied orbital (HOMO) of a base. That is, the HOMO from the base and the LUMO from the acid combine to a bonding molecular orbital. This definition was developed by Gilbert N. Lewis. Although not the most general theory, the Brønsted-Lowry definition is the most widely used definition. The strength of an acid may be understood by this defintion by the stability of hydronium and the solvated conjugate base upon dissociation. Increasing stability of the conjugate base will increase the acidity of a compound. This concept of acidity is used frequently for organic acids such as carboxylic acid. The molecular orbital description, where the unfilled proton orbital overlaps with a lone pair, is connected to the Lewis definition. Solutions of weak acids and salts of their conjugate bases form buffer solutions. Acid/base systems are different from redox reactions in that there is no change in oxidation state. Generally, acids have the following chemical and physical properties: * '''Taste''': Acids generally are sour when dissolved in water. * '''Touch''': Acids produce a stinging feeling, particularly strong acids. * '''Reactivity''': Acids react aggressively with or corrode most metals. * '''Electrical conductivity''': Acids are electrolytes. Strong acids are dangerous, causing severe burns for even minor contact. Generally, acid burns are treated by rinsing the affected area abundantly with water and followed up with immediate medical attention.

Nomenclature
Acids are named according to the ending of their anion. That ionic ending is dropped and replaced with a new suffix according to the table below. For example, HCl has chloride as its anion, so the -ide suffix makes it take the form hydrochloric acid. {| border="1" cellpadding="4" align="center" cellspacing="0" style="background: #f9f9f9; color: black; border: 1px #aaa solid; border-collapse: collapse;" !Anion Ending !Acid Prefix !Acid Suffix |- |per-anion-ate |per |ic acid |- |ate | |ic acid |- |ite | |ous acid |- |hypo-anion-ite |hypo |ous acid |- |ide |Hydro |ic acid |}

Chemical characteristics
In water the following Chemical equilibrium equilibrium occurs between an acid (HA) and water, which acts as a base: HA(aq) {{unicode|⇌}} H₃O⁺(aq) + A^-(aq) The acidity constant (or acid dissociation constant) is the equilibrium constant for the reaction of HA with water: :$K\_a\; =\; \{[\backslash mbox\{H\}\_3\backslash mbox\{O\}^+]\backslash cdot[A^-]\; \backslash over\; [HA]\}$ Strong acids have large ''K''_a values (i.e. the reaction equilibrium lies far to the right; the acid is almost completely dissociated to H₃O⁺ and A^-). Strong acids include the heavier hydrohalic acids: hydrochloric acid (HCl), hydrobromic acid (HBr), and hydroiodic acid (HI). (However, hydrofluoric acid, HF, is relatively weak.) For example, the ''K''_a value for hydrochloric acid (HCl) is 10⁷. Weak acids have small ''K''_a values (i.e. at equilibrium significant amounts of HA and A⁻ exist together in solution; modest levels of H₃O⁺ are present; the acid is only partially dissociated). For example, the K_a value for acetic acid is 1.8 x 10^-5. Most organic acids are weak acids. Oxoacids, which tend to contain central atoms in high oxidation states surrounded by oxygen may be quite strong or weak. Nitric acid, sulfuric acid, and perchloric acid are all strong acids, whereas nitrous acid, sulfurous acid and hypochlorous acid are all weak. Note the following: * The terms "hydrogen ion" and "proton" are used interchangebly; both refer to H⁺. * In aqueous solution, the water is protonated to form hydronium ion, H₃O⁺(aq). This is often abbreviated as H⁺(aq) even though the symbol is not chemically correct. * The strength of an acid is measured by its acid dissociation constant (''K''_a) or equivalently its p''K''_a (p''K''_a= - log(''K''_a). * The pH of a solution is a measurement of the concentration of hydronium. This will depend of the concentration and nature of acids and bases in solution.

Polyprotic acids
Polyprotic 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 acid''' (two potential protons to donate) and '''triprotic acid''' (three potential protons to donate) A monoprotic acid can undergo one dissociation (sometimes called ionization) as follows and simply has one acid dissociation constant as shown above: :::::HA(aq) + H₂O(l) {{unicode|⇌}} H₃O⁺(aq) + A⁻(aq)         ''K''_a A diprotic acid (here symbolized by H₂A) can undergo one or two dissociations depending on the pH. Each dissociation has its own dissociation constant, K_a1 and K_a2. :::::H₂A(aq) + H₂O(l) {{unicode|⇌}} H₃O⁺(aq) + HA⁻(aq)       ''K''_a1 :::::HA⁻(aq) + H₂O(l) {{unicode|⇌}} H₃O⁺(aq) + A²⁻(aq)       ''K''_a2 The first dissociation constant is typically greater than the second; i.e., ''K''_a1 > ''K''_a2 . For example, sulfuric acid (H₂SO₄) can donate one proton to form the bisulfate anion (HSO₄⁻), for which ''K''_a1 is very large; then it can donate a second proton to form the sulfate anion (SO₄²⁻), 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 (H₂CO₃) can lose one proton to form bicarbonate anion (HCO₃⁻) and lose a second to form carbonate anion (CO₃²⁻). Both ''K''_a values are small, but ''K''_a1 > ''K''_a2 . A triprotic acid (H₃A) can undergo one, two, or three dissociations and has three dissociation constants, where ''K''_a1 > ''K''_a2 > ''K''_a3 . :::::H₃A(aq) + H₂O(l) {{unicode|⇌}} H₃O⁺(aq) + H₂A⁻(aq)        ''K''_a1 :::::H₂A⁻(aq) + H₂O(l) {{unicode|⇌}} H₃O⁺(aq) + HA²⁻(aq)       ''K''_a2 :::::HA²⁻(aq) + H₂O(l) {{unicode|⇌}} H₃O⁺(aq) + A³⁻(aq)         ''K''_a3 An inorganic example of a triprotic acid is orthophosphoric acid (H₃PO₄), usually just called phosphoric acid. All three protons can be successively lost to yield H₂PO₄⁻, then HPO₄²⁻, and finally PO₄³⁻ , the orthophosphate ion, usually just called phosphate. An Organic compound organic example of a triprotic acid is citric acid, which can successively lose three protons to finally form the citrate ion. Even though the positions of the protons on the original molecule may be equivalent, the successive ''K''_a values will differ since it is energetically less favorable to lose a proton if the conjugate base is more negatively charged.

Neutralization
Neutralization is the reaction between equal amounts of an acid and a base, producing a salt and water (molecule) water; for example, hydrochloric acid and sodium hydroxide form sodium chloride and water: ::HCl(aq) + NaOH(aq) -> H₂O(l) + NaCl(aq) Neutralization is the basis of titration, where a PH indicator pH indicator shows equivalence point when the equivalent number of moles of a base have been added to an acid.

Common acids


Strong inorganic acids
* Hydrobromic acid * Hydrochloric acid * Hydroiodic acid * Nitric acid * Sulfuric acid * Perchloric acid

Medium to weak inorganic acids
* Boric acid * Carbonic acid * Chloric acid * Hydrofluoric acid * Phosphoric acid * Pyrophosphoric acid

Weak organic acids
* Acetic acid * Benzoic acid * Butyric acid * Citric acid * Formic acid * Lactic acid * Malic acid * Mandelic acid * Methanethiol * Propionic acid * Pyruvic acid * Valeric acid

Acids in food
* '''Acetic acid''': (E260) found in vinegar * '''Adipic acid''': (E355) * '''Alginic acid''': (E400) * '''Ascorbic acid''' (vitamin C): (E300) found in fruits * '''Benzoic acid''': (E210) * '''Boric acid''': (E284) * '''Citric acid''': (E330) found in citrus fruits * '''Carbonic acid''': (E290) found in carbonation carbonated soft drinks * '''Carminic acid''': (E120) * '''Cyclamic acid''': (E952) * '''Erythorbic acid''': (E315) * '''Erythorbin acid''': (E317) * '''Formic acid''': (E236)found in bee and ant stings * '''Fumaric acid''': (E297) * '''Gluconic acid''': (E574) * '''Glutamic acid''': (E620) * '''Guanylic acid''': (E626) * '''Hydrochloric acid''': (E507) * '''Inosinic acid''': (E630) * '''Lactic acid''': (E270) found in dairy products such as yoghurt and sour milk, also is product of cellular fermentation, the reason muscles burn * '''Malic acid''': (E296) * '''Metatartaric acid''': (E353) * '''Methanethiol''': found in cheese and some other fermented foods. * '''Niacin''' (nicotinic acid): (E375) * '''Oxalic acid''': found in spinach and rhubarb * '''Pectic acid''': found in fruits and some vegetables * '''Phosphoric acid''': (E338) * '''Propionic acid''': (E280) * '''Sorbic acid''': (E200) found in foods and drinks * '''Stearic acid''': (E570), a type of fatty acid. * '''Succinic acid''': (E363) * '''Sulfuric acid''': (E513) * '''Tannic acid''': found in tea * '''Tartaric acid''': (E334) found in grapes

Sources

- Listing of strengths of common acids and bases * Zumdahl, Chemistry, 4th Edition.

See also
* acid number Category:Chemical substances Category:Acids * bg:КиÑ?елина ca:Àcid cs:Kyselina da:Syre de:Säuren et:Hape es:Ã?cido eo:Acido fr:Acide gl:Ã?cido ko:ì‚° (화학) hr:Kiseline io:Acido id:Asam it:Acido he:חומצה lv:SkÄ?be lt:RÅ«gÅ¡tis hu:Sav mk:КиÑ?елина nl:Zuur (chemie) ja:é…¸ã?¨å¡©åŸº no:Syre nn:Syre nds:Süür pl:Kwas pt:Ã?cido ro:Acid ru:КиÑ?лота simple:Acid sk:Kyselina sl:Kislina sr:КиÑ?елина fi:Happo sv:Syra tl:Asido ta:அமிலமà¯? th:à¸?รด vi:Axít uk:КиÑ?лота zh:é…¸ :''For other uses of this term, see Acid (disambiguation).'' In databases, '''ACID''' stands for '''Atomicity''', '''Consistency''', '''Isolation''', and '''Durability'''. They are considered to be the key transaction processing features/properties of a ''database management system'', or DBMS. Without them, the integrity of the database cannot be guaranteed. In practice, these properties are often relaxed somewhat to provide better performance. In the context of databases, a single logical operation on the data is called a Database transaction transaction. An example of a transaction is a transfer of funds from one account to another, even though it might consist of multiple individual operations (such as debiting one account and crediting another). The ACID properties guarantee that such transactions are processed reliably. *Atomicity refers to the ability of the DBMS to guarantee that either all of the tasks of a transaction are performed or none of them are. The transfer of funds can be completed or it can fail for a multitude of reasons, but atomicity guarantees that one account won't be debited if the other is not credited as well. *Database consistency Consistency refers to the database being in a legal state when the transaction begins and when it ends. This means that a transaction can't break the rules, or ''integrity constraints'', of the database. If an integrity constraint states that all accounts must have a positive balance, then any transaction violating this rule will be aborted. *Isolation (computer science) Isolation refers to the ability of the application to make operations in a transaction appear isolated from all other operations. This means that no operation outside the transaction can ever see the data in an intermediate state; a bank manager can see the transferred funds on one account or the other, but never on both—even if she ran her query while the transfer was still being processed. More formally, isolation means the transaction history (or Schedule (computer science) schedule) is Serializability serializable. For performance reasons, this ability is the most often relaxed constraint. See the Isolation (computer science) isolation article for more details. *Durability (computer science) Durability refers to the guarantee that once the user has been notified of success, the transaction will persist, and not be undone. This means it will survive system failure, and that the database system has checked the integrity constraints and won't need to abort the transaction. Typically, all transactions are written into a database log log that can be played back to recreate the system to its state right before the failure. A transaction can only be deemed committed after it is safely in the log. Implementing the ACID properties correctly is not simple. Processing a transaction often requires a number of small changes to be made, including updating ''index (database) indices'' that are used by the system to speed up searches. This sequence of operations is subject to failure for a number of reasons; for instance, the system may have no room left on its disk drives, or it may have used up its allocated CPU time. ACID suggests that the database be able to perform all of these operations at once. In fact this is difficult to arrange. There are two popular families of techniques: Write ahead logging and Shadow paging. In both cases, Lock (computer science) locks must be acquired on all information that is updated, and depending on the implementation, on all data that is being read. In write ahead logging, atomicity is guaranteed by ensuring that information about all changes is written to a log before it is written to the database. That allows the database to return the database to a consistent state in the event of a crash. In shadowing, updates are applied to a copy of the database, and the new copy is activated when the transaction commits. The copy refers to unchanged parts of the old version of the database, rather than being an entire duplicate. Almost all databases used nothing but locking to ensure they were ACID until recently. This means that a lock must be acquired anytime before processing data in a database, even on read operations. Maintaining a large number of locks, however, results in substantial overhead as well as hurting concurrency. If user A is running a transaction that has read a row of data that user B wants to modify, for example, user B must wait until user A's transaction is finished. An alternative to locking is to maintain separate copies of any data that is modified. This allows users to read data without acquiring any locks. Going back to the example of user A and user B, when user A's transaction gets to data that user B has modified, the database is able to retrieve the exact version of that data that existed when user A started their transaction. This ensures that user A gets a consistent view of the database even if other users are changing data that user A needs to read. It is difficult to guarantee ACID properties in a network environment. Network connections might fail, or two users might want to use the same part of the database at the same time. Two-phase commit is typically applied in distributed transactions to ensure that each participant in the transaction agrees on whether the transaction should be committed or not. Care must be taken when running transactions in Parallel computing parallel. Two phase locking is typically applied to guarantee full Isolation (computer science) isolation. The 1995 MUMPS programming language standard includes Transaction Processing as one of its built-in commands. The ACID concept is described in Open Systems Interconnection ISO/IEC 10026-1:1992 Section 4. Category:Database management systems de:ACID (Informatik) es:ACID fr:Propriétés ACID it:ACID nl:ACID ja:ACID (コンピュータ科学) pl:ACID ru:ACID vi:ACID see ACiD Productions

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