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'{{Short description|Ionic compound composed of cations and anions}} {{About|the term as used in chemistry|the chemistry of table salt|Sodium chloride}} {{redirect|Salts|other uses|Salt (disambiguation)}} In [[chemistry]], a '''salt''' is a [[chemical compound]] consisting of an [[ion]]ic assembly of positively charged cations and negatively charged anions, which results in a compound with no net [[electric charge]].<ref>{{GoldBookRef |file= S05447 |title= salt }}</ref> A common example is [[Salt|table salt]], with positively charged [[sodium]] ions and negatively charged [[chloride]] ions. The component ions in a salt compound can be either [[inorganic compound|inorganic]], such as [[chloride]] (Cl⁻), or [[organic chemistry|organic]], such as [[acetate]] ({{chem|CH|3|COO|−}}). Each ion can be either [[monatomic ion|monatomic]], such as [[fluoride]] (F⁻), or [[polyatomic ion|polyatomic]], such as [[sulfate]] ({{chem|SO|4|2−}}). ==Types of salt== Salts can be classified in a variety of ways. Salts that produce [[hydroxide]] [[ions]] when dissolved in [[water]] are called ''[[alkali salt]]s'' and salts that produce [[hydrogen]] [[ions]] when dissolved in [[water]] are called ''[[acid salt]]s''. ''Neutral salts'' are those salts that are neither acidic nor alkaline. [[Zwitterion]]s contain an anionic and a cationic centre in the same [[molecule]], but are not considered salts. Examples of zwitterions are [[amino acid]]s, many [[metabolite]]s, [[peptide]]s, and [[protein]]s.<ref>{{cite book |ref = Voet |last1 = Voet |first1 = D. |last2 = Voet |first2 = J. G. |name-list-style = amp |year = 2005 |title = Biochemistry |edition = 3rd |publisher = John Wiley & Sons Inc. |location = Hoboken, New Jersey |url = http://www.chem.upenn.edu/chem/research/faculty.php?browse=V |isbn = 9780471193500 |pages = 68 |url-status = dead |archive-url = https://web.archive.org/web/20070911065858/http://www.chem.upenn.edu/chem/research/faculty.php?browse=V |archive-date = 2007-09-11 }}</ref> == Properties == [[File:ILfromOS.svg|thumb|[[BMIM-PF6|BMIM⁺PF₆⁻]], an [[ionic liquid]]]] === Color === Solid salts tend to be [[Transparency (optics)|transparent]], as illustrated by [[sodium chloride]]. In many cases, the apparent [[Opacity (optics)|opacity]] or [[Transparency (optics)|transparency]] are only related to the difference in size of the individual [[monocrystal]]s. Since light reflects from the [[Crystallite|grain boundaries]] (boundaries between crystallites), larger [[crystal]]s tend to be transparent, while the [[polycrystalline]] aggregates look like opaque powders or masses. Salts exist in many different [[color]]s, which arise either from their constituent anions, cations or [[Solvation|solvates]]. For example: * [[sodium chromate]] is made yellow by the [[chromate ion]] * [[potassium dichromate]] is made orange by the [[dichromate ion]] * [[cobalt nitrate]] is made red by the chromophore of hydrated cobalt(II) ([Co(H₂O)₆]²⁺). * [[copper(II) sulfate|copper sulfate]] is made blue by the copper(II) chromophore * [[potassium permanganate]] is made violet by the [[permanganate]] anion. * [[nickel(II) chloride|nickel chloride]] is typically made green by the hydrated nickel(II) chloride [NiCl₂(H₂O)₄] * [[sodium chloride]], [[Magnesium sulfate|magnesium sulfate heptahydrate]] appear colorless or white because the constituent cations and anions do not absorb light in the part of the spectrum that is visible to humans. Few [[minerals]] are salts, because they would be solubilized by water.{{dubious|date=December 2021}}{{clarify|date=December 2021}} Similarly, inorganic [[pigment]]s tend not to be salts, because insolubility is required for fastness. Some organic [[dye]]s are salts, but they are virtually insoluble in water. === Taste === Different salts can elicit all five [[basic taste]]s, e.g., [[Saltiness|salty]] ([[sodium chloride]]), [[sweet]] ([[lead diacetate]], which will cause [[lead poisoning]] if ingested), [[Sour (taste)|sour]] ([[potassium bitartrate]]), [[Bitter (taste)|bitter]] ([[magnesium sulfate]]), and [[umami]] or [[Umami|savory]] ([[monosodium glutamate]]). === Odor === Salts of strong acids and strong bases ("[[#Strong salt|strong salts]]") are non-[[Volatility (chemistry)|volatile]] and often odorless, whereas salts of either weak acids or weak bases ("[[#Weak salt|weak salts]]") may smell like the [[conjugate acid]] (e.g., acetates like acetic acid ([[vinegar]]) and cyanides like [[hydrogen cyanide]] ([[almond]]s)) or the conjugate base (e.g., ammonium salts like [[ammonia]]) of the component ions. That slow, partial decomposition is usually accelerated by the presence of water, since [[hydrolysis]] is the other half of the [[reversible reaction]] equation of formation of weak salts. === Solubility === {{see also|Solubility#Solubility of ionic compounds in water}} Many ionic compounds exhibit significant [[Dissolution (chemistry)|solubility]] in water or other polar solvents. Unlike molecular compounds, salts dissociate in solution into anionic and cationic components. The [[lattice energy]], the cohesive forces between these ions within a solid, determines the solubility. The solubility is dependent on how well each ion interacts with the solvent, so certain patterns become apparent. For example, salts of [[sodium]], [[potassium]] and ammonium are usually soluble in water. Notable exceptions include [[ammonium hexachloroplatinate]] and [[potassium cobaltinitrite]]. Most [[nitrates]] and many [[sulfate]]s are water-soluble. Exceptions include [[barium sulfate]], [[calcium sulfate]] (sparingly soluble), and [[lead(II) sulfate]], where the 2+/2− pairing leads to high lattice energies. For similar reasons, most metal [[carbonate]]s are not soluble in water. Some soluble carbonate salts are: [[sodium carbonate]], [[potassium carbonate]] and [[ammonium carbonate]]. === Conductivity === [[File:SegStackEdgeOnHMTFCQ.jpg|thumb|Edge-on view of portion of crystal structure of hexamethylene[[Tetrathiafulvene|TTF]]/[[TCNQ]] charge transfer salt.<ref>{{cite journal|author1=D. Chasseau|author2=G. Comberton|author3=J. Gaultier|author4=C. Hauw|journal=Acta Crystallographica Section B|title=Réexamen de la structure du complexe hexaméthylène-tétrathiafulvalène-tétracyanoquinodiméthane|year=1978| volume=34|issue=2|page=689|doi=10.1107/S0567740878003830|doi-access=free}}</ref>]] Salts are characteristically [[Insulator (electricity)|insulators]]. Molten salts or solutions of salts conduct electricity. For this reason, liquified (molten) salts and solutions containing dissolved salts (e.g., sodium chloride in water) can be used as [[electrolyte]]s. ===Melting point=== Salts characteristically have high melting points. For example, [[sodium chloride]] melts at 801&nbsp;°C. Some salts with low lattice energies are liquid at or near room temperature. These include [[molten salt]]s, which are usually mixtures of salts, and [[ionic liquid]]s, which usually contain organic cations. These liquids exhibit unusual properties as solvents. == Nomenclature == The name of a salt starts with the name of the cation (e.g., ''sodium'' or ''ammonium'') followed by the name of the anion (e.g., ''chloride'' or ''acetate''). Salts are often referred to only by the name of the cation (e.g., ''sodium salt'' or ''ammonium salt'') or by the name of the anion (e.g., ''chloride salt'' or ''acetate salt''). Common salt-forming cations include: * [[Ammonium]] {{chem|NH|4|+}} * [[Calcium]] {{chem|Ca|2+}} * [[Iron]] {{chem|Fe|2+}} and {{chem|Fe|3+}} * [[Magnesium]] {{chem|Mg|2+}} * [[Potassium]] {{chem|K|+}} * [[Pyridinium]] {{chem|C|5|H|5|NH|+}} * [[Quaternary ammonium cation|Quaternary ammonium]] {{chem|NR|4|+}}, R being an [[alkyl]] group or an [[aryl]] group * [[Sodium]] {{chem|Na|+}} * [[Copper]] {{chem|Cu|2+}} Common salt-forming anions (parent acids in parentheses where available) include: * [[Acetate]] {{chem|CH|3|COO|−}} ([[acetic acid]]) * [[Carbonate]] {{chem|CO|3|2−}} ([[carbonic acid]]) * [[Chloride]] {{chem|Cl|−}} ([[hydrochloric acid]]) * [[Citrate]] {{chem|HOC(COO|−|)(CH|2|COO|−|)|2}} ([[citric acid]]) * [[Cyanide]] {{chem|C≡N|−}} ([[hydrocyanic acid]]) * [[Fluoride]] {{chem|F|−}} ([[hydrofluoric acid]]) * [[Nitrate]] {{chem|NO|3|−}} ([[nitric acid]]) * [[Nitrite]] {{chem|NO|2|−}} ([[nitrous acid]]) * [[Oxide]] {{chem|O|2−}} ([[water]]) * [[Phosphate]] {{chem|PO|4|3−}} ([[phosphoric acid]]) * [[Sulfate]] {{chem|SO|4|2−}} ([[sulfuric acid]]) Salts with varying number of hydrogen atoms replaced by cations as compared to their parent acid can be referred to as ''monobasic'', ''dibasic'', or ''tribasic'', identifying that one, two, or three hydrogen atoms have been replaced; ''polybasic'' salts refer to those with more than one hydrogen atom replaced. Examples include: * [[Monosodium phosphate|Sodium phosphate monobasic]] (NaH₂PO₄) * [[Disodium phosphate|Sodium phosphate dibasic]] (Na₂HPO₄) * [[Trisodium phosphate|Sodium phosphate tribasic]] (Na₃PO₄) == Formation == [[Image:Lead(II) sulfate.jpg|thumb|Solid lead(II) sulfate (PbSO₄)]] Salts are formed by a [[chemical reaction]] between: *A [[base (chemistry)|base]] and an [[acid]], e.g., [[ammonia|NH₃]] + [[hydrochloric acid|HCl]] → [[ammonium chloride|NH₄Cl]] *A [[metal]] and an [[acid]], e.g., [[magnesium|Mg]] + [[sulfuric acid|H₂SO₄]] → [[magnesium sulfate|MgSO₄]] + [[hydrogen|H₂]] *A metal and a non-metal, e.g., [[calcium|Ca]] + [[chlorine|Cl₂]] → [[calcium chloride|CaCl₂]] *A [[base (chemistry)|base]] and an [[acid anhydride]], e.g., 2&nbsp;[[Sodium Hydroxide|NaOH]] + [[Dichlorine monoxide|Cl₂O]] → 2&nbsp;[[Sodium hypochlorite|NaClO]] + [[Water|H₂O]] *An [[acid]] and a [[base anhydride]], e.g., 2&nbsp;[[nitric acid|HNO₃]] + [[Sodium oxide|Na₂O]] → 2&nbsp;[[Sodium nitrate|NaNO₃]] + [[Water|H₂O]] *In the [[salt metathesis reaction]] where two different salts are mixed in water, their ions recombine, and the new salt is insoluble and precipitates. For example: *: Pb(NO₃)₂ + Na₂SO₄ → PbSO₄↓ + 2&nbsp;NaNO₃ ==Strong salt== Strong salts or strong [[electrolyte]] salts are chemical salts composed of strong electrolytes. These [[ionic compound]]s dissociate completely in [[water]]. They are generally odorless and [[Volatility (chemistry)|nonvolatile]]. Strong salts start with Na__, K__, NH₄__, or they end with __NO₃, __ClO₄, or __CH₃COO. Most group 1 and 2 metals form strong salts. Strong salts are especially useful when creating conductive compounds as their constituent ions allow for greater conductivity.{{Citation needed|date=December 2022}} == Weak salt== Weak salts or "weak electrolyte salts" are, as the name suggests, composed of weak [[electrolyte]]s. They are generally more [[volatility (chemistry)|volatile]] than strong salts. They may be similar in [[odor]] to the [[acid]] or [[base (chemistry)|base]] they are derived from. For example, [[sodium acetate]], CH₃COONa, smells similar to [[acetic acid]] CH₃COOH. == See also == *[[Bresle method]] (the method used to test for salt presence during coating applications) *[[Carboxylate]] *[[Fireworks#Pyrotechnic compounds|Fireworks/pyrotechnics]] (salts are what give color to fireworks) *[[Halide]] *[[Ionic bond]]s *[[Natron]] *[[Salinity]] == References == {{Reflist}} *[[Mark Kurlansky]] (2002). ''Salt: A World History''. Walker Publishing Company. {{ISBN|0-14-200161-9}}. {{Authority control}} [[Category:Chemical compounds]] [[Category:Salts| ]] [[Category:Alchemical substances]]'