Salt (chemistry) - Wikipedia https://en.wikipedia.org/wiki/Salt_(chemistry)

Salt (chemistry)

In chemistry, a salt is a chemical compound consisting of an ionic assembly of cations and anions.[1] are composed of related numbers of cations (positively charged ions) and anions (negatively charged ions) so that the product is electrically neutral (without a net charge). ese component ions can be inorganic, − − − such as chloride (Cl ), or organic, such as acetate (CH3CO2); and can be monatomic, such as fluoride (F ) 2− or polyatomic, such as sulfate (SO4 ).

Contents Types of salt Properties Color Taste Odor Solubility Conductivity Melting point Nomenclature Formation Strong salt Weak salt See also References

Types of salt

Salts can be classified in a variety of ways. Salts that produce hydroxide ions when dissolved in water are called alkali salts. Salts that produce acidic solutions are acid salts. Neutral salts are those salts that are neither acidic nor basic. Zwierions contain an anionic and a cationic centre in the same molecule, but are not considered to be salts. Examples of zwierions include amino acids, many metabolites, peptides, and proteins.[2]

Properties

Color

Solid salts tend to be transparent as illustrated by . + − In many cases, the apparent opacity or transparency are only BMIM PF6 , an ionic liquid related to the difference in size of the individual monocrystals. Since light reflects from the grain boundaries (boundaries between

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crystallites), larger crystals tend to be transparent, while the polycrystalline aggregates look like white powders.

Salts exist in many different colors, which arise either from the anions or cations. For example:

sodium chromate is yellow by virtue of the chromate ion potassium dichromate is orange by virtue of the dichromate ion cobalt nitrate is red owing to the chromophore of hydrated cobalt(II) 2+ ([Co(H2O)6] ). copper sulfate is blue because of the copper(II) chromophore potassium permanganate has the violet color of permanganate anion.

nickel chloride is typically green of [NiCl2(H2O)4] sodium chloride, magnesium sulfate heptahydrate are colorless or white because the constituent cations and anions do not absorb in the visible part of the spectrum

Few minerals are salts because they would be solubilized by water. Similarly inorganic pigments tend not to be salts, because insolubility is required for fastness. Some organic dyes are salts, but they are virtually insoluble in water.

Taste

Different salts can elicit all five basic tastes, e.g., salty (sodium chloride), sweet (lead diacetate, which will cause lead poisoning if ingested), sour (potassium bitartrate), bier (magnesium sulfate), and umami or savory (monosodium glutamate).

Odor

Salts of strong acids and strong bases ("strong salts") are non-volatile and oen odorless, whereas salts of either weak acids or weak bases ("weak salts") may smell like the conjugate acid (e.g., acetates like acetic acid (vinegar) and cyanides like hydrogen cyanide (almonds)) or the conjugate base (e.g., ammonium salts like ammonia) of the component ions. at 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

Many ionic compounds exhibit significant solubility in water or other polar solvents. Unlike molecular compounds, salts dissociate in solution into anionic and cationic components. e laice energy, the cohesive forces between these ions within a solid, determines the solubility. e solubility is dependent on how well each ion interacts with the solvent, so certain paerns 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 sulfates are water-soluble. Exceptions include barium sulfate, calcium sulfate (sparingly soluble), and lead(II) sulfate, where the 2+/2− pairing leads to high laice energies. For similar reasons, most metal carbonates are not soluble in water. Some soluble carbonate salts are: sodium carbonate, potassium carbonate and ammonium carbonate.

Conductivity

Salts are characteristically insulators. Molten salts or solutions of salts conduct electricity. For this reason,

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liquified (molten) salts and solutions containing dissolved salts (e.g., sodium chloride in water) are called electrolytes.

Melting point

Salts characteristically have high melting points. For example, sodium chloride melts at 801 ℃. Some salts with low laice energies are liquid at or near room temperature. ese include Edge-on view of portion of molten salts, which are usually mixtures of salts, and ionic liquids, crystal structure of which usually contain organic cations. ese liquids exhibit hexamethyleneTTF/TCNQ unusual properties as solvents. charge transfer salt.[3] Nomenclature

e 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 oen 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 NH4 2+ Calcium Ca 2+ 3+ Iron Fe and Fe 2+ Magnesium Mg + Potassium K + Pyridinium C5H5NH + Quaternary ammonium NR4 , R being an alkyl group or an aryl group + Sodium Na 2+ Copper Cu

Common salt-forming anions (parent acids in parentheses where available) include:

− Acetate CH3COO (acetic acid) 2− Carbonate CO3 (carbonic acid) − Chloride Cl (hydrochloric acid) − − Citrate HOC(COO )(CH2COO )2 (citric acid) − Cyanide C≡N (hydrocyanic acid) − Fluoride F (hydrofluoric acid) − Nitrate NO3 (nitric acid) − Nitrite NO2 (nitrous acid) 2− Oxide O 3− Phosphate PO4 (phosphoric acid) 2− Sulfate SO4 (sulfuric acid)

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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:

Sodium phosphate monobasic (NaH2PO4) Sodium phosphate dibasic (Na2HPO4) Sodium phosphate tribasic (Na3PO4)

Formation

Salts are formed by a chemical reaction between:

A base and an acid, e.g., NH3 + HCl → NH4Cl A metal and an acid, e.g., Mg + H2SO4 → MgSO4 + H2 A metal and a non-metal, e.g., Ca + Cl2 → CaCl2 A base and an acid anhydride, e.g., 2 NaOH + Cl2O → 2 NaClO + H2O An acid and a base anhydride, e.g., 2 HNO3 + Na2O → 2 NaNO3 + H2O Solid lead(II) sulfate (PbSO4) 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 NaNO3

Strong salt

Strong salts or strong electrolyte salts are chemical salts composed of strong electrolytes. ese ionic compounds dissociate completely in water. ey are generally odorless and 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.[4]

Weak salt

Weak salts or "weak electrolyte salts" are, as the name suggests, composed of weak electrolytes. ey are generally more volatile than strong salts. ey may be similar in odor to the acid or base they are derived from. For example, sodium acetate, NaCH3COO, smells similar to acetic acid CH3COOH.

See also Acid salt also known as "hydrogen salt" Alkali salts also known as "basic salts" Bresle method (the method used to test for salt presence during coating applications)

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Carboxylate Edible salt Electrolyte Fireworks/pyrotechnics (salts are what give color to fireworks) Halide Hypertension Ionic bonds Natron Old Salt Route Road salt Salinity (the deliberate massive use of salt to render a soil unsuitable for cultivation and thus discourage habitation) Sodium Table salt Zwitterion Brønsted–Lowry acid–base theory Ionic compound

References

1. IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "salt (https://goldbook.iupac.org/S05447.html)". doi:10.1351/goldbook.S05447 (https://doi.org/10.1351%2Fgoldbook.S05447) 2. Voet, D. & Voet, J. G. (2005). Biochemistry (https://web.archive.org/web/200709110 65858/http://www.chem.upenn.edu/chem/research/faculty.php?browse=V) (3rd ed.). Hoboken, NJ: John Wiley & Sons Inc. p. 68. ISBN 9780471193500. Archived from the original (http://www.chem.upenn.edu/chem/research/faculty.php? browse=V) on 2007-09-11. 3. D. Chasseau; G. Comberton; J. Gaultier; C. Hauw (1978). "Réexamen de la structure du complexe hexaméthylène-tétrathiafulvalène-tétracyanoquinodiméthane" (http s://doi.org/10.1107%2FS0567740878003830). Acta Crystallographica Section B. 34: 689. doi:10.1107/S0567740878003830 (https://doi.org/10.1107%2FS05677408 78003830). 4. "Acid and Base Strength" (http://chem.libretexts.org/Core/Physical_and_Theoretical _Chemistry/Acids_and_Bases/Ionization_Constants/Acid_and_Base_Strength). Home Bookshelves Physical & Theoretical Chemistry Supplemental Modules (Physical and Theoretical Chemistry) Acids and Bases Ionization Constants. MindTouch and Department of Education Open Textbook Pilot Project. 5 June 2019. Archived (http s://web.archive.org/web/20161213034814/http://chem.libretexts.org/Core/Physical_ and_Theoretical_Chemistry/Acids_and_Bases/Ionization_Constants/Acid_and_Base_S trength) from the original on 2016-12-13. Retrieved 6 November 2019.

Mark Kurlansky (2002). Salt: A World History. Walker Publishing Company. ISBN 0-14-200161-9.

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