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Silver nitrate is an inorganic compound with
chemical formula In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, ...
. It is a versatile precursor to many other
silver Silver is a chemical element with the symbol Ag (from the Latin ', derived from the Proto-Indo-European ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, white, lustrous transition metal, it exhibits the highest electrical ...
compounds, such as those used in
photography Photography is the art, application, and practice of creating durable images by recording light, either electronically by means of an image sensor, or chemically by means of a light-sensitive material such as photographic film. It is emplo ...
. It is far less sensitive to light than the halides. It was once called ''lunar caustic'' because silver was called ''luna'' by ancient alchemists who associated silver with the moon. In solid silver nitrate, the silver ions are three- coordinated in a trigonal planar arrangement.


Synthesis and structure

Albertus Magnus, in the 13th century, documented the ability of
nitric acid Nitric acid is the inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but older samples tend to be yellow cast due to decomposition into oxides of nitrogen. Most commercially available ni ...
to separate
gold Gold is a chemical element with the symbol Au (from la, aurum) and atomic number 79. This makes it one of the higher atomic number elements that occur naturally. It is a bright, slightly orange-yellow, dense, soft, malleable, and ductile ...
and
silver Silver is a chemical element with the symbol Ag (from the Latin ', derived from the Proto-Indo-European ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, white, lustrous transition metal, it exhibits the highest electrical ...
by dissolving the silver. Indeed silver nitrate can be prepared by dissolving silver in
nitric acid Nitric acid is the inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but older samples tend to be yellow cast due to decomposition into oxides of nitrogen. Most commercially available ni ...
followed by evaporation of the solution. The stoichiometry of the reaction depends upon the concentration of nitric acid used. :3 Ag + 4 HNO3 (cold and diluted) → 3 AgNO3 + 2 H2O + NO :Ag + 2 HNO3 (hot and concentrated) → AgNO3 + H2O + NO2 The structure of silver nitrate has been examined by X-ray crystallography several times. In the common orthorhombic form stable at ordinary temperature and pressure, the silver atoms form pairs with Ag---Ag contacts of 3.227 Å. Each Ag+ center is bonded to six oxygen centers of both uni- and bidentate nitrate ligands. The Ag-O distances range from 2.384 to 2.702 Å.


Reactions

A typical reaction with silver nitrate is to suspend a rod of
copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pink ...
in a solution of silver nitrate and leave it for a few hours. The silver nitrate reacts with copper to form hairlike crystals of silver metal and a blue solution of
copper nitrate Copper(II) nitrate describes any member of the family of inorganic compounds with the formula Cu( NO3)2(H2O)x. The hydrates are blue solids. Anhydrous copper nitrate forms blue-green crystals and sublimes in a vacuum at 150-200 °C. Common ...
: : 2 AgNO3 + Cu → Cu(NO3)2 + 2 Ag Silver nitrate decomposes when heated: : 2 AgNO3(l) → 2 Ag(s) + O2(g) + 2 NO2(g) Qualitatively, decomposition is negligible below the melting point, but becomes appreciable around 250 °C and fully decomposes at 440 °C. Most metal nitrates thermally decompose to the respective oxides, but silver oxide decomposes at a lower temperature than silver nitrate, so the decomposition of silver nitrate yields elemental silver instead.


Uses


Precursor to other silver compounds

Silver nitrate is the least expensive salt of silver; it offers several other advantages as well. It is non-
hygroscopic Hygroscopy is the phenomenon of attracting and holding water molecules via either absorption or adsorption from the surrounding environment, which is usually at normal or room temperature. If water molecules become suspended among the substance' ...
, in contrast to silver fluoroborate and silver perchlorate. It is relatively stable to light. Finally, it dissolves in numerous solvents, including water. The nitrate can be easily replaced by other ligands, rendering AgNO3 versatile. Treatment with solutions of halide ions gives a precipitate of AgX (X = Cl, Br, I). When making photographic film, silver nitrate is treated with halide salts of sodium or potassium to form insoluble silver halide in situ in photographic gelatin, which is then applied to strips of tri- acetate or polyester. Similarly, silver nitrate is used to prepare some silver-based explosives, such as the fulminate, azide, or acetylide, through a
precipitation reaction In an aqueous solution, precipitation is the process of transforming a dissolved substance into an insoluble solid from a super-saturated solution. The solid formed is called the precipitate. In case of an inorganic chemical reaction leading ...
. Treatment of silver nitrate with base gives dark grey silver oxide: :2 AgNO3 + 2 NaOH → Ag2O + 2 NaNO3 + H2O


Halide abstraction

The silver cation, , reacts quickly with halide sources to produce the insoluble silver halide, which is a cream precipitate if is used, a white precipitate if is used and a yellow precipitate if is used. This reaction is commonly used in inorganic chemistry to abstract halides: :(aq) + (aq) → AgX(s) where = , , or . Other silver salts with non-coordinating anions, namely silver tetrafluoroborate and silver hexafluorophosphate are used for more demanding applications. Similarly, this reaction is used in analytical chemistry to confirm the presence of
chloride The chloride ion is the anion (negatively charged ion) Cl−. It is formed when the element chlorine (a halogen) gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. Chloride s ...
, bromide, or iodide ions. Samples are typically acidified with dilute nitric acid to remove interfering ions, e.g.
carbonate A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate ...
ions and
sulfide Sulfide (British English also sulphide) is an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions. Solutions of sulfide salts are corrosive. ''Sulfide'' also refers to chemical compounds la ...
ions. This step avoids confusion of silver sulfide or silver carbonate precipitates with that of silver halides. The color of precipitate varies with the halide: white (
silver chloride Silver chloride is a chemical compound with the chemical formula Ag Cl. This white crystalline solid is well known for its low solubility in water (this behavior being reminiscent of the chlorides of Tl+ and Pb2+). Upon illumination or heat ...
), pale yellow/cream (
silver bromide Silver bromide (AgBr) is a soft, pale-yellow, water-insoluble salt well known (along with other silver halides) for its unusual sensitivity to light. This property has allowed silver halides to become the basis of modern photographic materials. A ...
), yellow ( silver iodide). AgBr and especially AgI photo-decompose to the metal, as evidence by a grayish color on exposed samples. The same reaction was used on steamships in order to determine whether or not boiler feedwater had been contaminated with
seawater Seawater, or salt water, is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% (35 g/L, 35 ppt, 600 mM). This means that every kilogram (roughly one liter by volume) of seawater has appro ...
. It is still used to determine if moisture on formerly dry cargo is a result of condensation from humid air, or from seawater leaking through the hull.


Organic synthesis

Silver nitrate is used in many ways in organic synthesis, e.g. for deprotection and oxidations. binds
alkene In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond. Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic ...
s reversibly, and silver nitrate has been used to separate mixtures of alkenes by selective absorption. The resulting adduct can be decomposed with
ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous ...
to release the free alkene. Silver nitrate is highly soluble in water but is poorly soluble in most organic solvents, except acetonitrile (111.8 g/100 g, 25 °C).


Biology

In
histology Histology, also known as microscopic anatomy or microanatomy, is the branch of biology which studies the microscopic anatomy of biological tissues. Histology is the microscopic counterpart to gross anatomy, which looks at larger structures v ...
, silver nitrate is used for silver staining, for demonstrating reticular fibers,
protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
s and nucleic acids. For this reason it is also used to demonstrate proteins in PAGE gels. It can be used as a stain in scanning electron microscopy.


Indelible ink

Silver nitrate produces long-lasting stain when applied to skin. An electoral stain makes use of this to mark a finger of people who have voted in an election, allowing easy identification to prevent double-voting.


Medicine

Silver salts have antiseptic properties. In 1881 Credé introduced the use of dilute solutions of AgNO3 in
newborn babies An infant or baby is the very young offspring of human beings. ''Infant'' (from the Latin word ''infans'', meaning 'unable to speak' or 'speechless') is a formal or specialised synonym for the common term ''baby''. The terms may also be used t ...
' eyes at birth to prevent contraction of gonorrhea from the mother, which could cause blindness. (Modern antibiotics are now used instead). Fused silver nitrate, shaped into sticks, was traditionally called "lunar caustic". It is used as a
cauterizing Cauterization (or cauterisation, or cautery) is a medical practice or technique of burning a part of a body to remove or close off a part of it. It destroys some tissue in an attempt to mitigate bleeding and damage, remove an undesired growth, or ...
agent, for example to remove
granulation tissue Granulation tissue is new connective tissue and microscopic blood vessels that form on the surfaces of a wound during the healing process. Granulation tissue typically grows from the base of a wound and is able to fill wounds of almost any siz ...
around a stoma. General Sir James Abbott noted in his journals that in India in 1827 it was infused by a British surgeon into wounds in his arm resulting from the bite of a mad dog to cauterize the wounds and prevent the onset of rabies. Silver nitrate is used to cauterize superficial blood vessels in the nose to help prevent nose bleeds. Dentists sometimes use silver nitrate-infused swabs to heal
oral ulcer A mouth ulcer (aphtha) is an ulcer that occurs on the mucous membrane of the oral cavity. Mouth ulcers are very common, occurring in association with many diseases and by many different mechanisms, but usually there is no serious underlying caus ...
s. Silver nitrate is used by some
podiatrist A podiatrist ( ) is a medical professional devoted to the treatment of disorders of the foot, ankle, and related structures of the leg. The term originated in North America but has now become the accepted term in the English-speaking world for ...
s to kill cells located in the nail bed. The Canadian physician C. A. Douglas Ringrose researched the use of silver nitrate for sterilization procedures, believing that silver nitrate could be used to block and corrode the fallopian tubes. The technique was ineffective.


Disinfection

Much research has been done in evaluating the ability of the silver ion at inactivating ''
Escherichia coli ''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus '' Esc ...
'', a microorganism commonly used as an indicator for fecal contamination and as a surrogate for pathogens in drinking water treatment. Concentrations of silver nitrate evaluated in inactivation experiments range from 10–200 micrograms per liter as Ag+. Silver's antimicrobial activity saw many applications prior to the discovery of modern antibiotics, when it fell into near disuse. Its association with argyria made consumers wary and led them to turn away from it when given an alternative.


Against warts

Repeated daily application of silver nitrate can induce adequate destruction of cutaneous warts, but occasionally pigmented scars may develop. In a placebo-controlled study of 70 patients, silver nitrate given over nine days resulted in clearance of all warts in 43% and improvement in warts in 26% one month after treatment compared to 11% and 14%, respectively, in the placebo group.


Safety

As an oxidant, silver nitrate should be properly stored away from organic compounds. Despite its common usage in extremely low concentrations to prevent gonorrhea and control nose bleeds, silver nitrate is still very toxic and corrosive. Brief exposure will not produce any immediate side effects other than the purple, brown or black stains on the skin, but upon constant exposure to high concentrations, side effects will be noticeable, which include burns. Long-term exposure may cause eye damage. Silver nitrate is known to be a skin and eye irritant. Silver nitrate has not been thoroughly investigated for potential carcinogenic effect. Silver nitrate is currently unregulated in water sources by the United States Environmental Protection Agency. However, if more than 1 gram of silver is accumulated in the body, a condition called argyria may develop. Argyria is a permanent cosmetic condition in which the skin and internal organs turn a blue-gray color. The United States Environmental Protection Agency used to have a maximum contaminant limit for silver in water until 1990, when it was determined that argyria did not impact the function of any affected organs despite the discolouration."Silver Compounds." Encyclopedia of Chemical Technology. Vol. 22. Fourth Ed. Excec. Ed. Jaqueline I. Kroschwitz. New York: John Wiley and Sons, 1997. Argyria is more often associated with the consumption of colloidal silver solutions rather than with silver nitrate, since it is only used at extremely low concentrations to disinfect the water. However, it is still important to be wary before ingesting any sort of silver-ion solution.


References


External links


International Chemical Safety Card 1116History of Kodak: About Film and Imaging
{{Authority control 13th century in science Antiseptics Electron microscopy stains Nitrates Photographic chemicals Silver compounds Staining dyes Alchemical substances Light-sensitive chemicals Oxidizing agents Chemical tests