Silver nitrate is an inorganic compound with chemical formula AgNO3. It is a colorless solid that is a precursor to many other silver compounds. Silver nitrate is highly soluble in water but is poorly soluble in most organic solvents, except acetonitrile (111.8 g/100 g, 25 °C). Silver nitrate is the least expensive salt of silver; it offers several other advantages as well. It is non-hygroscopic (in contrast to silver fluoroborate and silver perchlorate). In addition, it is relatively stable to light, and it dissolves in numerous solvents, including water. The nitrate can be easily replaced by other ligands.
Synthesis Albertus Magnus, in the 13th century, documented the ability of nitric acid to separate gold and silver by dissolving the silver. It was once called lunar caustic because silver was called luna by ancient alchemists who associated silver with the moon. Indeed silver nitrate can be prepared by dissolving silver in nitric acid followed by evaporation of the solution. The stoichiometry of the reaction depends upon the concentration of nitric acid.
3 Ag + 4 HNO3 (cold and diluted) → 3 AgNO3 + 2 H2O + NO Ag + 2 HNO3 (hot and concentrated) → AgNO3 + H2O + NO2
Structure Solid silver nitrate is a coordination polymer. 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. Because of range of Ag-O distances the coordination geometry about the Ag+ centers is ambiguous. The nitrate groups bridge between four Ag+ sites.
Reactions
Thermal properties Solid silver nitrate is robust and melts to give a dense (4.1 g/cm3), stable liquid above its 198 °C melting point. At temperatures around 250 °C it decomposes to release metallic silver and red-brown fumes of nitrogen dioxide. Full decomposition occurs at 440 °C.
2 AgNO3 → 2 Ag + O2 + 2NO2 Most metal nitrates thermally decompose to the respective oxides. This may be the case for silver nitrate. Unlike most metal oxides, however, silver oxide readily degrades to the elemental silver.
Salt metathesis Silver nitrate is a precursor for the laboratory-scale synthesis of many silver compounds. These include the dark brown oxide, yellow iodide, pale yellow bromide, and white chloride. Among the oxyanion derivatives, the following compounds can be produced by precipitation from aqueous silver nitrate: the white sulfate, white sulfite, pale yellow nitrite, and pale yellow carbonate. 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.
Redox Silver(I) salts are mild oxidants, as implicated by their role in silver-based photography and the staining of skin by silver metal upon contact with silver nitrate solutions. Characteristically, silver nitrate reacts with pieces of copper to form hairlike crystals of silver metal and a blue solution of copper nitrate:
2 AgNO3 + Cu → Cu(NO3)2 + 2 Ag
Uses
Halide analysis The silver cation, Ag+, reacts quickly with halide sources to produce the insoluble silver halide. This reaction is used in analytical chemistry to confirm the presence of chloride, bromide, or iodide. The same reaction was used on steamships in order to determine whether or not boiler feedwater had been contaminated with seawater. 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 finds some use in organic synthesis, e.g. for deprotection and oxidations.
2 AgNO3 + 2 NaOH → Ag2O + 2 NaNO3 + H2O
Argentation chromatography Ag+ binds alkenes reversibly, and silver nitrate has been used to separate mixtures of alkenes by selective absorption. This phenomenon is the basis of argentation chromatography. In some cases, alkene complexes can be isolated. The alkene can be liberated with ammonia.
Biology In histology, silver nitrate is used for silver staining, for demonstrating reticular fibers, proteins and nucleic acids. For this reason it is also used to demonstrate proteins in polyacrylamide gel electrophoresis (PAGE) gels. It can be used as a stain in scanning electron microscopy. Cut flower stems can be placed in a silver nitrate solution, which prevents the production of ethylene. This delays ageing of the flower.
Indelible ink
Silver nitrate produces long-lasting stain when applied to skin and is one of indelible ink's ingredients. 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. In addition to staining skin, silver nitrate has a history of use in stained glass. In the 14th century, artists began using a "silver stain" (also known as a yellow stain) made from silver nitrate to create a yellow effect on clear glass. The stain would produce a stable color that could range from pale lemon to deep orange or gold. Silver stain was often used with glass paint, and was applied to the opposite side of the glass as the paint. It was also used to create a mosaic effect by reducing the number of pieces of glass in a window. Despite the age of the technique, this process of creating stained glass remains almost entirely unchanged.
Medicine
… excerpt ends here. Continue reading the full article.
