Silver nitrate

Ag 1
N 1
O 3

5 atoms in one formula unit of an ionic lattice.

The drawing shows one formula unit of an ionic lattice, not a molecule; silver nitrate has no molecular shape.

IUPAC name: silver nitrate
Molar mass: 169.874(14) g/mol
Atoms: 5
SMILES: [N+](=O)([O-])[O-].[Ag+]
InChIKey: SQGYOTSLMSWVJD-UHFFFAOYSA-N
PubChem CID: 24470

Made of

In the US Geological Survey’s account, every other compound of silver is made from this one, which makes silver nitrate by far the metal’s most important commercial compound. It is prepared by dissolving silver in nitric acid. Fused into sticks, it has carried the name lunar caustic for centuries.

The salt pairs silver ions, Ag⁺, with nitrate ions, NO₃⁻, each built from one nitrogen atom and three of oxygen. Its IUPAC name is simply silver nitrate. Large crystals are transparent and small ones white, in the description of the Hazardous Substances Data Bank (HSDB). The commercial salt is practically pure, with only a trace of water. The Environmental Protection Agency’s 2023 data put US output at 4 to 5.5 million pounds, down from 7 to 8.5 million in 2022.

Structure and bonding

Silver and nitrate appear in the formula-unit drawing as two unjoined pieces: a silver ion marked +1 and a nitrate group of four atoms. Its nitrate is drawn with a double bond from nitrogen to one oxygen and single bonds to the other two. The drawing also gives nitrogen +1 and each single-bonded oxygen −1. That pattern is one of three equivalent resonance forms, drawings that move the double bond; in the real ion, set out with potassium nitrate, the three bonds are alike.

The silver ion is what ends as metal: at about 440 °C the salt decomposes into metallic silver, nitrogen, oxygen and nitrogen oxides, HSDB records.

The five atoms give the ratio of the ions, not a molecule: the lattice forms colourless rhombic crystals (HSDB). Water takes the lattice apart easily: HSDB gives 122 g dissolving in 100 mL of water at 0 °C. The salt follows the general solubility rule, given in Chem1, that all nitrates dissolve.

Where it turns up

In the laboratory silver nitrate is a widely used analytical reagent, by HSDB’s account. One such task is the Mohr titration, which measures chloride and is commonly run to find how salty a water sample is. Silver ions take the chloride out as solid silver chloride. Once that precipitate is nearly complete, a little chromate added at the start forms red-orange silver chromate, which marks the end by eye. Chloride in excess has the opposite effect, Chem1 notes: the precipitate redissolves as complex ions form, each a metal ion with other groups bound to it.

Outside the laboratory it goes into silver plating, sympathetic (invisible) and indelible inks, hair dye, porcelain colours and the etching of ivory, HSDB records. A US listing dated October 2021 allows it to colour eyebrows and eyelashes, in cosmetics applied externally by professionals only. A US rule of 2009 permits a solution of it with hydrogen peroxide as an antimicrobial in bottled water.

Why it matters

Photography has rested on silver salts since its beginnings in the 1820s, the US Geological Survey notes. Silver nitrate is the starting point for silver’s halogen compounds, the bromide and chloride among them (HSDB). Ambrotypes, images on glass made mostly between 1852 and 1881, came from a “wet-plate” process in which the plate was soaked in silver nitrate.

Mirrors are its other old craft. Silvering glass on a large scale, by chemically reducing silver nitrate to the metal, dates from Justus von Liebig’s process of 1835. Formaldehyde, glucose and other reagents reduce it readily.

Medicine uses it as an antiseptic and a caustic, a substance that destroys tissue. Its germicidal action may come from released silver ions, which, HSDB says, bind many groups in living matter and precipitate proteins, bacterial ones included. It is used to cauterise wounds, and sticks of lunar caustic serve to remove warts and treat surface ulcers. ATSDR, the US Agency for Toxic Substances and Disease Registry, also notes its use in burn salves.

Properties

Properties of silver nitrate Molar mass summed from IUPAC/CIAAW 2024 standard atomic weights; formula, atom and bond counts and PubChem's molecular weight from PubChem CID 24470.
Property	Value	Unit	Source
Formula (Hill order)	AgNO₃
Molar mass	169.874(14) g/mol	g/mol	IUPAC/CIAAW 2024
Silver atoms	1
Nitrogen atoms	1
Oxygen atoms	3
PubChem molecular weight	169.873 g/mol	g/mol	PubChem

Safety

Silver nitrate is corrosive: its EU classification carries the signal word Danger and the statement that it causes severe skin burns and eye damage. The International Chemical Safety Cards add that it attacks the respiratory tract and is corrosive if swallowed. It is also a strong oxidant that may intensify fire, and very toxic to aquatic life, with lasting effects. Fuller details are in the PubChem Laboratory Chemical Safety Summary and the NIOSH (US National Institute for Occupational Safety and Health) card for soluble silver compounds.

Questions

Is silver nitrate sensitive to light?

Not when it is pure, according to the Hazardous Substances Data Bank (HSDB) and the US Geological Survey. HSDB puts the darkening seen in practice down to small amounts of organic material, which promote a reduction driven by light. With organic matter present, air or light turns the salt grey or greyish-black. The International Chemical Safety Cards describe it turning grey in light, and CAMEO Chemicals describes it blackening on exposure to light or organic material.

Why was silver nitrate put in newborns' eyes?

For many years drops of it went into the eyes of newborn babies to prevent blindness caused by gonorrhoea, according to ATSDR, the US Agency for Toxic Substances and Disease Registry. MeSH, the Medical Subject Headings index, credits the salt with strong germicidal activity and records its topical use against ophthalmia neonatorum, an eye infection of the newborn. The US Geological Survey names erythromycin or tetracycline as alternatives for the same purpose.

Can silver nitrate turn skin blue?

It can, given long exposure. The condition is argyria, which the International Chemical Safety Cards describe as grey-blue staining of the eyes and skin. HSDB notes that every form of silver accumulates in body tissues, with very little excreted. ATSDR calls argyria permanent but apparently cosmetic, perhaps not otherwise harmful to health.

Is silver nitrate poisonous?

It is classed as harmful in several ways beyond its burns. Japan's national hazard classification adds fatal if swallowed, and organ damage from prolonged or repeated exposure. Some of the companies notifying the European Chemicals Agency classify it as able to damage the unborn child. The International Chemical Safety Cards report animal tests suggesting possible harm to human reproduction or development. HSDB adds that it is absorbed from the airways and gut, though not significantly through intact skin.