Silver(I) oxide
Encyclopedia
Silver oxide is the chemical compound
with the formula
Ag2O. It is a fine black or dark brown powder that is used to prepare other silver compounds.
and an alkali hydroxide
. Noteworthy is the fact that this reaction does not afford appreciable amounts of silver hydroxide due to the favorable energetics for the following reaction:
s, Ag2O is a three-dimensional polymer with covalent metal-oxygen bonding. It is isostructural with Cu2O. It is therefore expected that Ag2O is insoluble in all solvents, except by reaction. It is also slightly soluble in aqueous solution due to the formation of the ion, Ag(OH)2– and possibly related hydrolysis products. It dissolves in ammonia
solution to give soluble derivatives.
A slurry of Ag2O is readily attacked by acid
s:
where HX = HF
, HCl
, HBr
, or HI, HO2CCF3
. It will also react with solutions of alkali chlorides to precipitate silver chloride
, leaving a solution of the corresponding alkali hydroxide.
Like many silver compounds, silver oxide is photosensitive. It also decomposes at temperatures above 280 °C.
. In organic chemistry, silver oxide is used as a mild oxidizing agent. For example it oxidizes aldehydes to carboxylic acids. Such reactions often work best when the silver oxide is prepared in situ from silver nitrate and alkali hydroxide.
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
with the formula
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....
Ag2O. It is a fine black or dark brown powder that is used to prepare other silver compounds.
Preparation
Silver oxide is commercially available. It can be easily prepared by combining aqueous solutions of silver nitrateSilver nitrate
Silver nitrate is an inorganic compound with chemical formula . This compound is a versatile precursor to many other silver compounds, such as those used in photography. It is far less sensitive to light than the halides...
and an alkali hydroxide
Alkali hydroxide
The alkali hydroxides are a class of chemical compounds which are composed of an alkali metal cation and the hydroxide anion . The alkali hydroxides are:*Lithium hydroxide *Sodium hydroxide *Potassium hydroxide...
. Noteworthy is the fact that this reaction does not afford appreciable amounts of silver hydroxide due to the favorable energetics for the following reaction:
- 2 AgOH → Ag2O + H2O (pK = 2.875)
Structure and properties
Like most binary oxideOxide
An oxide is a chemical compound that contains at least one oxygen atom in its chemical formula. Metal oxides typically contain an anion of oxygen in the oxidation state of −2....
s, Ag2O is a three-dimensional polymer with covalent metal-oxygen bonding. It is isostructural with Cu2O. It is therefore expected that Ag2O is insoluble in all solvents, except by reaction. It is also slightly soluble in aqueous solution due to the formation of the ion, Ag(OH)2– and possibly related hydrolysis products. It dissolves in ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
solution to give soluble derivatives.
A slurry of Ag2O is readily attacked by acid
Acid
An acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red...
s:
- Ag2O + 2 HX → 2 AgX + H2O
where HX = HF
Hydrofluoric acid
Hydrofluoric acid is a solution of hydrogen fluoride in water. It is a valued source of fluorine and is the precursor to numerous pharmaceuticals such as fluoxetine and diverse materials such as PTFE ....
, HCl
Hydrochloric acid
Hydrochloric acid is a solution of hydrogen chloride in water, that is a highly corrosive, strong mineral acid with many industrial uses. It is found naturally in gastric acid....
, HBr
Hydrobromic acid
Hydrobromic acid is a strong acid formed by dissolving the diatomic molecule hydrogen bromide in water. "Constant boiling" hydrobromic acid is an aqueous solution that distills at 124.3 °C and contains 47.6% HBr by weight, which is 8.89 mol/L. Hydrobromic acid has a pKa of −9, making it a...
, or HI, HO2CCF3
Trifluoroacetic acid
Trifluoroacetic acid is the simplest stable perfluorinated carboxylic acid chemical compound, with the formula CF3CO2H. It is a strong carboxylic acid due to the influence of the electronegative trifluoromethyl group. TFA is almost 100,000-fold more acidic than acetic acid...
. It will also react with solutions of alkali chlorides to precipitate silver chloride
Silver chloride
Silver chloride is a chemical compound with the chemical formula AgCl. This white crystalline solid is well known for its low solubility in water . Upon illumination or heating, silver chloride converts to silver , which is signalled by greyish or purplish coloration to some samples...
, leaving a solution of the corresponding alkali hydroxide.
Like many silver compounds, silver oxide is photosensitive. It also decomposes at temperatures above 280 °C.
Applications
Commercially, silver oxide is used in a silver-oxide batterySilver-oxide battery
A silver oxide battery , not to be confused with a similar but different silver–zinc battery, which is a secondary cell, is a primary cell with relatively very high energy/weight ratio. They are costly due to the high price of silver...
. In organic chemistry, silver oxide is used as a mild oxidizing agent. For example it oxidizes aldehydes to carboxylic acids. Such reactions often work best when the silver oxide is prepared in situ from silver nitrate and alkali hydroxide.
External links
- Annealing of Silver Oxide Demonstration experiment: Instruction and video
- Silver Oxide, Ag2O