What is Silver Oxide?
Silver oxide is an inorganic chemical compound composed of two atoms of silver and one atom of oxygen. Molecular formula of silver oxide is Ag2O. Its IUPAC name is silver(I) oxide. In silver(I) oxide, (I) shows here the oxidation number of silver which is +1. It is a black or dark brown colored compound. It is mainly used in batteries and in the preparation of other silver compounds. It is also known as silver dust, argentous oxide and silver monoxide.
Structure of silver(I) Oxide
Silver oxide has the same structure as Cu2O molecule. It has two coordinate silver centers linked by tetrahedral oxides. It crystallizes in a cubic structure. In its unit cell Ag atoms arrange in face centered cubic sublattice and oxygen atom in base centered cubic sublattice. A quarter of the body diagonal shifts its one sublattice. The space group includes a point group with full octahedral symmetry. Structure of its unit cell is given below –
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Preparation of Silver (I) Oxide
Silver oxide can be prepared by using another silver compound which is silver nitrate. Aqueous solution of silver nitrate is prepared, and it is mixed with a solution of an alkali hydroxide. Alkali hydroxide are those compounds which are composed of an alkali metal cation and hydroxide anion, for example, LiOH, NaOH and KOH etc.
To prepare silver oxide from silver nitrate, we take 20ml of silver nitrate in a clear, dry test tube. Now pipette out 20ml of sodium hydroxide in the same test tube. Now mix both the reagents well. As both the reagents mix well, a dark brown or black colored precipitate forms which indicate the formation of silver oxide. Keep the test tube undisturbed for 20 minutes, so that the precipitate will settle down at the bottom. Now slowly separate the silver nitrate solution into the beaker and keep the remaining silver oxide of the test tube in a sealed container as it is a toxic compound and dry it.
Thus, when silver nitrate and any alkali metal hydroxide compound react, formation of Ag2O takes place. Reaction of formation of silver oxide by using silver nitrate and sodium hydroxide (alkali hydroxide) is given below –
2AgNO3 + 2NaOH 🡪 Ag2O + 2NaNO3 + H2O
Silver oxide must be stored in a dark place as it is a photosensitive compound. It decomposes at the temperatures above 280 ℃.
Properties of Silver(I) Oxide
Silver oxide shows following properties –
Its molar mass is 231.7 g/mol.
It is a dark brown or black colored compound which is found in solid powdered form at STP.
Its crystal structure is cubic.
It is an odorless compound.
Its density is 7.14 g/cm3.
Its melting point is 300 ℃.
It is slightly soluble in water but its solubility increases with temperature. Such as 0.013g of silver oxide is soluble in one - liter water at 20 ℃ while 0.025g silver oxide is soluble in one - liter water at 25 ℃. In the same way at 80 ℃, 0.053g of silver oxide is soluble in one – liter of water.
It is insoluble in ethanol.
It is soluble in acids and alkali solutions.
It gets decomposed at higher temperatures (>280 ℃). So, on heating silver oxide up to 300 ℃, silver(I) and oxygen are formed.
It is highly toxic and harmful.
It is soluble in ammonia and forms an important compound of Tollen’s reagent.
It easily reacts with hydrogen halide such as hydrogen fluoride, hydrogen bromide, hydrogen iodide and hydrogen chloride. General reaction is given below –
Ag2O + 2HX → 2AgX + H2O
Reaction with alkali chlorides – Silver oxide reacts with aqueous solution of alkali chlorides and forms precipitate of silver chloride and solution of corresponding alkali hydroxide. Reaction is given below with sodium chloride –
Ag2O + 2NaCl +H2O 🡪 2NaOH + 2AgCl
Reaction with ammonia and sodium nitrate solution – Silver oxide reacts with ammonia and sodium nitrate solution and forms diamine silver(I) complex which is an active compound of Tollen’s reagent. Reaction is given below –
Ag2O(s) + 4NH3 + 2NaNO3 + H2O → 2[Ag(NH3)2]NO3 + 2NaOH
Uses of Silver Oxide
Silver oxide is used for various purposes. Its few applications are listed below –
It is used in silver oxide batteries.
It is used in many reactions as a mild oxidizing agent such as in oxidation reactions of converting aldehydes to carboxylic acids.
It is used in synthesis of many compounds.
It is used in preparation of Tollen’s reagent as well.
As it is thermally stable, it is suitable for ceramic, and optic applications.
Its applications are being studied in aerospace and fuel cells as well.
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