Silver Oxide

In the study of Chemistry, the term oxides describe the reaction of metal or any element with oxygen atoms that results in Metal oxides. Silver oxide is an inorganic chemical compound composed of two atoms of silver and one atom of oxygen. The 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 coloured 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. The chemical compound of silver oxide with the formula is Ag₂O. The colour of silver oxide is black or dark brown. This powder is used to make other silver compounds. The silver oxide that is both Ag₂O and AgO work as a cathodic material (Control corrosion of a metal surface) in silver-zinc rechargeable batteries. 

Structure of silver(I) oxide 

Silver oxide has the same structure as the Cu₂O molecule. It has two coordinate silver centres linked by tetrahedral oxides. It crystallizes in a cubic structure. In its unit cell Ag atoms arrange in the face centred cubic sublattice and oxygen atoms in the base centred cubic sublattice. A quarter of the body diagonal shifts its one sublattice. The space group includes a point group with full octahedral symmetry. The 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. An aqueous solution of silver nitrate is prepared, and it is mixed with a solution of alkali hydroxide. Alkali hydroxide is those compounds that are composed of an alkali metal cation and hydroxide anion, for example, LiOH, NaOH, KOH, etc. 

To prepare silver oxide from silver nitrate, we take 20ml of silver nitrate in a clean, 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 coloured precipitate forms which indicates 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 an alkali metal hydroxide compound react, the formation of Ag₂O takes place. The reaction of formation of silver oxide by using silver nitrate and sodium hydroxide (alkali hydroxide) is given below –

2AgNO₃ + 2NaOH → Ag₂O + 2NaNO₃ + H₂O 

Silver compounds are usually photosensitive but Silver oxide is not photosensitive. That said silver oxide must be stored in a dark place as it decomposes at temperatures above 280 ^oC.

Properties of Silver(I) Oxide 

Silver oxide shows the following properties –

• Its molar mass is 231.7 g/mol.

• It is a dark brown or black coloured 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^oC.

• It is slightly soluble in water but its solubility increases with temperature. Such as 0.013g of silver oxide is soluble in one-litre water at 20 ^oC while 0.025g silver oxide is soluble in one-litre water at 25 ^oC. In the same way, at 80 ^oC, 0.053g of silver oxide is soluble in one – litre of water. 

• It is insoluble in ethanol. 

• It is soluble in acids and alkali solutions. 

• It decomposes at higher temperatures (>280 ^oC). So, on heating silver oxide up to 300 ^oC, 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 halides such as hydrogen fluoride, hydrogen bromide, hydrogen iodide and hydrogen chloride. The general reaction is given below –

Ag₂O + 2HX → 2AgX + H₂O

• Reaction with alkali chlorides – Silver oxide reacts with an aqueous solution of alkali chlorides and forms precipitate of silver chloride and solution of corresponding alkali hydroxide. The 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 the synthesis of many compounds. 

• It is used in the 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. 

Silver Oxide: Summary in Tabular form

Decomposition of Silver Oxide

To decompose silver oxide, we need to heat black silver oxide in a test tube to get metallic silver and gas. The gas released is then captured in a balloon. 

This particular activity can be used to demonstrate a decomposition reaction. The time taken to complete this activity is 10 minutes. This activity also illustrates the discovery process of chemical elements. 

Materials Needed for the Activity

• Balloon 

• Lighter 

• Alcohol Burner 

• Test tube clamp

• 125 millilitre Erlenmeyer Flask

• 5 grams of Ag₂O

• Test tube (175mm X 25mm) Do not use a culture tube

Discussion

In the history of chemistry, Lavoisier’s experiment of decomposition of mercuric oxide was revolutionary. There is reluctance in experimenting in the classroom due to the toxicity of mercury and its compounds. This activity is in parallel with Lavoisier’s experiment. Even though we are replacing mercury with silver. 

Procedure

• Ensure the mouth of the test tube is covered well by the balloon.

• Using the hottest part of the flame of the alcohol burner heats the bottom of the test tube. 

• In a few minutes, you will observe the balloon inflate slightly and the silver oxide will start turning silver. 

• Heat the silver oxide until completely decomposed.

• Place the test tube in the flask to cool down. 

Safety Precautions

• Silver oxide has to be treated carefully as it is a strong oxidizer. 

• Do not leave silver in contact with any combustible material. 

• Always clear the entire area of combustible material. 

• Always keep a fire extinguisher handy. 

Did you know? 

Did you know that Silver can make it rain? There is the use of a silver compound called the iodide which is used in cloud seeding. This causes clouds to produce rain and that is how Silver can make it rain. The other reason it can be used is to try to control hurricanes as well. 

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