Difference between revisions of "Silver oxide"

Latest revision as of 07:37, 13 August 2023

Silver oxide is the chemical compound with the formula Ag₂O.

Properties

Chemical

Silver oxide readily reacts with acids, forming silver salts. Thus, it is the most important precursor in the synthesis of Ag salts.

Ag₂O + 2 HX → 2 AgX + H₂O

Unlike other silver compounds, silver oxide does not break down when exposed to light, but will decompose to silver metal if heated above 200 °C:

Ag₂O → 2 Ag + ½ O₂

Silver oxide can be used to synthesize epoxides from halocarbons. For example, reaction with 1,2-diiodoethane at high temperatures, yields ethylene oxide.

Ag₂O + (CH₂)₂I₂ → 2 AgI + (CH₂CH₂)O

Silver oxide is a mild oxidizing agent, capable of oxidizing aldehydes to carboxylic acids.

Physical

Silver oxide is a dense black powder, odorless. It is slightly soluble in water due to the formation of the ion Ag⁺ or Ag(OH)⁻₂, and the solubility increases at high and low pH (amphoteric). A saturated solution in water has a pH of about 10, and the solubility is lowest at pH 12.^[1] It will also dissolve in aq. ammonia, producing active compound of Tollens' reagent.

Availability

Silver oxide can be bought from chemical suppliers, but it's not cheap.

Silver oxide can be found in silver oxide batteries, but it's impractical to extract it from them, as you need a large amount of batteries.

Preparation

The most common way of preparing silver oxide is by adding an alkali base, like NaOH, to an aq. solution containing soluble silver salts, like silver nitrate.

2 AgNO₃ + 2 NaOH → Ag₂O + 2 NaNO₃ + H₂O

Other salts, like silver perchlorate can be used, but this one is a bit more expensive than the nitrate.^[4]

It's possible to use silver salts that are poorly soluble in water, if silver nitrate is not available, like silver sulfate, and the reaction will work, provided that the silver sulfate is extremely fine. The trick is to stir the alkali suspension of Ag₂ for a while, until no more white precipitate is seen in the suspension. If the silver sulfate is not fine enough, any lumps of it will only react at the surface with the alkali hydroxide, and thus the final product will be contaminated with unreacted Ag₂SO₄. To check for any unreacted silver sulfate, take the dry crude Ag₂ and grind it using a mortar and pestle, an see if crushing any black lumps produces white powder. The crude silver oxide can be further purified, by dissolving it in an acid, like formic acid (if nitric acid is not available), then precipitated again with NaOH to silver oxide.

Projects

• Make silver salts
• Synthesis of ethylene oxide
• Compound collecting
• Make expensive thermite
• Make silver-oxide battery

Handling

Safety

Silver oxide is harmful if ingested or inhaled, and will stain the skin. Proper protection must be worn when handling the compound.

Storage

In closed bottles, plastic or glass, away from any acids or reducing agents. Unlike most silver compounds, it is not light sensitive, thus it's not necessary to be kept in dark.

Disposal

Silver oxide can be reduced to silver metal, which is recycled.

References

1. ↑ ^{1.0 1.1 1.2} Gmelins Handbuch der Anorganischen Chemie, Silber Teil B1, Verlag Chemie GmbH, Weinheim/Bergstraße, 8th edition 1971, p. 68, 96-98
2. ↑ A. Seidell, W. F. Linke, Solubilities of Inorganic and Metal-Organic Compounds, 4th edition, volume 1, Toronto, New York, London 1958, p. 124
3. ↑ Barin I. Thermochemical Data of Pure Substances. - VCH, 1995 pp. 12
4. ↑ An EXPENSIVE Metal Oxide Silver(I) Oxide

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