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Silver monoxide, Ag2O

Addition of the hydroxide of barium or of an alkali-metal to Silver nitrate solution precipitates the Silver monoxide, Ag2O, as a blackish, amorphous powder, which crystallizes from ammoniacal solution in violet crystals. Its density is given as 7.143 and 7.250. Ammoniacal silver oxide has been known to explode, the phenomenon being probably due to the formation of "fulminating silver".

The monoxide is decomposed by heat into silver and oxygen, the liberated metal playing the part of an autocatalyst in accelerating the reaction. Finely divided platinum and manganese dioxide also cause acceleration of the transformation. It is decomposed by the action of light, with evolution of oxygen, and possibly formation of silver suboxide.

Silver monoxide dissolves in water, forming an alkaline solution which turns red litmus blue. At 25° C. its solubility corresponds with 2.16 × 10-4 gram-molecule per litre of water, and at 15° C. Rebiere found the same value. It is a strong base, its salts having a neutral reaction. The solution is coloured reddish and decomposed by the action of light, the change being possibly attended by deposition of the suboxide or of colloidal silver.

Its heat of formation is about 6.4 Cal. It decomposes hydrogen peroxide, with liberation of metallic silver. With carbon tetrachloride it reacts at 250° C. in accordance with the equation

Ag2O + CCl4 = 2AgCl + COCl2.

In the moist condition it finds extensive application in organic chemistry to the replacement of halogen by hydroxyl. It can act as a reducer.

Argentic oxide, AgO. - A hot alkaline solution of potassium permanganate partially oxidizes silver monoxide to argentic oxide:

Ag2O + 2KMnO4 + 2NaOH = 2AgO + K2MnO4 + Na2MnO4 + H2O.

The reaction is reversible. This oxide is said to be formed by anodic oxidation of silver in alkaline solution. It is a weaker base than the monoxide, but its solution in concentrated nitric acid contains Ag(NO3)2. Barbieri regards it as belonging to the class of ozonides, and differing from the type of oxide exemplified by hydrogen peroxide, because its solution in concentrated nitric acid does not react with lead peroxide, manganese dioxide, or potassium permanganate.
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