Silver nitrate, AgNO₃

Silver, Silver monoxide, Silver sulphide, and Silver carbonate dissolve in nitric acid. Concentration of the solutions yields colourless, rhombic crystals of Silver nitrate, AgNO₃, of melting-point 208.6° C., and density 4.3554. It is characterized by its caustic action on the skin, its power of blackening it, its antiseptic properties, and its metallic taste.

The solubility of silver nitrate in water has been the subject of more complete investigation than that of any other salt of silver.

Solubility of Silver Nitrate.

Temperature, °C	0	10	20	30	40	50	60	80	100	120
Grams of silver nitrate in 100 g. of water	122	170	222	300	376	455	525	669	952	1900

To render the aqueous solution of silver nitrate stable, Liebert recommends exposing it to the action of light until the organic matter is exhausted. Light has no further action on a solution thus prepared.

The latent heat of fusion of silver nitrate is 17.6 Cal., and its heat of formation from its elements is 28.74 Cal.

Above 160° C. the stable form of silver nitrate belongs to the rhombohedral system. At lower temperatures the crystals are rhombic, the transition-temperature between the two varieties being between 159.2° and 159.7° C.

When heated, silver nitrate begins to decompose at 320° C. in accordance with the equation

2AgNO₃ = 2 AgNO₂ + O₂.

At a higher temperature the decomposition becomes more complex, being attended by evolution of oxygen and nitrogen, and reduction to metallic silver.

Silver nitrate is readily reduced by red-hot charcoal, but only slowly by hydrogen. Ozone converts it into a bluish-black peroxide. A solution of silver nitrate reacts with hydrogen peroxide containing a small proportion of potassium or sodium hydroxide, with formation of a black to greyish precipitate of silver and silver oxide, there being no silver peroxide formed. Brown has observed during the electrolytic oxidation of silver nitrate with non-corrodible electrodes the deposition of a black substance on the anode, and regards it as being probably silver peroxy nitrate, 2Ag₃O₄,AgNO₃. Silver nitrate is transformed by chlorine into the chloride and chlorate. Boiling sulphur gives the sulphide; and selenium the selenide, Ag₂Se, and selenite, Ag₂SeO₃. Phosphorus, hypophosphorous acid, and phosphorous acid reduce it to metallic silver, with formation of phosphoric acid. Phosphine produces an unstable, intermediate, yellow substance, PAg₃,3AgNO₃, which rapidly darkens in colour, with separation of silver.

Arsine reacts with a concentrated solution of silver nitrate, precipitating yellow Ag₃As,3AgNO₃, decomposed by water with liberation of metallic silver. With dilute silver nitrate the reaction occurs in two stages:

AsH₃ + 3AgNO₃ = Ag₃As + 3HNO₃;
Ag₃As + 3AgNO₃ + 3H₂O = H₃AsO₃ + 6Ag + 3HNO₃.

In presence of dilute ammonium hydroxide reduction to metallic silver takes place in three stages, ammonium arsenate and nitrate being simultaneously formed:

AsH₃ + 3(AgNH₃)NO₃ = Ag₃As + 3NH₄NO₃;
Ag₃As + 3(AgNH₃)NO₃ + NH₄OH + H₂O = NH₄AsO₂ + 6Ag + 3NH₄NO₃;
NH₄AsO₂ + 2(AgNH₃)NO₃ + 2NH₄OH = (NH₄)₃AsO₄ + 2Ag + 2NH₄NO₃.

The action of stibine is similar to that of arsine, but only about 2 per cent, of the antimonious acid formed dissolves, the rest remaining in the precipitate:

SbH₃ + 3AgNO₃ = Ag₃Sb + 3HNO₃;
Ag₃Sb + 3AgNO₃ + 3H₂O = H₃SbO₃ + 6Ag + 3HNO₃.

Excess of silver nitrate reacts with iodine in accordance with the equation

6AgNO₃ + 6I + 3H₂O = AgIO₃ + 5AgI + 6HNO₃.

When the iodine is in excess, the reaction is represented by the equation

5AgNO₃ + 6I + 3H₂O = HIO₃ + 5AgI + 5HNO₃.

The second reaction is applicable to iodometry, the titration of alkali-metal hydroxides, and the titration of silver nitrate.

With mercury a solution of silver nitrate yields various amalgams and crystalline double compounds of silver and mercury.

Silver nitrate forms double salts with the halides, cyanide, and thiocyanate of silver. It also yields with Silver sulphide a compound containing equimolecular proportions of the two salts, prepared as a yellowish-green precipitate by the action of hydrogen sulphide on a concentrated solution of silver nitrate. It forms other double salts with the nitrates of lithium and sodium, potassium, ammonium, and thallium. The solution of silver nitrate in ammonium hydroxide yields rhombic prisms, AgNO₃,2NH₃, isomorphous with silver nitrate.