silver+bromide


 * Silver bromide** (AgBr), a soft, pale-yellow, water insoluble salt well known (along with other silver halides) for its unusual [|sensitivity to light] . This property has allowed silver halides to become the basis of modern photographic materials. AgBr is widely used in photographic films and is believed by some to have been used for making the [|Shroud of Turin] . The salt can be found naturally as the mineral [|bromargyrite] (bromyrite). It has a wide range of solubilities.



Preparation
Although the compound can be found in mineral form, AgBr is typically prepared by the reaction of silver nitrate with an alkali bromide, typically potassium bromide AgNO3(aq) + KBr(aq) → AgBr(s)+ KNO3(aq) Although less convenient, the salt can also be prepared directly from its elements. Modern preparation of a simple, light-sensitive surface involves forming an emulsion of silver halide crystals in a gelatine, which is then coated on a film or other support. The crystals are formed by precipitation in a controlled environment to produce small, uniform crystals (typically < 1 μm in diameter and containing ~1012 Ag atoms) called grains.

Reactions
Silver bromide reacts readily with liquid ammonia to generate a variety of amine complexes: AgBr + nNH3 → Ag(NH3)21+ {AgBr(NH3)2} {AgBr2(NH3)2}1- {AgBr(NH3)} {AgBr2(NH3)}1-