Серебро бромид

Химические свойства

Silver bromide, AgBr, is pale yellow crystals or powder, that darken on exposure to light, finally turning black and soluble in potassium bromide, potassium cyanide, and sodium thiosulfate solutions, only very slightly soluble in ammonia water, insoluble in water, and light sensitive. Derivation is through silver nitrate dissolving in water and a solution ofalkali bromide added slowly. The precipitated silver bromide is washed repeatedly with hotwater. The operation must be carried on in a darkroom under a ruby-red light. Used in photographic film and plates, photochromic glass and as a laboratory reagent.

Физические свойства

Yellow cubic crystals or powder; refractive index 2.253; darkens on exposure to light; Mohs hardness 2.5; density 6.47g/cm³; melts at 432°C; vaporizes at 1,502°C; insoluble in water, alcohol, and most acids; slightly soluble in dilute ammonia and ammonium carbonate solutions; sparingly soluble in concentrated ammonia solution (0.33 g/100mL 10% ammonia solution at 12°C);soluble in alkali cyanide solutions.

Использование

A yellowish powder made by the combination of any soluble bromide with silver nitrate. Silver bromide could also be formed by exposing metallic silver to the fumes of bromine as in the daguerreotype process. It is soluble in sodium thiosulfate, potassium bromide, and potassium cyanide solutions. Silver bromides were secondary halides for the paper negative processes, albumen negative process, and wet or preserved collodion processes. Silver bromides were the primary halides for the silver bromide collodion emulsion negative and the silver bromide gelatin emulsion processes. Silver bromide is the most photosensitive silver halide.

Подготовка

Silver bromide is prepared by double decomposition reaction. An aqueous solution of alkali bromide, such as sodium or potassium bromide, is slowly added to an aqueous solution of silver nitrate:
Ag+ (aq) + Brˉ (aq) → AgBr(s)
The precipitate is washed repeatedly with hot water. Preparation should be in a dark room under a ruby red light.

Методы очистки

It is insoluble in dilute HNO3 or dilute NH3 but is soluble in conc NH3. Store it in the dark.