Ammonium bromide, NH4Br, is the ammonium salt of hydrobromic acid. The chemical crystallizes in colorless prisms, possessing a saline taste; it sublimes on heating and is easily soluble in water. It is an inorganic compound and it is composed of ammonium ions (NH4+) and bromide ions (Br-). On exposure to air it gradually assumes a yellow color because of the oxidation of traces of bromide (Br−) to bromine (Br2). This compound is a white crystalline solid that is soluble in water.
Ammonium bromide typically appears as a white, odorless crystalline powder or solid. It has a high melting point. It is soluble in water, and the solubility increases with temperature. It played a role in the development of photosensitive materials.
Properties
- Chemical formula: NH4Br
- Molar mass: 97.94 g/mol
- Appearance: white powder, hygroscopic
- Density: 2.429 g/cm3
- Melting point: 235 °C (455 °F; 508 K)
- Boiling point: 452 °C (846 °F; 725 K)
- Solubility in water: 60.6 g/100 mL (0 °C); 145 g/100 mL (100 °C)
Preparation
Ammonium bromide can be prepared by the direct action of hydrogen bromide on ammonia.
NH3 + HBr → NH4Br
It can also be prepared by the reaction of ammonia with iron(II) bromide or iron(III) bromide, which may be obtained by passing aqueous bromine solution over iron filings.
2 NH3 + FeBr2 + 2 H2O → 2 NH4Br + Fe(OH)2
Reactions
Ammonium bromide is a weak acid with a pKa of approximately 5 in water. It is an acid salt because the ammonium ion hydrolyzes slightly in water.
Ammonium bromide is a strong electrolyte when put in water:
NH4Br(s) → NH+4(aq) + Br−(aq)
Ammonium bromide decomposes to ammonia and hydrogen bromide when heated at elevated temperatures:
NH4Br → NH3 + HBr
Uses
Ammonium bromide is used for photography in films, plates and papers; in fireproofing of wood; in lithography and process engraving; in corrosion inhibitors; and in pharmaceutical preparations.
Health and Safety
As with any chemical compound, it is important to handle ammonium bromide with care. Inhalation, ingestion, or skin contact should be avoided, and appropriate safety precautions should be taken.
