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. On exposure to air it gradually assumes a yellow color because of the oxidation of bromide (Br−) to bromine (Br2).
Structure Ammonium bromide is a salt that crystallizes in a motif akin those for the alkali metal bromides chlorides. Several phases have been characterized, which are similar but not identical to those of ammonium chloride.
Ammonium bromide melts congruently but only under pressure.
When dissolved, the lattice disassembles into separate bromide and ammonium cations. At neutral pH, the N-H bonds rapidly exchange with water. 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 9 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) → (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.Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002,
Ammonium bromide has historically been used in limited flame-retardant formulations in the wood industry. However, due to concerns over toxicity, corrosive combustion products, and environmental impact, its use in fire-retardant wood treatments has been largely discontinued in Europe, with non-essential industrial applications effectively phased out in the early 2000s.
References