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).
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| Names | |
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| IUPAC name
Ammonium bromide | |
| Identifiers | |
3D model (JSmol) |
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| ChemSpider | |
| ECHA InfoCard | 100.031.973 |
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| Properties | |
| 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) |
| 60.6 g/100 mL (0 °C) 78.3 g/100 mL (25 °C) 145 g/100 mL (100 °C) | |
| −47.0×10−6 cm3/mol | |
Refractive index (nD) |
1.712 |
| Structure | |
| Isometric | |
| Hazards | |
| GHS labelling: | |
 [1] | |
| Warning | |
| H315, H319, H335[1] | |
| P261, P264, P271, P280, P302+P352, P304+P340, P305+P351+P338, P312, P321, P332+P313, P337+P313, P362, P403+P233, P405, P501 | |
| NFPA 704 (fire diamond) | |
| Related compounds | |
Other anions |
Ammonium fluoride Ammonium chloride Ammonium iodide |
Other cations |
Sodium bromide Potassium bromide |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Structure
editAmmonium 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.[2]
Ammonium bromide melts congruently but only under pressure.[2]
When dissolved, the lattice disassembles into separate bromide and ammonium cations. At neutral pH, the N-H bonds rapidly exchange with water.
Preparation
editAmmonium 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
editAmmonium 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) → NH+4(aq) + Br−(aq)
Ammonium bromide decomposes to ammonia and hydrogen bromide when heated at elevated temperatures:
- NH4Br → NH3 + HBr
Uses
editAmmonium 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.[3]
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
edit- 1 2 Sigma-Aldrich Co., Ammonium bromide.
- 1 2 Pistorius, Carl W.F.T. (1976). "Phase relations and structures of solids at high pressures". Progress in Solid State Chemistry. 11: 1–151. doi:10.1016/0079-6786(76)90012-1.
- ↑ Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN 0-07-049439-8