Ammonium bromide
Encyclopedia
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 traces of bromide
(Br-) to bromine
(Br2).
on ammonia
.
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.
because the ammonium
ion hydrolyzes
slightly in water.
Ammonium bromide decomposes to ammonia and hydrogen bromide
when heated at elevated temperatures:
s, plates and paper
s; in fireproofing of wood; in lithography
and process engraving; in corrosion inhibitors; and in pharmaceutical preparations.
Hydrobromic acid
Hydrobromic acid is a strong acid formed by dissolving the diatomic molecule hydrogen bromide in water. "Constant boiling" hydrobromic acid is an aqueous solution that distills at 124.3 °C and contains 47.6% HBr by weight, which is 8.89 mol/L. Hydrobromic acid has a pKa of −9, making it a...
. The chemical crystallizes in colorless prisms, possessing a saline
Salt
In chemistry, salts are ionic compounds that result from the neutralization reaction of an acid and a base. They are composed of cations and anions so that the product is electrically neutral...
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 traces of bromide
Bromide
A bromide is a chemical compound containing bromide ion, that is bromine atom with effective charge of −1. The class name can include ionic compounds such as caesium bromide or covalent compounds such as sulfur dibromide.-Natural occurrence:...
(Br-) to bromine
Bromine
Bromine ") is a chemical element with the symbol Br, an atomic number of 35, and an atomic mass of 79.904. It is in the halogen element group. The element was isolated independently by two chemists, Carl Jacob Löwig and Antoine Jerome Balard, in 1825–1826...
(Br2).
Preparation
Ammonium bromide can be prepared by the direct action of hydrogen bromideHydrogen bromide
Hydrogen bromide is the diatomic molecule HBr. HBr is a gas at standard conditions. Hydrobromic acid forms upon dissolving HBr in water. Conversely, HBr can be liberated from hydrobromic acid solutions with the addition of a dehydration agent, but not by distillation. Hydrogen bromide and...
on ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
.
- NH3 + HBr → NH4Br
It can also be prepared by the reaction of ammonia with iron(II) bromide
Iron(II) bromide
Iron bromide is the chemical compound FeBr2. This brownish-colored solid is a useful synthetic intermediate; for example it is employed to insert Fe into porphyrins.-Structure:...
or iron(III) bromide
Iron(III) bromide
Iron bromide is the chemical compound with the formula FeBr3. Also known as ferric bromide, this red-brown compound is used as a Lewis acid catalyst in the halogenation of aromatic compounds. It reacts with water to give acidic solutions....
, 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 ~5 in water. It is an acid saltAcid salt
Acid salt is a somewhat obscure term for a class of salts formed by the partial neutralization of diprotic or polyprotic acids. Because the parent acid is only partially neutralized, one or more replaceable hydrogen atoms remain. Typical acid salts have one or more alkali metal ions as well as one...
because the ammonium
Ammonium
The ammonium cation is a positively charged polyatomic cation with the chemical formula NH. It is formed by the protonation of ammonia...
ion hydrolyzes
Hydrolysis
Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...
slightly in water.
Ammonium bromide decomposes to ammonia and hydrogen bromide
Hydrogen bromide
Hydrogen bromide is the diatomic molecule HBr. HBr is a gas at standard conditions. Hydrobromic acid forms upon dissolving HBr in water. Conversely, HBr can be liberated from hydrobromic acid solutions with the addition of a dehydration agent, but not by distillation. Hydrogen bromide and...
when heated at elevated temperatures:
- NH4Br → NH3 + HBr
Uses
Ammonium bromide is used for photography in filmFilm
A film, also called a movie or motion picture, is a series of still or moving images. It is produced by recording photographic images with cameras, or by creating images using animation techniques or visual effects...
s, plates and paper
Paper
Paper is a thin material mainly used for writing upon, printing upon, drawing or for packaging. It is produced by pressing together moist fibers, typically cellulose pulp derived from wood, rags or grasses, and drying them into flexible sheets....
s; in fireproofing of wood; in lithography
Lithography
Lithography is a method for printing using a stone or a metal plate with a completely smooth surface...
and process engraving; in corrosion inhibitors; and in pharmaceutical preparations.