Bromide is the anion of bromine anion that possesses -1 charge. Bromide forms the acid radical (negative portion) of some inorganic salts such as sodium bromide, potassium bromide, calcium bromide, etc.
Abundance of bromide in nature: Bromide is present in nature in seawater with a concentration of 65 mg/L. This is considered to be around 0.2% of all dissolved salts in seawater. High levels of bromide salts are found in seafoods and deep sea plants. Crystalline silver bromide, commonly known as bromargyrite, is one of the most commonly known bromide salts although it is very rare. Another commonly known bromide salt is sodium bromide.
Preparation of Sodium Bromide: Sodium bromide (NaBr) can be prepared through the reaction of sodium hydroxide and hydrogen bromide as the following reaction:
NaOH + HBr → NaBr + H2O
Chemical Properties of Sodium Bromide: Sodium bromide is a white crystalline inorganic salt that dissolves in water producing colorless aqueous solution. It is both chemically and thermally stable. Sodium bromide is used as a bromine source and a brominating agent in organic synthesis.
Uses of Sodium Bromide: Sodium bromide is used as a disinfectant for swimming pools and as hypnotic in sedatives preparation. It is also used in preparation of dense fluids in oil wells. In addition, it has been used in photography, films, dyes and other industries.
Bromide ion is classified as a member of acidic radicals of the second group in which concentrated sulphuric acid is used as the group reagent. Sulphuric acid displaces bromide ions in its salts leading to liberation of reddish brown HBr gas. In addition, potassium permanganate is used as a reagent for detecting the presence of the bromide ion.
Furthermore, bromide could be detected through some confirmatory tests using silver nitrate solution or lead acetate solution since they react together forming silver chloride or lead chloride as a pale yellow or sugary white precipitates, respectively. This returns back to the low solubility product of silver and lead chloride salts so they precipitate very easily at very low concentrations.
Finally, cyclohexane test is carried out as a specific test for detection of bromide ion, where the result gives orange color in the cyclohexane layer.