Barium bromide is an inorganic ionic salt with the chemical formula BaBr2. It is formed from one barium ion and two bromide ions, representing a stable combination of an alkaline earth metal and a halogen. This commercially manufactured substance is used in various chemical processes, serving as a source for both barium and bromide. The compound is often handled in its anhydrous form or as the dihydrate, BaBr2·2H2O.
Fundamental Characteristics
Barium bromide appears as a white, crystalline solid or powder, typical of many pure ionic salts. This solid has an orthorhombic crystal structure similar to that of lead chloride. The anhydrous form has a high density of approximately 4.78 g/cm³ and a melting point of around 857 °C.
The compound’s high melting point results from its ionic nature, where strong electrostatic forces hold the barium (Ba²⁺) and bromide (Br⁻) ions together in a rigid lattice. It exhibits high solubility in water, dissolving at a rate of about 92.2 g per 100 mL at 0 °C, making it useful for aqueous reactions. Barium bromide is also hygroscopic, meaning it readily absorbs moisture from the air to form its dihydrate. The molecular weight of the anhydrous compound is approximately 297.14 g/mol.
Industrial Preparation Methods
Commercial production of barium bromide typically begins with a barium-containing starting material, such as barium carbonate (BaCO3) or barium sulfide (BaS). These compounds are reacted with hydrobromic acid (HBr) in a neutralization reaction to yield the product. When using barium carbonate, the reaction produces barium bromide along with carbon dioxide and water as byproducts.
Alternatively, reacting barium sulfide with hydrobromic acid generates barium bromide and hydrogen sulfide gas. The resulting barium bromide is present in a water solution, usually as a hydrated salt. The pure anhydrous BaBr2 is obtained by heating the dihydrate form (BaBr2·2H2O) to about 120 °C to remove the water molecules.
Key Applications
Barium bromide serves primarily as a precursor in the synthesis of other barium compounds and various bromides. For example, its aqueous solution readily reacts with sulfate ions to form an insoluble precipitate of barium sulfate (BaSO4). This reaction is a fundamental tool in analytical chemistry for testing the presence of sulfate.
The compound is used in the production of specialized glasses, where its inclusion enhances the material’s optical properties. Historically, one of its most famous uses was in the purification of radium, a process developed by Marie Curie. This technique, known as fractional crystallization, relied on the fact that radium bromide and barium bromide crystallize together, allowing for their eventual separation.
In the photographic industry, barium bromide is applied as a chemical precursor for manufacturing light-sensitive materials. Its ability to react to light makes it a component in certain film formulations and photographic papers. It also sees use today as a laboratory reagent for specific chemical reactions.
Safety and Handling Guidelines
As a soluble barium salt, barium bromide poses a significant health hazard and is toxic if ingested or inhaled. Soluble barium ions interfere with muscle and nerve function, potentially causing symptoms like muscle weakness and cardiac irregularities. Exposure to the compound, particularly dust or aerosols, must be avoided by working in a well-ventilated area, preferably under local exhaust ventilation.
Personal protective equipment is necessary when handling this substance, including safety glasses, protective gloves, and long-sleeved clothing to prevent skin and eye contact. Because the material is hygroscopic, containers must be kept tightly closed and stored in a cool, dry place to prevent moisture absorption. Disposal must be done at an approved hazardous waste collection point, following all local regulations.