lBarium chloride is the inorganic compound with the formula BaCl2. It is one of the most common water-soluble salts of barium. Like most other barium salts, it is white, toxic, and imparts a yellow-green coloration to a flame. It is also hygroscopic, converting first to the dihydrate BaCl2(H2O)2. It has limited use in the laboratory and industry.
Structure and properties
BaCl2 crystallizes in two forms (polymorphs). One form has the cubic fluorite (CaF2) structure and the other the orthorhombic cotunnite (PbCl2) structure. Both polymorphs accommodate the preference of the large Ba2+ ion for coordination numbers greater than six. The coordination of Ba2+ is 8 in the fluorite structure and 9 in the cotunnite structure. When cotunnite-structure BaCl2 is subjected to pressures of 7–10 GPa, it transforms to a third structure, a monoclinic post-cotunnite phase. The coordination number of Ba2+ increases from 9 to 10.
In aqueous solution BaCl2 behaves as a simple salt; in water it is a 1:2 electrolyte and the solution exhibits a neutral pH. Its solutions react with sulfate ion to produce a thick white precipitate of barium sulfate.
Ba2+ + SO42− → BaSO4
Oxalate effects a similar reaction:
Ba2+ + C2O42− → BaC2O4
When it is mixed with sodium hydroxide, it gives the dihydroxide, which is moderately soluble in water.
On an industrial scale, it is prepared via a two step process from barite (barium sulfate):
BaSO4 + 4 C → BaS + 4 CO
This first step requires high temperatures.
BaS + 2 HCl → BaCl2 + H2S
In place of HCl, chlorine can be used.
Barium chloride can in principle be prepared from barium hydroxide or barium carbonate. These basic salts react with hydrochloric acid to give hydrated barium chloride.
Although inexpensive, barium chloride finds limited applications in the laboratory and industry. In industry, barium chloride is mainly used in the purification of brine solution in caustic chlorine plants and also in the manufacture of heat treatment salts, case hardening of steel. Its toxicity limits its applicability.