Barium chloride

On an industrial scale, barium chloride is prepared via a two step process from barite (barium sulfate).^[8] The first step requires high temperatures.

BaSO₄ + 4 C → BaS + 4 CO

The second step requires reaction between barium sulfide and hydrogen chloride:

BaS + 2 HCl → BaCl₂ + H₂S

or between barium sulfide and calcium chloride:

BaS + CaCl₂ → CaS + BaCl₂^[2]

In place of HCl, chlorine can be used.^[7] Barium chloride is extracted out from the mixture with water. From water solutions of barium chloride, its dihydrate (BaCl₂·2H₂O) can be crystallized as colorless crystals.^[2]

Barium chloride can in principle be prepared by the reaction between barium hydroxideorbarium carbonate with hydrogen chloride. These basic salts react with hydrochloric acid to give hydrated barium chloride.

Ba(OH)₂ + 2 HCl → BaCl₂ + 2 H₂O

BaCO₃ + 2 HCl → BaCl₂ + H₂O + CO₂

BaCl₂ crystallizes in two forms (polymorphs). At room temperature, the compound is stable in the orthorhombic cotunnite (PbCl₂) structure, whereas the cubic fluorite structure (CaF₂) is stable between 925 and 963 °C.^[9] Both polymorphs accommodate the preference of the large Ba²⁺ ion for coordination numbers greater than six.^[10] The coordination of Ba²⁺ is 8 in the fluorite structure^[11] and 9 in the cotunnite structure.^[12] 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.^[13]

In aqueous solution BaCl₂ behaves as a simple salt; in water it is a 1:2 electrolyte^{[clarification needed]} and the solution exhibits a neutral pH. Its solutions react with sulfate ion to produce a thick white solid precipitateofbarium sulfate.

BaCl₂ + Na₂SO₄ → 2 NaCl + BaSO₄

This precipitation reaction is used in chlor-alkali plants to control the sulfate concentration in the feed brine for electrolysis.

Oxalate effects a similar reaction:

BaCl₂ + Na₂C₂O₄ → 2 NaCl + BaC₂O₄

When it is mixed with sodium hydroxide, it gives barium hydroxide, which is moderately soluble in water.

BaCl₂ + 2 NaOH → 2 NaCl + Ba(OH)₂

BaCl₂·2H₂O is stable in the air at room temperature, but loses one water of crystallization above 55 °C (131 °F), becoming BaCl₂·H₂O, and becomes anhydrous above 121 °C (250 °F).^[2] BaCl₂·H₂O may be formed by shaking the dihydrate with methanol.^[3]

BaCl₂ readily forms eutectics with alkali metal chlorides.^[3]

Although inexpensive, barium chloride finds limited applications in the laboratory and industry.

Its main laboratory use is as a reagent for the gravimetric determination of sulfates. The sulfate compound being analyzed is dissolved in water and hydrochloric acid is added. When barium chloride solution is added, the sulfate present precipitates as barium sulfate, which is then filtered through ashless filter paper. The paper is burned off in a muffle furnace, the resulting barium sulfate is weighed, and the purity of the sulfate compound is thus calculated.

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.^[7] It is also used to make red pigments such as Lithol red and Red Lake C. Its toxicity limits its applicability.^{[citation needed]}

Barium chloride, along with other water-soluble barium salts, is highly toxic.^[14] It irritates eyes and skin, causing redness and pain. It damages kidneys. Fatal dose of barium chloride for a human has been reported to be about 0.8-0.9 g. Systemic effects of acute barium chloride toxicity include abdominal pain, diarrhea, nausea, vomiting, cardiac arrhythmia, muscular paralysis, and death. The Ba²⁺ ions compete with the K⁺ ions, causing the muscle fibers to be electrically unexcitable, thus causing weakness and paralysis of the body.^[3] Sodium sulfate and magnesium sulfate are potential antidotes because they form barium sulfate BaSO₄, which is relatively non-toxic because of its insolubility in water.

Barium chloride is not classified as a human carcinogen.^[3]

• International Chemical Safety Card 0614. (anhydrous)
• International Chemical Safety Card 0615. (dihydrate)
• Barium chloride's use in industry.
• ChemSub Online: Barium chloride.