|Jmol-3D images||Image 1|
|Molar mass||171.34 g/mol (anhydrous)
189.39 g/mol (monohydrate)
315.46 g/mol (octahydrate)
|Density||3.743 g/cm3 (monohydrate)
2.18 g/cm3 (octahydrate, 16 °C)
|Melting point||78 °C (172 °F; 351 K) (octahydrate)
300 °C (monohydrate)
407 °C (anhydrous)
|Boiling point||780 °C (1,440 °F; 1,050 K)|
|Solubility in water||octahydrate:
1.67 g/100 mL (0 °C)
3.89 g/100 mL (20 °C)
11.7 g/100 mL (50 °C)
20.94 g/100 mL (60 °C)
101.4 g/100 mL (100 °C)
|Solubility in other solvents||low|
|Refractive index (nD)||1.50 (octahydrate)|
|Std enthalpy of
|EU classification||Harmful (Xn)|
|Other anions||Barium oxide
|Other cations||Calcium hydroxide
|Supplementary data page|
|n, εr, etc.|
Solid, liquid, gas
|Spectral data||UV, IR, NMR, MS|
|Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)|
|(what is: / ?)|
Barium hydroxide is the chemical compound with the formula Ba(OH)2. Also known as baryta, or baryta-water, it is one of the principal compounds of barium. The white granular monohydrate is the usual commercial form.
Barium hydroxide can be prepared by dissolving barium oxide (BaO) in water:
- BaO + 9 H2O → Ba(OH)2·8H2O
It crystallises as the octahydrate, which converts to the monohydrate upon heating in air. At 100 °C in a vacuum, the monohydrate gives BaO.
Barium hydroxide is used in analytical chemistry for the titration of weak acids, particularly organic acids. Its clear aqueous solution is guaranteed to be free of carbonate, unlike those of sodium hydroxide and potassium hydroxide, as barium carbonate is insoluble in water. This allows the use of indicators such as phenolphthalein or thymolphthalein (with alkaline colour changes) without the risk of titration errors due to the presence of carbonate ions, which are much less basic.
It has been used to hydrolyse one of the two equivalent ester groups in dimethyl hendecanedioate.
Barium hydroxide is used, as well, in the decarboxylation of amino acids liberating barium carbonate in the process. 
- It is also used to clean up acid spills.
- It is also used to neutralize sulfuric acid solutions. Use of Ba(OH)2 is particularly beneficial in complete removal sulphate ions because the BaSO4 formed is insoluble in water and precipitates out.
Barium hydroxide decomposes to barium oxide when heated to 800 °C. Reaction with carbon dioxide gives barium carbonate. Its aqueous solution, being highly alkaline, undergoes neutralization reactions with acids. Thus, it forms barium sulfate and barium phosphate with sulfuric and phosphoric acids, respectively. Reaction with hydrogen sulfide produces barium sulfide. Precipitation of many insoluble, or less soluble barium salts, may result from double replacement reaction when a barium hydroxide aqueous solution is mixed with many solutions of other metal salts. 
Reactions of barium hydroxide with ammonium salts are strongly endothermic. The reaction of barium hydroxide octahydrate with ammonium chloride  or ammonium thiocyanate is often used as a classroom chemistry demonstration, producing temperatures cold enough to freeze water and enough water to dissolve the resulting mixture.
Barium hydroxide presents the same hazards as other strong bases and as other water-soluble barium compounds: it is corrosive and toxic.
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