Barium hydroxide

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Barium hydroxide
Barium hydroxide octahydrate.jpg
Barium hydroxide octahydrate
Names
IUPAC name
Barium hydroxide
Other names
Barium dihydroxide
Baryta
Baryta-water
Properties
Ba(OH)2 (anhydrous)
Ba(OH)2·H2O (monohydrate)
Ba(OH)2·8H2O (octahydrate)
Molar mass 171.34 g/mol (anhydrous)
189.355 g/mol (monohydrate)
315.46 g/mol (octahydrate)
Appearance White solid
Odor Odorless
Density 4.5 g/cm3 (20 °C) (anhydrous)
3.743 g/cm3 (monohydrate)
2.18 g/cm3 (25 °C) (octahydrate)
Melting point octahydrate
78 °C (172 °F; 351 K)
monohydrate
300 °C (572 °F; 573 K)
anhydrous
407 °C (765 °F; 680 K)
Boiling point 780–800 °C (1,440–1,470 °F; 1,050–1,070 K) Decomposes
1.67 g/100 ml (0 °C)
2.48 g/100 ml (10 °C)
3.89 g/100 ml (20 °C)
5.59 g/100 ml (30 °C)
8.22 g/100 ml (40 °C)
13.1 g/100 ml (50 °C)
20.9 g/100 ml (60 °C)
101.4 g/100 ml (80 °C)[1]
Solubility Reacts with acids
Insoluble in hydrocarbons
Vapor pressure ~0 mmHg
Thermochemistry
124 J·mol-1·K-1
−944.7 kJ/mol
Hazards
Safety data sheet Sigma-Aldrich (octahydrate)
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
308 mg/kg (rat, oral)
255 mg/kg (rat, IP)
Related compounds
Related compounds
Magnesium hydroxide
Calcium hydroxide
Strontium hydroxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Barium hydroxide is a chemical compound with the chemical formula Ba(OH)2. The monohydrate (x = 1), known as baryta or baryta-water, is one of the principal compounds of barium.

Properties

Chemical

Barium hydroxide decomposes to barium oxide when heated to 800 °C.

Ba(OH)2 → BaO + H2O

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 is occasionally used in organic synthesis as a strong base, for example for the hydrolysis of esters and nitriles, and as a base in aldol condensations. It can be used to perform decarboxylation of amino acids.

Barium hydroxide is often used in ketonic decarboxylations for the preparation of various organic compound, like cyclopentanone from adipic acid[2] or in aldol reactions like in the preparation of diacetone alcohol from acetone.[3]

Physical

Barium hydroxide is a colorless solid, slightly soluble in cold water, but more soluble in hot water.

As barium carbonate is insoluble in water, clear solutions of barium hydroxide are free of any carbonates (but they go turbid quickly as they absorb carbon dioxide from the air). This property allows the use of barium hydroxide to be used in titration of acids using indicators such as phenolphthalein or thymolphthalein (with alkaline color changes) without the risk of titration errors due to the presence of carbonate ions, which are much less basic.

Availability

Barium hydroxide is sold by chemical suppliers.

Preparation

Barium hydroxide can be prepared by dissolving barium oxide (BaO) in water:

BaO + H2O → Ba(OH)2

The reaction is exothermic, and the heat produced may even melt the octahydrate.

It crystallizes as the octahydrate from water, which converts to the monohydrate upon heating in air above 78 °C.

If heated above 100 °C in a vacuum, the monohydrate will yield BaO and water.[4][5]

A simple route involves the double displacement of barium chloride with sodium hydroxide. Both solutions should be warmed before being mixed and hot filtered to remove small amounts of barium carbonate.

BaCl2 + 2 NaOH + 8 H2O → 2 NaCl + Ba(OH)2·8H2O ↓

Another possible preparation route, taking advantage of its moderate water solubility, involves the double displacement reaction of barium acetate and potassium hydroxide, reaction which takes place at high temperatures (60-80 °C). As the solution cools, the less soluble barium hydroxide precipitates out of the solution, while the much more soluble potassium acetate stays in solution.

Ba(CH3COO)2 + 2 KOH + 8 H2O → 2 CH3COOK + Ba(OH)2·8H2O ↓

Projects

  • Make barium salts
  • Titration of acids
  • Chemical demonstrations of endothermic reactions
  • Ketonic decarboxylations

Handling

Safety

Barium hydroxide is toxic if ingested, as it reacts with stomach acid to form the more soluble barium chloride. In case of ingestion, a non-toxic soluble sulfate solution (like sodium or magnesium sulfate) can be used as antidote.

Storage

Should be kept in air-tight plastic bottles.

Disposal

Can be mixed with a sulfate, to yield the insoluble barium sulfate, which is non-toxic.

References

  1. Rabinovich V.A., Khavin Z.Ya. Brief chemical reference book. - L.: Chemistry, 1977 (Рабинович В.А., Хавин З.Я. Краткий химический справочник. - Л.: Химия, 1977). Data retrieved from http://chemister.ru/Database/properties-en.php?dbid=1&id=375
  2. M. Renz, Eur. J. Org. Chem. 2005, 6, 979-988. doi:10.1002/ejoc.200400546
  3. J. B. Conant, N. Tuttle. Org. Synth. 1921, 1, 45, doi:10.15227/orgsyn.001.0045
  4. R. P. Seward, J. Am. Chem. Soc. 1945, 67, 7, 1189–1191, doi:10.1021/ja01223a049
  5. Gmelins Handbuch der anorganischen Chemie, Barium, Ergänzungsband, 8th edition 1960, Weinheim, Verlag Chemie, p. 289.

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