Barium hydroxide

Barium hydroxide
Identifiers
CAS number	17194-00-2 Y, 22326-55-2 (monohydrate) 12230-71-6 (octahydrate)
RTECS number	CQ9200000
Properties
Molecular formula	Ba(OH)2
Molar mass	171.34 g/mol (anhydrous) 189.39 g/mol (monohydrate) 315.46 g/mol (octahydrate)
Appearance	white solid
Density	3.743 g/cm3 (monohydrate) 2.18 g/cm3 (octahydrate, 16 °C)
Melting point	78 °C (octahydrate) 407 °C (anhydrous)
Boiling point	780 °C
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)
Solubility in other solvents	low
Basicity (pKb)	-2.02
Refractive index (nD)	1.50 (octahydrate)
Structure
Crystal structure	octahedral
Thermochemistry
Std enthalpy of formation ΔfHo298	−944.7 kJ/mol
Hazards
MSDS	External MSDS
EU Index	056-002-00-7
EU classification	Harmful (Xn)
R-phrases	R20/22
S-phrases	(S2), S28
NFPA 704	0 3 0
Flash point	non-flammable
Related compounds
Other anions	Barium oxide Barium peroxide
Other cations	Calcium hydroxide Strontium hydroxide
Supplementary data page
Structure and properties	n, εr, etc.
Thermodynamic data	Phase behaviour Solid, liquid, gas
Spectral data	UV, IR, NMR, MS
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Barium hydroxide is the chemical compound with the formula Ba(OH)₂. Also known as baryta, it is one of the principal compounds of barium. The white granular monohydrate is the usual commercial form.

Preparation

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

BaO + 9H₂O → 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.^[1]

Uses

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 weakly basic carbonate ions.^[2]

Barium hydroxide is used in organic synthesis as a strong base, for example for the hydrolysis of esters^[3] and nitriles.^[4][5][6]

It has been used to hydrolyse one of the two equivalent ester groups in dimethyl hendecanedioate.^[7]

It is also used in the preparation of cyclopentanone,^[8] diacetone alcohol^[9] and D-Gulonic γ-lactone.^[10]

Barium hydroxide is used in a demonstration of endothermic reactions since, when mixed with an ammonium salt, the reaction becomes cold as heat is absorbed from the surroundings.

Miscellaneous applications

• Under the name baryta it is used in homeopathic remedies.
• It is also used to clean up acid spills.

Reactions

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 decomposition reaction when a barium hydroxide aqueous solution is mixed with many solutions of other metal salts. ^[11]

Safety

Barium hydroxide presents the same hazards as other strong bases and as other water-soluble barium compounds: it is corrosive and toxic.

References

1. ^ (1960). Gmelins Handbuch der anorganischen Chemie (8. Aufl.), Weinheim: Verlag Chemie, p. 289.
2. ^ Mendham, J.; Denney, R. C.; Barnes, J. D.; Thomas, M.J.K.; Denney, R. C.; Thomas, M. J. K. (2000), Vogel's Quantitative Chemical Analysis (6th ed.), New York: Prentice Hall, ISBN 0-582-22628-7 
3. ^ Meyer, K.; Bloch, H. S. (1945). "Naphthoresorcinol". Org. Synth. 25: 73; Coll. Vol. 3: 637.
4. ^ Brown, G. B. (1946). "Methylsuccinic acid". Org. Synth. 26: 54; Coll. Vol. 3: 615.
5. ^ Ford, Jared H. (1947). "β-Alanine". Org. Synth. 27: 1; Coll. Vol. 3: 34.
6. ^ Anslow, W. K.; King, H.; Orten, J. M.; Hill, R. M. (1925). "Glycine". Org. Synth. 4: 31; Coll. Vol. 1: 298.
7. ^ Durham, L. J.; McLeod, D. J.; Cason, J. (1958). "Methyl hydrogen hendecanedioate". Org. Synth. 38:55; Coll. Vol. 4:635.
8. ^ Thorpe, J. F.; Kon, G. A. R. (1925). "Cyclopentanone". Org. Synth. 5: 37; Coll. Vol. 1: 192.
9. ^ Conant, J. B.; Tuttle, Niel. (1921). "Diacetone alcohol". Org. Synth. 1: 45; Coll. Vol. 1: 199.
10. ^ Karabinos, J. V. (1956). "D-Gulonic γ-lactone". Org. Synth. 36: 38; Coll. Vol. 4: 506.
11. ^ Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN 0070494398

External links

• Material Safety Data Sheet (MSDS)