Barium Hydroxide
Properties
| State | Solid at room temperature |
| Color | White powder or crystals |
| Solubility | Moderately soluble in water (5.6 g/100 mL at 25°C), much more at higher temperatures |
| Melting Point | 408°C |
| Boiling Point | 780°C |
About Barium Hydroxide
Barium hydroxide is the strongest of the alkaline-earth hydroxides commonly available in solid form, dissociating fully in dilute aqueous solution to give two hydroxide ions per formula unit. The eight-water hydrate Ba(OH)2·8H2O is what ships in most reagent bottles, and that hydrate is responsible for one of the most striking demonstrations in chemistry: mixing solid Ba(OH)2·8H2O with solid ammonium thiocyanate produces a vigorously endothermic reaction that draws heat so fast the beaker bottom can frost over and freeze to a wet wooden block. The ΔH for the reaction is around +170 kJ/mol, more than enough to drop the contents to -20 °C, and the spontaneity comes entirely from the entropy gain — eight bound water molecules and two solid reactants combine into a viscous slurry containing roughly twenty mobile ions and molecules per formula unit. The reaction is the textbook demonstration of why Gibbs free energy depends on both ΔH and ΔS, since enthalpically it should not run at all. Outside the demonstration, baryta water (saturated aqueous Ba(OH)2) is the classical CO2 detector — exhale through it and the dissolved CO2 immediately precipitates BaCO3 as a white turbidity. In organic chemistry, barium hydroxide is occasionally used as a strong, soluble base for hydrolyzing esters, nitriles, and amides under conditions where NaOH would over-hydrolyze, since the Ba²⁺ counterion sometimes coordinates to the substrate in useful ways.
Where you'll encounter it
If you've seen the 'wood-block freeze' demonstration in a general chemistry lecture — beaker plus baking sheet plus a few drops of water that locks the beaker to the wood as the contents drop below freezing — that demonstration uses Ba(OH)2·8H2O plus NH4SCN, and it remains one of the cleanest illustrations of an entropy-driven endothermic reaction available. In a research lab, baryta water is used by paper conservators and archivists to deacidify acid-paper documents from the 19th and early 20th centuries; the soluble OH⁻ neutralizes the gradual acid hydrolysis that's slowly destroying the cellulose, and the residual barium leaves behind a buffer of BaCO3 in the paper that resists future re-acidification. The technique has saved a substantial fraction of newspaper archives and library collections from chemical decay.
Common Uses
- Endothermic reaction demonstrations with NH4SCN or NH4Cl
- Baryta-water test for CO2 detection
- Strong-base ester and amide hydrolysis where Na+ is undesirable
- Paper deacidification in archival and conservation work
- Precursor for other barium chemistry and pigment manufacture
Safety Information
All soluble barium compounds are toxic at sub-gram doses through potassium-channel blockade in muscle. The strong alkalinity adds skin and eye corrosion to the toxicity profile — concentrated solutions saponify fats and cause severe burns. Handle with nitrile gloves and splash goggles; treat exposure as both alkali burn and barium ingestion. GHS H302, H314, H332.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.