Barium hydroxide

Crystal structure
Crystal structure of monoclinic β-barium hydroxide __ Ba 2+      __ OH -
General
Surname	Barium hydroxide
other names	Etching baryta Barite water (aqueous solution)
Ratio formula	Ba (OH) 2
Brief description	colorless odorless solid
External identifiers / databases
CAS number 17194-00-2 (anhydrous) 22326-55-2 (monohydrate) 12230-71-6 (octahydrate) EC number 241-234-5 ECHA InfoCard 100.037.470 PubChem 6093286 ChemSpider 26408 Wikidata Q407605
properties
Molar mass	171.34 g · mol -1
Physical state	firmly
density	4.50 g cm −3 (anhydrous) 2.18 g cm −3 (octahydrate)
Melting point	408 ° C (anhydrous) 78 ° C (octahydrate)
boiling point	Decomposes at> 600 ° C to barium oxide and water
solubility	little in water (72 g l −1 , octahydrate)
safety instructions
GHS labeling of hazardous substances danger H and P phrases H: 302-314 P: 260-280-301 + 312 + 330-303 + 361 + 353-304 + 340 + 310-305 + 351 + 338 + 310
MAK	0.5 mg m −3
Thermodynamic properties
ΔH f 0	−944.7 kJ / mol
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Barium hydroxide Ba (OH) ₂ is the hydroxide of the alkaline earth metal barium . It is a strong base in aqueous solution .

Extraction and presentation

Starting from barite ( barium sulfate ) BaSO ₄ Barium hydroxide is from barium oxide or barium sulfide obtained: barium oxide, barium hydroxide reacts with water to:

${\displaystyle \mathrm {BaO+H_{2}O\longrightarrow Ba(OH)_{2}} }$,

${\displaystyle \mathrm {Ba(OH)_{2}+8\ H_{2}O\longrightarrow Ba(OH)_{2}\cdot 8\ H_{2}O} }$.

Barium sulfide reacts with water to form barium hydroxide and hydrogen sulfide :

${\displaystyle \mathrm {BaS+2\ H_{2}O\longrightarrow Ba(OH)_{2}+H_{2}S} }$.

properties

Physical Properties

Barium hydroxide is a solid substance made up of colorless crystals. It's polymorphic . The α-phase is a high temperature form; it can be obtained metastable at room temperature by quenching. It crystallizes orthorhombically , space group Pnma (space group no. 62) , with the lattice parameters a = 11.01 Å , b = 16.50 Å and c = 7.095 Å. The β-form stable at room temperature is monoclinic , space group P 2 ₁ / n (No. 14, position 2) , with the lattice parameters a = 9.409 Å, b = 7.916 Å, c = 6.775 Å and β = 95.81 °. Barium hydroxide forms three hydrates , a monohydrate, a trihydrate and an octahydrate. The solubility in water is strongly dependent on the temperature; 56 g / l water dissolve at 20 ° C and 947 g / l water at 80 ° C. The aqueous solution, also called barite water , has a strong alkaline reaction , as barium hydroxide almost completely dissociates into ions . A saturated solution has a pH of 14.

Chemical properties

In aqueous solution with carbon dioxide or other carbonate-containing salts, barium hydroxide forms a poorly soluble precipitate of barium carbonate :

${\displaystyle \mathrm {Ba(OH)_{2}+CO_{2}\longrightarrow BaCO_{3}\downarrow +H_{2}O} }$

It can thus be used for the qualitative detection of carbonate ions.

use

• Glass and ceramic manufacture. Partly as a substitute for barium carbonate
• Water softening
• Used in conjunction with ammonium thiocyanate to make ice cream in the 18th century , due to the strongly endothermic reaction . (The reaction is exergonic .)
• For the detection of carbon dioxide and carbonates
• The octahydrate can be used as a heat store

Individual evidence

1. ↑ ^{a b c d e f g h i j} Entry on barium hydroxide in the GESTIS substance database of the IFA , accessed on July 23, 2016(JavaScript required) .
2. ↑ David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Standard Thermodynamic Properties of Chemical Substances, pp. 5-6.
3. ^ A. Friedrich, M. Kunz, R. Miletich: High-pressure behavior of Ba (OH) ₂ : Phase transitions and bulk modulus. In: Physical Review , 66, 2002, pp. 214103-1-214103-8, doi: 10.1103 / PhysRevB.66.214103 .
4. ↑ Wissenschaft aktuell: Heating with liquid salts