Barium hydroxide is a
chemical compound
A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...
with the
chemical formula
In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, ...
Ba(OH)
2. The monohydrate (''x'' = 1), known as baryta or baryta-water, is one of the principal compounds of
barium
Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in group 2 and is a soft, silvery alkaline earth metal. Because of its high chemical reactivity, barium is never found in nature as a free element.
Th ...
. This white granular
monohydrate is the usual commercial form.
Preparation and structure
Barium hydroxide can be prepared by dissolving
barium oxide
Barium oxide, also known as baria, is a white hygroscopic non-flammable compound with the formula BaO. It has a cubic structure and is used in cathode ray tubes, crown glass, and catalysts. It is harmful to human skin and if swallowed in larg ...
(BaO) in
water
Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as ...
:
:BaO + H
2O → Ba(OH)
2
It crystallises as the octahydrate, which converts to the monohydrate upon heating in air. At 100 °C in a vacuum, the monohydrate will yield BaO and water. The monohydrate adopts a layered structure (see picture above). The Ba
2+ centers adopt a
square anti-prismatic geometry. Each Ba
2+ center is bound by two water
ligand
In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's elect ...
s and six hydroxide ligands, which are respectively doubly and triply bridging to neighboring Ba
2+ centre sites. In the octahydrate, the individual Ba
2+ centers are again eight coordinate but do not share ligands.
Uses
Industrially, barium hydroxide is used as the precursor to other barium compounds. The monohydrate is used to dehydrate and remove sulfate from various products.
[Robert Kresse, Ulrich Baudis, Paul Jäger, H. Hermann Riechers, Heinz Wagner, Jochen Winkler, Hans Uwe Wolf, "Barium and Barium Compounds" in Ullmann's Encyclopedia of Industrial Chemistry, 2007 Wiley-VCH, Weinheim. ] This application exploits the very low solubility of
barium sulfate
Barium sulfate (or sulphate) is the inorganic compound with the chemical formula Ba SO4. It is a white crystalline solid that is odorless and insoluble in water. It occurs as the mineral barite, which is the main commercial source of barium and ...
. This industrial application is also applied to laboratory uses.
Laboratory uses
Barium hydroxide is used in
analytical chemistry
Analytical chemistry studies and uses instruments and methods to separate, identify, and quantify matter. In practice, separation, identification or quantification may constitute the entire analysis or be combined with another method. Separati ...
for the
titration
Titration (also known as titrimetry and volumetric analysis) is a common laboratory method of quantitative chemical analysis to determine the concentration of an identified analyte (a substance to be analyzed). A reagent, termed the ''titrant'' ...
of
weak acid
Acid strength is the tendency of an acid, symbolised by the chemical formula HA, to dissociate into a proton, H+, and an anion, A-. The dissociation of a strong acid in solution is effectively complete, except in its most concentrated solutions ...
s, particularly
organic acid
An organic acid is an organic compound with acidic properties. The most common organic acids are the carboxylic acids, whose acidity is associated with their carboxyl group –COOH. Sulfonic acids, containing the group –SO2OH, are ...
s. Its clear aqueous solution is guaranteed to be free of carbonate, unlike those of
sodium hydroxide
Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations and hydroxide anions .
Sodium hydroxide is a highly caustic base and al ...
and
potassium hydroxide
Potassium hydroxide is an inorganic compound with the formula K OH, and is commonly called caustic potash.
Along with sodium hydroxide (NaOH), KOH is a prototypical strong base. It has many industrial and niche applications, most of which exp ...
, 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
A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate ...
ions, which are much less basic.
Barium hydroxide is occasionally used in
organic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. Organic molecules are often more complex than inorganic compounds, and their synthesis has developed into one o ...
as a strong base, for example for the hydrolysis of esters and nitriles, and as a base in
aldol condensations.
:
:
There are several uses for barium hydroxide such as to hydrolyse one of the two equivalent ester groups in dimethyl hendecanedioate.
Barium hydroxide has also been used, as well, in the decarboxylation of amino acids liberating barium carbonate in the process.
It is also used in the preparation of
cyclopentanone
Cyclopentanone is the organic compound with the formula (CH2)4CO. This cyclic ketone is a colorless volatile liquid.
Preparation
Upon treatment with barium hydroxide at elevated temperatures, adipic acid undergoes ketonization to give cyclope ...
,
diacetone alcohol and
D-gulonic γ-lactone.
:
:
Reactions
Barium hydroxide decomposes to
barium oxide
Barium oxide, also known as baria, is a white hygroscopic non-flammable compound with the formula BaO. It has a cubic structure and is used in cathode ray tubes, crown glass, and catalysts. It is harmful to human skin and if swallowed in larg ...
when heated to 800 °C. Reaction with
carbon dioxide
Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...
gives
barium carbonate. Its aqueous solution, being highly alkaline, undergoes neutralization reactions with acids due to it being a strong base. It is especially useful on reactions that require the titrations of weak organic acids. Thus, it forms
barium sulfate
Barium sulfate (or sulphate) is the inorganic compound with the chemical formula Ba SO4. It is a white crystalline solid that is odorless and insoluble in water. It occurs as the mineral barite, which is the main commercial source of barium and ...
and
barium phosphate with sulfuric and phosphoric acids, respectively. Reaction with
hydrogen sulfide
Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic foul odor of rotten eggs. The under ...
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
The ammonium cation is a positively-charged polyatomic ion with the chemical formula or . It is formed by the protonation of ammonia (). Ammonium is also a general name for positively charged or protonated substituted amines and quaterna ...
salts are strongly
endothermic
In thermochemistry, an endothermic process () is any thermodynamic process with an increase in the enthalpy (or internal energy ) of the system.Oxtoby, D. W; Gillis, H.P., Butler, L. J. (2015).''Principle of Modern Chemistry'', Brooks Cole. ...
. The reaction of barium hydroxide octahydrate with
ammonium chlorideEndothermic Solid-Solid Reactions
/ref> 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.
Safety
Barium hydroxide presents the same hazards such as skin irritation and burns as well as eye damage, just as the other strong bases and as other water-soluble barium compounds: it is corrosive and toxic.
See also
* Baralyme Baralyme is a mixture of 80% calcium hydroxide and 20% barium hydroxide compounds that is used as an alternative to soda lime to absorb the exhaled carbon dioxide in a closed circuit anesthetic system.Mosby's Medical Dictionary, 8th edition. 2009, E ...
References
External links
Material Safety Data Sheet (MSDS)
{{Hydroxides
Barium compounds
Hydroxides