Cobalt(II) hydroxide or cobaltous hydroxide is the
inorganic compound
In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemist ...
with the formula , consisting of
divalent
In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with other atoms when it forms chemical compounds or molecules.
Description
The combining capacity, or affinity of an ...
cobalt
Cobalt is a chemical element with the symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, pr ...
cations
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...
and
hydroxide
Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a single covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. I ...
anions
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...
. The pure compound, often called the "beta form" (β-) is a pink solid insoluble in water.
[
The name is also applied to a related compound, often called "alpha" or "blue" form (α-), which incorporates other anions in its molecular structure. This compound is blue and rather unstable.][Xiaohe Liu, Ran Yi, Ning Zhang, Rongrong Shi, Xingguo Li, and Guanzhou Qiu (2008): "Cobalt hydroxide nanosheets and their thermal decomposition to cobalt oxide nanorings". ''Chemistry: An Asian Journal'', volume 3, issue 4, pages 732-738. ]
Cobalt(II) hydroxide is most used as a drying agent for paint
Paint is any pigmented liquid, liquefiable, or solid mastic composition that, after application to a substrate in a thin layer, converts to a solid film. It is most commonly used to protect, color, or provide texture. Paint can be made in many ...
s, varnish
Varnish is a clear transparent hard protective coating or film. It is not a stain. It usually has a yellowish shade from the manufacturing process and materials used, but it may also be pigmented as desired, and is sold commercially in various ...
es, and ink
Ink is a gel, sol, or solution that contains at least one colorant, such as a dye or pigment, and is used to color a surface to produce an image, text, or design. Ink is used for drawing or writing with a pen, brush, reed pen, or quill. Thi ...
s, in the preparation of other cobalt compounds, as a catalyst
Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
and in the manufacture of battery
Battery most often refers to:
* Electric battery, a device that provides electrical power
* Battery (crime), a crime involving unlawful physical contact
Battery may also refer to:
Energy source
*Automotive battery, a device to provide power t ...
electrode
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials de ...
s.
Preparation
Cobalt(II) hydroxide precipitates
In an aqueous solution, precipitation is the process of transforming a dissolved substance into an insoluble solid from a super-saturated solution. The solid formed is called the precipitate. In case of an inorganic chemical reaction leading ...
as a solid when an alkali
In chemistry, an alkali (; from ar, القلوي, al-qaly, lit=ashes of the saltwort) is a basic, ionic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a ...
metal hydroxide
Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a single covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. I ...
is added to an aqueous
An aqueous solution is a solution in which the solvent is water. It is mostly shown in chemical equations by appending (aq) to the relevant chemical formula. For example, a solution of table salt, or sodium chloride (NaCl), in water would be rep ...
solution of Co2+ salt.[O. Glemser "Cobalt(II) Hydroxide" in Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 1521.] For example,
:Co2+ + 2 NaOH → Co(OH)2 + 2 Na+
The compound can be prepared by reacting cobalt(II) nitrate
Cobalt is a chemical element with the symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, p ...
in water with a solution of triethylamine
Triethylamine is the chemical compound with the formula N(CH2CH3)3, commonly abbreviated Et3N. It is also abbreviated TEA, yet this abbreviation must be used carefully to avoid confusion with triethanolamine or tetraethylammonium, for which TEA ...
as both the base and a complexing agent
A coordination complex consists of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of bound molecules or ions, that are in turn known as ''ligands'' or complexing agents. Many m ...
.[ It can also be prepared by elecrolysis of a solution of cobalt nitrate with a ]platinum
Platinum is a chemical element with the symbol Pt and atomic number 78. It is a dense, malleable, ductile, highly unreactive, precious, silverish-white transition metal. Its name originates from Spanish , a diminutive of "silver".
Platinu ...
cathode.[P. Benson, G. W. D. Briggs, and W. F. K. Wynne-Jones (1964): "The cobalt hydroxide electrode—I. Structure and phase transitions of the hydroxides". ''Electrochimica Acta'', volume 9, issue 3, pages 275-280. ]
Reactions
Cobalt(II) hydroxide decomposes to cobalt(II) oxide
Cobalt(II) oxide is an inorganic compound that has been described as an olive-green or gray solid. It is used extensively in the ceramics industry as an additive to create blue colored glazes and enamels as well as in the chemical industry for pr ...
at 168 °C under vacuum
A vacuum is a space devoid of matter. The word is derived from the Latin adjective ''vacuus'' for "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often dis ...
and is oxidized by air.[ The thermal decomposition product in air above 300 °C is Co3O4.]
Like iron(II) hydroxide
Iron(II) hydroxide or ferrous hydroxide is an inorganic compound with the formula Fe(OH)2. It is produced when iron(II) salts, from a compound such as iron(II) sulfate, are treated with hydroxide ions. Iron(II) hydroxide is a white solid, but ev ...
, cobalt(II) hydroxide is a basic hydroxide, and reacts with acids to form cobalt(II) salts. It also reacts with strong bases to form solutions with dark blue cobaltate(II) anions, 4">o(OH)4sup>2− and 6">o(OH)6sup>4−.
Structure
The pure (β) form of cobalt(II) hydroxide has the brucite
Brucite is the mineral form of magnesium hydroxide, with the chemical formula Mg( OH)2. It is a common alteration product of periclase in marble; a low-temperature hydrothermal vein mineral in metamorphosed limestones and chlorite schists; and ...
crystal structure. As such, the anion and cation packing are like those in cadmium iodide
Cadmium iodide is the inorganic compound with the formula CdI2. It is a white hygroscopic solid. It also can be obtained as a mono- and tetrahydrate. It has few applications. It is notable for its crystal structure, which is typical for compound ...
, in which the cobalt(II) cations have octahedral molecular geometry
In chemistry, octahedral molecular geometry, also called square bipyramidal, describes the shape of compounds with six atoms or groups of atoms or ligands symmetrically arranged around a central atom, defining the vertices of an octahedron. The oc ...
.
The beta form can be obtained as platelets with partial hexagonal geometry, 100-300 nm wide and 5-10 nm thick.[
]
Alpha form
The so-called "alpha form" (α-Co(OH)2) is not a polymorph of the pure (β) form, but rather a more complex compound in which hydroxide-cobalt-hydroxide layers have a residual positive charge and alternate with layers of other anions such as nitrate
Nitrate is a polyatomic ion
A polyatomic ion, also known as a molecular ion, is a covalent bonded set of two or more atoms, or of a metal complex, that can be considered to behave as a single unit and that has a net charge that is not zer ...
, 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 g ...
, chloride
The chloride ion is the anion (negatively charged ion) Cl−. It is formed when the element chlorine (a halogen) gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. Chloride salts ...
, etc. (the hydrotalcite
Hydrotalcite or formerly also Völknerite is a layered double hydroxide (LDH) of general formula ·4, whose name is derived from its resemblance with talc and its high water content. Multiple structures containing loosely bound carbonate ions ex ...
structure).[ It is usually obtained as a blue precipitate when a base like ]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 alkali ...
is added to a solution of a cobalt(II) salt. The precipitate slowly converts to the beta form.
Nanotubes
Cobalt hydroxide can be obtained in the form of nanotube
A nanotube is a nanometer-scale hollow tube-like structure.
Kinds of nanotubes
* BCN nanotube, composed of comparable amounts of boron, carbon, and nitrogen atoms
* Boron nitride nanotube, a polymorph of boron nitride
* Carbon nanotube, includes g ...
s, which may be of interest in nanotechnology
Nanotechnology, also shortened to nanotech, is the use of matter on an atomic, molecular, and supramolecular scale for industrial purposes. The earliest, widespread description of nanotechnology referred to the particular technological goal o ...
and materials science.
References
{{DEFAULTSORT:Cobalt(II) Hydroxide
Cobalt(II) compounds
Hydroxides