Cobaltous hydroxide, cobalt hydroxide, β-cobalt(II) hydroxide
3D model (JSmol)
|Molar mass||92.948 g/mol|
|Appearance||rose-red powder or bluish-green powder|
|Melting point||168 °C (334 °F; 441 K) (decomposes)|
Solubility product (Ksp)
|Solubility||soluble in acids, ammonia; insoluble in dilute alkalis|
Std enthalpy of
|Safety data sheet||Oxford University|
|R-phrases (outdated)||R20 R21 R22 R36 R37 R38 R43|
|S-phrases (outdated)||S24 S26 S36 S37 S39|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|what is ?)(|
Cobalt(II) hydroxide or cobaltous hydroxide is the inorganic compound with the formula Co(OH)
2, consisting of divalent cobalt cations Co2+
and hydroxide anions HO−
. The pure compound, often called the "beta form" (β-Co(OH)
2) is a pink solid insoluble in water.
The name is also applied to a related compound, often called "alpha" or "blue" form (α-Co(OH)
2), which incorporates other anions in its molecular structure. This compound is blue and rather unstable.
- Co2+ + 2 NaOH → Co(OH)2 + 2 Na+
The compound can be prepared by reacting cobalt(II) nitrate in water with a solution of triethylamine N(C
3 as both the base and a complexing agent.. It can also be prepared by elecrolysis of a solution of cobalt nitrate with a platinum cathode.
Like iron(II) hydroxide, 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, [Co(OH)4]2− and [Co(OH)6]4−.
The pure (β) form of cobalt(II) hydroxide has the brucite crystal structure. As such, the anion and cation packing are like those in cadmium iodide, in which the cobalt(II) cations have octahedral molecular geometry.
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, carbonate, chloride, etc. (the hydrotalcite structure). It is usually obtained as a blue precipitate when a base like sodium hydroxide is added to a solution of a cobalt(II) salt. The precipitate slowly converts to the beta form.
|Wikimedia Commons has media related to Cobalt(II) hydroxide.|
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