Nickel(II) hydroxide is the inorganic compound with the formula Ni(OH)2. It is a lime-green solid that dissolves with decomposition in ammonia and amines and is attacked by acids. It is electroactive, being converted to the Ni(III) oxy-hydroxide, leading to widespread applications in rechargeable batteries.[6]
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| Names | |
|---|---|
| IUPAC name
Nickel(II) hydroxide | |
| Other names
Nickel hydroxide, Theophrastite | |
| Identifiers | |
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3D model (JSmol) |
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| ChemSpider | |
| ECHA InfoCard | 100.031.813 |
| EC Number |
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PubChem CID |
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| RTECS number |
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| UNII | |
CompTox Dashboard (EPA) |
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| Properties | |
| Ni(OH)2 | |
| Molar mass | 92.724 g/mol (anhydrous) 110.72 g/mol (monohydrate) |
| Appearance | green crystals |
| Density | 4.10 g/cm3 |
| Melting point | 230 °C (446 °F; 503 K) (anhydrous, decomposes) |
| 0.0015 g/L[1] | |
Solubility product (Ksp) |
5.48×10−16[2] |
| +4500.0·10−6 cm3/mol | |
| Structure[3] | |
| hexagonal, hP3 | |
| P3m1, No. 164 | |
a = 0.3117 nm, b = 0.3117 nm, c = 0.4595 nm α = 90°, β = 90°, γ = 120° | |
| Thermochemistry | |
Std molar entropy (S⦵298) |
79 J·mol−1·K−1[4] |
Std enthalpy of formation (ΔfH⦵298) |
−538 kJ·mol−1[4] |
| Hazards | |
| GHS labelling:[5] | |
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| Danger | |
| H302, H315, H317, H332, H334, H341, H350, H360, H372 | |
| P201, P260, P280, P284, P405, P501 | |
| Lethal dose or concentration (LD, LC): | |
LD50 (median dose) |
1515 mg/kg (oral, rat) |
| Safety data sheet (SDS) | External SDS |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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_reactions.JPG)
Properties
Nickel(II) hydroxide has two well-characterized polymorphs, α and β. The α structure consists of Ni(OH)2 layers with intercalated anions or water.[7][8] The β form adopts a hexagonal close-packed structure of Ni2+ and OH− ions.[7][8] In the presence of water, the α polymorph typically recrystallizes to the β form.[7][9] In addition to the α and β polymorphs, several γ nickel hydroxides have been described, distinguished by crystal structures with much larger inter-sheet distances.[7]
The mineral form of Ni(OH)2, theophrastite, was first identified in the Vermion region of northern Greece, in 1980. It is found naturally as a translucent emerald-green crystal formed in thin sheets near the boundaries of idocrase or chlorite crystals.[10] A nickel-magnesium variant of the mineral, (Ni,Mg)(OH)2 had been previously discovered at Hagdale on the island of Unst in Scotland.[11]
Reactions
Nickel(II) hydroxide is frequently used in electrical car batteries.[8] Specifically, Ni(OH)2 readily oxidizes to nickel oxyhydroxide, NiOOH, in combination with a reduction reaction, often of a metal hydride (reaction 1 and 2).[12][13]
Reaction 1 Ni(OH)2 + OH− → NiO(OH) + H2O + e−
Reaction 2 M + H2O + e− → MH + OH−
Net Reaction (in H2O) Ni(OH)2 + M → NiOOH + MH
Of the two polymorphs, α-Ni(OH)2 has a higher theoretical capacity and thus is generally considered to be preferable in electrochemical applications. However, it transforms to β-Ni(OH)2 in alkaline solutions, leading to many investigations into the possibility of stabilized α-Ni(OH)2 electrodes for industrial applications.[9]
Synthesis
The synthesis entails treating aqueous solutions of nickel(II) salts with potassium hydroxide. When the same reaction is conducted in the presence of bromine, the product is Ni3O2(OH)4.[14]
Toxicity
The Ni2+ ion is a carcinogen when inhaled.
See also
References
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