Nickelii Hydroxide
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.
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| Names | |
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| IUPAC name Nickel(II) hydroxide | |
| Other names Nickel hydroxide, Theophrastite | |
| Identifiers | |
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| ChemSpider | |
| ECHA InfoCard | 100.031.813 |
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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 | |
Solubility product (Ksp) | 5.48×10−16 |
| +4500.0·10−6 cm3/mol | |
| Structure | |
| 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 |
Std enthalpy of formation (ΔfH⦵298) | −538 kJ·mol−1 |
| Hazards | |
| GHS labelling: | |
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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). | |
_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. The β form adopts a hexagonal close-packed structure of Ni2+ and OH− ions. In the presence of water, the α polymorph typically recrystallizes to the β form. 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.
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. A nickel-magnesium variant of the mineral, (Ni,Mg)(OH)2 had been previously discovered at Hagdale on the island of Unst in Scotland.
Reactions
Nickel(II) hydroxide is frequently used in electrical car batteries. 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).
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.
Synthesis
The synthesis entails treating aqueous solutions of nickel(II) salts with potassium hydroxide.
Toxicity
The Ni2+ ion is a known carcinogen when inhaled. Toxicity and related safety concerns have driven research into increasing the energy density of Ni(OH)2 electrodes, such as the addition of calcium or cobalt hydroxides.
See also
References
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