What Is Nickel Hydroxide?
Nickel hydroxide, represented by various oxidation states, is most commonly found as nickel hydroxide (II). Due to its classification under multiple safety and health regulations, handling nickel hydroxide requires careful precautions.
Uses of Nickel Hydroxide
Nickel hydroxide (II) is crucial in rechargeable batteries, such as nickel-metal hydride, nickel-cadmium, and lithium-ion batteries, enhancing the performance of devices like cell phones and hybrid vehicles. It’s also used in surface treatment chemicals and plating, and as a catalyst.
Properties of Nickel Hydroxide
1. Nickel Hydroxide (I)
A dark blue precipitate, nickel hydroxide (I) is nearly water-insoluble and decomposes when exposed to moisture. It reacts with alkali sulfides and cyanides to form nickel (I) compounds.
2. Nickel Hydroxide (II)
This form is insoluble in water and alkaline solutions but dissolves in dilute acids, potassium cyanide, and ammonia.
3. Nickel Hydroxide (III)
With a density of 4.84 g/cm3 and a melting point of 600°C, nickel hydroxide (III) is often associated with black nickel oxide (Ni2O3).
Structure of Nickel Hydroxide
1. Nickel Hydroxide (I)
With the formula NiOH, it has a molar mass of 75.70 and is a monovalent nickel compound.
2. Nickel Hydroxide (II)
A light green crystal with the formula Ni(OH)2, it has a hexagonal cadmium hydroxide-type crystal structure and a density of 4.15 g/cm3.
3. Nickel Hydroxide (III)
Often considered an indeterminate nickel oxide, Ni2O3 is a trivalent nickel hydroxide with a molar mass of 165.39.
Other Information on Nickel Hydroxide
1. Synthesis of Nickel Hydroxide (II)
Formed by reacting alkali hydroxide with a nickel (II) salt solution, it can also be precipitated from a hexa-ammonium nickel (II) complex, yielding Ni(OH)2・1.5H2O, which becomes anhydrous in vacuum.
2. Reaction of Nickel Hydroxide (II)
Upon heating to 230°C, it dehydrates to nickel (II) oxide. While resistant to oxidation by air or hydrogen peroxide, it is oxidized by ozone to nickel hydroxide (III).