Nickel hydroxide, solubility

Nickel was first isolated in 1751, and a relatively pure metal was prepared in 1804. In nature, nickel is found primarily as oxide and sulfide ores (USPHS 1977). It has high electrical and thermal conductivities and is resistant to corrosion at environmental temperatures between -20°C and +30°C (Chau and Kulikovsky-Cordeiro 1995). Nickel, also known as carbonyl nickel powder or C.I. No. 77775, has a CAS number of 7440-02-0. Metallic nickel is a hard, lustrous, silvery white metal with a specific gravity of 8.9, a melting point of about 1455°C, and a boiling point at about 2732°C. It is insoluble in water and ammonium hydroxide, soluble in dilute nitric acid or aqua regia, and slightly soluble in hydrochloric and sulfuric acid. Nickel has an atomic weight of 58.71. Nickel is... 

Hexammino-niekel Sulphate, [Ni(NH3)e]S04.—Anhydrous nickel sulphate rapidly absorbs ammonia gas, heat is developed, and a bulky white powder produced of composition NiS04.6NH3. It is soluble in water, forming a blue solution and a precipitate of green nickel hydroxide. The solid when heated decomposes with loss of ammonia.2... 

An alternative approach is precipitation by combining an alkaline NaAlC>2 solution with an acidic nickel nitrate solution [51]. In this case as well, hydrotalcite-like species are probably formed first although, due to the very high nickel contents reported, some nickel hydroxide forms as well. Pure hydrotalcite-like structure are reported to form for Ni Al atomic ratios between 2 and 3 [52] or 4 [53] outside this range the hydroxides of the excess species form as additional phases. Rapid precipitation tends to form pure Al(OH)3 due to the lower solubility. Aging can lead to recrystallization of some of the pure hydroxides to the hydrotalcite structure as well. 

Nickelous Hydroxide, Nickel Dihydroxide, Ni(OH)2, is obtained as an apple-green precipitate upon warming aqueous alkali hydroxide with a solution of a nickel salt. The precipitate is not perfectly pure, but contains traces of alkali and of the original acid.6 It is very slightly soluble in water,7 but readily soluble in ammonium hydroxide, yielding a deep blue solution from which the nickel hydroxide is deposited in crystalline form on boiling. 

Nickel hydroxide dissolves in ordinary distilled water to the extent of 12-7 mgs. of Ni(OH)2 per litre at 20° C.10 It is soluble in acids, yielding nickel salts when heated, water is evolved, leaving a residue... 

The hexahydrate, Ni(N03)2.6H20, is dimorphous. It is obtained as green monoclinic crystals by concentration of a solution of nickel hydroxide or carbonate in dilute nitric acid at temperatures below 55° C.—most advantageously at about 40° C. Density 6 2-065 at 14° C. At low temperatures the salt separates out in crystalline lamellae. The crystals deliquesce in moist air and effloresce in the dry. Their solubility in water is as follows 7 ... 

Nickel Thiocarbonate Hexammoniate, NiCS,. 3XH3, is prepared 2 by gently warming nickel hydroxide with aqueous ammonia and carbon disulphide. It crystallises in ruby-red, transparent needles, which are but slightly soluble in water. On warming, carbon disulphide is evolved. Upon exposure to air both ammonia and carbon disulphide escape. 

If a carrier is to be incorporated in the final catalyst, the original precipitation is usually carried out in the presence of a suspension of the finely divided support or, alternatively, a compound or suspension, which will eventually be converted to the support, may initially be present in solution. Thus, a soluble aluminum salt may be converted to aluminum hydroxide during precipitation and ultimately to alumina. Alternatively, a supported nickel catalyst could be prepared from a solution of nickel nitrate, containing a suspension of alumina, by precipitation of a nickel hydroxide with ammonia. 

To explain this phenomenon we might postulate the formation of a complex ion, remembering the solubility of cupric hydroxide and nickel hydroxide in ammonium hydroxide with formation of ammonia complexes. This is indeed the explanation the complex ion which is formed is the rincate ion, Zn(OH)4, by the reaction... 

The hydrated salts of nickel such as nickel sulfate, NiSO GHgO. and nickel chloride, NiCU GHsO, are green in color. Nickelous hy droxide, Ni(OH)2, formed as an apple-green precipitate by addition of alkali to a solution containing nickelous ion. When heated it pro duces the insoluble green substance nickelous oxide, NiO. Nickelous hydroxide is soluble in ammonium hydroxide, forming ammonia com plexes such as Ni(NH3)4(HoO). + + and Ni(NHg)g+ +. ... 

The authors mentioned, that the dissolution of nickel hydroxide in alkaline solutions up to 15 M NaOH was so slight that only estimates of its solubility could be made. When the reported experimental data were re-evaluated it became evident that, at best, only one constant,, 3, can be determined. The solubility of Ni(OH)2(cr) increases with increasing NaOH molality, but the solubility curve flattens out at [OH ] > 1 m. This may be due to ion-ion interactions at the high ionic strengths, but there is no evidence whatever for formation of Ni(OH)4". Equation (A.7) can be fit reasonably to the data at lower NaOH molalities. When the SIT model is applied ... 

PHYSICAL PROPERTIES (nickel chloride) yellow or brown scales nickel chloride hexahydrate appears as green, deliquescent crystals or crystal powder anhydrous salt is golden yellow odorless solid soluble in ethanol and ammonium hydroxide soluble in water insoluble in ammonia MP (1,001°C, 1834°F) DN (3.55 g/cm at 20°C) SG (3.55) VD (NA) VP (1 mmHg at 671°C). (nickel sulfate) yellow cubes nickel sulfate hexahydrate appears as blue to blue-green tetragonal crystals of green transparent crystals becomes blue and opaque at room temperature odorless soluble in water, ethanol, and methanol insoluble in alcohol, ether, and acetone MP (840°C, 1544°F loses SOj) DN (3.68 g/cm at 20°C) SG (3.68) VD (NA). 

Figure 1. Comparison of solubilities of nickel carbonate (pKgo = 6.87) ar5. nickel hydroxide for active (p so aged (pKgo = 17,2)...

Orange-red crystals. The water of hydration is completely removed by heating to 100°C. Very soluble, even in cold water decomposed to Ni(CN)s by mineral acids. Forms black precipitates of higher nickel hydroxides on addition of hypobromites. 

According to E. Tupputi,33 a soln. of chromic acid dissolves nickel hydroxide or carbonate forming a yellow soln. which" deposits a powder soluble in a large excess of the acid. The soln. deposits a non-deliquescent mass of red crystals. 

The solubility of silica of low surface area (50 mVg) is weaker and its rate of dissolution is slower because of the smaller support-solution interface. Therefore, the amount of Si(OH)4 is low at the beginning of the deposition-precipitation (<4 h). So, Si-O-Ni heterocondensation is a minor reaction, and olation between the Ni(OH)2(OH2)4 complexes is the main reaction (step 9 in Figure 14.7). Further polymerization forms brucitic layers of Ni(II) (step 10), which grow on the brucitic layer of Ni(II) bonded to silica, and lead to the formation of supported nickel hydroxide. 

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