Nickel sulphate

Nickel(II) sulfate, or just nickel sulfate, usually refers to the inorganic compound with the formula NiSO4(H2O)6. This highly soluble blue-coloured salt is a common source of the Ni2+ ion for electroplating. Nickel(II) sulfate, or just nickel sulfate, usually refers to the inorganic compound with the formula NiSO4(H2O)6. This highly soluble blue-coloured salt is a common source of the Ni2+ ion for electroplating. Approximately 40,000 tonnes were produced in 2005. It is mainly used for electroplating of nickel. In 2005–06, nickel sulfate was the top allergen in patch tests (19.0%). At least seven sulfate salts of nickel(II) are known. These salts differ in terms of their hydration or crystal habit. The common tetragonal hexahydrate crystallizes from aqueous solution between 30.7 and 53.8 °C. Below these temperatures, a heptahydrate crystallises, and above these temperatures an orthorhombic hexahydrate forms. The yellow anhydrous form, NiSO4, is a high melting solid that is rarely encountered in the laboratory. This material is produced by heating the hydrates above 330 °C. It decomposes at still higher temperatures to nickel oxide. X-ray crystallography measurements show that NiSO4·6H2O consists of the octahedral 2+ ions. These ions in turn are hydrogen bonded to sulfate ions. Dissolution of the salt in water gives solutions containing the aquo complex 2+. All nickel sulfates are paramagnetic. The salt is usually obtained as a by-product of copper refining. It is also produced by dissolution of nickel metal or nickel oxides in sulfuric acid. Aqueous solutions of nickel sulfate reacts with sodium carbonate to precipitate nickel carbonate, a precursor to nickel-based catalysts and pigments. Addition of ammonium sulfate to concentrated aqueous solutions of nickel sulfate precipitates Ni(NH4)2(SO4)2·6H2O. This blue-coloured solid is analogous to Mohr's salt, Fe(NH4)2(SO4)2·6H2O.