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Nickel Iodate, Ni(IO3)2

Nickel Iodate, Ni(IO3)2, discovered by Rammelsberg, is interesting on account of its hydrates. The anhydrous salt is obtained as microscopic yellow needles by heating to 100° C. a mixture of nickel nitrate, iodic acid, and nitric acid. It is but slightly soluble in water, the solubility decreasing with rise of temperature.

Temperature ° C.30507590
Grams Ni(IO3)2 in 100 grams solution.1.1351.071.020.988

A monohydrate, Ni(IO3)2.H2O, was obtained by Rammelsberg as a bright green powder by concentrating solutions of nickel sulphate and sodium iodate or a solution of nickel hydroxide in aqueous hydriodic acid. Clarke was unable to find this salt.

The dihydrate, Ni(IO3)2.2H2O, exists in two isomeric forms known respectively as the α and β varieties.

The α-salt is obtained by allowing a mixture of nickel nitrate and iodic acid to stand for several days at 25° to 30° C., when a crystalline mass is formed. It is but slightly soluble in water.

Temperature ° C.0183050 (transition temperature)
Grams Ni(IO3)2 in 100 grams solution.0.530.680.861.78

At 50° C. in the presence of water the α-salt is converted into the β-salt, which crystallises in small prisms which are even less soluble in water. Thus:

Temperature ° C818507580
Grams Ni(IO3)2 in 100 grams solution.0.520.550.811.031.12

The trihydrate, Ni(IO3)2.3H2O, was first described by Ditte, who evaporated slowly a mixed solution of nickel nitrate and an alkaline iodate. The salt crystallises out in green transparent prisms.

The tetrahydrate, Ni(IO3)2.4H2O, separates out as green hexagonal prisms when a solution of nickel nitrate and sodium iodate is concentrated between 0° and 10° C. The solubility of the salt is as follows:

Temperature ° C01830
Grams Ni(IO3)2 in 100 grams solution0.731.011.41

The hexahydrate, Ni(IO3)2.6H2O, was prepared by Clarke by dissolving nickel carbonate in aqueous iodic acid and allowing to slowly evaporate. The salt yields small green crystals of density 3.70 at 22° C.

Two Periodates of nickel have been described, namely, the meso salt, Ni3(IO5)2, and the diperiodate, Ni2I2O9. The former is obtained as a greenish yellow amorphous salt by the action of nickel sulphate on a solution of Na2H3IO6 when, on boiling, the salt separates out as a flocculent precipitate. Ni2I2O9 occurs as a black crystalline salt obtained by drying at 100° C. the bluish green gelatinous precipitate resulting from mixing solutions of nickel sulphate and K4I2O9.
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