Potassium Tetracyanonickelate II

Potassium hexacyanocobaltate(III) crystals have a faint yellow color and belong to the monoclinic system. Their specific gravity is 1.906. The compound is not appreciably hydrolyzed iii solution, but concentrated mineral acids decompose it. On heating to moderately high temperatures it melts, with decomposition, to an olive-green mass. The crystals are very soluble in water at room temperature, only very slightly soluble in liquid ammonia at —33°, and insoluble in alcohol. The preparation of potassium hexacyanocobaltate(III) is sometimes used in qualitative analysis in the separation of cobalt and nickel. 

Submitted by W. C. FEENELius t and Joseph J. Buebagb Checked by Natbw.n E. BallouJ 

Potassium tetracyanonickelate(II) may be prepared by adding an excess of potassium cyanide to a solution of a soluble nickel salt and bringing the solution to crystallization. However, the preliminary precipitation of nickel 

Nickel Cyaxdde. Sixty grams of nickel sulfate, NiS04 6H 0, is dissolved in 200 ml. of water. To this solution is added slowly, with stirring, 29.7 g. of potassium cyanide dissolved in 70 ml. of water. A grayish- reen precipitate of nickel cyanide is immediately produced, which is washed free of sulfates and collected in a Buchner funnel. Yield 24.8 g. (98 per cent). 

Potassium Tetracyauonickelate(II). Twenty-nine and two-tenths grams of potassium cyanide is dissolved in approximately 30 ml. of water. To this solution is added the solid nickel cyanide, which dissolves to form a brilliant-red solution. This solution is heated on the hot plate until small crystals begin to form. They are redissolved, and the solution is permitted to cool. Large, well-formed crystals are obtained in this manner, and successive crops are taken. Yield 57.4 g. (97 per cent). 

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Silver halides can be dissolved in a solution of potassium tetracyanonickelate(II) in the presence of an ammonia-ammonium chloride buffer, and the nickel ion set free may be titrated with standard EDTA using murexide as indicator. 

The procedure involved in the determination of these anions is virtually that discussed in Section 10.58 for the indirect determination of silver. The anion to be determined is precipitated as the silver salt the precipitate is collected and dissolved in a solution of potassium tetracyanonickelate(II) in the presence of an ammonia/ammonium chloride buffer. Nickel ions are liberated and titrated with standard EDTA solution using murexide as indicator ... 

Hydrated Ni(CN)2 dissolves in aqueous KCN and the yellow diamagnetic potassium tetracyanonickelate(II) K2Ni(CN)4 (92) crystallizes upon evaporating the solvent (equation 111). 

SYNS DIPOTASSIUM NICKELTETRACYANIDE DIPOTASSIUM TETRACYANONTCKELATE POTASSIUM TETRACYANONICKELATE POTASSIUM TETRACYANONICKELATE(II)... 

A 3.650-g sample containing bromate and bromide was dissolved in sufficient water to give 250.0 mL. After acidification, silver nitrate was introduced to a 25.00-mL aliquot to precipitate AgBr, which was filtered, washed, and then redissolved in an ammoniacal solution of potassium tetracyanonickelate(II) ... 

An excess of potassium tetracyanonickelate(II) is necessary to prevent reduction to potassium tetracyanonickelate(O). The desired nickel (I) complex is the only reduction product if at least a twofold excess of the nickel(II) complex is present. 

The photo-oxidation of sulphur to H2SO4 by hydrogen peroxide takes place in aqueous tetrachloromethane and is intensified by methanol. The reaction of potassium tetracyanonickelate(ii) with molten sulphur, and with potassium tetra-sulphide in molten sulphur, has been studied. The physical adsorption of SO2, SFg, CO2, N2, Ar, and neopentane on rhombic sulphur has been reported. The chemical forms of trace quantities of sulphur in arsenic trichloride have been identified by radiochemical methods as elemental sulphur and SO2CI2. The reactions of sulphur vapour with lanthanide oxides (at 1050—1120 C), oxycarbo-nates, or oxalates (at 700 °C) has been shown to give the oxysulphide. The reactions are thought to proceed via the lanthanyl ion [LnO]" ... 

Potassium tetracyanonickelate(II) crystallizes in orange-red monocliniccrystals that have one molecule of water of hydration. This water is lost when the compoimd is dried at 100°. The salt is extremely soluble, even in cold water. It is decomposed by the action of the mineral acids with precipitation of nickel cyanide. Potassium tetracyanonickelate(II) is readily decomposed by the addition of sodium hypobromite, whence hydrated nickel peroxide is thrown down as a black precipitate. 

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