Potassium tetracyanonickelate

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 ... 

The method may be illustrated by the determination of bromide details for the preparation of the potassium tetracyanonickelate are given in Section 10.58. 

Pipette 25.0 mL of the bromide ion solution (0.01-0.02M) into a 400 mL beaker, add excess of dilute silver nitrate solution, filter off the precipitated silver bromide on a sintered glass filtering crucible, and wash it with cold water. Dissolve the precipitate in a warm solution prepared from 15 mL of concentrated ammonia solution, 15 mL of 1M ammonium chloride, and 0.3 g of potassium tetracyanonickelate. Dilute to 100-200 mL, add three drops of murexide indicator, and titrate with standard EDTA (0.01 M) (slowly near the end point) until the colour changes from yellow to violet. 

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)... 

Potassium tetrahydroxoaurate(III) Potassium tetracyanonickelate(O) Hexamminerhodium(III) nitrate Potassium hexacyanoosmate(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]" ... 

SHI/FUJ] Shibata, N., Fujinaga, T., Yoshihara, K., Kanchiku, Y., Hot-atom chemistry of potassium tetracyanonickelate, Radiochim. Acta, 5, (1966), 238-239. Cited on pages 226, 327. 

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... 

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. 

The second approach is much like the preceding method. The precipitate in which the anion to be determined is engaged is treated with a reagent that stoichiometri-cally liberates a cation that is titrated with a standard solution of EDTA. Hence, a halide (except the fluoride) or the thiocyanate ion is precipitated as the corresponding silver salt. The latter is treated with a solution of potassium tetracyanonickelate K2 [Ni(CN)4]. The silver salt dissolves into this solution with liberation of one nickel ion Ni + for two ions X . Ni + is titrated with EDTA in the presence of murexide. The reaction constituting the basis of the process is... 

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