Nickel turbidity

Nickel cupferronate, Ni(C6H5N202)2, or Ni(cup)a, was prepared as follows. 2 g of Ni(0Ac)2-4H20 was dissolved in 150 ml of milli-Q water (0.05 M), and 2.5 g of cupferron dissolved in 100 ml of milli-Q water (0.16 M) by sonication. The two solutions were cooled to 0 °C and the cupferron solution added dropwise to the Ni(OAc)2 solution under vigorous stirring. After a few minutes, the solution became turbid, indicating the formation of complex. It took another 30 min for completion of the reaction. Before filtration, the product was kept at 0 °C for 1 h. The product was filtered and washed with miiii-Q water and dried at room temperature. 

Nickel Borates.—Several borates of nickel have been described. The tetraborate, NiO.4B2O3.10H2O, is obtained 2 by slow evaporation of a solution of nickel carbonate in boric acid. The precipitate first formed becomes crystalline gradually, yielding small brilliant and clear green crystals soluble in cold water, but becoming turbid at 40° C. 

Volumetric Methods.—Nickel may be conveniently estimated volu-metrically in the absence of cobalt, copper, silver, gold, and the platinum metals by means of potassium cyanide.4 The solution containing the nickel is, if acid, neutralised with ammonia and some ammonium sulphate is added to render the indicator more sensitive. A little ammonia is now added, and a few drops of potassium iodide and silver nitrate. The solution becomes turbid in consequence of the precipitation of silver iodide. The liquid is now titrated with potassium cyanide solution until the turbidity just disappears. The reaction consists in converting the nickel salt into the double cyanide, Ni(CN)a.2KCN, after which any excess of potassium cyanide attacks the silver iodide, yielding the soluble double cyanide, AgCN.KCN. The disappearance of the turbidity therefore indicates the complete conversion of the nickel salt. A slight correction is necessary for the silver introduced. 

The 1,2,4-triazole ligand (0.1 mole, 6.91 g) in 50 mL water is added to nickel(II) nitrate (0.05 mole, 14.54 g of the hexahydrate) dissolved in 50 mL water, whereupon the solution turns dark blue. Then, ammonium thiocyanate (0.1 mole, 7.61 g) in 25 mL water is added. Any turbidity is removed by filtration. Upon standing for several days, purple crystals of a-[Ni(NCS)2(trz)2] are formed. The crystal size depends on the concentration of reactants and the temperature, and may be up to 0.2 mm long. The product is recovered by filtration, washed with water and dried under vacuum. The yield is about 14 g (89%). 

In the course of a study of nickel ammine complexes, in two experiments turbidity occurred, which was interpreted as an indication of formation of Ni(OH)2. When the solubility product (log,p = -13.8, 25°C) is extrapolated to / = 0 by means of the Davies equation the following constants were obtained (log, X°g= -14.64, log, X" = 13.36) [62DAV]. These values are in line with others which refer to freshly precipitated probably amorphous Ni(OH)2, see Table V-6 [380KA], [54FEI/HAR]. 

To 5 ml of water add two drops (or a few mg) of the amine, and if the latter is insoluble in water, two drops of concentrated hydrochloric acid. Place 1 ml of the nickel-carbon disulphide reagent in a test-tube, add 1 ml of concentrated ammonia solution and 1 ml of the amine solution. A precipitate indicates a secondary amine, while a slight turbidity may be due to the presence of a secondary amine as impurity. 

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