Nickel gravimetric determination

A process for the gravimetric determination of mixtures of selenium and tellurium is also described. Selenium and tellurium occur in practice either as the impure elements or as selenides or tellurides. They may be brought into solution by mixing intimately with 2 parts of sodium carbonate and 1 part of potassium nitrate in a nickel crucible, covering with a layer of the mixture, and then heating gradually to fusion. The cold melt is extracted with water, and filtered. The elements are then determined in the filtrate. 

Schiff s bases formed from o-hydroxyaldehydes often form reagents of service in analysis. For example, the base formed with ethylenediamine forms an insoluble complex with nickel (14) which has been used for its gravimetric determination. 2-(o-Hydroxyphenyl)benzoxazole (15a) has been... 

Compound (17-G-V) is used in analysis for the gravimetric determination of nickel. Phosphine complexes of the type tro/is-NiX and (L—L)NiX2 are used as precursors for numerous catalytic reactions some of these have also been discussed as potential anti-tumor agents.2 An unusual class of compounds are the metalladithi-olenes, for example, (17-G-VI) and (17-G-VII), which are readily oxidized to give, formally, Ni111 and Ni1 species. These compounds show metallic conductivity and may show low-temperature superconductivity.3... 

Prepare a spreadsheet similar to the one shown in Figure 3-7 for the gravimetric determination of nickel using dimethylglyoxime. See Section 37B-3 for details. Use the worksheet from Problem 3-9 to calculate the molar mass of Ni(DMG)2 if it is available. 3-4. Write an Excel formula using the FIND and MID functions to eliminate the square brackets and the uncertainty from the atomic mass of lithium in the lUPAC table and display the numeric characters of the atomic weight. 

Standard nickel solution 1 mg/ml. Dissolve 6.7300 g of (NH4)2Ni(S04)2.6H20 in water containing 2 ml of cone. H2SO4, and dilute the solution with water to 1 litre. It is also possible to prepare a more concentrated solution of a nickel salt, determine the concentration of nickel gravimetrically, and then dilute the solution with water until it contains exactly 1 mg of Ni per ml. 

Nickel is determined by the gravimetric dimethyl-glyoxime procedure after reduction of the compound with sulfur dioxide and hydrochloric acid. Iodine is determined as silver iodide after reduction with sulfur dioxide in sulfuric acid medium. Total active oxygen is calculated by measuring the quantity of iodine liberated from potassium iodide in acidic solution. Alkali metals are determined as sulfates in the filtrates from the nickel determinations. 

Of the four-coordinate complexes of Ni those with the square planar stereochemistry are the most numerous. They include the yellow [Ni(CN)4] , the red bis(A(-methyl-salicylaldiminato)nickel(ll) and the well-known bis(dimethylglyoximato)nickel lI) (Fig. 27.6b and c) obtained as a floccuicnt red precipitate in gravimetric determinations of nickel. Actually, in the solid state, this last compound consists of planar molecules stacked above each other. so that Ni-Ni interactions occur (Ni-Ni 325 pm), and the nickel atoms should therefore be described as octahcdrally coordinated. However, in non-coordinating solvents it dissociates into the square-planar monomer, while in bis-(ethylmethylglyoximato)nickel(Il) a much longer Ni Ni separation (475 pm) indicates that even in the solid it must be regarded as square planar. 

EXPERIMENT 5 GRAVIMETRIC DETERMINATION OF NICKEL IN A NICHROME ALLOY... 

Some of the most successful and widely used chelating reagents include dimethylglyoxime for the gravimetric determination of nickel 1,10-phe-nanthroline and its derivatives for the colorimetric determination of iron and copper dithizone for the separation and colorimetric determination of a number of metals but particularly lead, silver, zinc, cadmium, and mercury the dithiocarbamates such as diethylammonium diethyldithiocarbamate and ammonium pyrrolidinedithiocarbamate, used for colorimetry but more widely applied now as selective extractants and the most successful titrant, EDTA. 

Gravimetric determination of nickel A solution of dimethylglyoxime in ethanol precipitat3es ions from hot fliintly acidic solution. If the disodium salt of the reagent is available, a 2% solution is used to precipitate the red square planar diamaquatic complex (Fig. 15.1). 

Nickel also is deterrnined by a volumetric method employing ethylenediaminetetraacetic acid as a titrant. Inductively coupled plasma (ICP) is preferred to determine very low nickel values (see Trace AND RESIDUE ANALYSIS). The classical gravimetric method employing dimethylglyoxime to precipitate nickel as a red complex is used as a precise analytical technique (122). A colorimetric method employing dimethylglyoxime also is available. The classical method of electro deposition is a commonly employed technique to separate nickel in the presence of other metals, notably copper (qv). It is also used to estabhsh caUbration criteria for the spectrophotometric methods. X-ray diffraction often is used to identify nickel in crystalline form. 

Specifications, Analysis, and Toxicity. Dicyandiamide is identified quaHtatively by paper chromatography and quantitatively by ultraviolet spectrometry of the chromatogram. More commonly, total nitrogen analysis is used as a purity control or the dicyandiamide is converted by hydrolysis to guanylurea, which is determined gravimetrically as the nickel salt (50). Methods based on the precipitation of silver dicyandiamide picrate are sometimes used (51). Dicyandiamide can also be titrated with tetrabutylammonium hydroxide ia pyridine solution. Table 4 gives a typical analysis of a commercial sample. Dicyandiamide is essentially nontoxic. It may, however, cause dermatitis. 

Rostrup-Nielsen and Pedersen (209) recently studied sulfur poisoning of supported nickel catalysts in both methanation and Boudouard reactions by means of gravimetric and differential packed-bed reactor experiments. In their gravimetric experiments a synthesis mixture (H2/CO/He = 5/7/3) containing 1-2 ppm H2S was passed over a catalyst pellet of 13% Ni/Al203-MgO at 673 K and 1 atm. The rates of Boudouard and methanation reactions were determined from weight increases and exit methane concentrations respectively. In the presence of 2 ppm H2S a factor of 20 decrease was observed in both methanation and Boudouard rates over a period of 30-60 min. However, the selectivity or ratio of the rates for Boudouard and methanation reactions was constant with time. From these results the authors concluded that the methanation and Boudouard reactions involve the same intermediate, carbon, and that sulfur blocks the sites for the formation of this intermediate. 

Sulfur is determined gravimetrically by precipitation of barium sulfate after oxidation of an approximately 50-mg. sample by fusion with a sodium peroxide-sodium carbonate mixture in a nickel crucible. 

X 10 mol dm". After an equilibration time of 10 hours the dissolved amount of nickel(II) was determined gravimetrically. The solid phase was precipitated at elevated temperatures (333 - 343 K) by adding H2S to an aqueous solution of NiS04-7H20. No characterisation of the solid product was performed. The reaction time of 10 hours seems to be too short for equilibrium between the solid phase and the aqueous solution to be attained. 

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