Nickel/ions/salts determination

E. Miscellaneous methods. Exchange reactions between the tetracyano-nickelate(II) ion [Ni(CN)4]2 (the potassium salt is readily prepared) and the element to be determined, whereby nickel ions are set free, have a limited application. Thus silver and gold, which themselves cannot be titrated complexometrically, can be determined in this way. 

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 ... 

As an example, a sample that contains a mixture of copper(II) and nickel(II) salts can be analyzed by first electrolyzing the sample solution under acidic conditions with platinum electrodes such that the copper is plated onto a platinum gauze electrode. Because the solution is acidic, hydronium ion is reduced before nickel ion and there is no interference. After the electrolysis for copper is completed, the electrolysis solution can be neutralized and made basic with ammonia. Having determined the copper and removed it from the platinum electrode, one can electrolyze the remaining basic electrolysis solution to plate nickel on the platinum electrode. 

X-ray crystal structures of both dimers have been determined. The Ni—Ni distance of the mixed-valence dimer (2.514(5) A) is shorter than that of the Ni(II) dimer (2.564(1) A), suggesting stronger direct interaction between the two nickel ions. The crystal structure of [Ni2(CH3CS2)4l] consists of infinite chains of Ni2(CH3CS2)4 I Ni2(CH3CS2)4 — I —, which is similar to that of the Pt analogue. All the Ni atoms are equivalent. Vibrational spectra have been discussed (36). The reaction of nickel salt with dithiophenylacetic acid instead... 

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... 

BackTitrations. In the performance of aback titration, a known, but excess quantity of EDTA or other chelon is added, the pH is now properly adjusted, and the excess of the chelon is titrated with a suitable standard metal salt solution. Back titration procedures are especially useful when the metal ion to be determined cannot be kept in solution under the titration conditions or where the reaction of the metal ion with the chelon occurs too slowly to permit a direct titration, as in the titration of chromium(III) with EDTA. Back titration procedures sometimes permit a metal ion to be determined by the use of a metal indicator that is blocked by that ion in a direct titration. Eor example, nickel, cobalt, or aluminum form such stable complexes with Eriochrome Black T that the direct titration would fail. However, if an excess of EDTA is added before the indicator, no blocking occurs in the back titration with a magnesium or zinc salt solution. These metal ion titrants are chosen because they form EDTA complexes of relatively low stability, thereby avoiding the possible titration of EDTA bound by the sample metal ion. 

The method may also be applied to the analysis of silver halides by dissolution in excess of cyanide solution and back-titration with standard silver nitrate. It can also be utilised indirectly for the determination of several metals, notably nickel, cobalt, and zinc, which form stable stoichiometric complexes with cyanide ion. Thus if a Ni(II) salt in ammoniacal solution is heated with excess of cyanide ion, the [Ni(CN)4]2 ion is formed quantitatively since it is more stable than the [Ag(CN)2] ion, the excess of cyanide may be determined by the Liebig-Deniges method. The metal ion determinations are, however, more conveniently made by titration with EDTA see the following sections. 

These reactions take place with sparingly soluble silver salts, and hence provide a method for the determination of the halide ions Cl", Br, I-, and the thiocyanate ion SCN ". The anion is first precipitated as the silver salt, the latter dissolved in a solution of [Ni(CN)4]2", and the equivalent amount of nickel thereby set free is determined by rapid titration with EDTA using an appropriate indicator (murexide, bromopyrogallol red). 

The ability of metal ions to form complexes with formazans is utilized to determine these ions either directly (for low valent reducing ions) or indirectly in the presence of a reducing agent. Among others, molybdenum(VI) and vanadium(V) have been determined using this method.442,443 Indirect methods have been reported for the analyses of substances that do not reduce tetrazolium salts. Examples include arsenic in nickel ores436 and traces of selenium.437 A method for the extraction and analysis of a number of metal ternary ion association complexes has been described.444 - 448... 

However, when the reductions were carried out with lithium and a catalytic amount of naphthalene as an electron carrier, far different results were obtained(36-39, 43-48). Using this approach a highly reactive form of finely divided nickel resulted. It should be pointed out that with the electron carrier approach the reductions can be conveniently monitored, for when the reductions are complete the solutions turn green from the buildup of lithium naphthalide. It was determined that 2.2 to 2.3 equivalents of lithium were required to reach complete reduction of Ni(+2) salts. It is also significant to point out that ESCA studies on the nickel powders produced from reductions using 2.0 equivalents of potassium showed considerable amounts of Ni(+2) on the metal surface. In contrast, little Ni(+2) was observed on the surface of the nickel powders generated by reductions using 2.3 equivalents of lithium. While it is only speculation, our interpretation of these results is that the absorption of the Ni(+2) ions on the nickel surface in effect raised the work function of the nickel and rendered it ineffective towards oxidative addition reactions. An alternative explanation is that the Ni(+2) ions were simply adsorbed on the active sites of the nickel surface. 

For example, EDTA can be used to determine the percentage of nickel present in a nickel salt by complexometric titration. EDTA is a hexadentate ligand that binds in a 1 1 ratio with most metal ions, such as Ni +, forming a stable octahedral complex as shown in the diagram. 

Elemental composition (for anhydrous NiCb) Ni 45.30%, Cl 54.70% Percent composition of NiCl2 6H20 Ni 24.69%, Cl 29.83%, H2O 45.48%. Nickel may be analyzed in an aqueous solution of salt by various instrumental techniques (See Nickel). Chloride ion in the aqueous solution may be determined by titration with silver nitrate using potassium chromate indicator or preferably by ion-chromatography. The solutions must be appropriately diluted for all analyses. 

CO2 molecule, or Mg + and CO2 play the role of oxide acceptor to form water, carbonate, and MgC03, respectively [38]. The reactions of the iron carboxylate with these Lewis acids are thought to be fast and not rate determining. For the cobalt and nickel macrocyclic catalysts, CO2 is the ultimate oxide acceptor with formation of bicarbonate salts in addition to CO, but it is not clear what the precise pathway is for decomposition of the carboxylate to CO [33]. The influence of alkali metal ions on CO2 binding for these complexes was discussed earlier [15]. It appears the interactions between bound CO2 and these ions are fast and reversible, and one would presume that reactions between protons and bound CO2 are rapid as well. 

The concentrations of magnesium, calcium, and nickel(II) ions in an aqueous solution are 0.0010 mol-L (a) In what order do they precipitate when a KOH solution is added (b) Determine the pH at which each salt precipitates. 

I. Narin, M. Soylak, Enrichment and determinations of nickel (II), cadmium(II), copper(II), cobalt(II), and lead(II) ions in natural waters, table salts, tea and urine samples as pyrrolydine dithiocarbamate chelates by membrane filtration-flame atomic absorption spectrometry combination, Anal. Chim. Acta, 493 (2003), 205-212. 

The condensation of 2V,A -bis(3-aminopropyl)ethylenediamine (7V,A -ethylene-bis[l,3-propanediamine]) as its acid salt with 2,3-butanedione (biacetyl) in the presence of cobalt(II) or nickel(II) acetate gives complexes of 2,S-Mej [14] - 1,3-diene-l,4,8,11-N4 containing one a-diimine linkage. Experiments have shown that the presence of H ion determines whether or not a macrocyclic complex forms and that, in the presence of H, the time at which the metal acetate is added to the reaction mixture influences the yield of the complex. Unlike the reaction between biacetyl and 1,3-propanediamine to form 2,3,9,10-Me4[14]-1,3,8,10-tetraene-l,4,8,11-N4 (Sec. 4), the condensation of biacetyl withTVA -bis(3-aminopropyl)ethylenediamine is particularly sensitive to excess acetate so that the procedures given use the optimized conditions. 

USE Forms a complex compound with ferrous ions which is used under the name of Terrain as an indicator in oxidation reduction systems, eg., titration of ferrous salts. Also used in determination of nickel, ruthenium, silver and other metals. 

A number of metal salts have been found to induce delayed hypersensitivity, mainly of the contact type, in humans or in laboratory animals. Sensitivity to ions of chromium, mercury, platinum, nickel, beryllium, and others seem well established and Table 2 shows some recent findings. The best studied metal sensitizers are the chromium salts, since chromium eczema due to cement is the most important occupational dermatosis (Polak et al. 1973). Hexavalent chromium, in the form of potassium dichromate, is a better sensitizer than trivalent chromium. This seems related to the much better skin penetrating capacity of the dichromate, since numerous studies have shown that trivalent chromium compounds as opposed to hexavalent salt are the actual sensitizers (Polak et al. 1973). The same authors conclude that chromium is probably a component of the determinants formed with autologous carriers and does not produce autoantigens without further participation of the metal ion. In particular, oxidation reactions as generators of determinants seem inoperative in chromium hypersensitivity, since other strong oxidizers like... 

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