Cobalt/ions/salts determination

Discussion. An excellent method for the colorimetric determination of minute amounts of cobalt is based upon the soluble red complex salt formed when cobalt ions react with an aqueous solution of nitroso-R-salt (sodium 1-nitroso-2-hydroxynaphthalene-3,6-disulphonate). Three moles of the reagent combine with 1 mole of cobalt. 

In their first publication on this subject,59 Werner and Miolati showed that the molecular conductances (fx) of coordination compounds decreased as successive molecules of ammonia were replaced by acid residues (negative groups or anions). For cobalt(III) salts, they found that fi for luteo salts (hexaammines) > fi for purpureo salts (acidopentaammines) > /t for praseo salts (di-acidotetraammines). The conductance fell almost to zero for the triacidotriammine Co(N02)3-(NH3)3 and then rose again for tetracidodiammines, in which the complex behaved as an anion. By such measurements, Werner and Miolati determined the number of ions in complexes of cobalt(III), platinum(II) and platinum(IV). They not only found support for the coordination theory, but they also elucidated the process of dissociation of salts in aqueous solution and followed the progress of aquations. 

The association of four clathrochelates (Table 29) with perchlorate, sulphate, and malonate ions was detected from their CD spectra [118], The A-[Co(diNOsar)]2+ and A-[Co(NOMEsar)]3+ cations formed 1 1 associates with perchlorate cations in water. The association constant of the former cation with perchlorate ion was determined to be 0.54. The association constant for the perchlorate salt of the latter cation was not obtained, but it is expected to be lower than that for the A-[Co(diNOsar)]2+ cation. The 1 1 association constants for clathrochelate cobalt(III) cations with sulfate and malonate anions were determined from the CD spectra using a wavelength at which the CD intensity was not affected by the perchlorate anion concentration. The constants obtained are listed in... 

Knowing and understanding standard reduction potentials, E°, also helps determine whether a particular oxidation state will be stable and appropriate oxidants and reductants to use in a synthetic scheme. In reviewing the cobalt complex syntheses in Chapters 2 and 6, for example, complex ions are formed by oxidizing cobalt(II) salts to the more stable +3 state. 

If sodium is more abimdant, a mixed complex is formed with the composition K2Na[Co(N02)6]- The two complexes are alike in appearance. This reaction was used in the classical inorganic analysis to isolate potassium from the other alkali metals. The precipitate was isolated and washed and a determination was then performed colorimetrically on the cobalt ion. In many cases the silver, zinc, or lead salt of hexanitritocobaltate was used as a reagent. 

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. 

For colorimetric or gravimetric determination l-nitroso-2-naphthol can be used. For chromatographic ion exchange (qv), cobalt is isolated as the nitroso-(R)-salt complex. The cyanate complex is used for photometric determination and the thiocyanate for colorimetry. A rapid chemical analysis of... 

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. 

Elemental composition Co 38.03%, 8 20.68%, O 41.29%. 8ohd cobalt(Il) suhate is brought to aqueous phase by acid digestion, appropriately diluted, and analyzed for cobalt by flame or furnace AA or ICP. It also may be determined in the solid crystalline form by x-ray methods. The suhate anion may be measured by dissolving an accurately measured small amount of salt in measured quantities of water and analyzing the solution by ion chromatography. 

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 electrical conductivity.—E. Klein10 showed that if there is a difference between the conductivity of a mixture of salts in soln. and the mean conductivities of the separate constituents, a double salt is probably formed. The molecular conductivity of a salt, and if possible of its components at different dilutions, has been employed to determine the number of component ions in a soln. it was used, for example, by A. Werner (1893-1901) with the cobalt, chromium, platinum, and other ammines.11 In moderately cone. soln. the double salts are but little ionized, and the difference between the conductivities of eq. soln. of potassium zinc chloride, ZnCl2.2KCl, and of the sum of the constituents amounts to nearly 36 per cent., a value which is greatly in excess of that whieh would be due to the mutual influence of salts with a common ion. Tables of the molecular conductivities of salts show that with very few exceptions, at a dilution of 1024 litres and 25°, most salts have conductivities approximating those indicated in Table XIX. 

Complex Explosives. These are formed by a combination of two or more compds or ions. Several cobalt chromium complexes were studied by Tomlinson (Ref) to determine their promise as initiators or ingredients of priming compositions. As a class, chromic salts appeared to be more sensitive to initiation more brisanr, and to possess greater initiating ability than cobaltic compds. The latter type of complexes, however,... 

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. 

State. When both iron environments contain only iron(II), the resulting salt is not colored (Prussian White). The oxidation state localization in PB has been studied extensively. Structures, electrochemical behavior (electrodes batteries), and uses in medicine (treatment of Cs and of thallium poisoning) of Prussian Blue are mentioned in a review of cyanide complexes. In cobalt-iron Prussian Blue analogues, NaxCo3,Fe(CN)6-zH20 electronic and spin states are controlled by temperature and the ligand field strength around the Co + ions, which in turn is determined by the Co Fe ratio. ... 

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