Studies in bivalent chromium salts

Summary It has been shown that methylene blue, indigo carmine, neutral red, methyl red and phenosafranine serve as excellent internal indicators for the titration of ferric solution against chromous sulphate. It has been further demonstrated that in the presence of a large concentration of hydrochloric acid cupric salts are reduced quantitatively to the cuprous state. The latter titration can also be carried out with the help of visual indicators. The strengths of the chromous solutions calculated from titrations with ferric and cupric salts are in agreement within experimental error (±0.5%).The authors' thanks are due to Dr. R. N. Singh, Professor of Chemistry, B. R. College, Agra, for providing laboratory facility and encouragement.     

Studies in bivalent chromium salts

Summary A comparative study of reduction of triphenylmethane (rhodamine, rosaniline, methyl violet and aniline blue), indigoid (isatine) and quinoneimine (safranine) dyes with chromous sulphate and titanous chloride has been made and it has been shown that all these dye-stuffs can be successfully titrated against chromous sulphate. It thus provides an alternative method for the estimation of the dyes belonging to the various groups.

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Zusammenfassung Es wurde eine vergleichende Untersuchung über die Reduktion von Triphenylmethan-, Indigoid- und Chinoniminfarbstoffen mit Chrom(II)sulfat sowie Titan(III)-chlorid vorgenommen. Zur volumetrischen Bestimmung wird die Titration mit Chrom(II)-sulfatlösung empfohlen. Folgende Farbstoffe der einzelnen Gruppen wurden untersucht: Rhodamin, Rosanilin, Methylviolett, Anilinblau, Isatin, Safranin.

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Part IX: Tandon, J. P., and R. C. Mehrotra: Z. analyt. Chem. 187, 410 (1962).

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Thanks are due to Dr. R. C. Mehrotra, Professor and Head of the Department of Chemistry, for his keen interest in the work.     

Studies in bivalent chromium salts

Summary It has been demonstrated that colourless leuco-methylene blue is oxidised back quantitatively to the original dyestuff, by various oxidising agents. The methods for the estimation of potassium chromate, potassium persulphate, potassium periodate, ferric iron, sodium and hydrogen perioxide have been worked out by estimating the oxidised leuco-dye with chromous sulphate.The authors express their gratitude to the college authorities for providing the necessary facilities for work.Part IV: cf. Z. analyt. Chem. 159, 422 (1958).     

Studies in bivalent chromium salts

Summary The accuracy of the proposed visual technique of standardising chromous sulphate solution has been compared with the potentiometric method and it has been shown that there lies a fair agreement between the titre values obtained visually as well as potentiometrically. Both calomel and glass electrodes together with platinum electrode have been employed with equal facility in the present series of investigations. The use of glass electrode in place of saturated calomel electrode makes the measurements even more simpler and prevents the least possible contamination of chromous solution with mercurous salt. The simplicity as well as accuracy of the visual technique can thus be expected to increase the utility and applicability of chromous salts to a very great extent.

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Zusammenfassung Die Einstellung von Chrom(II)-lösungen wurde visuell und potentiometrisch durchgeführt. Es wird gezeigt, daß beide Methoden gut übereinstimmende Ergebnisse liefern. Sowohl die Kalomel- als auch die Glaselektrode wurden zusammen mit der Platinelektrode mit gleich, gutem Erfolg verwendet. Die Anwendung einer Glaselektrode an Stelle der ges. Kalomelelektrode macht jedoch die Messungen noch einfacher und verhindert auch die geringste Verunreinigung der Chrom(II)-lösung mit Quecksilbersalz. Die Einfachheit und Genauigkeit der visuellen Methode kann dazu beitragen, die Anwendbarkeit der Chrom(II)-salze erheblich zu erweitern.

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Part. VIII: Tandon, J. P.: Z. analyt. Chem. 167, 184 (1959).     

Studies in bivalent chromium salts

Summary It has been shown that chromous solution can be standardised with the help of potassium dichromate, sulphatocerate, potassium iodate, bromate and periodate solutions. N-phenylanthranilic acid, ferroin and diphenylbenzidine serve as reversible indicators for the titrations of potassium dichromate and ceric sulphate against chromous solution.The authors are indebted to Dr. R. N. Singh, Professor of Chemistry, B. R. College, Agra, for his kind encouragement and for providing laboratory facilities.Part II: See Z. anal. Chem. 158, 189 (1957).     

Studies in bivalent chromium salts

Summary As shown in the above investigations, chromous sulphate can be used for the quantitative reduction of compounds containing nitro, nitroso, quinoid, and azo groups. In the case of the first three, the estimations can be carried out by either of the two methods, direct titration by using neutral red, phenosafranine orp-ethoxychrysoidine as internal indicators, or by adding excess of chromous sulphate and titrating the excess with ferric solution, using thiocyanate as indicator. The comparative study of reduction of azodyes shows that the dyes can be estimated quantitatively with chromous sulphate as well. It is also possible to estimate the carbohydrates, since the unused copper sulphate can be directly titrated against chromous sulphate in presence of neutral red or phenosafranine as indicator. The results are fairly satisfactory and within experimental error (± 0.9°/0).The author is highly indebted to Dr. R. C. Mehrotra, Professor of Chemistry, Gorakhpur University, for his helpful suggestions and keen interest in the work.Part VII: See. Z. analyt. Chem. 164, 314 (1958).     

Studies in bivalent chromium salts

Summary It has been shown in these investigations that the titrations of methylene blue, indigo, crystal violet, eosin, malachite green, magenta and orange G can be carried out successfully with chromous sulphate solution. Comparative results with titanous chloride and chromous sulphate indicate a fair degree of agreement. However, the reduction is found to be more facile with chromous sulphate.Part I: See Z. analyt. Chem. 158, 20 (1957).The authors' thanks are due to Dr. R. N. Singh, Professor of Chemistry, B. R. College, Agra, for providing laboratory facility and encouragement.     

Studies in bivalent chromium salts

Summary As shown above, the estimations of potassium persulphate, hydrogen peroxide and dissolved oxygen in water, can be carried out with the help of chromous sulphate, by either of the two methods: (i) adding excess of chromous sulphate and titrating the excess with ferric solution using thiocyanate as indicator; (ii) adding to an excess of ferrous solution and titrating the ferric iron produced with chromous sulphate, using neutral red or thiocyanate as indicator. The results obtained by the above two methods are fairly satisfactory.Part III: cf. Z. analyt. Chem. 159, 5 (1958).The authors' thanks are due to the College authorities for providing the necessary facilities for work.     

Studies in bivalent chromium salts

Summary The above estimations show that stannous chloride and uranyl acetate can be estimated with the help of chromous sulphate. In the case of tin, excess of ferric iron is added and its excess found by titration with chromous sulphate, using neutral red or phenosafranine as indicator. In the case of uranyl acetate chromous salt titration, the above two indicators work satisfactorily in the absence of excess of sulphuric acid, whereas methyl red and p-ethoxycrysodine give good end points even in the presence of excess acid. In the alternative procedure for estimation of uranium, chromous sulphate serves the purpose of a Jone's reductor.Ammonium metavanadate solution can be titrated directly against chromous sulphate. N-phenylanthranilic acid, diphenylamine, diphenylbenzidine and diphenylamine sulphonic acid serve satisfactorily as internal indicators for the VO_3– to VO²⁺ change. It has been shown that ferric and cupric salts do not interfere in the above titrations. Mixtures of vanadate and dichromate or vanadate and ceric sulphate can also be titrated in the same manner using the same indicators.Part VI: cf. Z. analyt. Chem. 162, 33 (1958).     

Nitrogen dioxide multiphase chemistry: uptake kinetics on aqueous solutions containing phenolic compounds

The uptake coefficients of NO2 on aqueous solutions containing guaiacol, syringol and catechol were determined over the pH range from 1 to 13 using the wetted wall flowtube technique. The measured uptake coefficients were used to determine the rate coefficients for the reaction of the physically dissolved NO2 with the neutral and deprotonated forms of phenolic compounds listed above. These organic compounds are ubiquitous not only in biomass burning plumes but also in soils, where they form part of the building blocks of humic acids. The NO2 uptake kinetics on solutions containing guaiacol, syringol or catechol were observed to be strongly pH dependent with uptake coefficients increasing from below 10(-7), under acidic conditions, to more than 10(-5) at pH values above 10. This behaviour illustrates the difference of reactivity between the neutral phenolic species and the phenoxide ions. The corresponding second order rate coefficients were typically observed to increase from 10(5) M(-1) s(-1) for the neutral compounds to a minimum of 10(8) M(-1) s(-1) for the phenoxide ions.     

The kinetics of radical reactions in the radiolysis of aqueous solutions of organic nitro compounds

Pulsed radiolysis and computer simulation of gamma radiolytic decomposition of organic nitrates in aqueous solutions were performed to determine the rate constants for reactions with the participation of intermediates determining the mechanism of the process. 2,4,6-Trinitrotoluene, 2,4-dinitrotoluene, and cyclic nitramine, cyclotrimethylene-trinitramine, were used as substrates. The bimolecular rate constants for the reactions of hydrated electrons (e _aq ^? ) and hydroxyl radicals (^?OH) with the substrates and constants for the recombination of electron adducts and carbon-centered radicals (the products of the detachment of the H atom from the nitro compound molecule by the OH radical) were determined by direct measurements with the use of high-speed spectrophotometry. Computer simulation of the reaction scheme was used to estimate the rate constant for significant reactions, monomolecular forward and back reactions of electron adducts and electron transfer to molecular oxygen, and refine the rate constant for the reaction of e _aq ^? with tert-butanol.     

Enhanced copper surface protection in aqueous solutions containing short-chain alkanoic acid potassium salts

The ability of dissolved potassium monocarboxylate salts to produce surface passivation and to inhibit aqueous corrosion of copper was studied. The electrochemical measurements indicate that the inhibiting efficiency of these compounds, with a general formula Cn-1H2n-1COOK or CnK (n=3...12), is dependent on the hydrocarbon chain length. The inhibiting efficiency was higher for a longer hydrocarbon chain of n-alkanoic acid. The degree of copper protection was found to increase with an increase in n-alkanoic acid potassium salt concentration; the optimum concentration of potassium dodecanoate (C12K) in sulfate solutions was found to be 0.07 M. The protective layers formed at the copper surface subsequent to exposure in various n-alkanoic acid potassium salt solutions were characterized by contact angle measurements, electrochemical impedance spectroscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared reflection spectroscopy. Pronounced copper protection was attributed to the growth of a protective film on the copper surface, containing both copper oxides and copper carboxylate compounds. It is suggested that the organic molecules enhance copper protection by covering copper oxides with a thin and dense organic layer, which prevents water molecules or aggressive anions from interacting with the copper surface.     

Kinetics and mechanism of diethanolamine degradation in aqueous solutions containing carbon dioxide

The problem of diethanolamine (DEA) degradation in gas-treating processes was quantified through a detailed kinetic study. This reaction was found to be catalyzed by CO₂, and degradation occurs in a successive manner to 3-(2-hydroxyethyl)oxazolidone-2, to N,N,N′-tris(2-hydroxyethyl)ethylenediamine and then to N,N′-bis(2-hydroxyethyl)piperazine. A reaction mechanism consistent with these observations was proposed and tested through kinetic analyses. A satisfactory kinetic model which can be of practical use was derived.     

Densities of aqueous solutions containing model compounds of amino acids and ionic salts at T = 298.15 K

Densities of amino acids in aqueous and in aqueous electrolyte solutions have been measured by a high precision vibrating tube digital densitometer at T = 298.15 K under atmospheric pressure. The investigated systems contained amino acids of zwitterionic glycine peptides: glycine (Gly), diglycine (Gly₂), triglycine (Gly₃), and tetraglycine (Gly₄) and cyclic glycylglycine (c(GG)) with electrolytes of potassium chloride (KCl), potassium bromide (KBr) and potassium acetate (KAc). In this series of measurements, the aqueous samples were prepared with various concentrations of the amino acids, up to saturated conditions, and over salt concentrations from 1 to 4 M. The density increments resulting from the addition of the different model compounds of amino acids and the ionic salts were investigated, respectively. An empirical linear combination equation with an augmented term to account the interactions between amino acid and ionic salt was used to quantitatively correlate the experimental densities over the entire concentration ranges.     

The kinetics and mechanism of mechanochemical dissolution of chromium in nickel

The regularities of the formation of a solid solution in a Ni-Cr(20 at %) system are studied using X-ray diffraction, optical microscopy, and particle-size distribution analysis within the framework of an energetical approach to the analysis of the kinetics of mechanochemical synthesis. It is established that the curves of the consumption of chromium atoms and the formation of the reaction product (a solid solution of chromium in nickel) coincide with each other. The rate-limiting step of the reaction is the formation of a contact surface between chromium and nickel, while the “stirring” of chromium atoms in nickel matrix has a very high rate. The rate of the formation of the contact surface in the mixture of brittle chromium and plastic nickel is determined by the rate of chromium particle disintegration. To a conversion of about 60%, the reaction kinetics is described by a quadratic dependence on the dose (D) of the mechanical treatment (N ～ D ₂).     

Coordination compounds of chromium(III) with different complexones and citric acid in aqueous solutions

A spectrophotometric study of heteroligand chromium(III) complexes with iminodiacetic (H₂Ida), N-methyliminodiacetic (H₂Mida), N-(-hydroxyethyl)iminodiacetic (H₂Heida), nitrilotriacetic (H₃Nta), ethylenediaminetetraacetic (H₄Edta), and citric acids (H₄Cit) showed that complexation in ternary systems depends on the concentrations of the reagents and the pH of the medium. The resulting complexes were [Cr(HIda)(H₂Cit)], [Cr(HMida)(H₂Cit)], [Cr(HHeida)(H₂Cit)], [Cr(HHeida)(HCit)]^–, [Cr(HNta)(H₂Cit)]^–, [Cr(HNta)(HCit)]^2–, [Cr(Nta)(HCit)]^3–, [Cr(HEdta)(HCit)]^3–, and [Cr(Edta)(HCit)]^4–. The logarithms of their stability constants are 41.97 ± 0.47, 43.54 ± 0.62, 42.32 ± 0.62, 36.34 ± 0.26, 43.70 ± 0.25, 39.75 ± 0.45, 32.93 ± 1.56, 46.46 ± 0.80, and 41.71 ± 0.81 , respectively (I = 0.1 (NaClO ₄)).Translated from Koordinatsionnaya Khimiya, Vol. 30, No. 12, 2004, pp. 946–950.Original Russian Text Copyright © 2004 by Kornev, Mikryukova.