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 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 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.     

Analytical applications of the photochemical action of light: Determination of ferric iron by photochemical reduction in the presence of citric and mandelic acids

A new method has been developed for the determination of ferric sulphate through its photochemical reduction with citric and mandelic acids in sunlight. The method consists in irradiating with sunlight a measured volume of the ferric sulphate solution together with an excess of citric or mandelic acid in a quartz or pyrex glass beaker until reduction is complete. The ferrous salt formed is determined by titration with a standard solution of sodium vanadate in the presence of the proper concentration of sulphuric and phosphoric acids, employing diphenylbenzidine or diphenylamine sulphonate as internal indicators. The photoreduction is greatly retarded by sulphuric acid.     

Vanadametry Estimation of Thiosulphate

1.(a) We have found that sodium thiosulphate is quantitatively oxidized to tetrathionate in five minutes at room temperature (28°) by excess sodium vanadate in a medium containing sulphuric acid at 0.06N to 0.1N concentration and a little copper sulphate as catalyst. (b) Quantitative emulation of sodium thiosulphate to tetrathionate has also been achieved by the action of excess sodium vanadate during five minutes at room temperature in a medium containing 2.0N—8.0N acetic acid and a little copper salt as catalyst. Further oxidation to sulphate does not occur, even if the mixture is heated to boiling. (c) The excess of unreacted vanadate in 1(a) and 1(b) can be titrated with a standard solution of ferrous ammonium sulphate using diphenylbenzidine as indicator, after adding the requisite quantity of syrupy phosphoric acid. 2. On the other hand, sodium thiosulphate is easily and quantitatively oxidized to sulphate at room temperature, when. acted upon by excess sodium vanadate in a medium containing hydrochloric acid at an overall concentration of 5-6N and 1.0 ml of iodine monochloride as catalyst. The time required for reaction is ten minutes. The unreacted vanadate can be estimated by titration with a standard solution of ferrous ammonium sulphate, using N-phenylanthranilic acid as indicator or with diphenylbenzidine as indicator after suitably diluting and adding phosphoric acid.     

A new volumetric method for the determination of molybdenum(VI)

Summary A new volumetric method has been developed for the determination of molybdenum(VI). The method consists in the reduction of molybdenum(VI) by heating with a slight excess of hydrazine sulphate in 1 to 2 M hydrochloric acid medium for ten minutes on a water bath. The mixture is cooled and the molybdenum(V) obtained determined by titration with a standard solution of ceric sulphate at an overall acidity of 4 N hydrochloric acid, using diphenyl benzidine as indicator and adding 5 ml of syrupy phosphoric acid for 50 ml of the mixture. Alternately the molybdenum(V) can be titrated with a standard solution of ceric sulphate at an overall acidity of 3 N hydrochloric acid using ferroin as indicator and adding 5 ml of syrupy phosphoric acid for 50 ml of the titration mixture. The molybdenum(V) can also be titrated with a standard solution of sodium vanadate in 8 N sulphuric acid medium, using N-phenyl anthranilic acid as indicator. Alternately, the titration with sodium vanadate can be made with diphenyl benzidine as indicator in 4 N acid medium, adding 5 ml of syrupy phosphoric acid and 1 ml of 1.0 M oxalic acid to catalyse the indicator action. The method now proposed is much more convenient than the methods currently available. It is simple because it does not require any costly chemicals or complicated apparatus. Furthermore, it has the advantages of great rapidity and excellent precision.     

Volumetric estimation of uranium-part III, with ceric sulphate

Summary The use of diphenylamine, diphenylbenzidine, diphenylamine sulphonate and N-phenylanthranilic acid as inside indicators in the titration of uranium IV salt with ceric sulphate has been investigated in detail. Experimental conditions have been defined under which these indicators function efficiently.     

Sodium hypochlorite as volumetric reagent

Summary In presence of 5 N to 6 N hydrochloric acid, ferrous ethylenediamine sulphate was used as a reducing agent to determine indirectly potassium chlorate, potassium bromate, potassium metaperiodate, potassium dichromate, potassium ferricyanide, potassium permanganate, potassium persulphate, hydrogen peroxide, ceric sulphate and chloramine-T. An excess of ferrous ethylenediamine sulphate added to each of the substances in the acid medium was titrated with a standard solution of sodium hypochlorite. Iodine monochloride was used as catalyst and preoxidizer and chloroform was used as an indicator. Chloroform was coloured violet owing to the liberation of iodine during the titration and became very pale yellow at the end-point because of the formation of iodine monochloride.Part I: See Z. analyt. Chem. 160, 429 (1958).     

Analytical aspects of some organic acids

Summary Back titrimetric procedures for the estimation of aluminium, zirconium, and thorium have been developed, which involved the adjustment of the concentration of the metallic salts, concentration of EDTA,ph, and temperature, addition of indicator solution (namely, 2-hydroxy3-naphthoic acid and back titration with standard 0.1 M ferric chloride solution. This method is based on the fact that the excess EDTA, which is added to the metal solutions may be back titrated with iron(III), which forms a highly coloured complex with the indicator, when present in slight excess. Quantities of aluminium, zirconium and thorium as small as 10.8, 4.6, 11.6 mg respectively, can be back titrated with in experimental error, when present in a volume of 100 ml.Part IV: See Z. analyt. Chem. 172, 356 (1960).     

Determination of iodide with potassium dichromate and sodium vanadate in the presence of acetone

The determination of iodide with potassium dichromate and sodium vanadate in 6-8M phosphoric acid medium by potentiometric or visual titration is described. Ferroin and barium diphenylamine sulphonate (BDAS) are used as the indicators in the visual titration with potassium dichromate and sodium vanadate respectively. Acetone is used to stabilize the iodonium ions liberated, in the visual titration. Iodide can also be determined with sodium vanadate in 2-4M sulphuric acid medium with BDAS as indicator in the presence of oxalic acid as catalyst and acetone to stabilize the liberated iodine cations. The visual procedures are applied for the determination of iodide in tincture of iodine. The formal potentials of the iodine/iodide couple in various phosphoric acid media are reported.     

Mercurous nitrate as a reductimetric reagent : The titration of various oxidising agents

It has been found that when excess of a solution containing ferrous ions is added to certain oxidising agents, the equivalent amount of ferric iron produced can be titrated accurately with mercurous nitrate, enabling the original oxidant to be assessed. Oxidising agents which have been determined in this way are potassium permanganate, potassium persulphate, ceric sulphate, sodium vanadate, potassium chlorate, hydrogen peroxide and potassium dichromate. The last substance provides a convenient primary standard for the standardisation of mercurous nitrate solutions.     

Titration of antimony(III) with cerium(IV) sulphate and diphenylamine and its derivatives as reversible indicators

Diphenylamine, barium diphenylamine sulphonate, N-phenylanthranilic acid and 2-nitrodiphenylamine have been investigated as reversible indicators for the titration of antimony(III) with cerium(IV) sulphate in 0.5–2 M sulphuric acid medium. Diphenylamine is the most satisfactory in titrations of antimony(III) in chloride-free solutions, e.g. of potassium antimonyl tartrate. Even low chloride concentrations affect the indicator action of N-phenyl-anthranilic acid or 2-nitrodiphenylamine, but diphenylamine is satisfactory in 1 M hydrochloric acid media. Iodine catalyst is necessary to accelerate the reduction of the oxidized indicator by antimony(III). The indicator colour change is vivid and the colour of the oxidized indicator is stable. Titrations of antimony(III) in mixtures with iron(II) and arsenic(III) are also considered.     

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 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.     

Quantitative Separation of Citric Acid From Trichloroacetic Acid on Plates Coated with Calcium Sulphate Containing Zinc Oxide

Abstract

Thin-layer chromatographic behaviour of ten acids on coating of calcium sulphate containing ammonium molybdate, aluminium oxide, calcium carbonate, copper sulphate, ferric chloride, magnesium sulphate, phthalic anhydride, titanium oxide, zinc oxide etc. has been studied. Quantitative separation of citric acid from trichloroacetic acids has been achieved on calcium sulphate containirig zinc oxide in ethyl acetate. Herbicide, trichloroacetic acid can be separated from plant growth regulators such as indole-3-acetic, β-naphthaleneacetic and β-naphthoxy acetic acids and from other organic acids.     

2-Nitrodiphenylamine as a versatile high-potential reversible oxidation-reduction indicator

The use of 2-nitrodiphenylamine as a reversible indicator has been investigated in the titration of iron(II) with cerium(IV) sulphate, potassium dichromate and sodium vanadate in sulphuric acid media. Accurate results can be obtained with cerium(IV) sulphate in 0.5–5.0 M acid, with potassium dichromate in 5.0–7.0 M acid, and with sodium vanadate in 5.0–7.5 M acid. With cerium(IV) sulphate the titrations are preferably conducted in 2.0 M sulphuric acid or in a 1.0 M. sulphuric acid-1.0 M pechloric acid medium. Tungstic acid, acetic acid, arsenic(III) and manganese(II) do not interfere. In titrations of iron(II) with dichromate and vanadate, the colour changes at the end-point are much more vivid with 2-nitrodiphenylamine than with ferroin.     

Nicotinic acid complexes with uranyl salts

Summary The potentially bidentate ligand, nicotinic acid, forms 2 : 1 complexes with uranyl chloride, sulphate, nitrate and acetate which have been characterized by i.r. spectral measurements down to 200 cm^–1 in the solid state. These studies indicate conclusively that nicotinic acid coordinates onlyvia its pyridine ring nitrogen in all cases. The uranyl chloride arid sulphate complexes are monomeric hexacoordinated structures, while the nitrate and acetate complexes are octacoordinate around uranium.     

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.     

Volumetric determination of small amounts of uranium : Chromous chloride as reducing agent

A volumetric method is proposed for the rapid determination of small amounts of uranium. The hexavalent uranium is reduced to the quadrivalent state by chromous chloride, the excess of which is destroyed by air oxidation. A low potential redox indicator is used to follow the reduction and air oxidation. Ferric sulphate is added to the solution and the resulting ferrous ion titrated with dichromate solution.     

A new method for “ferrous iron” and “excess oxygen” in rocks, minerals, and oxides

A new method is given whereby oxygen excess or deficiency in many minerals and oxides may be simply determined. The method depends on the stability in phosphoric acid-pyrophosphate mixtures of both Mn^III and Mn^II. The sample is dissolved in a phosphoric acid mixture containing excess Mn^II, with or without the addition of standard oxidant, and Mn^III remaining in solution or produced by reaction with the sample is titrated with ferrous ammonium sulphate, using barium diphenylamine sulphate as indicator. The method is useful in many cases where existing methods are inapplicable or unsatisfactory. Accurate results can be obtained using relatively small samples.