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.     

Nile blue and brilliant cresyl blue as redox indicators in iron(II) titrations

Nile Blue and Brilliant Cresyl Blue, two compounds related to diaminophenoxazine, have been studied as indicators in titrations of iron(II) with cerium(IV)(in hydrochloric, sulphuric and perchloric acid media), dichromate, vanadate and permanganate. They are particularly suited for titrations in a fairly concentrated sulphuric acid medium and for titrations with dilute solutions. A probable indicator mechanism is suggested.     

Some observations on the redox behaviour of N-phenylanthranilic acid indicator in iron(II) titrations

The optimum conditions for the successful use of N-phenylanthranilic acid as indicator in titrations of iron(II) with dichromate, cerium(IV) sulphate and vanadate have been established. The influence of iron(III) on the indicator action, and the nature of a green compound formed from the indicator in iron(II) titrations, have been investigated spectrophotometrically.     

Enhanced capacity of chitosan for transition-metal ions in sulphate-sulphuric acid solutions

Batch measurements have shown that the collection yields of chitosan for chromium(III), iron(III), nickel, copper(II), zinc and mercury(II) from sulphuric acid solutions are higher when the solutions contain ammonium sulphate, or when chitosan conditioned in ammonium sulphate is used, particularly at pH 3.0 and 5.0. The contrary is verified for the oxy-anions vanadate, chromate and molybdate. Manganese is never collected. At pH 1.0 no collection occurs. A procedure for recycling chromatographic columns includes fixation of Cu or Ni from a sulphate solution at pH 3-5 on sulphate-conditioned chitosan, and elution with 0.1M sulphuric acid/0.1M ammonium sulphate at pH 1.0; the presence of sulphate in the eluent obviates the detrimental effect of sulphuric acid on the next cycle. Sulphate is the favoured counter-ion of the chelated cations and its action produces shorter chromatographic bands. The interaction of sulphate with chitosan is discussed in terms of crystallinity and steric distribution of the protonated amino-groups in the polymer. Data on the new diethylaminohydroxypropylcellulose are included.     

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.     

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).     

Titration of cerium (IV) sulphate with sodium oxalate at the room temperature using ferroin as internal indicator

Summary A method has been developed for the titration of cerium(IV) sulphate with sodium oxalate at the room temperature, using ferroin as internal indicator. A new principle has been utilised for facilitating the indicator action at the equivalence point. This involves the use of a photochemical reaction between the oxalate and iron(III) which is deliberately added to the mixture containing cerium(IV) sulphate and ferriin. When the mixture is titrated with the sodium oxalate solution under exposure to the light from a Philips Repro lamp, the addition of a very slight excess of sodium oxalate solution, after all the cerium(IV) sulphate has reacted, produces a vivid red colour. The slight excess of sodium oxalate added reacts with the iron(III) salt photochemically producing a trace of iron(II) salt which reduces the ferriin to the red ferroin. In titrations with 0.1 and 0.05 N solutions of sodium oxalate, the error is negligible. In titrations with sodium oxalate solution of lower strengths, the error amounts to 0.02 ml of 0.01 N oxalate which has to be subtracted from the titre.     

Simple conditions for the use of ferroin indicator in cerimetric titrations of antimony(III) alone and in mixtures with arsenic(III)

The titration of antimony(III) with cerium(V) sulphate in the presence of ferroin indicator at room temperature is entirely satisfactory in media consisting of 50% ($\text{v}\text{v}$) acetic acid and 1–3 M hydrochloric acid. In the absence of acetic acid, ferroin reacts with the antimony(V) formed in the very early stages, to give a sparingly soluble red complex, which remains in suspension and resists oxidation by cerium(IV). This titration provides a rational method for sequential visual titrations of antimony(III) and arsenic(III). The composition of the ferroin-antimony(V) complex is discussed. Titrations of antimony(III) in 0.5–1 M sulphuric acid medium do not require acetic acid but need iodine monochloride catalyst.     

Catalytic end-point indication in redox titrations

The applicability of catalytic end-point indication to redox titrations is demonstrated by the determination of 3–30 μmol of ascorbic acid (in 22.5 ml of solution) with standard dichromate solution; the chromium(VI)-catalyzed oxidation of o-dianisidine with hydrogen peroxide serves as indicator reaction. Oxidizing substances, such as vanadium(V), thallium(III) or cerium(IV) can be determined by addition of excess of ascorbic acid and back-titration.     

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.     

N-oxides of 4-(5-nonyl)pyridine and trioctylamine as extractants for cerium(IV) and its separation from thorium(IV)

Trace level cerium has been oxidized to the quadrivalent state with potassium dichromate and shown to be preferentially extracted from very dilute mineral acid solutions and also from moderate nitric acid media by 0.1M solutions of 4-(5-nonyl)pyridine oxide and trioctylamine oxide dissolved in xylene. The dependence of extraction on the type of N-oxide, acid concentration and the N-oxide concentration has been investigated. The influence of the concentration of salting-out agents is described. Separation factors for a number of metal ions relative to cerium(IV) are reported for 0.1 M 4-(5-nonyl)pyridine oxide/xylene-0.1M sulphuric acid system. The ratio of the D for Ce(IV) to that of Ce(III) is greater than 10⁵, and the D for Ce(IV) is much greater than that for thorium(IV). Separation of cerium(IV) from thorium has been achieved from 0.1M sulphuric acid solutions using 0.1M 4-(5-nonyl)pyridine oxide/xylene as an extractant.     

Rapid methods for the determination of iron(II) and vanadium (IV) in mixtures

Summary Rapid and accurate methods have now been developed for the titrimetric determination of iron(II) and vanadium(IV) in mixtures, using potassium permanganate or cerium(IV) sulphate. Chromium(III) does not interfere with these determinations.The procedures will be found to be much easier than the existing procedures because (1) the titrations can be carried out at the room temperature with a visual end point and (2) only one reagent is used for the determination of iron(II) and iron(II) plus vanadium(IV).

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Zusammenfassung Es werden Vorschriften gegeben zur schnellen und genauen titrimetrischen Bestimmung von Eisen(II) und Vanadium(IV) in Gemischen mit Hilfe von Kaliumpermanganat- oderCer(IV)-sulfatlösung. Chrom(III) stört die Bestimmungen nicht. Die beschriebenen Verfahren haben gegenüber den bisher üblichen Methoden den Vorteil, daß die Titration bei Zimmertemperatur mit visueller Endpunktsbestimmung durchgeführt werden kann und daß nur ein Reagens zur Bestimmung von Eisen(II) sowie von Eisen(II) + Vanadium(IV) gebraucht wird.

     

The use of the silver reductor in bromide solutions

The reduction of bromide solutions of various metals with the silver (walden) reductor is described. Iron(III) is quantitatively reduced to iron(II) in 0.1–4 M HBr; similarly, copper(II) is reduced to copper(I) in > 1.5 M HBr, and vanadium.(V) to vanadium(IV) and uranium(VI) to uranium(IV) in > 0.3 M HBr. Tin(IV) is only partly reduced to tin(II) below 6M HBr. Reduction of molybdenum(VI) to molybdenum(V) requires heating, whereas reduction of tungsten(VI) is never quantitative. Suitable conditions for the titrations are described.     

Integrated scheme for micro-determination of iron oxidation states in silicates and refractory minerals

A mirco-analytical scheme incorporating four methods is described for the determination of iron(II) and iron(III) in both hydrofluoric acid-soluble and refractory minerals. The acid-soluble minerals are analyzed for FeO by direct constant-current potentiometric titration with potassium dichromate, and a separate solution is titrated similarly after Zn/Hg reduction to give total iron. The micro-determination of FeO in chromite and other refractory minerals involves dissolution in a cerium(IV)/phosphoric acid mixture and constant-current potentiometric and indirect titration of excess of cerium(IV) (phosphatocerate) with iron(II). Lithium tetraborate micro-fusion is required for measurement of total iron by atomic absorption spectrometry or spectrophotmetry. The average relative standard deviation ranged between 0.73 and 1.08%.     

Manganese(II) catalysed oxidation of glycerol by cerium(IV) in aqueous sulphuric acid medium: a kinetic and mechanistic study

The manganese(II) catalysed oxidation of glycerol by cerium(IV) in aqueous sulphuric acid has been studied spectrophotometrically at 25 °C and I = 1.60 mol dm⁻³. Stoichiometry analysis shows that one mole of glycerol reacts with two moles of cerium(IV) to give cerium(III) and glycolic aldehyde. The reaction is first order in both cerium(IV) and manganese(II), and the order with respect to glycerol concentration varies from first to zero order as the glycerol concentration increases. Increase in sulphuric acid concentration, added sulphate and bisulphate all decrease the rate. Added cerium(III) retards the rate of reaction, whereas glycolic aldehyde had no effect. The active species of oxidant and catalyst are Ce(SO₄)₂ and [Mn(H₂O)₄]²⁺. A mechanism is proposed, and the reaction constants and activation parameters have been determined.     

A new oxidimetric reagent: potassium dichromate in a strong phosphoric acid medium--VII. Photometric titration of vanadium(IV) and of cerium(III) alone and in mixtures with iroN(II)

Vanadium(IV) can be accurately titrated with potassium dichromate in media containing phosphoric acid of 3-12M concentration: the change in absorption of vanadium(IV) is followed in the region 660 mmicro using a red filter. It is more convenient to carry out the titration in 3M phosphoric acid because at higher concentrations chloride, nitrate, cerium(III) and manganese(II) may interfere. Photoelcetric titration is more convenient than potentiometric because the former can be made in a 3M phosphoric acid medium, whereas the latter is possible only in 12M phosphoric acid. The simultaneous differential photometric titration of iron(II) and vanadium(IV) is also possible. Conditions have been found for the photometric titration of cerium(III) and of cerium(III) plus iron(II). The titration is carried out (at 450 mmicro or with a blue filter) in about 10.5M phosphoric acid. Application of the method to a cerium mineral is considered.     

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).     

Mechanistic study of cerium(IV) oxidation of antimony(III) in aqueous sulphuric acid in the presence of micro amounts of manganese(II) by stopped flow technique

The oxidation of antimony(III) by cerium(IV) has been studied spectrometrically (stopped flow technique) in aqueous sulphuric acid medium. A minute amount of manganese(II) (10⁻⁵ mol dm⁻³) is sufficient to enhance the slow reaction between antimony(III) and cerium(IV). The stoichiometry is 1:2, i.e. one mole of antimony(III) requires two moles of cerium(IV). The reaction is first order in both cerium(IV) and manganese(II) concentrations. The order with respect to antimony(III) concentration is less than unity (ca 0.3). Increase in sulphuric acid concentration decreases the reaction rate. The added sulphate and bisulphate decreases the rate of reaction. The added products cerium(III) and antimony(V) did not have any significant effect on the reaction rate. The active species of oxidant, substrate and catalyst are Ce(SO₄)₂, [Sb(OH)(HSO₄)]⁺ and [Mn(H₂O)₄]²⁺, respectively. The activation parameters were determined with respect to the slow step. Possible mechanisms are proposed and reaction constants involved have been determined.     

Oxalate interference in cerate oxidimetry

Summary A study of the kinetics of the cerium(IV)-oxalate reaction provides evidence in strong support of a simultaneous reaction model to account for errors found in the oxidation-reduction titrations of iron(II) with cerium(IV) in the presence of oxalic acid.

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Zusammenfassung Um die bei der Redoxtitration von Eisen(II) mit Cer(IV) in Gegenwart von Oxalsäure auftretenden Fehler aufzuklären, wurde eine kinetische Untersuchung vorgenommen. Die Ergebnisse der Messungen gaben Grund zu der Annahme, daß eine gleichzeitig verlaufende Oxydation der Oxalsäure vorhegt.

     

Amperometric ascorbimetric determination of cerium(IV) and Iron(III) with two polarized electrodes

Summary Amperometric ascorbimetric determinations of cerium(IV) and ferric iron have been carried out at 50°C with two polarized electrodes at 200 and 100 mV respectively. The results obtained are fairly accurate and precise within ±1.0 per cent. A simple method for successive determination of cerium and iron has been developed; and conditions for such estimations have been established. At an acidity of 2.5 M with respect to sulphuric acid, it is possible to ward off the reduction of ferric iron and thereby cerium(IV) is successfully titrated with ascorbic acid in this medium. After completion of the reaction and then lowering the acid concentration to p_H 1.5 with aid of ammonium hydroxide, Fe^III is titrated with standard ascorbic acid yielding good results.