G. Gopala Rao

A new reductimetric reagent: ironII in a strong phosphoric acid medium—II: Titration of molybdenumVI with ironII at room temperature

Abstract The formal redox potential of the FeIII/FeII couple has been determined in media of varying phosphoric acid concentration, and found to decrease steeply with increasing phosphoric acid concentration. Above a certain concentration of phosphoric acid, the difference between the formal potentials of the UVI/UIV and FeIII/FeII couples becomes sufficiently great to enable ironII to reduce uraniumVI even at room temperature. This is the reversal of the normal redox reaction—oxidation of uraniumIV by ironIII. A careful study of the various factors involved has enabled us to develop a new reductimetric titration of uraniumVI with ironII in strong phosphoric acid medium (11.0 to 13.5M) at room temperature using either a potentiometric end-point or a visual end-point with methylene blue or thionine as an internal redox indicator. Because the new procedure enables the titration to be carried out at room temperature, it is more convenient than procedures involving titaniumIII and chromiumII which require temperatures ranging from 60 to 90°. The new procedure has a further advantage in that it can be used for the determination of uraniumVI even in the presence of ironIII and tungstenIV, using an electrometric end-point. Also, the new procedure does not require the elaborate precautions which are necessary for the preparation and storage of titaniumIII or chromiumII solutions.

A new oxidimetric reagent: potassium dichromate in a strong phosphoric acid medium—I: Titrimetr1c determination of manganeseII

Abstract A new method has been developed for the direct titrimetric determination of manganeseII, depending on its oxidation to manganeseIII with potassium dichromate at room temperature in a strong phosphoric acid medium using a potentiometric or photometric endpoint. Oxygen of the air does not interfere. The potentiometric method gives results to an accuracy within ± 0.3% for 20–150 mg of manganese/50 ml of titration solution; with the photometric method 5–17 mg of manganese/40 ml of titration solution can be determined with an error of 0.3–1.0% depending on the amount present. Potassium dichromate in 12.0M phosphoric acid has a formal redox potential of about 1.5 V and this reagent appears to have great possibilities in titrimetric analysis.

Oxidimetric determination of ascorbic acid with potassium hexacyanoferrate(III) in acid medium

Conditions have been developed for the titrimetric determination of ascorbic acid with hexacyanoferrate(III), with potentiometric and visual end-points, in sulphuric, hydrochloric or phosphoric acid media. Several organic substances likely to be present in plant tissues do not interfere.

Titrimetric determination of vanadium (IV) with potassium permanganate at the room temperature, using phosphoric acid as catalyst and ferroin as internal indicator

SummaryThe observation that the reaction between vanadium(IV) and potassium permanganate is catalyzed by ortho phosphoric acid at the room temperature has been utilized to develop a new procedure for the titrimetric determination of vanadium(IV). In the absence of chromium(III) and other coloured ions the end point can be detected making use of the colour of permanganate itself, and applying the necessary correction. This procedure cannot, however, be employed for titrations with 0.01 N potassium permanganate when the use of ferroin must be resorted to indicate the end point. The use of ferroin in macro titrations helps to eliminate the correction and the interference of coloured ions like chromium(III) up to a reasonable limit. Titrations without the use of the ferroin indicator can be carried out within a wider range of acidity viz. 0.1 N to 1.0 N.ZusammenfassungEin neues Verfahren zur titrimetrischen Bestimmung von Vanadium-(IV) wird auf den katalytischen Einfluß gegründet, den Orthophosphorsäure bei Zimmertemperatur auf die Reaktion zwischen VIV und KMnO4 ausübt. Bei Abwesenheit von CrIII und anderen gefärbten Ionen kann der Endpunkt durch die Eigenfarbe des Permanganats festgestellt werden, wobei eine Korrektur erforderlich ist. Für kleinere Vanadiumgehalte (Titration mit 0,01 n KMnO4-Lösung) wird die Verwendung von Ferroin als Indicator empfohlen, wobei die Notwendigkeit einer Korrektur sowie der Einfluß störender Ionen bis zu bestimmten Grenzen vermieden wird. Titrationen ohne Indicator können bei einem Säuregehalt von 0,1 n–1 n ausgeführt werden.

A new volumetric method for the estimation of uranium VI through photochemical reduction with alcohol

Summary1.A new volumetric method for the estimation of uranium VI has now been developed. The method consists in exposing the uranium VI solution in 1.0 to 3.0 N sulphuric acid solution with an excess of ethanol in a glass vessel to sunlight or the light from a Philips Repro lamp for 30 to 60 minutes. The uranium IV salt formed is estimated by titration with a standard solution of sodium vanadate.2.The photochemical reduction method now proposed is not subject to the disadvantages of reduction by Jones Reductor or the Silver Reductor. The reduction does not proceed to the uranium III state under any conditions of exposure. Moreover, the photochemical reduction is carried out easily and rapidly, without the need for any equipment or special precautions.3.Phosphate, arsenate, perchlorate, fluoride and citrate ions do not interfere in the proposed method. Chloride, bromide and iodide markedly retard the photo-reduction of uranium VI to uranium IV. Oxalate slightly retards the reactions.4.Iron III, Molybdenum VI, Tungsten VI, Vanadium V are also reduced by alcohol in light to FeII, MoV, WV and VIV. Stannic tin is not reduced. Chromates are reduced only to Cr III and not Cr II as in the Jones reductor. Vanadium V, although reduced to Vanadium IV, does not interfere in the estimation because our method uses sodium vanadate as the titrant and this has no action on vanadium IV. It will be thus evident that the number of interefering metals and acid radicles is very much reduced in the photochemical method than in the Jones Reductor or the Silver Reductor.

Estimation of ferric salts through photochemical reduction with oxalic and lactic acids

Summary1.The photochemical reduction of ferric sulphate in sunlight by oxalic and lactic acids has been studied with a view to its analytical application. Conditions have been developed under which ferric sulphate is reduced quantitatively to the ferrous state, so that it can be estimated accurately by titration with a standard solution of sodium vanadate.2.The rate of photoreduction of ferric salt with oxalic acid is not very much influenced by variation of the concentration of sulphuric acid in the medium from 0.4 N to 1.6 N. Whereas, the speed of the photochemical reaction of ferric salts with lactic acid is greatly retarded by an increase in the sulphuric acid concentration. The results indicate that the photochemical reaction in either case is due to the formation of ferric complexes with the organic acid. The photochemically active ferri-oxalate complex or complexes appear to be stable in acid medium while the corresponding lactic acid complex appears to be stable in neutral or weak acid solution and to undergo appreciable dissociation with increasing acidity.

Titrimetric determination of vanadium(IV) with cerium (IV)sulphate at room temperature using ferroin as indicator

A procedure has been developed for the visual titrimetric determination of vanadium(IV) with cerium(IV) sulphate, using ferroin is redox indicator. The method has been extended to the determination of iron(II) and vanadium(IV) in mixtures.

A new oxidimetric reagent: potassium dichromate in a strong phosphoric acid medium-V: Potentiometric determination of uranium(VI)☆

Abstract A critical review of the more important methods for the determination of uranium(VI) through reduction to uranium(IV) and subsequent titration with an oxidimetric reagent is given. A new method is described involving reduction to uranium(IV) by an excess of iron(II) in a strong phosphoric acid medium followed by potentiometric titration with a standard solution of potassium dichromate. This method has the advantages that the uranium(VI) is reduced quantitatively only to the uranium(IV) stage and that the potentiometric titration can be carried out at room temperature without the need for an inert atmosphere. It is also subject to less interferences than the other methods.

Oxidimetric methods for the volumetric estimation of sulphite

Abstract 1. The use of permanganate, ceric sulphate, and dichromate for the estimation of sulphite has been reinvestigated, although these reagents have heen discarded as useless by earlier investigators. By using catalysts under controlled acid concentration, we have been able to develop conditions for the quantitative oxidation of sulphite to sulphate at room temperature by any one of these oxidizing agents, avoiding the formation of dithionate. Copper sulphate and iodine monochlonde have been found useful as catalysts with potassium permanganate and dichromate; but only iodine monochloride with ceric sulphate. 2. Sodium sulphite is also oxidized quantitatively to sulphate at room temperature, when added to excess of sodium vanadate solution containing 5 to 6N hydrochloric acid and iodine monochloride as catalyst.

A new oxidimetric reagent: potassium dichromate in a strong phosphoric acid medium-VI Potentiometric titration of vanadium(III) alone and in mixture with vanadium(IV).

Vanadium(III) can be titrated at room temperature with potassium dichromate in an 8-12M phosphoric acid medium. Two potential breaks are observed in 12M phosphoric add with 0.2N potassium dichromate, the first corresponding to the oxidation of vanadium(III) to vanadium(IV) and the second to the oxidation of vanadium(IV) to vanadium(V). In titrations with 0.05N dichromate only the first break in potential is clearly observed. The method has been extended to the titration of mixtures of vanadium(III) and vanadium(IV). Conditions have also been found for the visual titration of vanadium(III) using ferroln or barium diphenylamine sulphonate as indicator.