Thallimetric oxidations-VI Titrimetric and spectrophotometric methods for the determination of phosphite and analysis of binary mixtures of phosphite and oxalate.

Titrimetric and spectrophotometric methods have been developed for the estimation of phosphite at mmole and mumole levels, respectively. Thallium(III) is used as an oxidant and the thallium(I) produced is determined either oxidimetrically with potassium bromate or by measurement of the absorbance of thallium(III) at 260 nm in the presence of 0.1 M hydrochloric acid and 1 M perchloric acid. Based on the fact that phosphite and oxalate are oxidized under different conditions, methods are described for the analysis of binary mixtures of phosphite and oxalate. A method is also described for estimation of thallium(III) with phosphite as reluctant, and is applied for analysis of mixtures of thallium(I) and thallium(III).

Thallimetric oxidations-V Titrimetric and spectrophotometric determination of hydrogen peroxide.

Titrimetric and spectrophotometric methods have been developed for the determination of hydrogen peroxide at mmole and mumole levels respectively. In these methods thallium(III) is used as the oxidant and the reduced thallium(I) is determined oxidimetrically with potassium bromate in the titrimetric method and by measuring the absorbance of thallium(III) at 260 nm in the presence of 0.1M hydrochloric acid and 1M perchloric acid in the spectrophotometric method. Photochemical redox methods for the estimation of hydrogen peroxide in the presence of a number of diverse ions are described.

Photochemical reduction of thallium(III) with hydrogen peroxide.

A convenient method for determination of thallium(III) is based on photochemical reduction with hydrogen peroxide in the presence of bromide as catalyst, followed by oxidation of thallium(I) with potassium bromate.

Thallimetric oxidations-IV Estimation of malonic acid.

Malonic acid is quantitatively oxidized to carbon dioxide and water when refluxed for 120 min in sulphuric acid medium (concentration 1.5M) with at least four times as much thallium(III) as that stoichiometrically required for complete oxidation. The thallium(I) formed is estimated bromatometrically in the presence of 1.5-2M hydrochloric acid, with Methyl Orange as indicator. The indicator correction is negligible. The relative mean deviation is 0.2%. Possible side-reactions and their suppression are discussed.

Photochemical thallimetric oxidations-estimation of formic acid.

A simple, rapid and convenient redox method has been developed for the estimation of formic acid. Formic acid is photochemically oxidized with thallium(III) in the presence of bromide as catalyst, and the thallium(I) formed is determined by titration with potassium bromate. The procedure can also be used for the estimation of thallium(III) with formic acid as reductant.

A Photochemical redox method for the estimation of thallium(III).

A convenient photochemical redox method for the estimation of thallium(III) by reduction with oxalic acid followed by oxidation of thallium(I) with potassium bromate has been developed. The reduction is carried out in the presence of small concentrations of chloride and bromide as catalysts.

Tin(II) sulphate as a new reductimetric titrant--direct titration of thallium(III) with use of ion-pair and redox indicators.

The use of tin(II) sulphate as a direct reductimetric titrant for thallium(III) has been investigated, with potentiometric and visual detection of the end-point. Some azure dyes are used as redox indicators and Methylene Blue is used as both a redox and an ion-pair indicator.

Aquomolybdenum(III) chloride as a reducing titrant A potentiometric study.

The use of aquomolybdenum(III) chloride as a reducing agent for the direct potentiometric titration of Ce(IV), Cr(VI), Fe(III), V(V), Mo(VI), U(VI) and H(2)O(2) is described. The variation of the formal redox potentials of Mo(V)/Mo(IV) and Mo(IV)/Mo(III) in varying concentrations of hydrochloric, phosphoric and acetic acids is investigated. Aquomolybdenum(III) chloride is found to be a better reducing titrant than chloromolybdate(III) and gives better breaks in the titration curves. In the titration of molybdenum(VI) in 3M HCl the titration curve shows three jumps, corresponding to the reductions of Mo(VI) to Mo(V). and Mo(V) to Mo(IV) via an apparently intermediate oxidation state which presumably corresponds to a dimeric mixed-valence species. The aquomolybdenum(III) complex ion is a better reducing titrant than chloromolybdate(III) and has a wider applicability.

Titration of methylene blue with chloromolybdate(III).

The reaction of Methylene Blue with aquomolybdenum(III) chloride and chloromolyb-date(III) in hydrochloric acid media has been investigated. Chloromolybdate(III) can be satisfactorily used as a reductometric titrant for Methylene Blue in 6-8M hydrochloric acid medium. The end-point can be detected either potentiometrically or visually. Aquomolybdenum(III) chloride is not useful as a titrant for this estimation.

Dichromate titration of thallium(I).

The formal redox potentials of the thallium(III)-thallium(I) couple in different acids of varying strengths are reported. The minimum concentration of hydrochloric acid required for a direct titration of thallium(I) with potassium dichromate is 5M. Thallium(I) can be titrated directly with the primary standard oxidant, potassium dichromate, at room temperature, with ferroin as indicator, in 6M hydrochloric acid. Atmospheric oxygen must be excluded.

Sequential oxidimetric determination of thallium(I) and (III).

The reaction between thallium(III) and oxalic acid in sulphuric acid medium has been investigated. Spectrophotometric results show that thallium(III) can be quantitatively reduced to thallium(I) with oxalic acid in aqueous medium when heated to near boiling point. Conditions for the estimation of the excess of oxalic acid with cerium(IV) sulphate in the presence of thallium(I) and for the estimation of a mixture of thallium(I) and thallium(III) have been investigated. The method is simpler than many other redox methods reported for the determination of thallium(III) and is free from many interferences encountered in these titrations. The reagents are cheap and quite stable.