Volumetric titration of iron (III)-salts with disodium EDTA, using FeII-cacotheline as indicator

Summary A volumetric method has been developed for the determination of iron (III) with disodium EDTA, using a mixture of cacotheline and iron(II) as indicator. The titration of the iron (III) salt is carried out in a buffered solution ofph 4–5 in carbon dioxide atmosphere with magnetic stirring, until a pink color appears. The pink color is due to the reduction of cacotheline by ferrous-EDTA. The reduction occurs only when all the iron (III) is complexed by EDTA. The end point is sharp and the method has been found to give results accurate to±0.3 to±0.5 percent.     

Diphenic acid as an analytical reagent

Summary Diphenic acid can separate thorium completely from moderate amounts of ferrous iron and titanium in almost neutral solutions. As the reagent forms quantitative precipitates with ferric iron and zirconium, workable methods for their separation from thorium and their co-determinations in a mixture with the help of this reagent have also been developed. The reagent can separate thorium from zirconium by precipitating the latter below p_h2, and the same from iron(ic) can be accomplished by the use of ascorbic acid as a masking agent. Ferric iron can be precipitated from solution containing ascorbic acid, by the ammonium salt of the reagent. A convenient process for the estimation and separation of zirconium, thorium, iron(ic) and titanium, when present in a mixture, has also been described, which involves the proper control ofph and the use of ascorbic acid as a complexing agent for ferric iron.My sincere thanks are due to Dr. A.K. Mukherjee of the Indian Association for the Cultivation of Science, Calcutta for his valuable suggestions and to Dr. A. K. Ghosal, Principal, Darjeeling Government College for providing laboratory facilities.     

Amperometry with Two Polarizable Electrodes. Chelometric Determination of Rare Earths

Abstract

The method of determining rare earths by chelometric EDTA titration with biamperometric end-point indication using two stationary platinum electrodes was studied. The convenient pH range for the determination of lanthanum is 5.0 – 8.0, for yttrium 3.5 – 8.0 and for ytterbium 3.0 – 8.0. Rare earths have been determined in the presence of iron and thorium. Iron and thorium can be titrated at pH 1.5 – 2.0 and rare earths of the lanthanum group can be determined by successive titration at pH 5.0. Large amounts of rare earths of the yttrium group interfere with the determination of iron and thorium.     

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).     

Cacotheline as a specific reagent for the detection of iron(II)

Summary Cacotheline gives a blue colour with iron (II) in the p_H range 5.2 to 7.8 in the presence of a suitable complexing agent like sodium oxalate or sodium citrate. The blue colour is not stable in air. It has now been shown that if the test is carried out in a Thunberg tube with the exclusion of air, the colour is quite stable at p_H 7.4 (McIlvaine buffer). This reaction affords a sensitive test for iron (II). In a test tube reaction, the limit of identification has been found to be 11 g in about 5 ml of solution. On a spot plate, the limit of identification has been found to be 0.5 g and the dilution limit 1100,000. On special Whatman spot filter paper No. 542, the identification limit has been found to be 0.3 g and the dilution limit 1166,000. The test can also be applied to iron (III) after reduction with sodium oxalate under a Philips' Repro lamp. Reducing agents like sodium sulphite, sodium thiosulphate, sodium hypophosphite, thiourea and ascorbic acid which reduce cacotheline to a pink coloured compound, just like iron (II) (in the presence of oxalate, etc.) in an acid medium, do not give the blue colour with cacotheline in the basic p_H range; Sb^III, As^III, U^III, U^IV, Cu^I, Cr^II, Ce^III, Sn^II, V^III, Ge^II, and Ti^III also do not give the blue colour with cacotheline under the conditions where iron (II) answers the test. The colour reaction now developed appears to be quite specific for iron (II).In conclusion, two of us, V. Narayana Rao and Mrs G. Somidevamma desire to thank the Ministry of Education, Government of India for the award of Research Scholarships.See also Z. analyt. Chem. 152, 346 (1956).     

Cacotheline as a reagent for the detection of ferrous and ferric iron

1. Cacotheline has previously been employed as a colorimetric reagent for the detection of Sn⁺² and V⁺³ ions. The present investigation covers its use as a reagent for the detection of Fe⁺² and Fe⁺³ ions. 2. Fe⁺² ions give a pink colour with a solution of cacotheline at a pH lying between 1.48 and 4.58 in the presence of a sufficient concentration of sodium oxalate, which serves to bind the Fe⁺³ ions by complex formation. At a pH below 1.24, only a very light pink colour is produced and this develops slowly. When the pH of the solution is about 5.2, a blue colour is obtained. The limit of identification is 1.5 γ and the concentration limit is 1 : 40,000 of Fe⁺². While testing for Fe⁺² at very low concentration, it is necessary to employ a very dilute solution of cacotheline (0.025%), while for solutions of higher concentrations saturated cacotheline solution (about 0.25%) is recommended. A detailed investigation has been made concerning the conditions determining the stability of the pink colour. 3. It has also been observed that sodium malonate, sodium citrate, sodium malate, sodium tartrate and sodium lactate are effective as complexing agents for binding Fe⁺³ ions. 4. Orthophosphate has not been found effective as a complexing agent under the conditions adopted, while pyrophosphate and metaphosphate have been found effective. 5. Fe⁺³ ions are reduced to Fe⁺² by exposure to sunlight or the light from a Philip's Repro lamp in the presence of the appropriate buffer solution and sodium oxalate.     

Thorium complex of 2,7-dinitroso-1,8- dihydroxynaphthalene-3,6-disulphonic acid : Complexometric determination of thorium with ethylenediaminetetraacetic acid

Thorium forms a pinkish-violet coloured complex with dinitrosochromotropic acid, which has been used as an indicator in the titrimetric determination of thorium with EDTA. The method is based on the fact that this coloured complex is less stable than the thorium-EDTA complex and breaks down after a bulk of thorium has reacted with EDTA; this marks the end-point, which is the change from pinkish-violet to red. am little as 3.1 mg of thorium present in 50 ml volume of solution may be accurately determined within a pH range from 2.2 to 3.5. The study of interferences revealed that quite a number of elements do not interfere; iron may be masked with ascorbic acid. Thorium may be determined by the same method, after separating it from many interfering ions by precipitating it with o-anisilic acid.     

Organic azo-dyes in quantitative analysis

Summary Chrom red brown 5RD was used as an indicator for complexometric titration of thorium. The change in the colour at the end-point was from wine-red to yellow. It is recommended that the thorium buffered aliquot should not contain less then 200 g thorium per 10 ml for a precise estimation. A range of p_H from 2.5 to 3.5 has been found satisfactory for such a titration. Ferri, ferro and zirconium ions interfere; they should be separated beforehand.Part I: Zaki, M. R., and K. Shakir: Z. analyt. Chem. 174, 274 (1960).