Dey, Arun K.

Ghose, (Mrs) Ranjana (nee Bagchi)

Mahan, Ashok

English

NOPR

lndian Journal of ChemistryVol. 14A, July 1976, pp. 518-520Simultaneous Titrimetric Determination of La(lII) & Ce(IV) inTheir Mixtures(Mrs) RANJANA GHOSE (nee BAGCHI), ASHOK MAHAN & ARUN K. DEY*Department of Chemistry, University of Allahabad, Allahabad 211002Received 16 July 1975; accepted 15 September 1975A rnethod has been developed for the strrrulraneous deterrnination of lanthanum andcerium with EDTA. The method involves both redox and cornplexornetrfc principles. Thefirst titration has been perforrned in 0'5N H2SO" and it gives the value corresponding to fourequivalents of Ce(IV) per mole of EDTA, ferroin being the indicator. In the second step of titra-tion the pH of the solution is raised by the addition of pyridine (pH = 8·4 ± 0·2) or 20% solutionof (NH.)2C03 (pH::::: 8·25) using erfochrorne black T and tropaeoline 00 rnixture or pyrogallolred as the indicator, respectively. This titration gives the total value equivalent to La(llI)and Ce(III). In another titration, La(III) or Ce(III) has also been estimated as a single componentin pyridine medium. The optimum conditions for titrations and the interferences due to variousanions and cations have been studied.METHODS based on direct and back-titrationsof La(III) and Ce(III) with EDTA (disodiumsalt) have been described=". In thesemethods, the ions, and other rare earth ions, ifpresent, are co-titrated and therefore the titrevalues give the total metal ions present. Bromo-pyrogallol red-, murexide+", alizarin red 9, thoron-,and alizarin sulphonate (ammonium salt) and methy-lene blue mixture! are the usual indicators in thesetitrations. The colour of the indicator dyes isdischarged in the presence of the oxidant Ce(IV)and the evaluation of a correct end-point becomesimpossible. EDT A is oxidized by Ce(IV) in anacidic solution, while in an alkaline medium themetal ion hydrolyses and the oxidation of theindicator interferes.Malinina et al.6,? investigated the Ce(IV)-EDTAsystem in detail. They concluded a compositionof 1: 1 for the complex and discussed the natureof the reduction of Ce(IV) in the presence of EDT A.The kinetic investigation of oxidative decarboxy-lation of EDTA has also been reported by Carrolland coworkerss-", who found that four equivalentsof Ce(IV) are used for one mole of EDTA. Rao+,however, found two equivalents of Ce(IV) areneeded for one of EDTA. Our observations arein agreement with those of Carroll et al.In this work, advantage has been taken of t~ereductive property of EDTA for Ce(IV) and Itssubsequent complexation with Ce(III) for the chelo-metric determination of Ce(IV). The procedurehas enabled the determination of Ce(IV) and La (III)when present together. The addition of pyridinein the titration of Ce(III) or La(III) sharpens theend-point due to its buffering action and non-aqueous effect.Materials and MethodsA 0'10M solution of Ce(IV) was prepared bydissolving ceric ammonium sulphate (BDH, AnalaR)*To whom all correspondence may be addressed.518in cone. H2S04 (overall acidity ~0·5M) and stan-dardized against ferrous ammonium sulphate.A 0'05M solution of La(III) was prepared by dis-solving lanthanum carbonate (Fluka) in a suitableamount of nitric acid and standardized againstEDTA.A stock solution of EDTA (0'05M) was preparedfrom the disodium salt (E. Merck).The indicators used were: pyrogallol red (E. Merck),0·1% alcoholic solution; ferroin (E. Merck), O'025Msolution; and eriochrome black T (BDH indicatorgrade) -l-tropaeoline 00 (BDH indicator grade) +NaCl (2: 1: 500).The buffers employed were: Undiluted pyridine(BDH, AnalaR) used (sp. gr. 0·98); (NH4)2COa(BDH, AnalaR), 20% aq, solution; buffer PH = 5(NaOAc/HCl); buffer pH = 10 (NH4Cl/liquor ammo-nia); and buffer PH = 8·5 (boric acid/borax).All other reagents used were of analytical grade.Procedure- J: Determination of La(J II) or Ce(II J)-To an aliquot of lanthanum solution, pyridine(2-5 ml) was added and the mixture diluted to ,...,50ml. A wine-red coloration developed on the additionof the indicator (eriochrorne black t-j-tropaeo-line 00 mixture). It was titrated against a standardEDT A solution till colour changed to bottle green.The same titration was repeated using borax-boricacid buffer in place of pyridine. The comparativeresults (average of a number of determinations)are summarized in Table 1. Both direct and back-titrations [against standard Zn(NOa)2] were per-formed and were found satisfactory.Direct titration of Ce(III) against EDTA did notyield satisfactory end-points probably due to blockingof indicator. Hence, Ce(III) was determined byback-titration using Zn(NOa)2 solution (table 2). Toa Ce(IV) solution, a pinch of tartaric acid was addedand it was reduced by solid ascorbic acid followed bythe addition of excess of EDT A, pyridine (2-5 ml)and mixed indicator. During titration the colourchanged from bottle green to wine-red and againGHOSE et al.: DETERMINATION OF La(III) & Ce(IV) IN THEIR MIXTURESTABLE 1 - LA 'TRANUM (III)-EDTA TITRATIONLa(III) Titrant Direct titration Back titrationtaken EDTA(mg) X 102M Pyridine media Buffer media Pyridine media Buffer media-------- -------EDTA La(III) EDTA La (III) EDTA La(III) EDTA La(III)(ml) found (ml) found (ml) found (mI) found(mg) (mg) (mg) (mg)58·62 10·2040 4·14 58·68 4'14 58·68 4·14 58·6844·12 5·1229 6·20 44·12 6·24 44·40 6·18 43·99 6·12 43·5517-65 1·9841 6·40 17·64 6·34 17'47 6·38 17·58 6·36 17'538·82 0·9542 6'64 8·80 6·60 8·75 6·66 8·83 6'54 8'674'41 0·4902 6·52 4·44 6·54 4·45 6·50 4·43 6·58 4·481·76 0·2000 0·36 1·77 6·44 1·79 6·22 1·72 6·38 1'770·88 0'1000 6·56 0·83 6·72 0·85TABLE 2 - CERIUM (III)-EDTA TITRATION TABLE 3 - OXIDIMETRICTITRATIONSOFCe(IV) IN PRESENCE OF La(III)Ce(IV) Titrant EDTA Amount found Ce(IV) La(III) Titrant EDTA Ce(IV)taken EDTAxl02M (mI) as Ce(III) taken present EDTA (mI) found(mg) (mg) (mg) (mg) xl02M mg109·90 10·4380 7·52 109·98 137·37 174·0 10·4380 2·36 138·0668·68 5·2190 9.40 68·74 82·42 87·0 5·2190 2·82 82·4932·97 2·0876 11·26 32·94 41·21 43·5 2·0876 3·52 41·1934·34 1·0444 23·50 34'39 27·47 43·5 1·0444 4·70 27·495·49 0·5219 7·50 5·48 17·17 21·7 0·5219 5'80 16·973'85 0·2088 13·20 3-86 6·87 21·7 0·2088 6·00 7·02the end-point was corrected by EDTA to bottlegreen. .A mixture of Ce(III) and La(III) when titratedgave titre values corresponding to the sum of thesemetal ions.Procedure-Tl : Oxidimetric determination of Ce(IV)in 0·5N H2S04 solution - To an aliquot of Ce(IV)solution, a suitable amount of standard H2S04was added to get an overall. ac!dity 0·5N in --:50ml. Ferroin was used as indicator, and duringtitration with EDT A the colour changed fromgreen to red. The titre value corresponded t~ 0·25equivalent of EDT A for one of Ce(IV). No inter-ference was observed by La(III) (Table 3).Procedure-III: Simultaneous determination of Ce(IV)and La(II I)- In a solution containing both Ce(IV)and La(III), Ce(IV) was determined by p~oced~re-II.To the same solution, a pinch of tartanc acid wasadded and then the PH of the solution raised bythe addition of pylidine or of 20% (NH~)2C03 so.lu-tion, and titration against EDT A contmued usmgmixed indicator (pyridine medium) or pyr.ogallolred (carbonate medium). A titre value equivalentto total Ce(III) and La(III) was then. obtained.The amount of lanthanum was determined usmgthe expressionTLa = T Proce. III -4X T Proce, IIThe total cations were also determined in separatesample solutions by reducing Ce(IV) with ascorbicacid and then titrating against EDTA. Th~ results(Table 4) obtained in both the cases are in g?odagreement. However, the Iatter method requirestwo samples for the two separate titrations.Results and DiscussionEriochrome black T is often used as an indicatorin the direct titration of a number of metal cationsat PH ~ 1O. The transition from red to blue at theend-point is not very sharp. Some workerst? foundthat the end-point improves by producing a colourchange from red to green by the addition of yellowdyes such as methyl orange, methyl yellow, methylred, titan yellow, tropaeoline 00, etc. In the presentinvestigation eriochrome black T and tropaeoline00 mixture has been found appropriate. At roomtemperature (~200), Ce(IV) oxidizes EDTA andthe reaction is found to be quantitative's".Ce(IV) is quantitatively reduced to Ce(III) duringredox titration and Ce(III) is then titrated in thecomplexometric titration along with La (III) inequinormal proportions. Therefore, the total EDT Aconsumed for Ce(IV) is 1·25 equivalent. The end-point of redox titration is comparatively less sharpthan in the complexometric titration. Vigorousshaking, however, improves the end-point. Theoxidative property of Ce(IV) for EDTA makes theprocedure specific in the presence of other rareearths. At moderate concentrations, the end-pointmay be judged even in the absence of an indicator,the yellow colour of Ce(IV) being discharged. Whenlow concentrations are used, ferroin is employedas a redox indicator. The end-point of cornplexo-metric titration becomes a bit sluggish due toscreening of mixed indicator when ferroin is used.The performance of redox and complexometnctitrations separately yields more accurate results.51 <}INDIAN J. CHEM., VOL. 14A, JULY 1976TABLE 4 - TITRE VALUES OF CERIUM AND LANTHANUMIN ARTIFICIALMIXTURESLa(III) Ce(IV) Titrant Titre value Titre value Vol. of EDTA Lanthanum Ceriumtaken taken EDTA of EDTA of EDTA corresponding found found(mg) (mg) xl0'M reqd in reqd for to La(III) (mg) (mg)redox titn La(I1I) (ml)(ml) + Ce(III)(ml)*48·71 34·34 5·2190 1·18 11·44 6·72 48·72 34·524'18 68'68 5'2190 2·34 11·08 1·72 4·15 68·4555·68 10·99 5·2190 0·38 9·20 7'68 55·68 11·1113-92 13·73 2·0876 1-18 9·52 4'80 13-91 13-8041·76 8·24 2·0876 0·70 17·20 14'40 41·76 8·196·96 6·87 1·0444 1·18 9-62 4'90 6·96 6·903'48 16·47 1·0444 2·82 13-70 2·42 3·51 16·518'35 4·81 0·5219 1-68 18'30 11-58 8'39 4·916·96 10'30 0·5219 3·58 23·98 9·66 7·00 10'473·34 4·12 0·2088 3·60 26·20 11·80 3·42 4'210·97 0·89 0·1044 1·56 13-14 6·90 1·00 0·91*Average of two types of titration values which have been performed separately: (I) in the same sample solution, and(II) Ce(IV) is reduced to Ce(III) by ascorbic acid in the separate sample.The addition of a pinch of tartaric acid keeps themetal ion in solution because in (NH4)zC03 mediumLa(III) precipitates out as carbonate, while inpyridine cerium is hydrolysed, and there are chancesof co-precipitation when both are present.The redox titration is only affected by otherredox systems if present. An appreciable deviationhas been observed in complexometric titration inthe presence of a number of cations [Mg2+, Ca2+(partial), AP+, Fe2+, Fe3+, Cr3+, Ga3+, In3+, T13+,C02+, Ni2+, Cu2+, Zn2+, Cd2+, Mn2+, Sn2+, Sb3+,Se4+, UO~+ and Th4+J and anions, citrate, tartrate(excess), tungstate, molybdate, metavanadat e, BO~-,CzOi-, POi-, F-, S20~-, S2-, HCOii, Fe(CN)~-,and Fe(CN)~-. The platinum metal ions, Ag+.Be2+, Sr2+, Ba2+ and Bi3+ and HCOO-, CH300-,cr-, Be, 1-, N02, xo, SO~-, SOi- and SCN- donot interfere.AcknowledgementThe work was supported by the CSIR, New Delhi,and the financial assistance to one of the authors(R,G.) is gratefully acknowledged.520References1. WELCHER, F. J., The analytical uses of EDTA (VanNostrand, New York), 1958, 181.2. SOMMER, L., The coordination and analytical chemistryof N-heterocyclic azo dyes, Folia (Chemiaj, University,Brno, Czechoslovakia.3. WEST, T. S. & SYKES, A. S., Analytical applica-tions of diamino-ethane-tetra-acetic acid (BDH, Poole),19604. MALIK, VIT. U., SHARMA,C. L. & ASHRAF, Y., Z. analyt.Chem.,247 \1969), 315.5. DABHADE,S. B. & SANGAL,S. P., Indian J. appl. Chem.,32 (1969), 23.6. MALININA, E. A., MARTY~ENKO, L. I., PECHUROVA,N. 1. & SPITYN, V. I., Dokl. Akad. Nauk. S.S.S.R.,183 (1968), 632; Chem. A bstr. , 70 (1969), 51181n;Izv. Akad. Nauk. S.S.S.R. Ser. Khim.,9 (1969), 2075;Chem. Abstr., 72 (1970), 25501p.7. MALININA, E. A., MARTYNENKO,L. I. & PECHUROVA,N. I., Vestn. Mosk. Univ. lI.him., 23 (19681, 75; Chem.Abstr., 71 (1969), 64690g.8. HANNA, S. B., AL-HASHIMI, S., \VEBB, W. H. & CARROLL,W. R., Z. analyt. Chem., 246 (1969) 231.9. HANNA, S. B., HESSLEY, R., WEBB, \V. H. & CARROLL,W. R., Z. analyt, Chem., 255 [1971), 30.10. SINHA, B. C. & Roy, S. K. Analyst, 98 \1973),289.11. RAO, G. N., Indian J. Chem., 8 (1970), 328.

Simultaneous Titrimetric Determination of La(lII) & Ce(IV) in Their Mixtures

http://nopr.niscair.res.in/bitstream/123456789/53776/1/IJCA%2014A%287%29%20518-520.pdf

Simultaneous Titrimetric Determination of La(lII) & Ce(IV) in Their Mixtures

Abstract

Similar works

Full text

Available Versions

NOPR