,1. DOLEZAL, J., LUKSYTE, E., RYBACEK, L. & ZYKA, J.,Colln Czech. chem, Commun., 29 (1964). 2597.

12. ALFARO, H., DOLEZAL, J. & ZYKA, J., Chemist Analyst,56 (1966), 84.

.13. JAFFE, E., Annali Chim. Appl., 22 (1932). 737.

Determination of Iodide, Ferrocyanide &Hydrazine with Mn(III) & Mn(IV)

'{Mrs) N. RUKMINI, K. RAMA RAO & V. S. N. P. KAV'ITHA

Department of Chemistry, Andhra UniversityWaltair 530003

Received 24 December 1977; revised 27 March 1978;accepted 14 April 1978

The determination of iodide and hexacyanoferrate(lI)'in 1M sulphurlc acid medium with Mn(llI) and Mn(IV)is described. Acetone is added in the titration of iodideto stabilize the 1+produced durini the titration. Fer-roin is used as the indicator. This method hasbeen applied for the determination of iodide intinctures of iodine. An indirect determination ofhydrazine, in which hydrazine is oxidized to nltrogenwith potassium hexacyanoferrate (III) in alkalinemedium and by the titration of hexacyanoferrate (II)in acid medium is also developed.

SINGH et al» determined iodide with Mn(III)in 3-4N hydrochloric acid using chloroform

for extractive end-point. They used iodine mono-chloride as catalyst and preoxidizer, The deter-mination of ferrocyanide with Mn(III) has notbeen attempted so far. Recently Mn(IV) has beendeveloped- as an oxidant. In this communicationwe report a simple and direct titrimetric procedurefor the determination of iodide and hexacyano-ferrate (II) in sulphuric acid medium by oxidationtitration with Mn(III) and Mn(IV) using ferroinas an indicator. In the titration of .iodide acetoneis used to stabilize the 1+, produced during thetitration. The titration of iodide is applied forthe determination of iedide in tinctures of iodine.

The titration of ferrocyanide is also applied forthe indirect determination of hydrazine. The hy-drazine is oxidized by hexacyanoferrate(III) tonitrogen in alkaline medium" followed by titratingthe formed hexacyanoferrate (II) in acid mediumwith Mn(III) and Mn(IV).

Stock solutions of 0'05M iodide, O·lM hexacyano-ferrate (II) and 0'025M hydrazine sulphate were pre-pared and their strengths determined". Manganese(III) solution (O'lM) Was prepared by oxidizingmanganous sulphate with nitric acid in phosphoricacid medium+and standardized with ferrous (II)ammonium sulphate". Manganese (IV) solution(0'05M) was prepared and standardized according tothe procedure of Mandal and Sant". Ferroin solution{0'025M) was used as an indicator. Redistilledacetone (AR) Was used. All the other reagentsused were of AR grade.

Procedure - An aliquot containing 15-150 mgof iodide or of hexacyanoferrate(II) was treatedwith 20 ml of 5M sulphuric acid (20 ml of acetone

NOTESwas added in the titration of iodide). The abovemixture Was diluted to 100 ml with distilled waterand titrated with a standard Mn(III) or Mn(IV)solution using 0·05 rnl of ferroin as an indicator •to a sharp colour change from orange red to paleblue in the case of iodide or orange red to yellow[due to hexacyanoferrate(III)] in the case of hexa-cyanoferrate(II) .

Hydrazine was oxidized with excess potassiumhexacyanoferrate(III) in alkaline mediums. Tothis 5M sulphuric acid (20 ml) was added and theformed hexacyanoferrate(II) titrated as describedabove.

Quantitative results are obtained with both Mn-(III) and Mn(IV) in I-2M sulphuric acid medium.Below 1M sulphuric acid hexacyanoferrate(II) isprecipitated as manganous hexacyanoferrate(II) asreported by Kolthoff et at.3 with potassium permanga-nate also". Above 2M sulphuric acid turbidityappeared probably due to the isolation of ferrocyanicacid as pointed by Bates et al.a. Low values areobserved for iodide in sulphuric acid medium >2M. probably due to interference by atmosphericoxygen but quantitative results are obtainedup to 4M sulphuric acid, if the titration is carriedunder CO2 atmosphere. Some typical results aregiven in Table 1. The indicator correction is foundto be negligible in such titrations. Titrations arealso carried with O'OlM solutions. In such titra-tions the indicator correction is found to be 0·2 mlof O'OlM Mn(III) or 0'005M Mn(IV) solutions.

Generally 1- is oxidized to 1+ with powerfuloxidizing agents such as permanganate, Ce(IV) sul-phate, bromate, iodate etc", which forms hypoiodousacid. This hypoiodous acid in the absence ofstabilizing agents, again combines with 1- to form12, Berg? used acetone to stabilize the 1+. produced

TABLE 1 - DETERMINATION OF IODIDE, HEXACYANO-FERRATE(II) AND HYDRAZINE WITH Mn(III) AND Mn(IV)

Determination with Mn(III) Determination with Mn(IV)------------

Taken Found Error Taken Found Errormg mg (%) mg mg (%)

IODIDE

15·08 15·03 0·40 38·35 38·61 0·1625'60 25-66 0'23 54·75 54·62 0'2457'24 57'30 0'12 87·38 87'60 0'25

102-50 102·84 0·34 109·84 110'18 0·31153·80 153·30 0·33 152-68 152·96 0'18

FERROCYANIDE

29-82 29'94 0'40 26'72 26'83 0'4165·60 65·76 0'24 48'10 48·24 0·2989-46 89·71 0·28 80'16 80·32 0'20

149·10 149·50 0·27 112·22 112·61 0·35172-96 173-46 0·29 133'60 133'42 0'13

HYDRAZINE

8·01 8·04 0'40 6'92 6'75 0'4220·03 20'10 0·35 16·83 16,88 0'3132·04 32-12 0-25 23-56 23-64 0'3438·65 38'80 0·39 30'29 30·34 0'1748·07 48·28 0'44 40·38 40'56 0·45

915

INDIAN J. CHEM., VOL. 16A, OCTOBER 1978

the above procedure [For the purpose of calculationit is considered that the 12is oxidized to 21+ withMn(III) and Mn(IV)J. From the two tit rationsiodide present in the tinctures of iodine can be cal-culated. The results are given in Table 2.

Chloride does not interfere when it is present upto 50-fold excess to the titrant. Bromide does notinterfere when present in an amount equal tothe iodide, but at higher concentrations, it causesinterference. Bromide does not interfere in thetitration of hexacyanoferrate(II). Acetate, borate,tungstate, molybdate, U(VI) and AI(III) do notinterfere at all concentrations. Oxalate, tartrate,nitrite, Fe(II) , As(III) and ascorbic acid interfereat all concentrations.

Two of the authors (K.R.R. and V.S.N.P.K.)express their deep sense of gratitude to the UGC,New Delhi, and the CSIR, New Delhi, for the awardof junior research fellowships.

TABL&.2 - DETERMINATION OF IODIDE IN TINCTURES. OF IODINE

Iodide found bythe BP method

(g per 100 mI)

SD Iodide found bypresent method(g per 100 ml)

SD

TITRATIONWITH Mn(III)

2·7052·657

2·7042·658

0·0020·0015

0·0020·002

TITRATIONWITH Mn(IV)

2·6982'656

0·0030'003

0·00250·001

2·7002'659

during the titration with permanganate and iodate.Later Lewis" also used acetone to stabilize the 1+in the titration of iodide with cerium(IV) sulphate.Recently Murty and Ra09 used acetone in thetjtration of iodide with potassium dichromate andsodium vanadate. The normality of iodide solutionis found to be exactly twice the molarity as in thecase of permanganate", iodate", cerium(IV)sulphate",dichromate" and vanadate".

Higher stability of Mn(III) solution renders ita better titrant compared to Mn(IV) solution.

Determination of iodide in tinctures of iodine-The titration of iodide was applied for the deter-mination of iodide in tinctures of iodine. Theresults obtained are compared with those of officialBP methodw. Free iodine was first titrated witha standard solution of sodium thiosulphate, andthen the total iodideand iodine was determined using

916

References1. SINGH, B., SAHOTA,S. S. & VERMA, B. CH., Res. Bull.

Punjab Univ., 10 (1956), 261; Chem. A bstr,, 54 (1960),.24096.

2. MANDAL,S. K. & SANT, B. R., Talanta, 23 (1976), 285.3. KOLTHOFF,I. M., BELCHER,R., STENGER,V. A. & MATSU-

YAMA,G., Volumetric analysis (III) (Interscience, NewYork), 1957, pp. 127, 142, 148.

4. INGAMELLS,C. 0., Talanta, 2 (1959), 171.5. BERKA, A., VULTERIN,J. & ZYKA, J., Newer redox titrants

(Pergamon Press, London). 1965, 11.6. BATES, J. C., DAVIES, K. M. & STEDMAN,G., J. chem,

Soc., (Dalton) (1974), 246.7. BERG, R., Z. analyt. Chem., 69 (1926), 369.8. LEWIS, P., Ind. Engng Chem. (Anal. Edn) , 8 (1936), 199.9. KRISHNAMURTY,N. & RAMA RAO, K., Tolanta, (in press).

10. The British pharmacopoeia (Pharmaceutical Press, Lon-don), 1968, 518.