Purkayastha, B. C.

Sinhamahapatra, N.

English

NOPR

Indian Journal of ChemistryVol. lA, June 1976, pp. 396-398Study of the Transition Temperature of Mohr's Salt Analogue ofMnCII) by Distribution Measurement*B. C. PURKAYASTHA & N. SINHAMAHAPATRANuclear Chemistry Division, Saha Institute of Nuclear Physics, 92 Acharya Prafulla Chandra RoadCalcutta 700009Received 22 July 1975; accepted 23 August 1975Study of the distribution coefficient of the guest at tracer level with morphologically ana-logous host having a greater range of stability shows a prominent break at the transitiontemperature of the guest component. Mohr's salt, stable in the range of our observation (from4° to 50°), has been used as host and Mn(II) as guest in the system with 64Mnas radioactivetracer. The prominent change in the pattern of uptake between 12·5° and 13°has been assumedto be due to morphological transition of (N1I4)2S0•.MnSO•.61120.TRANSITION temperatures of many com-pounds in the series M'2MH(S04)2.6HzO (whereM'= monovalent cation and M*= divalentcation) have not been determined. Double saltof Mn(Il) of the formula (NH4)2S04..MnS04.6HzOhas been described in the literature-, though datapertaining to its transition temperature are lacking.It has been established in our laboratory that in'an isomorphous mixed crystal system the distri-bution factor between the host and the guest under-goes a prominent change at the point of transitionof the guest components. It was concluded thatthe transition temperature of a guest componentcan be determined by the study of the distributioncoefficient at different temperatures with a morpho-logically analogous host having a greater rangeof stability.Our point of interest was to extend the sameprocess for the determination of the transitiontemperature of (NH4)2S04.MnS04.6H20. It wasalso anticipated that this would give a clue as tothe selection of temperature for the preparationof the salt in its different morphological states.Materials and MethodsMohr's salt of BDH Analar quality was usedas host. Radioactive manganese (54Mn) used astracer in the experiment, was procured from BARC,Bombay. A few drops of carrier-free 54Mn solutionwas added to a solution of inactive manganesesulphate (inactive manganese 2-3 mg). Manganesewas precipitated as manganous sulphide by addingammoniacal sulphide solution. The precipitateobtained was washed several times with hot waterand then dissolved in dilute sulphuric acid. Theoperation was repeated and thus a stock solutionof Mn(II) activity in 0'5N H2S04 was prepared.The first step in the study of the homogeneousdistribution factor of the system was to prepare*Presented at the Annual Convention of Chemists held atMadurai, 1974.396a saturated solution of the host compound con-taining guest component. As a medium of studyO'5N H2S04 was chosen. Sufficient amount ofMohr's salt was taken in a L-shapcd tube, whichcontained 0'5N H2S04 and to it was added 64Mnactivity. The tube was placed in a thermostatand shaken overnight to allow sufficient time forattaining saturation. Care was taken so that alittle salt remained undissolved at the end.The time required for attainment of equilibriumbetween the tracer in the solution and tracer insidethe solid host component was then detumined.A series of bulbs with a constriction a.t the mouthwere taken and into each of them was inserted 25ml of saturated solution of Mohr's salt containing54Mn activity. About the same amounts of Mohr'Ssalt, ground to 120 mesh, was weighed and putinto each of them. Bulbs were then fused at theconstriction, immersed in the thermostatic-bathand shaken at a rate of 50-60 vibrations per minute.The temperature of the bath was the same as thatof the saturated solution. At an interval of 12 hra tube was opened and an aliquot of the solutionwas removed by a pipette with a filter paper capfitted at the mouth to prevent any solid particleentering the solution. Activity left in the sol~t~onwas measured with a GM counter and the activityremaining in the solid was computed therefrom.D was calculated according to the equation ofHenderson and Kracek'',(Tracer) __ D( Tracer)Carrier solid - Carrier solutionA plot of D versus time showed that equilibriumwas established within two days. To determinethe distribution coefficient at different temperaturesthe solid phase was equilibrated in contact withthe saturated solution for three days, giving anadditional day in each case to allow for the satemargin. In order to examine the constancy of D,the solid surface was changed by introducing diffe-rent amounts of solid into the ampoules.PURKAYASTHA & SINHAMAHAPATRA: TRANSITION TEMPERATURE OF (NH.)z SO., MnSO•.6H.0Studies were made from 4° to 50°. Temperaturefluctuation of the cold-bath was within + 0·5° andsensitivity of the hot-bath was ± 0.1°. -Iron(II) in the saturated solutions at differenttemperatures was determined volumetrically bystandard dichromate solutions.Results and DiscussionThe study of uptake of Mn(II) by Mohr's saltwas made from 4° to 50° to find out whether therewas any prominent change in the pattern of uptakein between these temperatures. In order to deter-mine constancy in the distribution factor, the per-centage of solid carrier was varied in all theexpenments. In the case of mixed crystal for-mation D values should remain within experimentalerrors for different percentages of solid carrier.A scrutiny of the results presented in Table 1 showsthat the constancy of the distribution factor withsuch variations are observed within reasonablelimits above 13°. It can, therefore, be assumedthat from 13° upwards the uptake follows the lawof mixed crystal formation.From 12·5° downward a significant divergencein D values with variation in the percentage ofsolid carrier is observed. At these points D valuediminishes with increase in the percentage of solidcarrier. In the presence of preponderant amountof host solid the change is not so prominent at about12.5°, but as the temperature is lowered this diver-gence increases. Fig. 1 shows that at 12·5° and10° the uptake follows Friendlich's Jaw of adsorptionisotherm.Mohr's salt is a well known compound in thehexahvdrated double sulphate series and is knownto be - stable in the range of our study. This isfurther corroborated by the solubility curve ofthe compound in the range of our study wheresolubility of the host plotted against temperaturedescribe a smooth straight line course. It can,therefore, be concluded that (NH4)2S04·MnS04.6H20undergoes a morphological change between 12·5° and13°C. It can further be concluded that othermorphological state of the salt exists below the 13°TABLE 1 - DISTRIBUTIONOF 54Mn BETWEEN PREFORMED(NH.).SO., FeSO. 6H20 CRYSTALSAND ITs SATURATEDSOLUTIONIN 0'5N H2S04 ACID[Initial manganese(II) concentration =2·469 X 10-' M thesolubility of Mohr's salt at 10° and 40° arc respectively 0'7ooMand 1'071M]Tempera- Fraction Fraction Dture (%) of Fe2+ (%) of tracer°C ill the solid ·'Mn withphase solid phase4 34·5354'5367·4431'1041·4050·5160'8140'6751'6858·6430'8140'6750'6759'8420'0323'3622'5311'6814·4215·7617·9517·0422'4726'0611-5416'8119·7926'680·4930'2540'1390'2910'2380'1680'1410'3000'2780·2480'2930'2940'2400·244Av. 0·2680'1920·1960'186Av. 0'1910'3120'2250'2320'225Av. 0'2480'2350'2690·213Av. 0'2390'2600'3720'290Av. 0'307-1.97 -1.991012-51315 40'6540·7740·4411'6411·9111·22)lIE-5.1'"!:-4.9-4.730 27·4439·5348·3357·S010'5412'8117'8123·52-1.95- 4. 5 ..------'- ....L .l- -...J~ _L.-1.91 -1.93 -2.0140 22·2932'0744'136'3311·2614·45log CFig. 1 - Freundlich adsorption isotherm of carrying' ~>f manganese tracer by preformed (NH.).SO" FeSO., 6Hl0[x, amount of manganese carried (g/litre); c, concentration of manganese remaining in solution (g/litre); m, amount ofhost solid (gfIitre)]50 22'3430'5340·926·9514'0516·71397INDIAN J. CHEM., VOL. 14A, JUNE 1976and any attempt to isolate (NH4)2S0,.MnS04.6H20should be done above 13°. In fact the salt preparedat 20° was analysed and found to contain 6molecules of water of crystallization. However,salt prepared at 10° on analysis showed nodifference in the number of molecules of waterof crystallization. Probably the ether morphologicalstate is metastable with respect to the stablehexahydrated variety, and its existence can beshown only through mixed crystal formation. Therange of our study was, however, limited and sofurther change at higher temperature may bemissed.398AcknowledgementOne of the authors (N.S.) gratefully acknow-ledges the cooperation of Dr S. Sarkar in this work.References1. REMY, H., Treatise on inorganic chemistry (Elsevier,New York), 1956,220.2. PURKAYASTJiA, B. C. & SARKAR, 5., J. inorg, nucl, cu«;28 (1966), 347.3. HENDERSON, L. M. & KRACEK, F. C., J. Am. chem:Soc., 49 (1927), 738. .4. VOGEL, A. I., A text book of quantitative inorganic analysls(ELBS & Longmans Green, London), 1962, 310.-'

Study of the Transition Temperature of Mohr's Salt Analogue of Mn(II) by Distribution Measurement

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Study of the Transition Temperature of Mohr's Salt Analogue of Mn(II) by Distribution Measurement

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