Indian Journal of ChemistryVol. 16A. September 1978. pp. 736-738

Partial Molal Volumes & Ionic Partial Molal Volumes of SomeElectrolytes in Aqueous Solution*

SP. SHANMUGA~ATHAN, S. VIVEKANANDA~t & K. RAM MOHANtDepartment of Chemistry, Pachaiyappa's College, Madras 600030

Received 12 December 1977; accepted 20 February 1978

The partial molal volumes (PMV's) have been determined at 35° for potassium persulphate..ammonium metavanadate, potassium hydrogen phthalate (PHP) and uranyl nitrate. Forpotassium dichromate, strontium nitrate, sodium molybdate and sodium tungstate these quan-tities and apparent molal expansibilities (.pE's) have been determined at 30°, 35°, 40° and 45°.The law of additivity of PMV is found to be valid under our experimental conditions. Usingthe temperature coefficient of ionic PMV's, ionic PMV's for some ions at specific temperatureshave also been obtained. The experimental slope, sZ for all the salts have been evaluated.Cooperative effect has been studied for the latter four salts. An attempt made to interpret theexperimentally Observed trends shows an order of field strength of ions as: CrzO;- ~ Sr=+>WO~-~ CI-.

THE present work deals wit.hour systema ticattempt to obtain a fairly complete set ofdata pertaining to partial molal volumes(PMV's) and related quantities 17;. S; and cp; forsome hitherto uninvestigated and not so well in-vestiga ted electrolytes, viz, potassium persulpha te,ammonium meta vanadate, potassium hydrogenphthalate (PHP), uranyl nitrate, potassium dichro-mate, strontium nitrate, sodium molybdate andsodium tungstate.

Materials and MethodsSodium chloride, potassium dichromate, potas-

sium persulphate and ammonium metavanadatewere of AR grade. Sodium tungstate (BDH),sodium molybdate (E. Merck) and strontium nitra te(E. Merck) were recrystallized twice from conducti-vity water and dried ~n. »acuo-, The sol,utions at10 to 12 different mola lities were prepared m doublydistilled water and their densities determined usingan Ostwald-Sprengel pyknometer (25 ml). Thecp/s were calcula ted using the expression

cp _ 1000(d-do) _ M2v- mddo d

where d = density of the solution at the specifictemperature, do= density of water at that tempe-rature, m = molality of the solution, and M2=molecular weight of the solute.

The cpv's were plotted against "hn. The experi-mental slope S;, and the intercept cp: were obtainedfrom the graph and "17;'5 were calculated usingthe method of least squares (Fig. 1).

*Presented at the 'Chemistry Symposium - 1977' heldat the llT, Madras 600036.

tPresent address: Department of Physical Chemistry,eniversity of Madras, A.C. College Campus, ~1adr~s.600025.

'Forms part of the M.Sc. thesis of ILR., Madras University,19'76,

736

Results and Discussion

Our pilot work on the determination of partial.molal volumes and apparent molal volumes ofsodium chloride at 35° gave a value (17·10 ml) ingood agreement with that of Dunn- (17·16 ml). 'VIlefollowed the same procedure for other elec-trolytes and obtained 17g at 30°, 35°, 40° and 45°(Table 1).

The cpv determina tions ha d to be restricted to'only one temperature for ammonium metavana da tea.nd potassium persulpha te due to the sparing solubi-lity of the former and the thermolytic decompositionof the latter. The data obtained for uranyl nitrateat 35° were quite erratic probably due to "extensivephotolysis- in 2 queous medium.

Additivity - The additive nature of PMV's of:various electrolytes in aqueens solution he s been

530°- - - ~n.0 -

-v5

0.1 0.2 0.3 0.4 as:::!Jm- ~, 35°.

I

v V -vv! J

0.1 0.2 0.3 04 0.5 0.6.rm4(0

~I J I r I J J J

0.1 0.2 0.31ffi 0.4 0..5 0..6 I~~ II I J I

55

SHAXMVGAl'\ATHA~ et al.: PARTIAL MGLAL VOLUMES OF SOME ELECTRvLYTES

TABLE 1 - PMV's AT VARIOUS TE~JPERATURES AND "'~'s TABLE 3 - VALUES OF EXPERIMENTAL SLOPE (Su') OJ'THE PLOT OF "'v VERSUS ym

Electro- V~ ml "''Iilyte ----- ._._---- ml deg-1 Electro- Sv·30° 35° 40° 45° lyte ---------.----- ---30° 35° 40° 45"

XaCI 17·10K.S.O. 81·74 ](.Cr207 7·8343 12·8322 9'1489 11·0555XH.VO. 37'50 ](.S.\ 8 47·6500PHP 101)'64 Xa.Mou, 4'4584 -9·0635 1'6611 S·233')K.Cr.07 92'14 92·98 92·90 93·2(, 0·065566 Na.WO. 742479 62·6130 50149 35636Sr(Xu3). 46·92 44·19 48'67 46·75 0'079258 Sr(:'Ii 03J. 6'1363 3·7261 4·1373 18·88-1-7Xa.Mu. 66'27 74·07 6S-40 75'63 0'447829 NaCI 2·9730Xa.\Vll. 35·87 48'73 68·67 69'03 2·388358 PHP 11·7922

TABLE 2 -. PMV's AND IONIC PMV'g AT DIFFERENTTEMPERATURES

Electrolyte/ PMV in ml1011 -_.__ ._ .._--_._------ ..... ---------

30° 35° 40° 45°

Hel (CI-) 18'16 18'20 18·39 17·84XaCI 16·97 17'10 17·62 17·65KCI 29·92 27W O!- :::ci-,

Cooperative effect - This w.s studied by plottirgtl.pv/tly'm vs ym (Fig. 2). It w: s Iour.d thr t , first,site filling effect occurs up to 0'1722, 0·1056 ;:J d0·2070 m respectively for Sr(N03)2' Nr 2W04" ~r dNr 2MoO.. After these concentrt tior s, the grossstructure is .ffccted " rod the structure tends tow; rdsthr t of a sa It hvdra te with further " dditior s of thesolute. Brsed on S. moilov's-" views, it could besta ted the' t the eutectic composition for these sa Itsshould lie a t the vicin ities of these molalities. Anc ttempt to verify this conclusion by the methodof refr. ctive index Wi'S not fruitful.

737

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

of W(VI) and Mo(VI) than Cr(VI) for formingvarieties of complexes.

100

140

60

200.1 0.2 0.3

rmFig. 2 - flt/>v/flym versus ym plot of Sr(NOs)2 for the

study of cooperative effect

Apparent molal expansibility - The apparent molalexpansibility at infinite dilution, cpl, was obtainedby differentiating the cp~ with respect to tempe-rature and calculated by the method of least squares.The temperature effect is not so pronounced in thecase of Cr20~- and Sr2+ in contrast to WO!-. MoOtshows an intermediate tendency. This could beattributed to the more pronounced ionic interactionswith water in WO:- and MoOi- than in the Cr20;-.This is also justified by the predominating tendency

738

Acknowledgem.ent

The authors thank the authorities of the Pachai-yappa's Trust Board for providing the necessaryfacilities for this work.

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