Blokhra, R. L.

Verma, P. C.

English

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INDIAN J. CHEM., VOL. 14A, SEPTEMBER 1976TABLE 2 - VALUES OF CONSTA!'TSA AND B AT 25°D:\fAwt %0·010·020·040·060·075·085·0A B0·0047(0·0050)·0·00230·02070·02640·01510·01960·0181-0·0737(-0·0755)*-0·1019-0·1257-0·1181-0'05310·12860·5468*Values in parentheses are literature values at 25° (ref. 11).attaining a maximum value. The maximum visco-sity was found at about 62 wt % of DMA, whichis in agreement with the reported data-".The Jones-Dole equation in the form('IJ!"1)°-l)!el/2= A+Bc1/2has been used for the analysis of experimental data.The coefficients A and B have been calculated bvthe method of least squares end recorded in Table 2.It can be noted that the coefficient B for potassiumiodide in mixed solvent diminishes with the additionof small amounts of DYL\. in water, reaches a mini-mum value and then starts increasing with furtheraddition of DMA. The solvent dependence of Bmay be explained on the basis of the view of Stokesand Millsll, according to which the viscosity ofdilute electrolyte solution is equated to the viscosityof solvent plus the contributions from solutes inthe following manner:Y) = tj0+tj*+YjE+I)A+YjD •. ,(2)where n* is the positive increment in viscositycaused by coulombic interaction, 'fjE is the positiveincrement due to the shape and size of an ion, 'ljAis the increment due to the alignment or orientationof the polar molecules by the ionic field and YjD isthe change in viscosity associated with distortionof the solvent structure leading to greater fluidity(structure breaking effect).Combining Eqs. (1) and (2) and cancelling theterm due to coulornbic interaction from both wehaveYjE+"fjA+"1)D= Yjo Be ... (3)Therefore, at a given concentration the B coeffi-cient can be discussed in terms of different viscosityeffects. It is known that K+ and I- ion de-troythe water structure and this property leads to theirnegative B values-", In KI both the K+ and l-ions have large radius (within a group) and smallsurface charge density. Therefore, these wouldcause a very weak orientation effect in their imme-diate vicinity and consequently will lead to verysmall values of "1)E and fJA. On the other hand,there is considerable distortion of solvent structurein the close proximity of such ions due to the com-petitive force" between the ionic field and the bulkstructure. Thus, "fjE+"tjA <tjD and B coefficientwill be negative for KI in aqueous solution. Theaddition of small amounts of DMA enhances thestructure of water and a more dense liquid structureis obtained-". Therefore, ions responsible for break-696ing the structure would give much larger valuesof "fjD in mixed solvents than in pure water. Thus,"fjE+'lJA~YjD and still lower (more negative) valuesof B coefficient are obtained. With further additionof DMA the water structure is broken and hencethe change in "tjD will be smaller than in the previouscase. Therefore, 'ljE+ fJA ~ ·rp and we see that thevalues of coefficient B becomes le-s and less negativeand finally positive when 'fjE+Y/>1)D,It was noticed that a minimum in B value wasobtained corresponding to about 30 wt % DMA.It mav be concluded that the solvent at this com-position is most structured. The minimum in Bvalue can be interpreted as the maximum ion-solventinteraction and thus giving maximum breakingof the solvent structure on the addition of structurebreaking electrolyte (Kl).In the solvents containing high wt % DMA theions start orienting the solvent molecules and aconsiderable change in the value of 1JE occurs.Therefore, I')E+tjA~'I)D and we get high positivevalues of B coefficient.The authors express their gratefulness to LateDr D. Singh for initiating this work.References1. JONES, G. & DOLE, M., J. Am. chem, Soc., 51 (1929),2950.2. FALKENHAGEN,H. & DOLE, :\1:.,Physik. Z., 30 (1929), 611.3. FALKENHAGEN,H., Physik. Z., 32 (1931), 745.4. FALKENHAGEN,H. & VERNON, E. L., Phil. Mag., 14(1932), 537.5. GURNEY, R. W., Ionic processes in solution (1cGraw-Hill, New York), 1953.6. HAROLD-SIMMONS-BoOTH,Inorg. Synth., 1 (1939), 163.7. PAUL, R. c., BANAIT, J. S. & NARULA, S. P., Aust. J.Chem., 28 (1975), 321.8. CANNON,M. R., MANNING,R. E. & BELL, J. D., Analvt,Chern., 32 (1960), 355. -9. Hand book of chemistry &- physics (Chemical RubberPublishing Co., Cleveland, Ohio), 1962.10. ASSARSSON,P. & EIRICH, F. R., ]. phys. Chem., 72(1968), 2710.11. STOKES,R. H. & MILLS, R., The international encyclopediaof physical chemistry &- chemical physics, 3 (1965), 39.12. KAMINSKY,M., Discus. Faraday Soc., 24 (1957), 171.13. ROHDEWALD, P. & MOLDNER, M., J. phys . Chem., 77(1973), 373.Conductance of Lithium Acetate in Water &Aqueous Methyl AcetateR. L. BLOKHRA& P. C. VERMAChemistry Department, Himachal Pradesh UniversitySimla 171001Received 13 August 1975; accepted 22 December 1975Conductance of lithium acetate in water and aqv-methyl acetate (20%, vjv) has been measured at 40°,45° and 50° and in different concentrations of theelectrolyte. Experimental data have been analysed onthe basis of Onsager's equation and Onsager-Fuoss-Skinner equation. The ion-size parameter, a (A) hasalso been obtained at different temperatures employ-Ing Onsager-Fuoss-Sklnner equation. Temperaturedependence of the Walden-products is also discussedin terms of the srructure-breaktngjrnaklng charac-teristics of the salt.THE conductivity of lithium acetate in water andaqueous methyl acetate (20% v]» at 25°) havebeen measured at different temperatures with aview to (i) testing the validity of Onsager's equation!and the Onsager-Fuoss-Skinner+ equations, (ii)estimating the solute-solvent interaction and (iii)evaluating the contact distance between the ionsin the solution at infinite dilution.Lithium acetate (BDH, England) was used aftercrystallization from ethanol. Methyl acetate waspurified by treating it with potassium carbonateand distilling after keeping overnight over PZOfi.Anhydrous methyl acetate had the following physicalcharacteristics: density = 0·9206 g ml+, 7J = 0·00351poise, conductance = 3·8 X 10-6 ohm-! cnr? at 30°and the values are comparable with the literaturevaluess-s. Water of conductivity of the order of10-6 ohrrr+ crrr ! was used for making solutions oflithium acetate in methyl acetate. Aqueous mixtureof methyl acetate was prepared at 25°. All solutionswere made by weight. Conversion between equi-valent concentration and molality was done fromthe usual relationships. Measurements were carriedout at 40°, 45° and 50°. Densities of the solutions(d) were determined with the help of a method des-cribed elsewhere". Conductance measurements werecarried out in the manner reported in our earlierpubli cat ions'c",The equivalent conductance values of lithiumacetate in water and in aq.-methyl acetate atdifferent temperatures are summarized in Table 1.The values of the constant () in the Onsager'sequation for solutions of lithium acetate at 40°, 45°and 50° are 0'2344, 0·2369 and 0·2396 respectivelywhereas those of the constant <1 at these tempera-tures are 82·38, 90-58 and 99·09 respectively. Forsolutions of lithium acetate in aq-methyl the valuesof () at 40°, 45° and 50° are 0'3097, 0·3125 and0·3154 respectively whereas those of (j at thesetemperatures are 72·09, 81·06 and 89·74 res-pectively.The plots of A versus yt are linear for solutionsin water, but for solutions in aq.vmethyl acetate,linear plots are obtained only up to the concentration~0·01N_ The values of the limiting conductances,1\0' obtained on extrapolation of A versus v'Cplots to v'C~0, for solutions in water and in aq_-methyl acetate at 40°, 45° and 50° respectively alongwith theoretical and experimental Onsager slopesare given in Table 2.Table 2 shows that the deviation in the Onsagerslopes are less in aqueous solutions than in aqueousmethyl acetate. The large discrepancies in theslopes in solutions of aq.vmethyl acetate can beattributed to the incomplete dissociation of lithiumacetate and formation of ion-pairs. To prove theformation of ion-pairs in this solution, a plotbetween log A and log C is drawn according to thetheory of Fuoss- Kraus-". Further, according toBjerrum!-, the limiting slope (d log Aid log e) shouldbe equal to - 0·5 and the experimentally observedvalue is found to be - 0·46, indicating a fair agree-ment between the theory and the experiment.Further, the conductance equation is also related-!NOTESTABLE 1 - EQUIVALENT CONDUCTANCE OF SOLUTIONS OFLITHIUM ACETATE IN WATER AND AQ_-METHYL ACETATE AT40°, 45° AND 50°Water Aq.-methyl acetateCx 10' A obs. Cx 10' A obs.(g_ eq.jtitre) ohm-1 cm2 (g. eq.jlitre) ohm=! cms40°7-65 107'50 6·12 124-6114-99 103'02 8·13 119-5822-50 100-00 13-82 104'5838-43 94-02 32-85 89·2155-68 88-04 51-51 80·2876-44 83-51 71-55 78-0099-22 79-06 90-96 70·1945°9-02 113·50 7-09 130-2415-62 109·50 9-66 120-5323·25 106-02 20'67 108·7837·51 101-68 39-82 98·8155-01 95-61 61-74 89-0978-34 91·20 81-88 82-38123·07 78-30 115-10 76'7450°3·30 128·50 5·84 136'137-65 124·50 7·76 129-3413-22 121-02 9-95 125·0919-53 118-13 18-86 119-2240-35 107-46 39-63 105·3679-00 100-63 59-94 96-46107-26 95-00 80-84 87·410-00 0-00 110-86 80-13TABLE 2 - LIMITING CONDUCTANCE (Ao) ANDONSAGER'S SLOPES IN WATER AND INAQ_-METHYL ACETATE AT 40°, 45° AND 50°Temp. Ao K Deviation(0C) (ohm-1 ems) (%)Onsager Obs.40 119-0 110-2 125·0 13-0(163-5) (122-7) (511-1) (316-3)45 126-0 120-4 128'5 6·0(165-5) (130-7) (433-3) (231'3)50 135-0 131-4 128·5 2'0(169-0) (143'0) (433,3) (202'9)Values in aq.smethyl acetate are given in parentheses.to the dissociation function, (Kl) and the mass lawconstant, (k) according to the relationt-:Aye = AolyKl+v'Kl A;2.e ...(1)According to Eq. (1), plot of Aye versus e shouldbe linear and it has been found to be so in the diluteregion. At higher concentrations, curvature is ob-tained which suggests12,13 that some associatedcomplex formation has occurred in aq.smethylacetate.The data have been further analysed by the Fuoss-On sager-Skinner equation for the dissociated salts.The values of the limiting equivalent conductances,Ao, the contact distances a ( A) of the ions in solutionalong with the Walden product-, Ao1J, at differenttemperatures are given in Table 3.697INDIAN J. CHEM., VOL. 1+A, SEPTEMBER 1976TABLE 3 - VALUES OF 1\0' 1\0'" AND a (A) AT DIFFERENT TEMPERATURESFOR LITHIUM ACETATEIN WATER ANDAQUEOUSMETHYL ACETATEOBTAINED FROMTHE TEST OF THE FUOSS-ONSAGER-SKINNEREQUATIONTemp. 1\0 (ohm " cm-) 1\0 (ohrrr" cm-) 1\0'1 a (A)(0C) "Vater Aq.-methylacetate Water Aq.-methyl Vlater Aq.-methy\acetate acetate+0 121'9 128·+ 0·80 1-06 H 1·7+5 130·2 135·5 0·78 0·99 1·6 1·950 133·2 1+3'6 0·73 0·95 2·2 2·0The data in Table 3 reveal that the limitingequivalent conductances obtained by Onsager ex-trapolation method and Fuoss-Onsager-Skinnerequation differ slightly for solution in water, but forsolutions in aq.-methyl acetate, there is largedifference in 1'1.0 values. This large difference maybe due to the fact that (a) the Fuoss-Onsager-Skinnerconductance equation takes into account the pointsat higher concentrations also whereas these pointsshow deviations from simple Onsager plots and (b)manual extrapolation in Onsager plots may be thesource of error.The structural effects on the conductance of ionsin aqueous solutions are derived by a comparisonof their Walden-products in aqueous and non-aqueoussolutions at different temperatures-v-". From theTable 3, it is clear that as the temperature increasesthe Walden-product goes on decreasing. The Ao'YJversus t plots are almost linear for both the solutionsand have negative temperature coefficient. Thenegative temperature coefficient' suggests that thelithium acetate acts as a structure-breaker both inwater and in aq.-methyl acetate. The slight in-crease in the ion size parameter a (A) with tempera-ture for lithium acetate in water and aqueousmethyl acetate may be interpreted? as an indica-tion "of the structure-breaking tendency of theelectrolyte in a solvent.The structure-breaking capacity of lithium acetatein water and aqueous methyl acetate is also sup-ported from the viscosity measurementst",One of the authors (p.e.v.) is thankful to eSIR,New Delhi, for the award of a junior researchfellowship.References1. MAcINNES, D. A., The principles of electrochemistry(Dover, New York). 1967, 327; 360.2. Fuoss, R. M., ONSAGER,L. & SKINNER, J. F., J. pbys.Chem. Ithaca, 69 (1965), 2581.3. TIMMERMANS, 1., Physico-chemical constants of pureorganic compounds, Vol. I (Elsevier, New York), 1950,+13.+. LANGE, N. A., Handbook of chemistry (McGraw-Hill,New York). 1967, 1221.5. SHOEMAKER,D. P. & GARLAND,C. W., Experiments inphysical chemistry (McGraw-Hili, New York), 1967,131.6. BLOKHRA,R. L. & SEHGAL,Y. P., Indian J. Chem., 14A(1976), 162.7. BLOKHRA,R. L. & PARMAR,M. L., J. electroanal, Chem.,57 (197+), 117.8. BLOKHRA,R. L. & SEHGAL,Y. P., J. electroanal. Chem.,62 (1975), 381.9. BLOKHRA, R. L. & SEHGAL, Y. P., Z. phys. Chem., 93(197+), 155.69810. Fuoss, R. M. & KRAUSS, C. A., J. Am. chem, Soc., 55(1933), 1019; 2387.11. BJERRUM, N., Det. Kgl. Danske Viden, 9 (1926), 2.12. BLOKHRA,R. L. & SEHGAL, Y. P., Indian J. Chem., 12(197+), 998.13. BLOKHRA,R. L. & PARMAR,M. L., J. electroanal. Chem.,59 (1975), 226.1+. KAY, R. L. & EVANS, D. F., J. phys. Chem, Ithaca, 70(1966), 366; 2325.15. KAY, R. L., CUNNINGHAM,G. P. & EVANS, D. F.,Hydrogen bonded solvent systems, edited by A. K.Govington & J. Jones (Taylor & Francis, London),1968, 2+9.16. BLOKHRA, R. L. & VERMA, P. C., Electrocbim, Acta,(in press).Study of Hydrolysis Kinetics & Lactone-Acid-Salt Equilibria of 'Y-D-MannonoiactoneS. K. DUTTA· & SUVA BRATO Rov]Department of Pharmacy, Jadavpur UniversityCalcutta 700032Received 2 August 1975; accepted 31 January 1976Specific rate constant (hH) for the hydrolysis of "(-D-mannonolactone in aqueous solution has been deter-mined conductometrically, the values at 25° and 37°are 2·04 and 5·37 x 10-6 see? respectively. Activationenergy (Ea=14·73 kcal mote<) has been found from theArrhenius plot. The overall equilibrium constant (Keq)for the hydrolysis of the lactone, hA for mannonic acidand the equilibrium constant kL for the hydrlysis of thelactone have been determined from pH and opticalrotation measurements and are found to be 2·48±0·10x 10-5, 1·60±0·16 X10-' and 0·18 respectively. Lactoni-zation constants hI for mannonic acid at 25° and 37°are 1·34 and 2·98 x 10-5 see= respectively.THE hydrolysis kinetics of industria lly importantaldonolactone .;, viz. n-glucono-Svlactonc-, lac-tobiono-Sdactone'', maltobiono-Svlactone'', cello-biono-Svlactone- and Y-D-galactonolactone 6 havebeen reported earlier, but such data on Y-D-manno-no lactone are wanting. A systematic study ofthe hydrolysis kinetics of this lactone and lactone-acid-salt equilibria are reported in this note.Y-D-A1annonolactone - n-Mannose (45 g) waselectrolytically oxidized in the presence of NaHC03(25 g) and 1% sodium bromide in 800 m) water·To whom correspondences are to be directed.tAbstracted from a dissertation submitted by Suva BratoRoy, Department of Pharmacy, Jadavpur University,Calcutta 32, in part fulfilment of Masters degree of Pharmacyrequirements.

Conductance of Lithium Acetate in Water & Aqueous Methyl Acetate

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Conductance of Lithium Acetate in Water & Aqueous Methyl Acetate

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