CONDUCTOMETRIC INVESTIGATIONS ON OXALIC ACID IN 2-PROPANOL + WATER MIXTURES AT , , AND K

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1 CONDUCTOMETRIC INVESTIGATIONS ON OXALIC ACID IN -PROPANOL + WATER MIXTURES AT 98.5, 0.5, 08.5 AND.5 K Shivakuar H R, Siju N Antony, Surekha M Prof & Head, Associate Professor, Departent of Cheistry KVG College of Engineering ( Affiliated to Visvesvaraya Technological University, Belgau, Sullia, D.K, Karnataka State, ( India Associate Professor, Departent of Cheistry, MVJ College of Engineering ( Affiliated to Visvesvaraya Technological University, Belgau, Bangalore, Karnataka State, ( India ABSTRACT Electrical conductivity of oxalic acid has been easured in -propanol + water ixtures covering the approxiate range of dielectric constant 7.0 ε 49.6 at 98.5, 0.5, 08.5 and.5 K. The conductance data have been analysed by using Shedlovsky equation to obtain liiting olar conductance, association constant and Walden product. The liiting olar conductance and Walden product values were found to decrease with increase in x pr (ole fraction of -propanol. Oxalic acid is found to be a structure breaker in the solvent edia explored. The results obtained fro the study were used to elicit the nature of ionion and ion-solvent interactions. Keywords: Liiting Molar Conductance, Walden Product, -Propanol, Oxalic Acid I. INTRODUCTION Investigations on transport property of an electrolyte and the effect of ion solvation on it in various aqueous and partial aqueous edia have received uch attention in recent years, since it gives valuable inforation regarding ion-ion and ion-solvent interactions [-5]. In continuation of our works on electrolytes in -propanol + water ixtures, we have chosen oxalic acid as the electrolyte due to its ability to for stable coplexes with various etal ions, and its substantial iportance in any industrial, geological, and biological systes [6]. Moreover, it is a weak electrolyte and is expected to for hydrogen bonds with both water as well as - propanol. Oxalic acid on dissociation gives oxalate ion and hydrogen ion. The forer is a structure breaker [7] and the latter is a kosotrope capable of breaking hydrogen bonds. However, oxalic acid is reported to show structure breaking properties in soe water + organic solvent ixtures [8]. In contrast to other dicarboxylic acids, conductance of oxalic acid in aqueous ediu at 98.5 K was repeatedly easured by Ostwald [9], Collie [0], and the ost extensive easureents by Darken []. Darken incorporated a sall correction in the deterined conductances considering the second dissociation of the acid. Using Quint-Viallard conductivity equation Lee and Wheaton further analysed Darken s conductance data. With an exception of Darken s work, other reports were of liited value and hence Barthel et al [6] ade systeatic and precise easureents of electrical conductivities of dilute aqueous oxalic acid solutions in the teperature range K. 76 P a g e

2 However, conductoetric investigations on oxalic acid in -propanol + water ixtures are not reported in the literature. -Propanol + water ixtures are of special interest due to the clathrate-like structures present in the []. II. METHODOLOGY Oxalic acid (Merck, AR Grade, triply distilled water (specific conductance 0-6 ho c - and -propanol purified by using standard procedure [8] were used for preparing M oxalic acid stock solutions in different - propanol + water ixtures. These solutions were further diluted to obtain solutions of desired concentrations. Conductance easureents were ade using a digital icroprocessor based conductivity eter Systronics India Liited. All the easureents were ade in a therostat aintained at the desired teperature with an accuracy of ±0. C III. RESULTS AND DISCUSSION. Liiting Molar Conductance ( (Model-08, Molar conductance of oxalic acid in -propanol + water ixtures were calculated using the specific conductance obtained fro a direct reading digital conductivity eter at (98, 0, 08 and K. The resulted olar conductance values were analysed by Shedlovsky odel [], a variant of Fuoss-Kraus odel, which includes corrections for inter ionic effects on ionic obilities and for ionic activity coefficients. Shedlovsky equation used for deterining liiting olar conductance and association constant K a is given below: S C Sf K a ( where C 4 C S ; ( T 8.5 ( T ; where log f ( C /( T R( C /( T S and e R q kt ; f is the ean activity coefficient, estiated fro the extended Debye-Huckel equation; R is ion size paraeter which is equal to the Bjerru s critical distance q; k is Boltzann s constant and T is the teperature in Kelvin. The Shedlovsky plots are presented in Fig. and values obtained are given in TABLE. 77 P a g e

3 Fig. : Plot of /SΛ (oh c - ol Vs CΛ Sƒ ± for oxalic acid in -propanol + water ixtures at Different Teperatures As expected the liiting olar conductance values are quite large ainly due to the presence of highly conducting hydrogen ions. The anoalously large obility of proton in aqueous ediu is often explained in ters of Grotthus echanis and quantu echanical tunneling [4]. The increase in dissociation and ionic obility caused the liiting olar conductance to show sharp increase with increase in teperature. A sharp decline in liiting conductance is noticed with increasing x pr. Various factors such as decrease in dielectric constant, increased viscosity of solvent ixture [], increased basicity, destruction of tetrahedral-like structure of water and increased solvated ion size ust have played a critical role in reducing the conductance. It is also known that the anoalous conductivity of proton declines with increasing alcohol content [5]. Liiting conductance is not reported beyond 0.67 ole fraction of -propanol due to poor linearity of the Shedlovsky plot. 78 P a g e

4 Table : Experiental olar conductance at infinite dilution ( : ho c ol - for oxalic acid in -propanol + water ixtures at different teperatures obtained fro Shedlovsky odel T (K x pr Association Constant (K a Association constants calculated fro the Shedlovsky odel is given in TABLE. Association is expected to predoinate over dissociation since the electrolyte under consideration is weak. Except for x pr = 0.057, association constant is found to increase with increase in teperature suggesting the endotheric nature of the syste. Siilar behavior is reported for tartaric acid in water + ethanol/ethanol systes [6]. The trends in the variation of K a with respect to ole fraction of -propanol is rather ausing. The initial addition of -propanol to water is found to reduce the association constant as against the usual increasing trend with declining dielectric constant. Thus the coputed K a values at x pr = and x pr = are lower than expected. The iniu K a values noticed at x pr = can be explained on the basis of changes in water structure induced by the sall quantities of -propanol added. Water is a highly associated solvent due to the presence of hydrogen bonds that helps in the foration of polyeric aggregates of water. Hence pure water can stabilize the ion-pairs by foring chain structure around it [7]. On adding sall aounts of -propanol, depolyerisation of water chain occurs and hence ion-pairs are less stabilized. Larger K a values found at at x pr = 0.67 is due to the predoinating influence of decrease in dielectric constant favouring association. Table : Experiental values of K a for oxalic acid in -propanol + water ixtures at different teperatures T (K x pr Walden Product Walden product was calculated for oxalic acid in different copositions of -propanol + water ixtures at four different teperatures using the forula: 79 P a g e

5 Walden product = ( where ɳ is the viscosity coefficient of solvent ixture. The linear plot of Walden product versus teperature provided in Fig. is having negative slope indicating structure breaking behavior of oxalic acid in aqueous as well as in -propanol + water ixtures. The Walden product is found to decrease with increasing x pr and consequently solvation is strengthened in that direction. The oentous deviation fro Walden rule with increasing ole fraction of -propanol ay be a consequence of change of ion solvation and of the solvent structure [8]. Fig. : Plot of walden product (S c ol - poise vs teperature (K for oxalic acid in - IV. CONCLUSIONS propanol + water ixtures The sharp decline in conductance with respect to increase in -propanol content in the solvent ixture is explained on the basis of different factors influencing ionic conductance. The endotheric nature of the syste is evident fro the K a values for different systes at different teperatures. The structure breaking character is established fro the variation of Walden product with teperature. V. ACKNOWLEDGEMENTS The financial support for this investigation given by Visvesvaraya Technological University, Belgau, India under the grant Ref. No. VTU/Aca/00-/A-9/9 dated 7 th Deceber 00 is gratefully acknowledged. REFERENCES []. H. R. Shivakuar and Siju N. Antony, Conductoetric studies of potassiu thiocyanate in -propanol + water ixtures, Asian Journal of Cheistry,, 00, []. J. Gregorowicz, A. Bald, A. Szejgis and A. Chielewska, Gibbs energy of transfer and conductivity properties of NaI solutions in ixtures of water with butan--ol at 98.5 K, and soe physicocheical properties of ixed solvent, Journal of Molecular Liquids, 84, 000, P a g e

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