Partial molal volume and partial molal compressibility of polyethylene glycol in water

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1 Indian Journal of Chemistry Vol. 41 A, April 02, pp Partial molal volume and partial molal compressibility of polyethylene glycol in water A K Puri, N K Soni*, Amit Pandey & Ashish K Sharma Department of Chemistry, Uni versity of Allahabad, Allahabad , India Received 14 Jllly 00; re vised 31 Jllly 01 Using the ex perimental data of Gerecze [ACIISlica, 38 ( 1977) 51 Ion ultrasonic ve locity, density and refractive index or aqueous polyethylene glycol, the va lues of partial molal volume (<1»'), experimental slope (S v) and partial molal compressibility (<I>KO) at different temperatures, interac tion coefficient (Q ), mo lal volume of Vand's eq uati on at C (V) and mol ar refraction (Rill) have been calculated. Validity of Vand's equati on and molar refraction equation for polyethylene glycol is displayed. Temperature dependence hydrati on nature of polyethylene glyco l has also been di scussed. In recent years, there has been considerable interest in the solute-solvent interactions of dilute solutions of non-electrolytes. Enhanced stabilisation of water structure around the solute molecule in the form of clusters or cages in the ethylene-glycol water system has been discussed by Glew l. Abnormalities in many thermodynamic behaviour including partial molal volume and partial molal compressibility were discussed by Frank and Ives 2. According Hioland 3, parti al molal vo lume (<Pvo) and partial molal compressibility (<PKO) of polyfunctional alcohols having several hydroxy l groups, are capable of hydrogen bonding water molecul e. Adi abatic and isothermal apparent molal compressibilities of secondary alcohols and ethers in water were reported by Cabini4. Viscosity of non-electrolyte solutes in water was anal yzed in the light of Vand 5, Moulik 6 and Thomson 7 equations.. AI exan d er el a, propose d an equation. describe the viscosity B-coefficient for dilute so lutions of non-electrolytes in water. Islam et al. 11 reported B-coefficient and apparent molal volume at infinite dilution (<Pvo) for tetraalkyl halides in ethyl ene gycol-water mixture. RecentlyI 2-16, ultrasoni c velocity, density and viscosity data have been used sati s facrily study various types of interactions in multicomponent systems contammg some very important bio molecules and ions. In the present note, we present the results of calculations of partial molal volume (<Pvo) and parti al molal compressibility (<PK 0), interaction coefficient (Q), molar volume of Vand's equation (V) and molar refraction (Rm) of aqueous polyethylene glycol solutions using the volumetric, ultrasonic, viscometric and refracmetric data of Gerecze l7. Equations used Apparent molal volume, (<Pv), has been calculated using the relation (d o - d) M v = +- m.d o do... (I) where do and d are the density of solvent and soluti on respectively, and other sy mbol s have their usual notation. The apparent molal volume (<Pvo) at infinite dilution has been obtained using equation (2).... (2) Isentropic compressibility, (Ks) has been obtained from sound velocity (u) and density (d) data using the relation: Apparent molal compressibility, (<PK) from the equation:... (3) t S computed... (4) where Ks and Ks.o are the isentropi c compressibility coefficients of solution and solvent respectively. Apparent molal compress ibility at infinite dilution, (<PKO) has been obtained from ex pression,... (5) Refractive index data have been used for obtaining the mol ar refraction (Rill) using the relation 2 2 RIll=(no - lin D + I) + Mid... (6) where no is the index of refraction (sodium D line) and M is the molec ul ar of polyethylene glyco l.

2 752 INDIAN J CHEM, SEC A, APRIL 02 Table I-Apparent molal volume, (<I>v), apparent molal compressibility, (<I>K), and isentropic compressibility, (f3s), of polyethylene glycol in water at, and C <l>v x 10 3 <l>k X IO J f3s X Weight (mol kg- I) (011 mo)'l) (cm 3 mol-i bar- I) Cll1 2 dyne- I At C, Al C, ! ! Al C, (Comd)

3 NOTES 753 Table I-Apparent molal volume, (<!>v), apparent molal compressibility, (<!>K), and isentropic compressibility, (~s), 01" polyethylene glycol in water at, and C-Contd <!>vx 10) <!>K X 10.1 ~sx Weight (mol r l) (mlmorl) (cm) mol- I bar- I) cm 2 dyne- 1 At C Q Table 2:-Apparent molal volume at infinite dilution, (<!>vo) and experimental slope, Sv of polyethylene glycol at different temperatures and concentrations T (mol kg- I) <!>VOx 10 2 (ml mor l ) Sv, Table 3-Apparent molal compressibility at infinite dilution, (<!>KO) of polyethylene glycol at different temperatures and concentrations,000 T (0C) Concentration range m m <!>KOX 10) (cm' mol bar- I) III OO53m m I I Q m O.lm m 0.34m Results and discussion In Table 1, values of apparent molal volume (<Pv), apparent molal compressibility (<PK) along with the values of isentropic compressibility (~s) have been recorded for polyethylene glycol in water at, and C. The values of partial molal volume (<Pvo) for the systems under present investigation are presented in Table 2 along with the experimental slope, Sv. The values of partial molar compressibility (<PKO) are recorded in Table 3. The values estimated for interaction coefficient, Q, molar volume of Yand's euqation (V), at 0 e are recorded in Table 4. It is obvious from Table 2, that the values of apparent molal volume at infinite dilution (<Pvo) are gradually decreasing with increase in concentration. It is concluded that, polyethylene glycol is more hydrated

4 754 INDIAN J CHEM, SEC A, APRIL 02 at higher temperatures than at lower temperatures. Thus, both temperature and concentration are responsible for the solute-solvent interaction with respect molecular of solute. On the other hand, Sv values considerably increase with temperature but the trend is not the same in the entire range of concentration. It IS evident from the recorded values, Sv are hi gher at high temperatures, suggesting strong solutesolute interaction. rt is evident from Table 3, that va lues of <PK 0 increase with temperature and decrease Table 5- refraction of polyethylenc glycol- Col/ld (mol kg-i) " Rill, Table 4- The coefficicnt Q and molar volume V of Vand's viscosity equati on at C we ight,000 (mol kg l ) Q V Table 5- refraction of polyethylene glycol,000,000,000 T (0C) (mol kg- I) (Con/d) h J

5 NOTES 755 sharply with increase in concentration. The values of <PKO are highly influenced by the molecular size of solute. In the present investigation, negative values for <PK 0 can be associated wi th structure promoti ng ability of solvent, i.e., loss of structure compressibility of water on account of increase in population of four bonded water molecule. Critical evaluation of physico-chemical data leads the conclusion that there must be reinforcement of water structure in the neighbourhood of alcohol molecule in dilute solution. It is seen from Table 4 that viscosity interaction coefficient, Q, is constant for all ranges of concentration with respect molecular size of solute molecule. It is concluded, therefore, that hydrophobic interactions are mainly dependent on size of polyethylene glycol. The stability of solvent water increase with decrease in molecular size of polyethylene glycol. On the other hand, molar volume, (V) decreases with increase in polyethylene glycol concentration and can be ascribed the decrease in hydrophobic interaction between water dipole and ion of polyethylene glycol with respect molecular size. It is evident from Table 5 that the molar refraction, Rnll values increase with increase in the molecular of polyethylene glycol but is almost constant between the temperature range 10 C and C. Acknowledgement The authors are thankful Prof. J. D. Pandey (Former Head) and Dr Ranjan Dey, Department of Chemistry, University of Allahabad, for valuable suggestions. References I Glew D N & Rath N S, Can J Chem, 45 ( 1970) Frnnk F & Ives, D J G, QU[/I'I Rev Chelll Soc, ( 1966) I. 3 Hioland & Halvik H J, J.wln Ch em, I ( 1878) Cabini S & Cant G, J.1'0/11 Ch elll, 8 ( 1979) II. 5 Vand V, J {lhys Colloid Chem, 52 ( 1948) Moulik, J Indian chelll Soc, 79 (1984) Thompson P T, Fisher B & Wood R N, J.1'0/11 Chelll, II (1982) I. 8 Alexander D M & May DC, AIISI J Chelll, 35 ( 1982) Alexander D M & May DC, AuSI J Ch ell1, 35 ( 198 1) Alexander D M & May DC, AUSI J Chell1, 34 ( 1984) II Islam N & Qudesia Rehana, Indian J Chern, 2 1 A ( 1982) Pandey J D, Puri A K, Tiwari A & Sharma A K, Proc Indiall Acad Sci, III (1999) Pandey J D, Haroon S, Puri A K & Misra K, Indiall J Ch elll, 36A (1997) 393, Pandey J D, Misra K & Mushran V, ACLIslica, 80 ( 1994) Pandey 1 D, Misra K & Mushran V, ACLIslica, 8 1 ( 1994) Pandey J D, Haroon S, Dey R, Upadhyay M & Mi sra K, Call J Chem, 78 (00) Gerecze N G. AClIslica, 38 (1977) 51.

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