Available online at www.scholarsresearchlibrary.com Archives of Physics Research, 213, 4 (2):13-111 (http://scholarsresearchlibrary.com/archive.html) ISSN : 976-9 CODEN (USA): APRRC7 Adiabatic compressibility of aqueous ehylene glycol and copper sulphate mixture at different temperatures * N. S. S. V. Raja Rao 1, V. Brahmajirao 2 and A. V. Sarma 3 1 Godavari Institute of Engineering and Technology, Rajahmundry, A. P., India 2 Department of Nanoscience and Technology,School of Biotechnology, MGNIRSA, Hyderabad, A. P., India 3 Department of Physics, Andhra University, Visakhapatnam, A. P., India ABSTRACT Ultrasonic Velocity (U) and Density (ρ) have been measured using Antonpaar s DMA M in a concentration range of.1.6 M and eleven compositions at 298, 3, 8, 313 and temperatures for a ternary mixture of Aqueous Ethylene Glycol and Copper Sulphate system to study ion- solvent interactions and Eigen-Tomm Ion Pair formation Mechanism (ETIPM). It is observed that the values of density and ultrasonic velocity of any ionic liquid vary with increase in concentration of solutions, mainly due to the change in structure of solvent or solutions as a result of hydrogen bond formation or dissociation or hydrophobic or hydrophilic character of solute, or the solventsolvent interactions, between Ethylene Glycol and water. Adiabatic compressibility (β) data indicate an ordering interaction leading to the formation of an ionic complex. The ionic complex formation in an ionic system is due to ionic association. Keywords: Ultrasonic velocity, Density, Adiabatic compressibility, Binary Solvent Mixture(BSM), Ion pairs, ionsolvent interactions, Eigen Tomm Ion Pair Mechanism (ETIPM). INTRODUCTION Margaret Robson Wright [1], finds that Ultrasonic and Spectroscopic techniques probably allow a distinction to be made with reasonable certainty between outer and inner-sphere ion pairs, as was expressed by Ohtaki and Radnai [2]. Amongst the many techniques [3], the measurement of speed of sound in solution hitherto was being used to elucidate the structure of the solutions. By taking ultrasonic technique into account, the important consequences of ion solvation, such as reduced volume and the compressibility of the solvent molecules can be studied. The propagation of ultrasonic pulses through a medium can be made use of in the investigation of physical properties of the medium have led to the development of various methods for measuring velocity and attenuation. One such method is by the usage of a vibrating tube made to resonate to an external excitation. The Austrian made ANTONPAAR experimental setup, DSA-M is used for the very accurate determination of ultrasonic velocity and density. Adiabatic Compressibility can be calculated from the observed values of ultrasonic velocity and density of mixture at different temperatures. MATERIALS AND METHODS All the important precautions for the maintenance [4, 5] of the purity of the liquids used are very carefully implemented. CuSO 4 (5H 2 O), Ethylene Glycol both are analytical reagents(ar) purchased from Merck with Assay 13
N. S. S. V. Raja Rao et al Arch. Phy. Res., 213, 4 (2):13-111 99.8%- 12% and 99.8% respectively. The copper sulphate used is in the form of a penta- hydrate (molecular weight 249.69). Ethylene Glycol is used as binary solvent mixture with water. The mixtures of the desired composition were prepared by weighing on a very accurate digital micro balance, Sartorius CPA -225D, to determine the mass of the electrolyte with a precision of ±.1 g. In order to prepare the solutions under investigation in the form of aqueous ionic liquids, a stock solution of ml of each concentration is prepared. This stock solution is added to ethylene glycol (redistilled) to makeup ionic liquids of the required composition. Each composition of 5ml is injected into the setup using a syringe. Range and Accuracy: Ultrasonic velocity: - 2 m/sec with accuracy of.5 m/sec Density: - 3 gram/cc with accuracy of. 5 gram/cc Temperature: - C with accuracy of.3 C. Adiabatic compressibility, β: It can be evaluated by the formula, β = 1/U 2 ρ where, U is ultrasonic velocity, ρ is density of the solution. The data of U and ρ have been given in Tables: 1 and 2. Adiabatic Compressibility is inversely proportional to square of the ultrasonic velocity. The deviations in this parameter may be due to difference in size and shape of the molecules. The compressibility data, presented in Table: 3 indicate an ordering interaction leading to the formation of an ionic complex. The ionic complex formation in an ionic system is due to ionic association. The plots are drawn with concentration as abscissa and β as ordinate. RESULTS AND DISCUSSION Adiabatic compressibility increases with increase in temperature and decreases with increase in concentration. Increases in compressibility were attributed to the formation of hydrogen bonds between solute and solvent molecules [6]. Table: 1. Ultrasonic velocity data (in m/s) of CuSO 4 for 6 concentrations (gm.mol/lit or M) in 11 compositions of BSM of EG+WATER at different temperatures % composition of water in BSM 1 2 1 2 TEMPERATURE:.1M.2M.3M.4M.5M.6M EG+WATER 1682.3 11.18 171. 18.56 1697.2 1673.91 1642.2 12.65 1556.94 16. 1645.43 1671.4 16.79 1. 1.48 1691.29 16.71 1642.15 16.21 1564.54 1517.54 1678.86 11.34 1711.55 171.34 1699.24 1676.15 1641.89 13.86 1553.21 151.41 1683.11 1699.87 1711.49 1712.12 1699.58 1675.1 1649.12 11.99 1565.56 1517.35 1683.89 12. 1711.81 1711.27 1699.79 1677.49 1648.35 1611.99 1568.92 1521. TEMPERATURE : 3K 1645.43 1645.43 1645.43 1667.67 1671.74 1672.77 16.82 1689.14 1691.83 12.11 11.94 12.28 12.1 1696. 13.7 1693.14 1693. 1693.81 1672.73 1671. 1673.96 1641. 1648.51 1647.85 17.41 15.73 1614.94 1561.12 1572.48 1575.53 1521.63 1528.5 1532. 1683.7 11.39 1711.53 1712.32 12.82 1683.54 1651.78 1616.91 1571. 1529.89 1645.43 1671.84 16.78 11.87 13.98 1696.48 1679.61 1651.11 1619. 1577.97 1539.77 1684.95 13.87 1712.58 1713.38 14.52 1683.96 1656.29 1617.4 15.69 1537.35 1645.43 1673.63 1693.28 12.76 15.35 1698.8 1679.99 1655.29 1619.79 1586.65 1546.82 1682. 1.79 171.11 17.28 1694.97 1668.52 1629.82 1599.91 1545. 1497.8 1645.43 1671. 16.35 1.72 1699.45 1689.22 1657.78 16.77 13.61 1553.89 19.33 14
N. S. S. V. Raja Rao et al Arch. Phy. Res., 213, 4 (2):13-111 1 2 1 2 1 2 1633.63 1659. 16.6 1691.11 1692.18 1684.88 1668.89 1641.31 18. 15.78 1527.44 1621.83 1648.7 1669.24 1681.11 1683.46 1678.2 1662.53 1639.74 161.44 1575.77 1535. 19.99 1636.46 1658.28 16.91 1674. 16. 1657.57 1637.45 1611.16 1579.53 1542.86 TEMPERATURE : 8K 1633.63 1633.63 1633.63 1656.18 16.28 1661.39 1679.96 1678.27 16.98 1692.63 1692.7 1692.33 1693.59 16.93 1694.58 1686.54 1686.72 1687.25 1668.73 1667.72 1669.88 1641.11 1647.15 1646.58 19.92 18.47 1616.89 1567.66 1578.15 15.93 1531.35 1537.32 15.92 TEMPERATURE : 1621.83 1621.83 1621.83 1644.63 1648.76 1649.93 1669. 1667.32 16.4 1682.78 1681.98 1682.19 1684.79 1684.71 1685.82 1679.52 1679.63 16.28 1664.19 1663.22 1665.27 1639.56 1645.4 1644.56 1611.43 161.18 1617.88 1572.89 1582.56 1585.1 1539.55 1545.9 1548.32 TEMPERATURE : 19.99 1632.99 1657.92 1672.73 1675.69 1672.14 1659.8 1637.24 1611.96 1576.87 1546.29 19.99 1637.18 1656.23 1671.72 1678.8 1672.18 1658.14 1642.18 161.92 1585.79 1551. 19.99 1638.39 1658.99 1671. 1676.77 1672.97 16.1 1641.81 1617.91 1588.1 1554.32 1633.63 16.39 1679.84 1691.86 1695.46 1689.67 1675.8 1649.68 1621.11 1583.32 1548.23 1621.83 1648.87 1668.79 1681.63 1686.58 1682.46 16.2 1647.51 1621.76 1587.43 1555.22 19.99 1637.27 1657.63 1671.26 1677.36 1674.88 1664.45 1644.62 1621.48 15.39 15.85 1633.63 1662.45 1682. 1692.63 1696.72 1691.16 1675.48 1653.54 1621.48 1591.27 1554.74 1621.83 1651.1 1671.42 1682.32 1687.74 1683.84 16.46 1651.6 1622.23 1594.76 1561.21 19.99 1639.45 16.33 1671.88 1678.67 1676.13 1664.94 1647.88 1622.4 1597.12 1566.32 1633.63 16.41 1679.59 1691.14 1691.31 1683.1 1662.53 16.89 16.35 15.94 1519.74 1621.83 1648.97 1668. 1681.32 1682.86 1676.39 1658.58 16.21 18.1 1566.94 1528.75 19.99 1637.51 1657.67 1671. 1674.9 1669.35 1654.8 1628.73 18.88 1571.17 1536. Table: 2. Density data (in kg/m 3 ) of CuSO 4 for 6 concentrations (gr.mol/lit or M) in 11 compositions of BSM of EG+WATER at different temperatures % composition of water in BSM 1 2 1 2 TEMPERATURE:.1M.2M.3M.4M.5M.6M EG+WATER 119.558 113.881 198.368 1.749 181.9 172.837 161.966 1.912 139.19 126.831 113.166 116.66 1.425 194.948 187.4 178.7 169.8 159.271 148.499 137.25 125.59 111.664 119.558 115.5 111.13 194.163 188.678 1.5 171.9 1.552 1.671 138.683 129.484 119.558 117.86 113.158 198.8 188.521 187.477 178.16 172.212 161.671 154.354 145.243 119.558 116.477 114.974 112.78 196.555 191.525 184.237 177.996 171.329 161.648 153.861 TEMPERATURE: 3K 116.66 116.66 116.66 112.99 113. 112.998 197.681 199.721 111.544 1.8 195.5 198.748 185.479 185.662 193.361 177.566 184.458 188.526 168.567 175.274 181.465 158.124 169.714 175.487 148.547 159.5 169.115 136.893 152.4 159.715 127.916 143.593 152.153 119.558 111.255 119.166 118.189 115.544 112.493 198.278 192.368 187.446 1.925 176. 116.66 116.734 115.715 114.818 112.269 199.4 195.447 189.823 185.164 178.9 174.283 119.558 1111.5 1113.92 1112.892 1111.574 119.212 116.91 113.245 198.62 194.796 1.656 116.66 118.79 119.638 119.5 118.3 116.142 113.245 1.651 196.318 192.3 188.753 119.558 112.542 195.158 185.94 175.316 164.974 151.6 136.523 127.143 11.938 997.241 116.66 199.79 191.757 181.811 172.1 162.35 148.863 134.231 125.13 9.281 995.844 15
N. S. S. V. Raja Rao et al Arch. Phy. Res., 213, 4 (2):13-111 1 2 112.551 196.921 191.492 184.68 175.579 166.826 156.469 145.967 134.785 123.12 9.951 TEMPERATURE: 8K 112.551 112.551 112.551 198.1 1.97 199.489 194.219 196.242 198.73 187.497 192.115 195.357 182.224 182.659 1.98 174.491 181.361 185.431 165.733 172.426 178.597 155.573 167.92 172.859 146.272 157.262 166.749 134.918 1.385 157.2 126.137 141.737 1.243 112.551 113.148 112.223 111.395 198.941 196.4 192.517 187.152 182.731 176.762 172.281 112.551 114.563 116.145 116.67 115.43 112.987 1.2 197.933 193.879 1.459 186.668 112.551 195.588 188.318 178.479 168.982 159.24 146.133 131.3 122.3 7.425 994.236 1 2 1 2 199.14 193.391 188.1 1.662 172.292 163.6 153.571 143.318 133.297 12.974 8.43 195.459 189.838 184.475 177.28 168.949 1.514 1.583 1.551 129.872 118.681 5.946 199.14 195.75 1.721 184.88 178.912 171.338 162.2 152.4 143.851 132.769 124.1 195.459 191.532 187.189 1.6 175.539 168.113 159.778 1.115 141.292 1.459 122.22 TEMPERATURE: 199.14 199.14 199.14 196.561 195.9 199.6 192.729 194.563 198.694 188.681 191.912 197.925 179.585 186.775 195. 178.185 182.264 193.92 169.484 175.633 189.491 164.354 1.114 184.364 154.828 164.241 1.1 148.145 155.323 174.428 139.697 148.155 1.13 TEMPERATURE: 195.459 195.459 195.459 192.996 192.385 196.91 189.179 191.16 195.126 185.21 188.42 194.7 176.373 183.391 191.674 174.937 179.18 189.8 166.446 172.574 186.372 161.1 167.256 181.464 152.256 161. 177.458 145.7 152.889 171.939 137.484 145.896 167.764 199.14 111.13 112.613 112.5 111.675 199.751 197.266 195.98 191.292 188.51 184.414 195.459 197.439 199.45 199.49 198.242 196.434 194.134 192.153 188.569 185.494 182. 199.14 192.68 184.8 175. 165.725 155.938 143.294 129.248 12.556 5.387 992.42 195.459 188.521 181.328 171.674 162.9 152.777 1.361 126.573 118.69 3.183 9.417 Table 3. Adiabatic Compressibility data (β in kg -1 ms 2 ) of CuSO 4 for 6 concentrations in 11 compositions of BSM of EG+WATER at different temperatures % composition of water in BSM 1 2 1 2 TEMPERATURE:.1M.2M.3M.4M.5M.6M х1-9 х1-9 х1-9 х1-9 х1-9 х1-9.3283.3283.3283.3283.3283.3283.322.329.3188.3185.31.3169.3146.3138.3138.3123.3114.95.3133.312.317.96..64.3166.31.3134.3114.85.63.3236.325.3183.31.3128.313.3361.3322.36.3277.3212.3188.3528.3498.3429.3414.3355.34.3747..36.3592.3517.3481.18.3991.3869.3827.3746.3656.4352.4258.4155.98.3892.3879.3339.3254.3195.3179.326.3268.3382.3537.3738.3985.4292.3339.3263.3187.3164.31.3237.3345.36.3691.3957.422 TEMPERATURE : 3K.3339.3339.3242.32.3187.3172.3157.31.32.3153.3216.322.3325.3.34.3424.36.3586.3842.31.414..3339.3233.3164.3125.3124.31.3236.3366.3513.3722.3926.3339.3222.3143.319.312.3135.3212.3316.3477.3635.3839 EG+WATER х1-9.3283.322.3157.3151.31.3268.3416.3632.33.4141.4474.3339.3255.326.3196.3229.3.3469.3636.3793.413.4278 16
N. S. S. V. Raja Rao et al Arch. Phy. Res., 213, 4 (2):13-111 1 2.3399.331.3246.3226.3247.32.3399.3549.3734.3961.4244.3398.3319.3238.321.3222.3272.33.3518.3688.3932.4156 TEMPERATURE : 8K.3399.3399.3298.3295.3239.3223.3198.3188.32.3194.32.3236.3353.3325.3454.3438.3656.3586.3823.3783.62.1.3399.3288.3215.3172.3165.3195.3262.33.3514.35.3891.3399.3276.3194.3156.3143.31.3237.3331.3477.3622.37.3399.3311.3257.3242.32.3334.3458.3644.3789.74.4355 1 2 1 2.3459.3367.3299.3274.3291.3339.3434.3565.3732.3945.426.3522.3426.3353.3325.3336.3378.3464.3584.3741.3935.4176 TEMPERATURE :.3459.3459.3459.3376.3355.3352.3291.3292.3276.3254.3247.3236.3265.3263.3238.39.3288.3273.3397.33.3352.3533.3472.3455.3689.3657.35.3914.39.3771.4119.29.39 TEMPERATURE :.3522.3522.3522.3436.3413.341.3346.3347.33.37.3297.3287.3311.3299.3283.3348.3327.3311.3428.3411.3383.3553.3493.3476.3696.3662.3599.33.33.3766.92.5.3958.3459.3345.3268.3221.329.3232.3291.3398.352.3693.3864.3522.33.3323.3271.3256.3271.3323.3419.35.3688.3844.3459.3332.3246.325.3187.327.3266.33.3482.3614.3783.3522.33.31.3255.3231.3246.3297.3372.3492.3612.376.3459.3368.331.32.3313.33.3487.3656.3789.52.4312.3522.3426.3365.3341.3359.39.3513.3672.3795.38.4278 The adiabatic compressibility of aqueous electrolytic solutions is due to about 64% configurational and 36% vibrational compressibility. In dilute solution the adiabatic compressibility is predominantly governed by the configurational compressibility whereas in the concentrated solutions it is due to the vibrational compressibility [7]. In aqueous electrolytic solutions the ion-solvent interactions dominate up to a certain concentration forming a rigid hydration shell and beyond this concentration a transition from ion-solvent to ion-ion interactions occurs leading to the formation of ion-pairs (Solvent-separated, solvent-shared and contact). This critical concentration depends on the nature of the electrolyte. The configurational compressibility contributes to the adiabatic compressibility up to that concentration and beyond that, the vibrational compressibility dominates in the solution. The general assumption of zero compressibility of the primary hydration shell is not collaborated by experimental observation. When a Cu 2+ ion is added to a solvent, certain solvent molecules get attracted towards itself by wrenching the molecule in bulk of the solvent due to the forces of electrostriction. Consequently the available solvent molecules for the next incoming ions get decreased. The compressibility measures the ease with which a medium can be compressed. Thus the compressibility of a solvent is higher than that of solution and it decreases with the increase in concentration of the electrolyte in the solution. With increase in ionic concentration, the electrostrictive forces causes the structure to break [8] and the water molecules surrounding Cu 2+ are more compactly packed and therefore compressibility decreases with increase in Cu 2+ concentration. The decrease in adiabatic compressibility indicates the enhancement of the bond strength at that concentration. On increasing the salt concentration in the solution, the number of free water molecules around the ion decreases gradually until a situation is reached where all the water molecules are involved in the primary hydration shell of the solute. The adiabatic compressibility at that concentration becomes independent of temperature and assigned as critical adiabatic compressibility. Such a condition may be correlated with the saturation of the primary hydration shell since the water molecules are not compressed further and become independent of temperature. Beyond this 17
N. S. S. V. Raja Rao et al Arch. Phy. Res., 213, 4 (2):13-111 concentration, co- spheres of cation and anion start to overlap leading to the formation of ion pairs such as solventseparated, solvent- shared and contact ion pairs [9]..345.3.335.3.325.32.315.1.2.3.4.5.6 WATER:EG::1: 3K 8K.335.3.325.32.315.31 WATER:EG::2: 3K 8K.1.2.3.4.5.6.335.3.325.32.315.31.5.1.2.3.4.5.6 WATER:EG::: 3K 8K 18
N. S. S. V. Raja Rao et al Arch. Phy. Res., 213, 4 (2):13-111.334.332.3.328.326.324.322.32.318.316.314.312.31.8.6 WATER:EG::: 3K 8K.1.2.3.4.5.6.338.336.334.332.3.328.326.324.322.32.318.316.314.312.31 WATER:EG::: 3K 8K.1.2.3.4.5.6.348.346.344.342.3.338.336.334.332.3.328.326.324.322.32.318.1.2.3.4.5.6 WATER:EG::: 3K 8K 19
N. S. S. V. Raja Rao et al Arch. Phy. Res., 213, 4 (2):13-111.3.355.3.345.3.335.3 WATER:EG::: 3K 8K.1.2.3.4.5.6.372.366.3.354.348 WATER:EG:::2 3K 8K.1.2.3.4.5.6.5..395.3.385.3.375.3.365.3 WATER:EG:::1 3K 8K.1.2.3.4.5.6 11
N. S. S. V. Raja Rao et al Arch. Phy. Res., 213, 4 (2):13-111 CONCLUSION The adiabatic compressibility is rendered sensitive not only to the ionic and molecular interactions but also dependent on the dipolar behaviour of the solvent molecules. This makes it a precious tool to probe into solventsolvent, Ion- solvent, and ion- ion interactions precisely and divulges valuable conceptions to understand the ion pair formation mechanism. Many authors tried to compute the hydration compressibility [1] by using the Passynskii model. This model is based on the assumption that the solvent molecules solvating ions were fully compressed by the electrical forces of ions. As a result, the compressibility of the solvent molecules in the hydration shell is assumed to be zero. However this fact is not collaborated by the experimental confirmations [11,12]. REFERENCES [1] Robinson Wright, Book, An introduction to Aqueous Electrolyte Solutions Art. 1.12 page: 18, John Wiley and Sons Ltd., England, 27. [2] HitoshiOhtaki and Tamas Radnai, Chem. Phys., 1993, 93, 1157. [3] Rohman et. al., Theory and Applications of Chem. Engg., 22, 8(1). [4] Schwan et. al., J. Rev. Sci. Instrum, 19, 31, 59. [5] <https://uk.vwr.com/app/header?tmpl=/quality_control/hpc_merck_hgp.htm> [6] Palani et. al., Archives of Physics Research, 21, 1(4), 111. [7] Eisenberg and Kauzman, Book, The Structure and Properties of Water Oxford University Press, Oxford, 1969. [8] Shinde et. al., Archives of Physics Research, 211, 2(2), 17. [9] Akhilan. C at. Al., J. Phys. Chem. B, 26, 11(), 14961. [1] Bockris and Saluja, J. Phys. Chem., 1972, 76, 21. [11] Rohman, Korean Journal of Chem. Engg., 22, 19(4), 679. [12] Onori, J. Chem. Phys., 1988, 89, 51. 111