Accepted Manuscript Title: ION SOLVATION IN SALT OF BIOLOGICALLY IMPORTANT RARE EARTH METAL WITH AQUEOUS SUGAR ALCOHOL (SORBITOL) MIXED-SOLVENT SYSTEM Authors: Jayanta Kumar Dash, Susmita Kamila PII: DOI: Reference: S1658-3655(17)30011-0 http://dx.doi.org/doi:10.1016/j.jtusci.2016.10.007 JTUSCI 356 To appear in: Received date: Revised date: Accepted date: 17-5-2016 7-10-2016 20-10-2016 Please cite this article as: {http://dx.doi.org/ This is a PDF file of an unedited manuscript that has been accepted for publication As a service to our customers we are providing this early version of the manuscript The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain ION SOLVATION IN SALT OF BIOLOGICALLY IMPORTANT RARE EARTH METAL WITH AQUEOUS SUGAR ALCOHOL (SORBITOL) MIXED-SOLVENT SYSTEM b* a Jayanta Kumar Dash and Susmita Kamila a Department of Chemistry, Biju Pattnaik College of Science & Education, Bhubaneswar- 751 001, India b Department of Chemistry, East Point College of Engineering and Technology, Bangalore -560 049, India *Corresponding Author: sushkam@yahoo.co.in ABSTRACT Acoustic investigation have been carried out for the salt of rare earth metal like lanthanum(III) chloride in sorbitol-water mixed solvent system of different concentration at 303.15K temperature and atmospheric pressure Various parameters have been calculated from the measured values of ultrasonic velocity, density and viscosity data These parameters shed light on the ion-solvent interaction and also supportive of the structure promoting tendency in the present solute-mixed solvent system The values of limiting solvation number, of lanthanum(III) chloride is maximum in water than in sorbitol-water mixed solvent systems and this is attributed to an interesting outcome regarding the behaviour of sorbitol for water in comparison to other saccharides Keywords: Rare-earth metal, Sugar alcohol, Acoustic parameters, solvation number, limiting solvation number, solute-solvent interaction INTRODUCTION Most of the chemical reactions that carried out in industries, biological systems and chemical synthesis involve different types of interactions between solute and the solvents Therefore, the influence of solvent nature on thermodynamics, kinetics and mechanism is of great importance One of the fundamental aspects of the solvent effect in electrolyte solutions is the extent of cation-solvent interactions or ionic solvation [1,2] Wide varieties of physicochemical methods have been employed in studying the ionic solvation and determination of solvation numbers of ions in water and in nonaqueous solvents [3-5] In an ionic solution, the interaction between the ionic solute and solvent is predominantly of ion- dipole type The ion-dipole interaction depends on the size of ions and polarity of solvent The dissolution of ionic salt in a solvent causes a volume contraction due to interaction between ions and solvent molecules This might affect different properties involving thermodynamics and acoustical etc, Extensive work has been carried out to understand the nature of ion-ion and ion-solvent interactions in solutions of electrolytes and electrolytes in mixed solvents [6-11] However, studies related to trivalent rare earth cation in mixed solvents are scarce in literature Lanthanum is a trivalent cation and representative of the lanthanides It is the second most abundant rare earth after cerium Lanthanum (III) chloride is used efficiently in various fields such as in industry, agriculture, medicine and petrochemicals etc In addition, this compound is of great interest due to its solubility both in water as well as in alcohol and this made Lanthanum (III) chloride to be widely used in different fields, which often allows this to be accumulated into human body Bone formation in mammals is stimulated by the application of lanthanum (III) compounds in low doses, whereas higher doses lead to neurotoxicological disorders [12] Therefore, understanding the effects of lanthanum (III) chloride on health has becomes a major concern On the other hand, sorbitol is commonly known as sugar alcohol and is having wide range of applications starting from food, healthcare to cosmetics and medicines etc, It is also used as a binding agent and syrup base in lanthanum(III) chloride medicines to cure bone disorders The importance of using this compound is its ability to form multiple hydrogen bonding with water Therefore, sorbitol has been chosen as one component of the mixed solvent system In continuation of our earlier work on lanthanum (III) chloride in other mixed solvent systems [13-15], it is a further attempt to investigate systematically the thermo-acoustical behaviours of lanthanum(III) chloride in water and also in sorbitol-water mixed solvent systems of various compositions at 303.15K and at atmospheric pressure These measured values were utilized for the calculation of different thermodynamic and acoustic parameters, which shed light on solvation property as well as the ionsolvent, solvent-solvent interactions that take place in the solutions EXPERIMENTAL Analytical grade sorbitol was procured from Qualigen Chemicals and hepta hydrated Lanthanum (III) chloride (99.9%) was obtained from Indian Rare Earth Ltd India Stock solutions of sorbitol in distilled water were prepared by accurate weighing Similarly, the stock solutions of 2M lanthanum (III) chloride were prepared in approximate solvents and were estimated by titration against EDTA using xylenol orange as indicator Different concentrations of lanthanum (III) chloride (1.0 to 2.0mol.dm-3) have been prepared from this stock solution The solutions were kept for 2hours in a thermostat at 303.15K with an accuracy of 0.01K before the measurements The densities of all the solutions were measured by a bicapillary pyknometer with deionized double distilled water with 0.9960 ×103 kg m-3 as its density at temperature 303.15 K the precision of density measurement was within ±0.0003 kg m-3 The ultrasonic velocity was measured at 303.15K temperature and atmospheric pressure by a singlecrystal variable-path ultrasonic interferometer operating at 5MHz by circulating water from a thermostatically regulated bath (Toshniwal, India) around the sample holder for constant temperature (within ±0.01K) The velocity measurements were précised to ± 0.5 ms-1 The viscosities of the solutions were measured with a calibrated Ostwald viscometer, immersed in a constant temperature water bath maintained within ±0.01K, and the time of flow was determined RESULTS Different acoustic parameters such as isentropic compressibility, s, acoustic impedance, Z, intermolecular free length, Lf, molar sound velocity, R , Molar compressibility W etc were calculated from the measured values of velocity, U, density, , and viscosity, , using standard formulae [16-18] Parameters like relative association, RA, relaxation time, , apparent molar compressibility, k, apparent molar volume, v, were calculated by the following formulae [10,19] RA = /0 (U0/U)1/3 (1) = 4/3U (2) 1000(β ρ − β ρ) β M + (3) cρρ ρ ∅ = ∅ = 1000(ρ − ρ) M + (4) cρρ ρ where 0 and s are the density and isentropic compressibility of the solvent (aqueous-sorbitol), and s are those of solution, respectively c is the molarity of the solution and M is the molar mass of the solute (lanthanum(III) chloride).The limiting apparent molar volume v was determined from Masson’s equation [20] based on Debye- Huckel theory [21] v = v+Sv c 1⁄2 (5) 1/2 where v and Sv are the intercept and slope respectively in the plot of v versus c Similarly the limiting apparent molar compressibility k is obtained from Gucker’s limiting law [22] and according to that law, k is 1/2 k = k + Sk c , (6) where Sk is the slope and related to ion-solvent interaction and k is the intercept related to ion-ion interaction The slope and intercept are obtained from the plot of k vs c1/2 Besides, the solvation number, Sn, defined by Passynski [23], is calculated by using the following relation: S = 1− (7) where n0 and n i are the moles of solvent and solute, respectively The variation of the solvation number with molar concentration of solute leads to a limiting solvation number S lim ∅ = − S V β → n which is evaluated by (8) where is the molar volume of the solvent with n1 moles of solvent Apart from this, Jones and Dole coefficient, B [24] for concentrated solutions (c 0.1M) is calculated from relative viscosity by the following relations [25,26] η = = + Bc (9) where η is the relative viscosity and η is the viscosity of solvent In the present investigation, lanthanum (III) chloride in sorbitol-water mixed solvent system with the concentration range 1.0 – 2.0 mol dm-3 has been studied and all the parameters have been calculated The measured values of density, viscosity, ultrasonic velocity, and computed values of other relevant acoustic parameters of lanthanum (III) chloride in water and sorbitol-water mixtures have been summarized in Table and Besides, few parameters are graphically represented [figures 1-6] DISCUSSION It has been observed from Table-1 that the ultrasonic velocity, viscosity and density values are increasing with increase in concentration of lanthanum (III) chloride in all systems This increase in velocity [fig-1] may be due to the cohesive forces by ionic hydration and it is indicative of molecular association The increase in density indicates the existence of solute solvent interaction and also it may be interpreted to the structure maker of the solvent due to H-bonding [27] Similarly, increase in viscosity may be due to the fact that the solute particles lying across the fluid streamlines tend to rotate and absorb energy, which causes the increase in viscosity of the solutions [28, 29] The results are similar to our observations on dextrose-water systems in the concentration range of 1.0 – 2.0 mol dm-3 of lanthanum (III) chloride [15] The values of apparent molar volume, v, increase with increase in concentration of lanthanum (III) chloride concentration and decrease with sorbitol content The limiting apparent molar volume, v0 values obtained from plot of v vs c1/2 is a measure of the ion-solvent interaction [20] Positive values for both v and v0 are indicative of the presence of solute-solvent interaction and it increases with increase in sorbitol content Isentropic compressibility, s decreases with increase in both lanthanum chloride concentration and sorbitol content [fig-2] This confirms the presence of ion-solvent interactions through ion-dipole type between lanthanum ions and surrounding water molecules In general the compressibility of solvent is higher than that of solution and the compressibility reduces with the increase in concentration of the solution The values of Intermolecular free length, Lf, show similar trend as those for the compressibility values [fig-3] The decreased compressibility brings the molecules closer resulting in a decrease of intermolecular free length The decrease in free length on increasing of the concentration of solute indicates significant ions - solvent interactions between the molecules and it also suggests a structure promoting tendency of the added solute [30] The apparent molar compressibility, k is negative for all systems, i.e., pure water and mixed solvent systems The values decrease with increase in concentration of lanthanum(III) chloride indicating poor compressibility of the solvent in the vicinity of ions due to electrostrictive stiffening Same effects are also observed with increasing sorbitol content for a given concentration of lanthanum(III) chloride ∅ and Sk are the intercept and slope of the equation (6), calculated from the plot of k vs c1/2 for pure water as well as mixed solvent systems Negative values of ∅ indicate ion-solvent interaction and positive values of Sk indicate ion-ion interaction [Table- 2] The molar sound velocity, R, also known as Rao’s constant, increases linearly (Fig-5) with increase in concentration of lanthanum(III) chloride in water as well as in sorbitol-water mixed solvents Similar trend is also observed in case of molar compressibility, W in figure-6 and this is due to the presence of solute-solvent interaction [17] Relaxation time, values (Table 1) increases with increase in concentration of lanthanum (III) chloride for all the systems and also with increase in sorbitol content in mixed solvents This variation of suggests structure making capacity of solute and is therefore, indicative of ion-solvent interaction [26] The values of relative association, RA increase with increase in lanthanum (III) chloride concentration This reflects ion-solvent interaction leading to structure promotion by lanthanum (III) chloride in all the systems studied The acoustic impedance, Z is found to increase linearly with increase in concentration of lanthanum (III) chloride in water as well as sorbitolwater mixed solvents and it also increases with the increase in percentage of sorbitol for the same lanthanum(III) chloride concentration (Fig- 4) The increase in Z with increase in lanthanum (III) chloride concentration may be due to the disruption of solvent-solvent interaction making less number solvent aggregates available [31] The solvation number, Sn, also explains the solute and solvent interactions and it is the number of solvent molecules attached to the solute molecule Sn gives the information about the structure breaking or structure making tendency of a compound in solutions Depending upon the structure of compound, the solvation number is either positive or negative In the present study, solvation numbers are positive and this suggested an appreciable solvation of Solute [32] Again it has been observed that the solvation number decreases with increase in the concentration of LaCl3 According to Kannappan et al this type of variation may attain the primary solvation in pure crystalline state [5] The solvent molecules are attached to the ions by strong covalent bond in primary sheath of solvation and in secondary sheath, there are weak forces of attraction between solute and solvent species Review of literature [26, 33] shows that the values of in the range 0–2.5 are indicative of the presence of unsolvated species and that of above this value suggest the solvation of ions In the present study, calculated by Passynski method are all greater than 2.5 [equation 8], which indicate distinct solvation of the ions The limiting solvation number for pure water (14) is found to be close to Bockris data [34] The viscosity coefficient, B-value is a measure of the effective hydrodynamic volume of the solvated ions and is governed by ion-solvent interactions In present investigation, the B-values are positive for all the mixed solvent systems and this is similar to our previous observations with dextrose-water systems [15] It has been observed that the values are positive for all the concentrations of lanthanum (III) chloride and the B-values increase with the concentration of lanthanum (III) chloride This observation is due to increase in ion-solvent interaction These values also increase with the increase in sorbitol concentration [1.0% w/V - 10.0% w/V] at a given lanthanum (III) chloride concentration Increment in viscosity is due to the structure making of the ions in the systems that leads to the ordering of the solvent molecules This however, predominates over decrease in solvent viscosity [35] As a result, there is net increase in viscosity with increase in lanthanum (III) chloride concentration The increase of B-coefficient with increase in sorbitol content for a fixed concentration of lanthanum (III) chloride is due to strong association between water and sorbitol through multiple hydrogen bonding [31] Comparison between dextrose-water and sorbitol water systems shows that B-values are higher for sorbitol-water systems for a given lanthanum (III) chloride concentration due to greater ordering of the solvent molecules CONCLUSION In the present investigation, it is revealed that there is presence of strong interaction among the solute and solvent This solute-solvent or ion-solvent interaction promotes the structure-forming tendency, whereas ion-ion or solute-solute interaction enhances the structure-breaking properties in the systems In addition, the sign and magnitude of various parameters attributed to the strength and existence of intermolecular association, which is mostly due to H-bonding REFERENCES R M Izatt, S J Bradshaw, S A Nielsen, J D Lanb, J J.Christensen, Chem Rev., 85, 271(1985) O.Popovych, , R.P.T,Tomkins, Non-aqueous solution chemistry, John Wiley and sons, NewYork, 1981 U Mayer, Pure & Applied Chem, 41, 291(1975) A Popov, Pure &Applied 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2140(1972) 35 R H Stokes, R Mills, Viscosity of electrolytes and related properties, Pergamon Press, New York , 1965 Caption for figures Figure – : Variation of ultrasonic velocity, U vs Conc of lanthanum(III) chloride in water and sorbitol-water mixture at temperature 303.15K Figure – : Variation of isentropic compresiibility,s vs Conc of lanthanum(III) chloride in water and sorbitol-water mixture at temperature 303.15K Figure – : Variation of intermolecular free length, Lf vs Conc of lanthanum(III) chloride in water and sorbitol -water mixture at temperature 303.15K Figure- : Variation of acoustic impedance, Z vs Conc of lanthanum(III) chloride in water and sorbitol -water mixture at temperature 303.15K Figure – : Variation of molar volume, R vs Conc of lanthanum(III) chloride in water and sorbitol -water mixture at temperature 303.15K Figure – : Variation of molar compressibility, W vs Conc of lanthanum(III) chloride in water and sorbitol -water mixture at temperature 303.15K LaCl3 in water LaCl3 in 1.0%(w/V) sorbitol water bsx 10-12N.m-2 U ms-1 LaCl3 in Water LaCl3 in 1.0% (w/V) sorbitol water LaCl3 in 2.5% (w/V) sorbitol water LaCl3 in 5.0%(w/V) sorbitol water LaCl3 in 10.0%(w/V) sorbitol water LaCl3 in 2.0%(w/V) sorbitol water LaCl3 in 5.0%(w/V) sorbitol water Conc in mole.dm-3 Fig: LaCl3 in 10.0%(w/V) sorbitol water" Conc in mole.dm-3 Fig: LaCl3 in water LaCl3 in 1.0% (w/V) sorbitol water LaCl3 in 2.5% (w/V) sorbitol water LaCl3 in 5.0% (w/V) sorbitol water Z x 10 -6kg.m-2.s-1 Lf X 1011 m LaCl in 1.0%(w/V) sorbitol water LaCl3 in 2.5% (w/V) sorbitol water LaCl3 in 5.0% (w/V) sorbitol water LaCl3 in 10.0%(w/V) sorbitol water LaCl3 in water Conc in mole.dm-3 Conc in mole.dm-3 Fig: LaCl3 in water Conc in mole.dm-3 Fig: LaCl3 in 1.0%(w/V) sorbitol water LaCl3 in 2.5%(w/V) sorbitol water LaCl3 in 5.0% (w/V) sorbitol water W x 104Pa1/7.m3.mol-1 R x 104m10/3.mol-1.s-1/3 Fig: LaCl3 in water Conc in mole.dm-3 Fig: LaCl3 in 1.0% (w/V) sorbitol water LaCl3 in 2.5%(w/V) sorbitol water LaCl3 in 5.0% (w/V) sorbitol water .. .ION SOLVATION IN SALT OF BIOLOGICALLY IMPORTANT RARE EARTH METAL WITH AQUEOUS SUGAR ALCOHOL (SORBITOL) MIXED- SOLVENT SYSTEM b* a Jayanta Kumar Dash and Susmita Kamila a Department of Chemistry,... extent of cation -solvent interactions or ionic solvation [1,2] Wide varieties of physicochemical methods have been employed in studying the ionic solvation and determination of solvation numbers of. .. numbers of ions in water and in nonaqueous solvents [3-5] In an ionic solution, the interaction between the ionic solute and solvent is predominantly of ion- dipole type The ion- dipole interaction depends