untitled European Journal of Chemistry 6 (1) (2015) 37‐43 European Journal of Chemistry ISSN 2153‐2249 (Print) / ISSN 2153‐2257 (Online)  2015 Atlanta Publishing House LLC ‐ All rights reserved ‐ Printed in the USA http://dx.doi.org/10.5155/eurjchem.6.1.37‐43.1146 European Journal of Chemistry Journal webpage: www.eurjchem.com Conductometric, spectrophotometric and thermodynamic studies of nickel sulfate in aqueous polyvinyl alcohol + methanol systems at different temperatures Summyia Masood *, Rehana Saeed and Maria Ashfaq Department of Chemistry, University of Karachi, Karachi 75270, Pakistan * Corresponding author at: Department of Chemistry, University of Karachi, Karachi 75270, Pakistan. Tel.: +92.21.992613006/2290. Fax: +92.21.992613006. E‐mail address: smasood@uok.edu.pk (S. Masood). ARTICLE INFORMATION ABSTRACT DOI: 10.5155/eurjchem.6.1.37‐43.1146 Received: 09 September 2014 Received in revised form: 25 October 2014 Accepted: 25 October 2014 Published online: 31 March 2015 Printed: 31 March 2015 The electrical conductance of nickel sulfate (NiSO4.6H2O) solutions in aqueous, aqueous polyvinyl alcohol (PVOH; 0.1, 0.5 and 0.9 g/dL), aqueous methanol (CH3OH) system (30%, v:v) and aqueous PVOH+CH3OH systems were measured in the concentration ranges 0.4×10‐2 to 10×10‐2 mol/L, at different temperatures (298, 303, 308, 313 and 318 K). Ionic interactions of nickel sulfate in aqueous and mixed solvent systems were measured by conductometric analysis. Different relations were used to evaluate conductometric data, for the calculation of molar conductance, molar conductance at infinite dilution (Ʌ°m), degree of dissociation (), dissociation constant (Kd) and Walden product. The increased in Ʌ°m values with the increase in percent composition of aqueous PVOH, show that PVOH interaction with solvents (water and methanol) was higher as compare to PVOH interaction with NiSO4. Solvent effect was also studied by spectrophotometric analysis of NiSO4 in aqueous, aqueous PVOH and aqueous PVOH + CH3OH system. Thermodynamic parameters for dissociation process such as energy of activation (Ea#), free energy change of activation (ΔGd#), enthalpy change of activation (ΔHd#), and entropy change of activation (ΔSd#) were also calculated as a function of temperature and solvent composition. KEYWORDS Nickel sulfate Ionic interaction Polyvinyl alcohol Molar conductivity Spectrophotometric Thermodynamic parameters Cite this: Eur. J. Chem. 2015, 6(1), 37‐43 1. Introduction Methods of physicochemical analysis have been found to be useful tools in getting sound information about the structure of various liquids and in studying ion‐solvent interactions in binary and ternary systems [1]. The physical properties of the mixed solvents are very much different from that of water. Methanol is a protic solvent, which is known to be extensively self‐associated through hydrogen bonding in the pure state. The presence of a small amount of alcohol in water alters the solvent structure, by changing the hydrogen bond configurations. The addition of organic solvent to an aqueous solution of electrolyte brings about a change in ion solvation that often results in a large change in the reactivity of dissolved electrolyte [2‐7]. Solute‐solvent interaction has great importance in biological chemistry, physical chemistry, surface chemistry, environmental chemistry and geochemistry. According to Eigen and Tamm [8,9], the association of strongly solvated ions in aqueous solution take place by a three‐step process in which the free hydrated ions initially combine with their (inner) hydration sheaths basically intact to form a double‐ solvent‐separated ion pair (2SIP). This is followed by successive losses of water molecules to form a solvent‐shared ion pair (SIP) and then a contact ion pair (CIP) as shown in Figure 1 [10,11]. Polyvinyl alcohol is a water‐soluble polyhydroxy polymer, employed in practical applications because of its excellent chemical resistance and physical properties and is completely degradable. Polyvinyl alcohol serves as a thickening agent for various emulsions and suspensions and used as wet‐strength adhesive. An important use of polyvinyl alcohol is as the plastic inter layer for automotive and aircraft also for coating electrical wire [12]. Divalent transition metal sulfates play a vital role in life systems as vitamins, enzymes and proteins [13]. They are widely used in agriculture as antifungal and antibacterial agents. Such solutions also find application as a mordant for dyeing as an activator for the forth flotation of various ores, as a molluscicide and for algae control. Thermodynamic and transport properties of electrolyte solutions are important for a variety of applications in the chemical processing industries [14]. Transport properties are very useful for the study of ionic solvation. These properties can give information on the effective size of moving particles in solution and are sensitive to strong ion‐solvent interactions, which not only affected by the size of the ions, and also to any 38 Masood et al. / European Journal of Chemistry 6 (1) (2015) 37‐43                                                  31 2 KK Km n m n m n m n (aq) (aq) 2 2 2 2aq aq aq M L M OH OH L M OH L M OH L Free ions 2SIP SIP CIP (a) (b) (c) Figure 1. Schematic representation of ion pair types: (a) solvent separated (2SIP), (b) solvent shared (SIP), and (c) contact (CIP) ion pair. modification in the structure of the solvents. The conduc‐ tometric method can best be used to study the ion‐solvent interactions [15‐17]. Conductometric analysis of electrolytes in mixed solvents has received considerable attention in recent years. It is a simple, accurate and reliable method to study the solvents effects, nature of ion, ion‐solvent interaction existing in the system, and modification in the structure of a solvent due to the presence of an ion and ionic movement in a solution. The study of variation in molar conductance with temperature and solvent composition provides information about ionic mobility and solvent viscosity, hydrogen bonding ability, dielectric constant and specific interactions of ions with the solvent. The influence of various temperatures on conductivity measurement can give detailed information of ion‐ion and ion‐solvent interaction for different electrolytes solution [18‐30]. Molecular associations in liquid system and their variations with composition and temperature were studied by thermodynamic data [31‐38]. Transition metals occupy the space between group II and group III of the periodic table and due to their unique physical and chemical properties are of great interest. They form colored compounds which are often paramagnetic and show variable oxidation states but among them nickel is stable with maximum energy and 2+ oxidation state. The dissolution of nickel sulfate in water gives solution containing the ion [Ni(H2O)6]2+ ion. The interaction of nickel sulfate in mixed solvent systems is the main interest for this research. The present work deals with the study of the nature of nickel sulfate in aqueous, aqueous PVOH, aqueous methanol and aqueous PVOH + methanol systems. Ionic interactions were studied as a function of composition of solvent, concentration and temperature by conductometric method. Effect of solvent was also studied by spectrophotometric analysis of NiSO4 in aqueous, aqueous PVOH and aqueous PVOH + CH3OH system. Thermodynamic parameters also confirmed the mode of interaction in the presence of particular mixed solvent systems. 2. Experimental All glassware used was of Pyrex A grade quality. Polyvinyl alcohol (PVOH; 98% hydrolyzed) and methanol (CH3OH) of Merck 99.9% pure were used for the experimental work. Average molecular weight of polyvinyl alcohol at 298 K was calculated by Mark‐Houwink relation. int   vkM (1) where, the values of k and α are 33.88×10‐5 and 0.716 for polyvinyl alcohol at 298 K [12] and the average molecular weight thus found were approximately 46835 Da. The structural formula of polyvinyl alcohol is shown in Figure 2. Figure 2. Structural formula of polyvinyl alcohol. Different compositions of nickel sulfate in aqueous, aqueous PVOH (0.1, 0.5 and 0.9 g/dL) and aqueous PVOH (0.1, 0.5 and 0.9 g/dL) + CH3OH systems (10, 20 and 30%, v:v) were prepared in doubled distilled water having a conductivity of 0.06 µS/cm. Nickel sulfate hexahydrate (NiSO4.6H2O, Mol. Wt = 262.86 g/mol) of Merck, 99% pure was used without further purification. Stock solutions of 0.01 mol/L NiSO4.6H2O were prepared by dissolving calculated amount of nickel sulfate in aqueous, aqueous methanol and aqueous PVOH + methanol systems. Solutions in various concentration ranges from 0.4×10‐2 to 10×10‐2 ±0.0001 mol/L were prepared from stock solutions. Digital direct reading conductivity meter of Jenway‐ 4510 having least count 0.01 S/cm used to measure the conductivities. An Ostwald viscometer type Techniconomial constant 0.05 Cs/s, capillary ASTMAD 445 USA was used to measure the viscosity of solvent. The densities of solvent were measured with relative density bottle having the capacity of 10 cm3 at different temperatures. The temperature was kept constant by keeping all solutions in thermostatic water bath (circulator, model YCW‐0.1, Taiwan R. O. C.) for about 10‐15 minutes and controlled within ±0.01 K. An electronic balance (Sartorius, Germany) was used for mass determination. A stopwatch Japan CBM Corp, QsQ was used for determination of time of flow of solvent. Reproducibility of the results was checked by replicate measurements. The uncertainty in the experimental data for conductivity, density and viscosity was found to be ±0.02 mS/ cm, ±0.0001 g/mL and ±0.02 mPa.s, respectively. Absorption spectra were recorded by double beam UV‐Visible spectrophotometer (UV‐160A, Shimadzu Co., Japan). Masood et al. / European Journal of Chemistry 6 (1) (2015) 37‐43 39 3. Results and discussion Specific Conductance(L) of nickel sulfate were measured, ranging from concentrations of 0.4×10‐2 to 10×10‐2 mol/L in aqueous, aqueous methanol (10, 20 and 30%, v:v), aqueous PVOH (0.1, 0.5 and 0.9 g/dL) and aqueous PVOH + CH3OH systems at different temperatures (298 to 318 K) with a difference of 5 K. The molar conductance of NiSO4 were calculated from specific conductance data at different temperatures in aqueous, aqueous CH3OH, aqueous PVOH and aqueous PVOH + CH3OH systems as shown in Table 1 to 3, respectively, by applying relation (2): m 1000. Λ L C (2) where, L is the conductivities of electrolytes, C is the concentration of electrolytes and Ʌm is the molar conductance. Table 1. Molar conductance (Ʌm) for NiSO4 in aqueous and aqueous methanol systems at different temperatures. [Salt].102 (mol/L) Molar conductance (S.cm2/mol) at temperatures (K) 298 303 308 313 318 Aqueous system 0.40 152.5 152.5 155.0 157.5 160.0 0.60 131.6 133.3 134.6 138.3 140.0 0.80 122.5 123.7 125.0 126.2 128.7 1.00 114.0 117.0 118.0 119.0 121.0 2.00 94.00 94.50 95.00 95.50 96.50 4.00 76.25 74.25 73.75 73.50 69.25 6.00 67.33 66.33 66.00 65.00 64.50 8.00 60.00 58.50 56.25 56.87 55.12 10.0 53.80 53.40 51.90 50.00 49.60 Aqueous methanol system, 30% (v:v) 0.40 82.50 85.00 87.50 90.00 92.50 0.60 75.00 76.66 78.33 80.00 81.66 0.80 71.25 72.50 75.00 76.25 77.50 1.00 65.00 66.00 68.00 69.00 70.00 2.00 53.50 54.00 55.00 56.50 57.50 4.00 45.00 45.75 46.50 47.00 47.50 6.00 39.66 41.16 41.50 42.33 43.33 8.00 37.00 37.87 38.50 38.87 39.50 10.0 34.70 35.00 35.20 35.70 35.80 Table 2. Molar conductance (Ʌm) for NiSO4 in aqueous PVOH systems at different temperatures. [Salt].102 (mol/dm3) Molar conductance (S.cm2/mol) at temperatures (K) 298 303 308 313 318 Aqueous PVOH system, 0.1 g/dL 0.40 155.0 155.0 157.5 160.0 162.5 0.60 138.3 140.0 143.3 146.6 148.3 0.80 123.7 125.0 126.2 127.5 130.0 1.00 118.0 119.0 120.0 122.0 124.0 2.00 95.00 95.50 96.50 97.50 98.00 4.00 76.25 75.75 75.50 75.25 75.00 6.00 67.33 66.33 66.00 65.00 64.50 8.00 60.00 58.50 56.37 56.87 55.12 10.0 53.80 53.40 51.90 50.00 49.60 Aqueous PVOH system, 0.5 g/dL 0.40 175.0 180.0 185.0 190.0 197.5 0.60 160.0 161.6 166.6 175.0 180.0 0.80 155.0 157.5 160.0 162.5 168.7 1.00 146.0 147.0 152.0 156.0 160.0 2.00 120.0 126.5 130.0 131.5 134.0 4.00 105.0 107.5 108.0 108.5 108.7 6.00 93.66 93.33 92.66 91.50 88.83 8.00 82.75 82.25 80.37 78.50 78.00 10.0 71.90 71.80 71.50 71.20 70.50 Aqueous PVOH system, 0.9 g/dL 0.40 200.0 200.0 207.5 210.0 217.5 0.60 175.0 180.0 185.0 191.6 193.3 0.80 162.5 168.7 170.0 172.5 176.2 1.00 157.0 159.0 160.0 162.0 165.0 2.00 128.5 133.0 133.5 134.0 135.0 4.00 109.2 109.2 109.2 109.0 109.0 6.00 96.33 95.00 94.00 93.33 92.50 8.00 85.00 84.25 83.00 81.75 80.62 10.0 72.60 72.30 71.80 71.50 71.00 Table 3. Molar conductance (Ʌm) for NiSO4 in aqueous PVOH+30 % (v/v) methanol systems at different temperatures. [Salt].102 (mol/dm3) Molar conductance (S.cm2/mol) at temperatures (K) 298 303 308 313 318 Aqueous PVOH+30% (v:v) methanol system, 0.1 g/dL 0.40 90.00 92.50 95.00 97.50 100.0 0.60 83.33 85.00 86.66 88.33 90.00 0.80 75.00 76.25 77.50 78.75 81.25 1.00 70.00 71.00 72.00 73.00 75.00 2.00 56.50 57.00 58.00 59.00 60.00 4.00 45.50 46.25 47.00 47.50 48.25 6.00 41.16 41.50 41.83 42.66 43.16 8.00 38.12 38.50 38.75 38.87 39.37 10.0 35.20 35.30 35.40 35.50 35.80 Aqueous PVOH+30% (v:v) methanol system, 0.5 g/dL 0.40 107.5 110.0 115.0 117.5 122.5 0.60 91.66 93.33 95.00 98.33 101.6 0.80 80.00 82.50 85.00 86.25 88.75 1.00 74.00 76.00 77.00 78.00 80.00 2.00 59.00 59.50 60.00 61.00 62.50 4.00 47.00 47.25 48.00 48.50 49.00 6.00 45.00 45.33 45.66 46.00 46.33 8.00 38.75 39.00 39.25 39.50 39.75 10.0 36.20 36.40 36.60 36.80 37.00 Aqueous PVOH+30% (v:v) methanol system, 0.9 g/dL 0.40 127.5 132.5 135.0 137.5 140.0 0.60 103.3 106.6 108.3 111.6 116.6 0.80 91.25 92.50 95.00 98.75 100.0 1.00 85.00 86.00 88.00 90.00 92.00 2.00 63.00 64.00 65.00 66.50 67.00 4.00 48.50 49.75 50.25 51.00 52.00 6.00 45.66 45.83 46.00 46.16 46.33 8.00 39.25 39.50 39.75 40.00 40.50 10.0 36.80 37.00 37.10 37.20 37.30 The values of molar conductance (Ʌm) tabulated in Tables 1‐3 for NiSO4 in aqueous, aqueous CH3OH, aqueous PVOH and aqueous PVOH + CH3OH systems respectively, show that molar conductivity decreased with the increase in concentration of electrolytes in aqueous and aqueous methanol systems. This shows that with the increase in concentration there was an increased in number of ions of solute which decreased the ionic velocity due to hindrance in movement of ions or at higher concentration ion‐pair formation favored thus the molar conductance decreased, while with dilution ions become free and show high values of molar conductance. Results also show that molar conductance increased with the increase in temperature due to the high mobility of the ions as a result of the increased in thermal energy, vibrational, rotational and translational energy. With the rise of temperature the viscosity of the solvent also decreased which makes the ions to move freely towards the electrodes. The decreased in values of molar conductance at higher concentration with the rise in temperature show the removal of conducting species due to favoring in ion‐pair formation. Results tabulated in Tables 1‐3, show that molar conductance of nickel sulfate decreased with the increase in proportions of the aqueous methanol solvent system at the particular temperature. The trend in molar conductance is as follows: 30% < 20% < 10% < aqueous system. This behavior was due to the formation of hydrogen bond between alcohol and H2O molecules, and thus reduced the ionic mobility results a decrease in the molar conductance values with higher percentages of the organic solvent. Further solvent viscosity resists the motion of ions, and dielectric properties of the solvent control the effective field strength and inter‐ionic potential. They affect not only ionic viscosity but also the attraction between ions and consequently the extent of pairing specific solvation of ions can affect both mobility and association. It may also be stated that bulkier and low dielectric constant methanol entering into the solvated or hydrated ion and replaces certain water molecule from either primary or secondary hydration sheath of the ion, leading to decrease in conductance. Increased in solvated ionic size brings about the increased in density as well as viscosity. 40 Masood et al. / European Journal of Chemistry 6 (1) (2015) 37‐43 Table 4. Limiting molar conductance (Ʌ°m) for NiSO4 in aqueous, aqueous methanol and aqueous PVOH+Methanol systems at different temperatures. Temperature (K) Molar conductance at infinite dilution (S.cm2/mol) in different PVOH systems 0.0 0.1 0.5 0.9 Aqueous PVOH systems 298 156.673(±0.07) 160.840(±0.05) 187.633(±0.07) 207.433(±0.07) 303 158.853(±0.07) 162.469(±0.01) 192.289(±0.01) 212.470(±0.05) 308 163.753(±0.07) 165.922(±0.08) 198.778(±0.02) 217.832(±0.08) 313 164.637(±0.03) 169.377(±0.03) 205.754(±0.06) 222.496(±0.04) 318 167.558(±0.02) 172.543(±0.07) 213.790(±0.05) 228.138(±0.02) Aqueous PVOH+30% (v:v) methanol systems 298 86.467(±0.03) 94.372(±0.08) 105.744(±0.06) 123.342(±0.08) 303 88.338(±0.02) 96.476(±0.04) 108.429(±0.01) 126.948(±0.02) 308 91.071(±0.09) 98.653(±0.07) 111.749(±0.01) 129.763(±0.07) 313 93.181(±0.09) 100.807(±0.03) 114.429(±0.01) 133.577(±0.03) 318 95.247(±0.03) 103.525(±0.05) 118.719(±0.01) 136.990(±0.05) Figure 3. The CH3OH‐water mixtures are divided into three regions (I, II and III) on the basis of the clustering structures. The increase in the viscosity made the system to have lesser conductivity. On the basis of the mass spectra for alcohol water mixtures measured at various the mole ratios, three regions I, II and III were observed [31] as shown in Figure 3. In region I, the alcohol molecules are existing as a part of inherent hydrogen bonding network of water. In the region II, the layer structure composed of the nearly equal number of alcohol and water, will be formed as stable clusters. In region III, the formation of the alcohol self‐aggregating clusters becomes energetically favorable as it started from much lower concentrations. As the hydrophobicity of alcohol water mixtures increases, the region II and III shift to the lower alcoholic content. Tsierkezos and Molinou [27] have studied the limiting molar conductance of Ni(II), Cd(II), Mn(II) and Cu(II) sulfates in methanol mixtures at 293.15 K and similar behaviour was observed. Results show that with the increase in aqueous PVOH compositions from 0.1 to 0.9 g/dL molar conductance increases. It shows that solvation of ion decreases as PVOH‐ water interaction increases with the increase in aqueous PVOH compositions through H‐bonding. As a result of association of polymer chain with water the ions become less solvated and their mobility increased. While with the increase in aqueous methanol percent compositions 10 to 30% in composition of aqueous PVOH there is a decrease in conductance. This is also due to increase in viscosity of solvent which decreased the mobility of ions and also due to decrease in dielectric constant of medium which decreases the no of ions per cm3 of the solution. The conductance behaviour of many electrolytes in mixed solvent systems is reported to be influenced by a number of factors like density, viscosity, dielectric constant of the medium, ion‐solvent interactions and solvent‐solvent interactions. Ion‐solvent interactions stabilize the ion by solvating it. The values of Ʌ°m (limiting molar conductance) also depend on the composition of the binary solvent mixtures. Resulted data was analysed to obtain molar conductance at infinite dilution (Ʌ°m). Molar conductance of an electrolyte solution increased with dilution and approaches a limiting value at infinite dilution. ° ° m m mΛ Λ ‐ ΛA B. C (3) where, Ʌ°m is the molar conductance at infinite dilution and ‘A’ and ‘B’ are the constants for an electrolyte of a given valence type in each particular solution. The values of molar conductance at infinite dilution or limiting molar conductance (Ʌ°m) have been determined from intercept of linear regression plots of Ʌm versus √C and results are tabulated in Table 4. The representative plots of Ʌm versus √C for nickel are shown in Figures 4‐6. Result tabulated in Table 4 show that the molar conductance at infinite dilution decreased with the increase in solvent percent composition because of low dielectric constant of the medium which favor ion pair formation resulting a decrease in solute‐solvent interactions. An ion‐pair can be considered as a whole is electrically neutral and ceases to play its role in the ionic cloud. Therefore the ion‐ pair does not respond to an externally applied electric field and does not participate in the conduction of current. An examination of molecular models suggest that when methanol solvates the ions, perhaps a steric hindrance occurs. Because of this steric hindrance, the oxygen atoms of methanol are not in direct contact with the ions; consequently, the ions move freely and they have a tendency to associate through ion‐ion interactions. Figure 4. Plot of Ʌm versus √C for NiSO4.6H2Oin aqueous and aqueous methanol systems at 303 K. The decreased in limiting molar conductance as the methanol content is increased is also due to less strong hydration and presence of a short range interaction. At infinite dilution, neither the relaxation nor the electrophoretic effects Masood et al. / European Journal of Chemistry 6 (1) (2015) 37‐43 41 are effective on the drift of ions; both these effects depend for their existence on a finite‐sized ionic cloud. Figure 5. Plot between Molar Conductance (m) versus C1/2 for NiSO4 in aqueous and aqueous PVOH system at 303 K. Figure 6. Plot between molar conductance (m) versus C1/2 for NiSO4 in 0.9% aqueous PVOH and 0.9% aqueous PVOH + Methanol systems at 303 K. Walden product is helpful from the point of view of ion‐ solvent interaction [22]. In solutions ions are solvated, so degree of solvation as well as size of solvating molecules varies with the nature of the solvent. As regards electrolyte‐solvent interactions, more information can be supplied by the dependence of Walden product changes versus composition of the mixtures. The variation of the Walden product reflects the change of total solvation. Walden product relates Ʌ°m to the viscosity of solvent by the relation. Walden Productm    (4) where, η° is the viscosity of the solvent. The values of Walden product tabulated in Table 5 shows that its value increased with the increase in alcohol content as the higher the viscosity lesser will be the mobility of ions in the solution. Thus the decrease in conductance is more prominent when the viscosity of solvent increased. The increased in the values of Walden product indicate weak solvation while decreased in values represents strong solvation. It was also noticed that the value of Walden product decreased with increasing temperature. These negative temperature coefficients of Walden product may be related to the increase in the size of solvated ions in the mixtures as temperature increase. This is because of the variation of the proportion of the organic solvent and water molecules in the sheath of solvation with temperature. The values of the degree of dissociation (α = Ʌm / Ʌ°m) tabulated in Table 6 show the decreased in values with the increase in percent composition of methanol. It was also observed that with the increase of alcohol content the degree of dissociation decreased because of low dielectric constant of the medium. A state of equilibrium between ionized and unionized molecule in solution is determined by the dissociation constant (Kd): 2 d 1‐ α K C α        (5) where, Kd is the dissociation constant, (1‐α) is the remaining fraction of an electrolyte un‐dissociated. The values of dissociation constant for nickel sulfate (NiSO4.6H2O) are tabulated in Table 6. The variation of Kd with percent composition and temperature was observed due to the selective solvation of the ion by the solvent. The variation in values of Kd with composition is primary due to change in dielectric constant and it also indicates that the electrolyte causes reduction in the thickness of the ionic environment, surrounding ionic species. It may reduce the repulsion between different ionic species by increasing the aggregation number capacity. It may also, due to bulky organic molecules, either enter the solvation shell or come out of it during the movement of the solvated ion in the bulk of the solution. In mixed solvent system decrease in hydration of ions also led to decrease in values of Kd. The effect of temperature on molar conductivity was shown by the Arrhenius relation [19,32]. # o a mlog Λ log A ‐ 2.303.R .T E (6) where, R is the molar gas constant, Ea# is the energy of activation which determines the rate of movement of ions, A is the frequency factor and the T is the absolute temperature. The energy of activation was calculated by the plot of log Ʌ°m against 1/T, representative plot is shown in Figure 7. The results tabulated in Table 7, show that the values of energy of activation increased from aqueous to aqueous methanol system. It shows that the rate of movement of electrolyte is slow in high percent composition of solvent (30% aqueous methanol) as compared to aqueous system. Therefore the values of limiting molar conductance for nickel in aqueous system were higher than aqueous methanol system. El‐ Dossoki [33] has also reported that activation energy of transport process increased as the proportion of organic solvent increased. Figure 7. Plot between log limiting molar conductance versus T‐1 for NiSO4 in aqueous and aqueous PVOH systems. 42 Masood et al. / European Journal of Chemistry 6 (1) (2015) 37‐43 Table 5. Values of Walden product (Ʌ°m η°) for NiSO4 in aqueous, aqueous methanol and aqueous PVOH + Methanol systems at different temperatures Temperature (K) Walden product (S.cm2/mol1.poise) for aqueous, aqueous PVOH %(w:v), aqueous methanol and aqueous PVOH+methanol systems 0.0 0.1 0.5 0.9 Aqueous PVOH system 298 1.400(±0.05) 1.474(±0.06) 2.542(±0.08) 3.173(±0.07) 303 1.272(±0.08) 1.384(±0.06) 2.055(±0.05) 2.721(±0.09) 308 1.183(±0.07) 1.272(±0.08) 1.894(±0.06) 2.343(±0.07) 313 1.080(±0.02) 1.197(±0.03) 1.771(±0.09) 2.164(±0.06) 318 1.003(±0.07) 1.119(±0.01) 1.633(±0.07) 2.007(±0.03) Aqueous PVOH+30%(v:v) aqueous methanols 298 2.905(±0.05) 3.510(±0.08) 5.444(±0.06) 9.769(±0.01) 303 2.823(±0.07) 3.122(±0.08) 4.230(±0.07) 7.855(±0.05) 308 2.376(±0.04) 2.840(±0.08) 3.763(±0.07) 7.129(±0.01) 313 2.251(±0.09) 2.572(±0.08) 3.511(±0.09) 6.630(±0.03) 318 2.081(±0.09) 2.404(±0.06) 3.242(±0.08) 5.908(±0.02) Table 6. Degree of dissociation (α) and dissociation constant (Kd) for 0.01 mol/dm3 NiSO4 in different solvent systems at 303 K. Solvent system Degree of dissociation and dissociation constant in different solvent system α ×102 Kd (mol/dm3) ×102 Aqueous 73.65 2.058 Aqueous methanol, 30% (v:v) 74.71 2.207 Aqueous PVOH, 0.9 g/dL 67.74 2.224 Aqueous PVOH (0.9 g/dL) + methanol (30% (v:v)) 74.83 1.422 Table 7. Thermodynamic parameters for 0.01 (mol/dm3) NiSO4 in different solvent systems at different temperatures. Temperature (K) Energy of activation Ea# (kJ/mol) Enthalpy change of activation Hd# (kJ/mol) Free energy change of activation Gd# (kJ/mol) Entropy change of activation −Sd # (kJ/mol.K) Aqueous 298 2.747 0.2694 9.765 9.495 303 0.2278 9.783 9.535 308 0.1862 10.20 10.02 313 0.1447 10.33 10.19 318 0.1031 10.51 10.40 Aqueous Methanol System, 30% (v:v) 298 3.980 1.502 9.374 7.871 303 1.460 9.608 8.147 308 1.419 9.775 8.355 313 1.377 10.04 8.662 318 1.336 10.29 8.958 Aqueous PVOH system, 0.9 g/dL 298 3.831 1.502 9.289 7.935 303 1.460 9.588 8.276 308 1.419 9.978 8.707 313 1.377 10.24 9.019 318 1.336 10.49 9.306 Aqueous PVOH (0.9 g/dL) + Methanol system (30% (v:v)) 298 3.911 1.502 10.36 8.928 303 1.460 10.71 9.323 308 1.419 10.88 9.530 313 1.377 11.12 9.818 318 1.336 11.34 10.07 Free energy change of activation for dissociation (Gd #) refers to the maximum amount of energy free to do useful work: Gd# = –2.303 RT log Kd (7) Table 7, shows the values of free energy change of activation for dissociation of nickel sulfate. The positive values of Gd# indicate that the dissociation process was non spontaneous and lower stability of species in solvent media. There was observed increased in values of free energy change of activation with the increase in percent composition of methanol show that ionic species are more stable in solvent mixture than in aqueous system. Thus, the resulting lower value of conductivity in solvent mixture of aqueous methanol than in aqueous system. The enthalpy change of activation for dissociation “Hd#” was calculated by Equation (8), # # d a ‐R .TH E (8) The values of enthalpy change of activation for dissociation of nickel sulfate were shown in Table 7. The values forHd# decreased with the increase in temperature indicate the endothermic nature of ionic process. The low value of enthalpy change of activation shows that ion‐ dissociation decreased and ion–association increased, in high percent composition of methanol. Entropy change of activation for dissociation“Sd#” is a measure of randomness or disorderness of a system significantly connected with solvent structural perturbation and calculated by the relation: # # # d d d Δ ‐Δ Δ T H G S (9) Entropy change of activation increased with the increase in percent composition (0 to 30%) for nickel sulfate is also tabulated in Table 7. The increased in percent composition of aqueous methanol results an increase in the values of entropy change of activation as solvent structure disturbed by the change in percent composition of methanol in aqueous medium, which caused more hindrance in the flow of the ions and responsible for the decreased in conductivity of electrolytes i.e. NiSO4in aqueous methanol system. Masood et al. / European Journal of Chemistry 6 (1) (2015) 37‐43 43 Table 8. Condutometric data comparison with literature. Solvent system Ʌm (S.cm2/mol) Reported Solvent system Ʌm (S.cm2/mol) Observed Aqueous 203.0 (293.15 K) 0.001 mol/dm3 Aqueous 152.5 (298 K) 0.004 mol/dm3 X = 0.1233 Aq. methanol 116.0 (293.15 K) 0.001 mol/dm3 [29] Methanol 20% (v:v) 115.0 (298 K) 0.008 mol/dm3 The results of present work can be compared with earlier work in many respects. The results are compared with respect to influence of solvent and temperature on conductance as shown in Table 8. Akilan et al. [11] have studied that in NiSO4, CoSO4 and CuSO4 solutions three ion pair types exist simultaneously depending on temperature and concentration range as in present work observed ion pair formation may occur with the rise of temperature, concentration and with the change in medium. Saeed et al. [12] observed through viscometric data that at higher concentration of PVOH, strong association of polymer with water was present as compared to solvent interaction with ions. While show small interaction with ions at lower concentration of PVOH, as observed in present work though conductometric data. Pan et al. [35] studied the electrical conductance of nicotinic acid in aqueous PVOH also concluded that with the addition of PVOH degree of dissociation decreases. In the present work it was also found that degree of dissociation decreased for divalent transition metal sulfates. Bešter‐Rogač et al. [7] have also reported the negative entropy change of activation for divalent transition metal sulfates in water as obtained in the present work. 3.1. Spectral analysis of NiSO4 in aqueous, aqueous PVOH and aqueous PVOH + methanol systems For the confirmation of divalent metal sulfate‐polyvinyl alcohol complexation, spectroscopic analysis was carried out. Geckeler [36] and Lin et al. [37] have studied the polymer‐ion complexation. Results indicate that there was no significant change in the values of λmax = 393.5 nm, obtained in aqueous, aqueous PVOH and aqueous PVOH + methanol systems for NiSO4 solutions which confirm that divalent transition metal salt is stable in aqueous, aqueous PVOH and aqueous PVOH + methanol system and no side reaction or any other product formation occur. 4. Conclusion It was concluded that molar conductance of NiSO4 at different temperatures decreased with the increase in percent composition of aqueous methanol and concentration of the electrolyte, the decrease in molar conductance was due to strong H‐bonding between water and methanol, which is also confirmed by increased in values of Walden product with increase in percent composition of aqueous methanol. The strong interaction between water and alcohol by hydrogen bonding decreased the dielectric constant of water as a result degree of dissociation decreased. 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