Electrical Conductivity of Sodium Chloride and Potassium Chloride in Water Soluble Polymers at Different Temperatures

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1 Research Article Electrical Conductivity of Sodiu Chloride and Potassiu Chloride in Water Soluble Polyers at Different Teperatures Rehana Saeed*, Suyia Masood and Syed Muhaad Rehan Ullah Departent of Cheistry, University of Karachi, Karachi, Pakistan. ABSTRACT The ionic conductivities of sodiu chloride (NaCl) and potassiu chloride (KCl) in water soluble polyer systes (aqueous polyvinyl alcohol and aqueous polyacrylaide) of 0.1, 0.5 and 1.0 g.dl -1 were easured in various concentrations (2x -3 to x -3 ol.d -3 ) and at different teperatures ranges fro 298 to 318 K with interval of 5 K. The conductivity data were analyzed by various equations to evaluate liiting olar conductance ( ), degree of dissociation (α), dissociation constant (K d), and energy of activation (E a). The data obtained fro conductoetric studies used to investigate the ion-solvent interaction and ion-ion interactions of electrolytes in aqueous polyer syste. Increased in the value of liiting olar conductance ( ) with the increase in coposition of solvents, showing strong solvent-solvent interaction. Therodynaic paraeters for dissociation processes such as free energy change of activation (ΔG*), enthalpy change of activation (ΔH*) and entropy change of activation (ΔS*) were also calculated. Keywords: Molar conductance, Ionic interactions, Electrolytes, Polyvinylalcohol. 1. INTRODUCTION Water-soluble polyers are showing their practical iportance as viscosityenhancing agents, flocculating agents, as well as food additives, etc 1. Polyvinyl alcohol (PVOH) and polyacrylaide (PAM) are chiefly popular because of their low cost. The interactions of PAM with other synthetic water soluble polyers have also been studied 2. Polyvinyl alcohol and polyacrylaide both are iportant synthetic polyers. PVOH a polyhydroxy polyer contains vinyl group as a onoer while PAM derived fro acrylaide onoer. Because of their high stability over wide ph intervals as well as siplicity and widespread applications both PVOH and PAM becoe today the ediu of choice in various processes 3. PVOH is resistant to oil, grease and soe solvents. These properties have led to its wide industrial use, in such areas as ebrane, textile sizing and finishing, adhesive, coatings and paints 4. An iportant use of polyvinyl alcohol is as the plastic interlayer for autootive and aircraft. PAM and its copolyers are used as coagulants and flocculants in waste and potable water treatent applications, as displacing fluids in the enhanced oil recovery (EOR), drag reduction agents (DRAs) in water and crude oil transportation pipelines, polyeric additive in water-based drilling fluids, and as water clarifier in industries such as ining and paper aking 5,6. The interaction of salts with solvents is used to study the solvent property like structural behavior of water. It is iportant to investigate the polyers and their interaction with the electrolytes in solution for. Realizing this iportant aspect, soe researchers 7-12 has reported the solution properties of water soluble polyers. Conductoetric studies of different electrolytes in aqueous 13,14, nonaqueous and ixed solvent systes have been reported 20,21 in literature. Transport properties have been observed in acroolecules, including electrical conductivity, dielectric perittivity and relaxation. A coparison of these transport properties in polyer-water Vol. 1 (4) Oct-Dec

2 solutions can help to elucidate the effects of hydration on the transport properties 22. Saeed et al. 23,24 worked on the ionic interaction of electrolytes (ZnSO 4. 7H 2 O and KCl) in dilute solution of polyvinyl alcohol conductoetrically and viscoetrically respectively. It was found that association of polyvinyl alcohol is stronger with water as copared to solvent interaction with ion. Interaction of polyvinyl alcohol with various organic solvents at different teperatures was also discussed 25. The effect of NaCl on the viscous flow of polyvinyl alcohol fro dilute to extree dilute concentration was discussed by Yang et al. 26. The interolecular H- bonding in extreely dilute aqueous polyvinyl alcohol solution was investigated by Liu et al. 27. Ahed et al. 28 evaluated the activation paraeters of polyvinyl alcohol at different teperatures. Durrani and coworkers 29 studied the different solution properties like viscosity, conductance, surface tension and light scattering of polyethylene oxide dissolved in water, in the absence as well as presence of soe salts (LiCl, NaCl and KCl). Ma et al. 30 studied nonionic (PBAM3) and ionic (PBAMS) hydrophobically associating polyacrylaide with and without the addition of NaCl. Mixed water-organic solvents are a subject of very intensive investigation. The purpose of this work is to study the behavior of electrolyte in a different solvent ediu for conductoetric study like aqueous polyer systes. It is iportant to investigate the polyers and their interactions with the electrolytes in solution. 2. EXPERIMENTAL Polyvinyl alcohol (E. Merck, average Mol. Wt = Da) and polyacrylaide (BDH, average Mol. Wt = 5,000,000 Da), sodiu chloride (NaCl, Mol. Wt. = g.ol -1 ) and potassiu chloride (KCl, Mol. Wt. = g.ol -1 ) were used without further purification. Structural forula of polyvinyl alcohol and polyacrylaide are shown in Fig. 1 and 2 respectively: CH 2 CH OH Fig. 1: Structural forula of polyvinyl alcohol CH 2 CH C NH 2 O Fig. 2: Structural forula of polyacrylaide All the weighing was done by an analytical balance, Model BL-S, Sartorius having least count of ±0.001 g. Different copositions (0.1, 0.5 and 1.0 g.dl -1 ) of aqueous polyvinyl alcohol (PVOH) were prepared in a known volue of hot (353±1K) deionized water. The solutions were constantly stirred by agnetic stirrer with hot plate 78HW-1 (ade in Czechoslovakia) to ake the solutions hoogenized, resultant solutions were then cooled to roo teperature and the volue was ade up to the ark with deionized water. Aqueous polyacrylaide (PAM) of different copositions and 1.0 g. dl -1 were also prepared. Priary stock solutions of 0.01 ol.d -3 of sodiu chloride (NaCl) and potassiu chloride (KCl) were prepared by dissolving calculated aounts in aqueous polyvinyl alcohol and aqueous polyacrylaide (0.1, 0.5 and 1.0 g.dl -1 ). Different solutions of the electrolytes (NaCl and KCl), ranging in concentration fro 2x 3 to 8x 3 ±0.001 ol.d -3 were prepared fro the priary stock solution. Conductivities were easured at various teperatures (298, 303, 308, 313 and 318 K) by a digital direct reading conductivity eter (Jenway 45) having uncertainty of ±0.5 %, connected with a dip type probe having n n Vol. 1 (4) Oct-Dec

3 cell constant of 0.99 c -1. The teperatures of desired level were attained and kept constant with the help of a therostatic water bath, (Circulator Model YCM-01, ade in Taiwan R.O.C). An Ostwald viscoeter type (Techniconoial constant 0.05 Cs.s -1, capillary ASTMAD 445, ade in England) was used to easure the viscosity. A relative density bottle (R.D bottle) having capacity.0 l by volue was used. The densities of different copositions of aqueous polyvinyl alcohol and aqueous polyacrylaide (0.1, 0.3, 0.5, 0.7 and 0.9 g.dl -1 ) solutions were easured at 303 K by the help of R.D bottle. The uncertainty in the experiental data for density was found to be ± g.l -1. For viscosity easureent viscoeter was fixed vertically with clap in a glass tube present in therostatic bath having a constant circulation of water. A definite volue of solvent (aqueous polyvinyl alcohol and aqueous polyacrylaide i.e. 0.1, 0.3, 0.5, 0.7 and 0.9 g.dl -1 ) under exaination was taken into the viscoeter kept for 15 to 20 inutes at 303 K in a water bath to attain the required teperature. Through a outh suction rubber tube the solvent was drawn up into the upper bulb and tie required for its eniscus to fall between the calibration arks was accurately easured. Each easureent was taken at least three ties to attain the reliability in the results. The uncertainty in the experiental data for viscosity was found to be ±0.002 Pa.s. 3. RESULTS AND DISCUSSION Conductivities (L) of various concentrations of electrolytes e.g., NaCl and KCl, ranging in concentration fro 2x 3 to x 3 ol.d -3 in 0.1, 0.5 and 1.0 g.dl -1 aqueous polyvinyl alcohol (PVOH) and aqueous polyacrylaide (PAM) at teperatures 298, 303, 308, 313, and 318 K were tabulated in Tables 1 and 2 respectively. These values were used to copute the olar conductance (Λ ), reported in Tables 3 and 4. 00L C (1) where, Λ is the olar coductance and C is the concentration of salt (NaCl and KCl). Results show that potassiu chloride (KCl) has higher conducting capability than sodiu chloride (NaCl) in both aqueous polyvinyl alcohol and aqueous polyacrylaide systes; this is due to the degree of solvation which is higher in sodiu chloride (NaCl) than potassiu chloride (KCl). The increase in olar conductance with teperature shows high obility of ions of electrolytes, which is due to the reason that viscosity of the solvent (aqueous polyer solution) decreases with the rise of teperature, which enables the ions to ove freely towards the electrodes. The tabulated results also show a decreasing pattern of olar conductance with the increase of concentration for sodiu chloride (NaCl) and potassiu chloride (KCl) in aqueous polyvinyl alcohol (PVOH) and aqueous polyacrylaide (PAM), as at low concentrations, ions are far part and hence inter ionic attraction is not as high as it would be in the case of solutions in which concentration of electrolyte is higher. This inter ionic forces are responsible for the retardation of oveent of ions which actually causes olar conductance to descend as the concentration of the electrolyte increases. A direct relation of olar conductance with the increasing concentration of the aqueous polyer is also observed. Results tabulated in Table 3 and 4 also show an increase in olar conductance with the increase in concentration of aqueous PVOH and aqueous PAM. The solvent effects conductance priarily, through its viscosity, hydrogen bonding capability, dielectric constant, and its specific interaction with ions. The viscosity of the solvent actually resists the otions of ions and dielectric constant controls the effective field strength. Ostwald dilution law was also eployed to obtain olar conductance at infinite dilution. 1/ 2 [ ] C (2) where, Λ o is the olar conductance at infinite dilution. The result of olar conductance at infinite dilution (Λ o ) for Vol. 1 (4) Oct-Dec

4 NaCl and KCl in aqueous PVOH and aqueous PAM tabulated in Table 5, have been calculated fro the intercept of linear regression plot of Λ and C 1/2, representative plot is shown in Fig. 3. Molar conductance at infinite dilution has been regarded as a easure of solutesolvent interaction, greater the agnitude of olar conductance at infinite dilution, the lesser would be the solute-solute interaction. In view of the fact that in the state of infinite dilution, the obility of an ion is liited exclusively by its interaction with surrounding solvent olecules, there are no other ions with in a finite distance. The results show that olar conductance at infinite dilution increased with the increase in coposition of solvent, which shows that polyer interaction increased with the increase in concentration of solvent through H-bonding between water olecules with hydroxyl group or carbonyl group which decreased the solvation around ions in aqueous PVOH and in aqueous PAM systes. The data is in good coparison with the literature values of liiting olar conductance reported for NaCl and KCl in aqueous ediu and S.c 2.ol -1 respectively by Boruń et. al. 21. Results show that olar conductance data for particular electrolyte (NaCl and KCl) in aqueous PAM was higher than aqueous PVOH. Higher value of olar conductance for NaCl and KCl in aqueous PAM as copare to aqueous PVOH is due to structural differences between these two polyers as shown in Fig. 1 and 2. PAM has two hydrogen atos on the aino group of each repeat unit, while PVOH has only single hydrogen ato in the for of hydroxyl group. Due to difference in priary structure which is responsible for different solubility and conforation in water. In aqueous ediu, polyer chain fors intraolecular hydrogen bonding through hydrogen atos of aino groups and the oxygen atos in carboxyl groups. Tanaka et al. 31 reported hydrogenbonding-stabilized conforation of PAM in water was not the regular helical structure but the noral one. As shown in Fig. 4, intraolecular hydrogen bonding in polyvinyl alcohol via a six-ebered ring. Fig. 4: Repeating units in polyvinyl alcohol deonstrating the capability to for intraolecular hydrogen bonds Therefore it was observed that higher value of olar conductance for NaCl and KCl in aqueous PAM as copare to aqueous PVOH as PAM for strong H- bonding with water olecules allows the ions to igrate freely. Another reason for this difference in value of olar conductance for NaCl and KCl is that polyer chain becoes stiffer when larger substituent groups (as hydroxyl groupin PVOH) exist and the internal steric effects of polyer chain will affect the whole properties of polyers. Three types of hydrogen bonding were observed by Tanaka et al. 31 in D 2 O syste as shown in Fig. 5. NaCl aqueous PVOH < NaCl aqueous PAM KCl aqueous PVOH < KCl aqueous PAM Fig. 5: Scheatic diagra showing three types of hydrogen bonding expected in D 2 O solution of polyacrylaide: (I) intraolecular hydrogen bonding in the helical structure; (II) intraolecular hydrogen bonding in extended segents; (III) interolecular hydrogen bonding Vol. 1 (4) Oct-Dec

5 In aqueous polyvinyl alcohol, the hydroxyl group becoes ready acceptor for hydrogen bonding, not only increased its interaction with the water olecules but also allows the polyvinyl alcohol olecules to interact slightly with each other, such that at higher concentrations, a polyvinyl alcohol solution becoes slightly viscous. The polyer atrix surrounding the water olecule is firly held together by hydrogen bonds and that the jup of the water olecule fro one place to another requires breakage of hydrogen bonds. The long life of the polyer-polyer hydrogen bonds ust be a ajor factor that retards the jup rate. This behavior of aqueous PVOH ay also be responsible for lower values of conductivity of NaCl and KCl as copare to in aqueous PAM systes. The values of degree of dissociation (α) and dissociation constant were tabulated in Table 6, show the inverse relation of teperature with the degree of dissociation. Values of degree of dissociation for NaCl and KCl in aqueous PVOH were higher than aqueous PAM which also confirs the higher value of conductance. It was also found that the values of degree of dissociation for sodiu chloride (NaCl) were greater than for potassiu chloride (KCl). This variation represents the electrostatic ion-solvent interaction in aqueous polyer systes. The saller the ion, the strongest is the electrostatic interaction, and hence greater is the size of solvation. Therefore solvation size of NaCl is greater than KCl which also confirs its low value of conductivity as degree of dissociation of NaCl is higher than KCl. With the increase in concentration of solvent, the values of dielectric constant decreased resulted decrease in degree of dissociation. A state of equilibriu between ionized and unionized olecule in solution explained in ters of dissociation constant (K d ). 2 C (1 ) K d (3) where, α is the degree of dissociation and ( 1- α ) is the reaining fraction of an electrolyte in undissociated for. The values of dissociation constant for sodiu chloride (NaCl) and potassiu chloride (KCl) are also tabulated in Table 6. Results show that with the increase of solvents coposition and teperature, decreasing values of dissociation constant with sae variation was observed. The variation of dissociation constant with coposition of the solvent was due to the selective solvation of the ions with the solvent. It is also observed that in ost cases the dissociation constant has followed a decreasing trend with the increase in concentration of the electrolyte. This is because of inter ionic attraction between ions increased with the increase in concentration of the electrolyte, favoring ion association phenoenon. Since the conductance of an ion depends on its rate of oveent, it sees reasonably to treat conductance in a anner analogous to that eployed for other processes taking place at a defined rate which increases with teperature. The activation energy was deterined by using the relation between conductance and teperature. 0 E a log log A (4) 2.303RT where, R is the olar gas constant, E a is the energy of activation, which deterines the rate of oveent of ions, A is the frequence factor, and T is the absolute teperature. The results of energy of activation (E a ) for sodiu chloride (NaCl) and potassiu chloride (KCl) tabulated in Table 7 have been calculated fro the slope of plots between log Λ o and 1/ T, as shown in Fig. 6. The results show the descending pattern of energy of activation with the increase in the coposition of the polyer solvent, it is due to the rate of oveent of ions which was low in the solutions in which concentration of aqueous polyer syste (solvent) was lower than the solutions in which solvent s concentration were of higher degree. Results tabulated in Table 7, show higher values of E a for NaCl and KCl in aqueous PVOH as copare to in aqueous PAM Vol. 1 (4) Oct-Dec

6 syste and also higher values were observed for NaCl than KCl. The increase in values of activation energy of the transfer process indicates ore energy consued for transfer process. This increase in values of activation energy is due to viscosity, dielectric constant and increase in association process of electrolytes. This increase in value of E a for NaCl and KCl in aqueous PVOH syste as copare to aqueous PAM also confirs conductivity data, because increased in the value of energy of activation led to the decrease in the value of. With the help of free energy change, it is possible to predict whether the reaction will proceed spontaneously or not. Free energy change of activation for dissociation process is represented by a sybol ΔG * and can be calculated by using the relation: * G 2.303RT log (5) K d The results tabulated in Table 8, show the values of free energy change of activation are positive which indicate the endotheric nature of the electrolytes, i.e., sodiu chloride (NaCl) and potassiu chloride (KCl), in polyer systes. The positive values of ΔG * show the lower stability of the electrolytes in solvent edia which also indicate that the dissociation processes in aqueous polyer solvent syste were nonspontaneous. Higher value of ΔG * for NaCl and KCl was observed in aqueous PAM syste as copared to aqueous PVOH solvent syste. It was also observed that the free energy change of activation of electrolytes increased with the rise in teperature for aqueous polyer syste show endotheric nature. The enthalpy change of activation for dissociation ΔH * is calculated by plotting log K d as a function of 1/ T, representative plot is shown in Fig. 7. Entropy change of activation (ΔS * ) was calculated by the relation. * * H G * S (6) T Entropy is significantly connected with the solvent structure perturbation brought about by the disordered ions. Entropy change of activation was reported in Table 9. The increased in values of entropy change of activation with the rise in teperature showed that randoness increased. The higher value of ΔS * was observed for aqueous PAM as copare to aqueous PVOH syste indicate that by the addition of the NaCl and KCl the structure of PAM disturb ore strongly than aqueous PVOH. 4. CONCLUSIONS On the basis of obtained results, it is concluded that, potassiu chloride (KCl) showed ore conducting capability than sodiu chloride (NaCl) also in aqueous polyer syste as in aqueous ediu. Conducting capability for NaCl and KCl in aqueous PAM is higher than in aqueous PVOH due to difference in hydrogen bonding. Therodynaic paraeters also confired sae behavior in aqueous polyer solvent systes. ACKNOWLEDGMENT The author (Saeed R.) gratefully acknowledges the financial support by Dean Science Research Grant by Karachi University. Vol. 1 (4) Oct-Dec

7 3 [Salt] (ol d -3 ) Table 1: Conductivity ( L ) of NaCl and KCl in aqueous Polyvinyl alcohol systes at different teperatures L (S c -1 ) at teperatures (K) NaCl 0.1 (g.dl -1 ) Aqueous PVOH Syste (g.dl -1 ) Aqueous PVOH Syste (g.dl -1 ) Aqueous PVOH Syste KCl 0.1 (g.dl -1 ) Aqueous PVOH Syste (g.dl -1 ) Aqueous PVOH Syste (g.dl -1 ) Aqueous PVOH Syste Vol. 1 (4) Oct-Dec

8 Table 2: Conductivity ( L ) of NaCl and KCl in aqueous Polyacrylaide systes at different teperatures 3 [Salt] (ol d -3 ) L (S c -1 ) at teperatures (K) NaCl 0.1 (g.dl -1 ) Aqueous PAM Syste (g.dl -1 ) Aqueous PAM Syste (g.dl -1 ) Aqueous PAM Syste KCl 0.1 (g.dl -1 ) Aqueous PAM Syste (g.dl -1 ) Aqueous PAM Syste (g.dl -1 ) Aqueous PAM Syste Vol. 1 (4) Oct-Dec

9 Table 3: Molar Conductance ( ) of NaCl and KCl in aqueous Polyvinyl alcohol systes at 3 [Salt] (ol d -3 ) different teperatures (S c 2 ol -1 ) at teperatures (K) NaCl 0.1 (g.dl -1 ) Aqueous PVOH Syste (g.dl -1 ) Aqueous PVOH Syste (g.dl -1 ) Aqueous PVOH Syste KCl 0.1 (g.dl -1 ) Aqueous PVOH Syste (g.dl -1 ) Aqueous PVOH Syste (g.dl -1 ) Aqueous PVOH Syste Vol. 1 (4) Oct-Dec

10 Table 4: Molar Conductance ( ) of NaCl and KCl in aqueous Polyacrylaide systes at 3 [Salt] (ol d -3 ) different teperatures (S c 2 ol -1 ) at teperatures (K) NaCl 0.1 (g.dl -1 ) Aqueous PVOH Syste (g.dl -1 ) Aqueous PVOH Syste (g.dl -1 ) Aqueous PVOH Syste KCl 0.1 (g.dl -1 ) Aqueous PVOH Syste (g.dl -1 ) Aqueous PVOH Syste (g.dl -1 ) Aqueous PVOH Syste Vol. 1 (4) Oct-Dec

11 Table 5: Liiting olar conductance ( ) for NaCl and KCl in aqueous polyer systes at Teperature (K) different teperatures (S.c 2.ol -1 ) in different solvent systes Aqueous PVOH Systes 0.1 (g.dl -1 ) 0.5 (g.dl -1 ) 1.0 (g.dl -1 ) NaCl KCl NaCl KCl NaCl KCl (±0.03) (±0.06) (±0.01) (±0.05) (±0.04) (±0.08) (±0.08) 219 (±0.01) (±0.01) (±0.09) (±0.09) (±0.01) (±0.06) (±0.05) (±0.05) (±0.06) (±0.04) (±0.03) (±0.04) (±0.04) (±0.01) (±0.05) (±0.08) (±0.09) (±0.01) Aqueous PAM Systes (±0.02) (±0.01) (±0.08) (±0.06) (±0.05) 0.1 (g.dl -1 ) 0.5 (g.dl -1 ) 1.0 (g.dl -1 ) NaCl KCl NaCl KCl NaCl KCl (±0.01) (±0.05) (±0.09) (±0.05) (±0.05) (±0.05) (±0.06) (±0.09) (±0.02) (±0.07) (±0.03) (±0.02) (±0.01) (±0.06) (±0.09) (±0.06) (±0.03) (±0.04) (±0.06) (±0.08) (±0.05) (±0.06) (±0.02) (±0.05) (±0.04) (±0.09) (±0.08) (±0.07) (±0.04) (±0.03) (±Standard deviations) Table 6: Values of degree of dissociation (α), dissociation constant K ) and Walden product for 4x -3 ol.d -3 NaCl and KCl in different solvent systes at ( d different teperatures Teperature (K) 2 α 4 K d (ol d -3 ) NaCl 0.5 (g.dl -1 ) Aqueous PVOH Syste (g.dl -1 ) Aqueous PAM Syste KCl 0.5 (g.dl -1 ) Aqueous PVOH Syste (g.dl -1 ) Aqueous PAM Syste Vol. 1 (4) Oct-Dec

12 Table 7: Energy of activation (E a ) for NaCl and KCl in different solvent systes E a (kj ol -1 ) Solvent Systes Aqueous PVOH Systes NaCl KCl (g.dl -1 ) Aqueous PAM Systes NaCl KCl Table 8: Free energy change of activation (ΔG * ) for 4x -3 ol.d -3 NaCl and KCl in different solvent systes Teperature (K) ΔG * (kj ol - 1 ) 0.5 (g.dl - 1 )Aqueous PVOH Systes NaCl KCl (g.dl -1 ) Aqueous PAM Systes NaCl KCl Table 9: Entropy change of activation (ΔS * ) for 4x -3 ol.d -3 NaCl and KCl in different solvent systes Teperature (K) ΔS * (kj ol -1 K -1 ) 0.5 (g.dl -1 ) Aqueous PVOH Systes NaCl KCl (g.dl -1 ) Aqueous PAM Systes NaCl KCl Vol. 1 (4) Oct-Dec

13 Fig. 3: Plots of Λ vs C 1/2 for sodiu chloride (NaCl) and potassiu chloride (KCl) in 1.0 g.dl -1 aqueous PAM at 298 K Fig. 6: Plots of log Λ o vs 1/ T for NaCl in 0.1, 0.5 and 1.0 g.dl -1 aqueous PVOH Fig. 7: Plot of log K d vs 1/ T for 8x -3 ol.d -3 NaCl and KCl in 1.0 g.dl -1 aqueous PAM Vol. 1 (4) Oct-Dec

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