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1 i-ionic Potential Studies forsilver ThiosulphateParchment- Supported membrane Khaled MuftahElsherif *1, shraf El-Hashani, bdelmeneim El-Dali 3, Rajab El-kailany 4 1 enghazi University, Faculty of Science, Chemistry Department, enghazi-libya, , Elsherif7@yahoo.com enghazi University, Faculty of Science, Chemistry Department, enghazi-libya, , aiiya600@yahoo.co.uk 3 enghazi University, Faculty of Science, Chemistry Department, enghazi-libya, , a_eldali@yahoo.com 4 enghazi University, Faculty of Science, Chemistry Department, enghazi-libya, , kailany@hotmail.com bstract The bi-ionic potential (IP) values across the parchment supported silver thiosulphate membrane with various combinations of 1:1 electrolytes at different concentrations have been measured.theoretical values of IP have been calculated using the IP theories developed recently by Toyoshima et al based on principles of non equilibrium thermo dynamics. Comparison of experimental and theoretical IP values shows that theoretical equations of IP are applicable to the parchment supported membrane. Keywords:i-ionic potential, parchment-supported membrane Corresponding uthor:khaled Muftah Elsherif INTRODUCTION Preparation of membrane with specific properties and study the transport processes which occur across synthetic membranes are of great interest to chemist, chemical engineers, and biologist and large number of works have been published which belong to various fields of science such as surface chemistry, solution theory, colloid chemistry, polymers, electrochemistry, etc.lso, large number of theories has been developed in order to understand the mechanism of transport across the membranes. To test these theories, chemists have synthesized membranes with desired properties to use them as models. Inorganic precipitate membranes have been used as a model for the study of transport phenomena and to testify the theories of membrane potential and bi-ionic potential [1-8] In this paper, we describe the preparation of silver thiosulphate parchment supported membrane. The recent theory of Toyoshima and Nozaki [9] for bi-ionic potential has been tested R S. Publication, rspublicationhouse@gmail.com Page 638

2 MTERILS ND METHODS Preparation of Membrane ll the reagents used were of R grade (DH) without further purification and their solutions were prepared in deionized water. Parchment supported silver thiosulphatewas prepared by the method of interaction described by Weiser [10, 11] and Siddiqi et al. [1-16]. First parchment (Supplied by M/s aird and Tatlock London Ltd.) was soaked in distilled water for about two hours and then tied to the flat mouth of a beaker containing 0. M silver nitratesolution. This was suspended for 7 hours in a 0. M sodiumthiosulphatesolution at room temperature. The two solutions were interchanged and kept for another 7 hrs. In this way fine deposition of silverthiosulphatewas obtained on the surface of parchment paper. The membrane thus obtained was well washed with deionized water for the removal of free electrolytes. The membrane was clamped between two half cells of an electrochemical cell. The membrane prior to the measurements had been aged by about 4 hrs immersion in 1 M in the testing electrolyte. Membrane Potential Measurements (E m ) The potential developed by setting up a concentration cell of the type shown in scheme 1 and described by Siddiqi et al. [17]. The membrane potential was obtained by taking the same electrolyte at different concentrations on the two sides of the membrane, such that the concentration ratio σ = 10. The potentials were monitored by means of Knick Digital Potentiometer (No. 646). ll measurements were carried out using a water thermostat at 5 ± 0.1 o C. The solutions were vigorously stirred by a pair of magnetic stirrer in order to be maintained uniform in both the half cells. The uniunivalent electrolytes examined were lithium chloride, sodium chloride, potassium chloride, and ammonium chloride. Saturated Calomel Electrode(SCE) (C 1 ) Membrane (C ) Saturated Calomel Electrode (SCE) C = 10 C 1 Scheme 1 i-ionic Potential Measurements (IP) The measurements were recorded by constructing another new cell of the following type: Saturated Calomel Electrode (SCE) P Membrane P Saturated Calomel Electrode (SCE) Scheme In this cell, concentrations of both P and P electrolytes solutions were equal on both sides of the membrane. The bi-ionic potentials were measured at 5 ± 0.1 o C across parchment supported silver thiosulphate membrane using LiCl-NaCl, LiCl-KCl, LiCl-NH 4 Cl, NaCl-KCl, NaCl-NH 4 Cl, and KCl- NH 4 Cl electrolytes sets in each successive measurement. The solutions were stirred by means of magnetic stirrer in order to be maintained uniform on both sides of the membrane. t first, the solutions were left as they were for 1 hr at least till the fluxes of the all species reached to steady state, and then we exchanged them for new identical solutions and measured the emf. The measurements were recorded when three changes in the test solutions did not lead to potential R S. Publication, rspublicationhouse@gmail.com Page 639

3 variation 0. mv. The bi-ionic potentials were measured by means of Knick Digital Potentiometer (No. 646). RESULTS ND DISCUSSION The bi-ionic potential (IP) has been defined as the dynamic membrane potential which arises across a membrane separating the solutions of two electrolytes at the same concentration with different critical ions; which are able to exchange across the membrane, and the same non-critical ions for which the membrane is impermeable [18]. The critical ions in the case of electronegative membranes; such as collodion membranes, are the cations, conversely in the case of electropositive membranes, the critical ions are the anions. The sign and the magnitude of the IP are determined by the relative ease with which the two critical ions penetrate the membrane [19]. Marshal and Krinbill [0] developed the following equation for the bi-ionic potential: RT au E IP ln (1) F au u, where is the mobility ratio in the membrane phase of the two ions u Most recently Toyoshima and Nozaki [9] derived various theoretical equations for membrane potential and bi-ionic potential which are applied and tested with parchment supported silverthiosulphate membrane. The theoretical equation for bi-ionic potential using variables which contains four parameters (V, V ), ( ), ( ), (g, g ), and (K, K ) is given by: K RT K ( JV 1) E IP ( )[ln ln ] () F K ( JV 1) K, where is the selectivity constant of a membrane for positive ion species to K o o P K o u u V 1 (3) V 1 (4) o u up For the evaluation of flux J of ion species, Toyoshima and Nozaki [9] gave the following equation which also used in the present investigation: ( g J) ( JV 1) g ( J 1)ln ln ln 0 (5) ( g J) ( JV 1) g, where: K C K C g 1 1 ( ) (6) g 1 1 ( ) (7) The apparent transference number t -app of anion is defined by: 1 ( 1) 1 VN ( VN 1) (8) t ln K C app The above equation was used for the evaluation of V N and N, where N =,, σ = 10. R S. Publication, rspublicationhouse@gmail.com Page 640

4 The apparent transference number t -app can be calculated using the following equation: E 1 t ) ln (9) mr ( app, where ΔE mr is the value of reduced membrane potential defined by: FE E mr (10) RT The values of membrane potential measured across parchment supported silverthiosulphatemembrane in contact with different concentrations of various 1:1 electrolytes are given in Table 1 Table 1.Observed membrane potential (mv) across silver thiosulphate membrane at 5±0.1 o C (C /C 1 ), M Measured membrane potential (mv) LiCl NaCl KCl NH 4 Cl 1.0/ / / / / / / / pparent transference numbers for co-ions are calculated using equation (9) and given in Table. Table.pparent transference number of co-ions for various electrolytes at 5±0.1 o C (C /C 1 ) M t -app LiCl NaCl KCl NH 4 Cl 1.0/ / / / / / / / Equation (8) predicts a linear relationship between 1 1 and t C. The values of V N and membrane electrolyte system can be evaluated from the ordinate intercept and initial slope of 1 vs C [Figure 1]. The values of V N and app so obtained are given in Table 3. for a t 1 app R S. Publication, rspublicationhouse@gmail.com Page 641

5 1 1 Figure 1. Plot of against for silver thiosulphate membrane in contact with different electrolytes t app C Table 3. V N and for the membrane in contact with various 1:1 electrolyte solutions Electrolyte V N ϕx/ LiCl NaCl KCl NH 4 Cl The values of bi-ionic potential measured across parchment supported silver thiosulphate membrane in contact with different set of electrolytes are given in Table 4. The values derived for mobility ratios across the membrane for 1:1 set of electrolytes according to equation (1) are given in Table 5. Table 4. Measured bi-ionic potentials (IP) in mv obtained across silver thiosulphate membrane for various sets of electrolytes at different concentrations E IP, mv C, M LiCl-NaCl LiCl-KCl LiCl-NH 4 Cl NaCl-KCl NaCl-NH 4 Cl KCl-NH 4 Cl R S. Publication, rspublicationhouse@gmail.com Page 64

6 Table 5.Mobility ratios across silver thiosulphate membrane for various sets of electrolytes at different concentrations C, M u /u LiCl-NaCl LiCl-KCl LiCl-NH 4 Cl NaCl-KCl NaCl-NH 4 Cl KCl-NH 4 Cl These values of V N and may now be utilized to give the values for g N [Table 6] using equations 6 and 7. Once the membrane parameters V N,, and g N for a membrane electrolyte system are known, one can calculated the theoretical IP using equations and 5. The values of IP thus calculated are plotted in Figures a, b, c, d, e, f as a function of electrolyte concentration C. Table 6. g N values for silver thiosulphate membrane in contact with various 1:1 electrolyte solutions at different concentrations electrolyte g N at different concentrations given in M LiCl NaCl KCl NH 4 Cl a. LiCl-NaCl R S. Publication, rspublicationhouse@gmail.com Page 643

7 b. LiCl-KCl c. LiCl-NH 4 Cl d. NaCl-KCl R S. Publication, rspublicationhouse@gmail.com Page 644

8 e. NaCl- NH 4 Cl f. KCl- NH 4 Cl Figure. Plots of observed and theoretically calculated IP for different electrolyte systems The comparison demonstrates that the theoretical predictions are quite satisfactorily borne by our experimental results, thereby confirming the validity of Toyoshima and Nozaki theory to the system under investigation. CONCLUSION The theory of bi-ionic potential developedby Tyoshima et al. based on the thermodynamics of irreversible processes has been examined. The closedagreements between the theoretical and the observed values confirms the applicability of the derived relationship tothe membrane electrolyte systems used in these investigations R S. Publication, rspublicationhouse@gmail.com Page 645

9 REFERENCES [1] K. M. Elsherif,. El-Hashani, and. El-Dali, Der ChimicaSinica, 4 (6), 13, 013 [] K. M. Elsherif,. El-Hashani, and. El-Dali, Journal of pplicable Chemistry, (6), 1543, 013 [3] K. M. Elsherif,. El-Hashani, and. El-Dali, nnalen der Chemischen Forschung, 1 (3), 15, 013 [4] M. Rashid, S. li, and M.. nsari, Der Chimica Sinica, 013, 4 (4), 97 [5] P. Prakash, K.C. Joshi, and N. Singh, Oriental Journal of Chemistry, (3), 3905, 006 [6] adrul Islam and S. Elhaddad, International Journal of Chemical Science, 10 (), 1043, 01 [7] M. N. eg and I.ltaf, Journal of pplied Polymer Science, 39 (7), 1495, 1990 [8] M. Rashid, S. li, and M.. nsari,journal of pplicable Chemistry, (4), 738, 013 [9] Y. Toyoshima and H. Nozaki, Journal of Physical Chemistry, 74 (13), 704, 1970 [10] H.. Weiser, Journal of Physical Chemistry, 34 (), 335, 199 [11] H.. Weiser, Journal of Physical Chemistry, 34 (8), 186, 199 [1] F.. Siddiqi, M. N. eg,. Haq, and S. P. Singh, Electrochimicacta, (6), 631, 1977 [13] F.. Siddiqi, M. N. eg,. Husain, and. Islam, Lipids, 14 (7), 68, 1979 [14] F.. Siddiqi, M. N. eg,. Husain, and. Islam, Journal of Indian Chemical Society, 7,199, 1980 [15] F.. Siddiqi, M. I. Khan, S. K. Saksena, and M.. hsan, Journal of Membrane Science, 15, 1935, 1977 [16] F.. Siddiqi, M. N. eg, S.. Khan, and M.. hsan, Journal of Colloid and Interface Science, 99 (1), 86, 1984 [17] F.. Siddiqi and S. Pratap, Journal of Electroanalytical Chemistry, 3 (1), 137, 1969 [18] H. P. Gregor and K. Sollner, Journal of Physical Chemistry, 50 (1), 53, 1946 [19] L. Michaelis, Kolloid Zeitschrift, 6,, 1933 [0] C. E. Marshal and C.. Krinbill, Journal of merican Chemical Society, 64 (8), 1814, 194 R S. Publication, rspublicationhouse@gmail.com Page 646