Article Cite This: J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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Thermodynamic Study of (KCl + N,N‑Dimethylformamide + Water) System Based on Potentiometric Measurements Toba Nasiri-Lohehsara and Bahram Ghalami-Choobar*
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Department of Chemistry, Faculty of Science, University of Guilan, P.O. Box 19141, Rasht, Iran ABSTRACT: In this research, the thermodynamic properties of (KCl + N,N-dimethylformamide + water) system were determined based on potentiometric technique. The electromotive force measurements were carried out by using self-made electrodes on the galvanic cell of type Ag|AgCl|KCl (m), N,Ndimethylformamide (w), and H2O (1 − w)|K-ISE in various mass fractions of N,N-dimethylformamide in water (0, 0.10, 0.20, and 0.30) in the molality ranging from 0.0094 to 2.5200 mol· kg−1 at T = (298.2 and 308.2) K and P = 0.1 MPa. Thermodynamic properties modeling was implemented using the Debye−Hückel extended equation, Pitzer ion interaction, and Pitzer−Simonson−Clegg models. Subsequently, unknown parameters for each model were determined and utilized to calculate the thermodynamic properties such as the mean activity coefficients, the osmotic coefficients, the excess Gibbs free energy, and the solvent activity for the system under investigation. mixed solvent systems was done by our research group.14−18 The activity coefficients, osmotic coefficients, and excess Gibbs free energy for these electrolyte systems were determined by using ion-selective electrodes. Amides are well-studied solvents that are widely used as reagents and reaction media. N,NDimethylformamide (DMF) is a dipolar, aprotic solvent with a dipole moment lower than that of water as well as a low dielectric constant. It has good donor−acceptor properties,19 which enable it to dissolve a wide range of both organic and inorganic substances. This solvent plays a significant role in the production of resins, adhesives, films, and printing inks as well as in the manufacturing of synthetic fibers and leathers.20−23 Thus there is a great need to study aqueous mixtures containing DMF. However, the literature survey showed that the thermodynamic properties of KCl + DMF + water system have not been reported up to now. Among the experimental techniques, such as potentiometric method,24,25 isopiestic vapor pressure,26 and other measurements,27,28 the former method is more used to study the thermodynamic properties of electrolyte solutions. The cell potential method presents advantages such as rapidity, stability, and relative simplicity to generate experimental data with regard to the other methods.29,30 In this research, the thermodynamic properties of the (KCl + N,N-dimethylformamide + water) system were determined based on potentiometric technique. This work is an extension of our studies on the thermodynamic properties of alkali metal salts in mixed solvent systems.14−18 The cell potential
1. INTRODUCTION There is a growing interest in the determination of thermodynamic properties of electrolytes in multicomponent mixtures containing both electrolytes and nonelectrolytes. Electrolyte solutions are involved in several chemical, biological, biochemical, geological, and engineering processes.1,2 Damage prevention of industrial equipment and environmental worries require accurate thermodynamic knowledge of electrolytes during a process. In addition, introducing some organic solvents into electrolyte solutions is able to modify the physicochemical properties of state solutions, which can be very important in the context of theoretical and application study of fluid chemistry, particularly for separation and purification processes.3 Therefore, the prediction of the thermodynamic properties of multicomponent electrolyte solutions poses an important challenge for many fields. Up to now, many works have been done concerning measurement of the thermodynamic properties of electrolyte solutions. Hernandez-Luis et al. measured the activity coefficients of NaF in N-methylformamide + water4 and NaCl in formamide + water and PEG 4000 + water mixtures.5,6 Deyhimi et al. determined the activity coefficient of NH4Cl and NaCl in some mixed solvents.7−9 The Pitzer ion-interaction model has been successfully used by these investigators. In addition, thermodynamic properties of (RbF + RbCl + H2O), (CsF + CsCl + H2O), (RbF + Rb2SO4 + H2O), and (CsF + Cs2SO4 + H2O) systems were studied by Huang and coworkers.10,11 Hu et al. reported the thermodynamic properties of (CsF + urea + H2O), (CsF + N-methylformamide + H2O), and (RbCl/CsCl + ethylene carbonate + H2O) ternary systems.12,13 Moreover, the thermodynamic investigation of KCl in (glucose, formamide, diethanolamine, 1-PrOH, and proline + water) © XXXX American Chemical Society
Received: January 4, 2018 Accepted: June 11, 2018
A
DOI: 10.1021/acs.jced.8b00009 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
Journal of Chemical & Engineering Data
Article
measurements were performed by a galvanic cell of type: Ag| AgCl|KCl (m), DMF (wt %), H2O (1 − wt)%|K-ISE. This galvanic cell includes a potassium polymeric membrane (KISE) and Ag−AgCl electrodes that were made in our laboratory. In these measurements, KCl electrolyte concentration was varied at molality ranging from 0.0094 to 2.5200 mol·kg−1 in DMF + water mixtures containing 0, 0.10, 0.20, and 0.30 mass fractions of DMF at T = (298.2 and 308.2) K and P = 0.1 MPa. The Debye−Hückel extended equation, Pitzer ion interaction, and Pitzer−Simonson−Clegg models were used to describe the nonideal behavior of the electrolyte system. The unknown parameters of each model were evaluated for the system under investigation. To end with, the values of the mean activity coefficients, the osmotic coefficients, the solvent activity, and the excess Gibbs free energy for under studied system were found.
of dry freshly distilled THF was used to this aim. The ISE preparation method was entirely described in our previous work.25 Also, the Ag−AgCl wire electrodes were made ready by the electrolysis technique, as described in ref 31. The Ag− AgCl electrodes were used as both chloride-selective electrodes and internal reference electrodes. Also, a saturated calomel reference electrode was used to calibrate the fabricated K-ISE and Ag−AgCl electrodes. The calibration was done in KCl standard solutions with concentration ranging from 10−3 to 1 mol·dm−3. 2.3. Potentiometric Measurements. The operational cells (A and B) contain K-ISE, and Ag−AgCl self-made electrodes were employed for potentiometric investigation of the KCl + DMF + water system. The galvanic cell arrangements were described as follows A: Ag|AgCl|KCl (m), H 2O|K‐ISE
2. EXPERIMENTAL SECTION 2.1. Apparatus and Reagents. The potentiometric data were measured through a digital multimeter (Martini instrument Mi180). The cell potential records were taken with a fluctuation of 0.1 mV. A Martini instrument was attached to a personal computer equipped with the Mi 5200 software and Microsoft Excel (Office 2007) software for data acquisition and calculations. A magnetic stirrer (Delta Model HM-101) at a slow constant rate was employed to avoid concentration gradients in the test solutions. All measurements were performed in a double-walled glass container, and temperature of the work solution was kept constant at T = (298.2 and 308.2) K ± 0.1 K by employing a Model GFL circulation water bath. The materials used in this research were purchased from chemical companies, as presented in Table 1. Purity of the
B: Ag|AgCl|KCl (m), DMF (w), H 2O (1 − w)|K‐ISE
where m and w are the KCl molality and DMF mass fraction in the mixed solvent, correspondingly. The cell potential measurements were carried out to determine the activity coefficients for KCl in the ternary system (KCl + DMF + H2O). The standard addition procedure was performed to measure the cell potential data according to previous work.25
3. THERMODYNAMIC MODELS 3.1. Extended Debye−Hückel Equation. The extended Debye−Hückele equation was utilized to explain the nonideal properties of electrolyte mixtures. This equation is considered as an ion-interaction model that involves electrolyte-specific regression parameters.32,33 According to the extended Debye− Hückel model, the mean activity coefficient, γ±, for 1−1 type electrolytes, such as KCl, is written as
Table 1. Company and Purity Value of Compounds Used chemical used KCl N,N-dimethylformamide (DMF) tetrahydrofuran (THF) dibutyl phthalate potassium tetrakis(pchlorophenyl) borate poly(vinyl chloride) polyanetholesulfonic sodium salt carbon nanotube
CAS registry number
mass fraction purity
Merck Sigma-Aldrich
7447-40-7 68-12-2
>0.99 >0.99
Merck Merck Fluka
109-99-9 84-74-2 14680-77-4
>0.99 >0.99 >0.98
BDH Laboratory Sigma-Aldrich
9002-86-2 55963-78-5
Neutrino
308068-56-6
company
log γ± = −
A I + cI + dI 2 − log(1 + 0.002IMs) 1 + Ba I (1)
where I represents the total ionic strength based on molal concentration, a is the ion size parameter, c and d are ioninteraction parameters, and Ms is the average molar mass of the mixed solvent system. The Debye−Hückel model constants, A and B, are given by
0.996 0.98 >0.95
A=
reagents was >98% (by mass fraction), as specified by the supplier, and used with no further purification. An analytical balance (A&D HR 200) with accuracy ±0.0001 g was used to weigh all samples. All primary stock solutions were prepared by directly weighing appropriate amounts of KCl and DMF into the proportion volume of double-distilled water that had the definite density at certain temperature and specific conductance
