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Conductometric and volumetric study of copper sulphate in aqueous ethanol solutions at different temperatures
Accepted Manuscript Title: Conductometric and volumetric study of copper sulfate in aqueous ethanol solutions at different temperatures Author: Esam A. Gomaa Amr Negm Mohamed A. Tahoon PII: DOI: Reference:
S1658-3655(16)30060-7 http://dx.doi.org/doi:10.1016/j.jtusci.2016.08.007 JTUSCI 327
To appear in: Received date: Revised date: Accepted date:
8-3-2016 26-8-2016 28-8-2016
Please cite this article as: E.A. Gomaa, A. Negm, M.A. Tahoon, Conductometric and volumetric study of copper sulfate in aqueous ethanol solutions at different temperatures, Journal of Taibah University for Science (2016), http://dx.doi.org/10.1016/j.jtusci.2016.08.007 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.
Conductometric and volumetric study of copper sulfate in aqueous ethanol solutions at different temperatures Esam A. Gomaa, Amr Negm, Mohamed A. Tahoon* Chemistry Department, Faculty of Science, Mansoura University, 35516-Mansoura, Egypt
ABSTRACT
cr
ip t
An Anton Par Model 55 densimeter is used to measure the densities at 298.15 K, 303.15 K, 308.15 K, and 313.15 K of copper sulfate solutions in H 2O and in EtOH-H 2O. The acquired information was utilized to ascertain the apparent molar volumes, limiting partial molar volumes, and transfer partial molar volumes, for copper sulfate. These computed parameters are utilized to decipher the solute–solute and solute–solvent interactions of copper sulfate in aqueous ethanol solution. The ion solvation behavior of copper sulfate in water and aqueous ethanol in the scope of 298.15 to 313.15K, using electrical conductivity principle has been studied. Kraus–Bray and Shedlovsky models of conductivity were used to analyze obtained conductance data. The limiting molar conductance λmo, association constant KA, the energy of activation of the rating process (Ea), and related thermodynamic parameters have been determined. Walden product (λmoη0) has been determined. Standard thermodynamic parameters of association (∆G°A, ∆H°A) were calculated and discussed. Increased ion–solvent and solvent–solvent interactions is suggested by increasing the amount of ethanol which indicated by limiting molar conductance values. The negative ∆G°A values indicate that the association processes in all studied systems are spontaneous processes. The negative estimation of (∆H°A) demonstrating that the association processes is exothermic in nature.
us
Keywords: Partial molar volume; Copper sulfate; Binary mixtures; Transfer volumes
an
* Corresponding author. Tel.: +201098351007.
E-mail address: [email protected] (M. A. Tahoon).
1. Introduction Significant data provided from the physicochemical properties of salts in aqueous solutions explain (solute + solute) and (solute + solvent) interactions that imperative in comprehension the dependability of these systems and are ensnared in a few biochemical and physiological procedures in a living cell. Due to the existence of many interactions, the determination of the physical and chemical properties of organic solvents + inorganic salts solutions (partially solvated melts) in the wide concentration range is very complex. Strong ion–ion interactions are dominant in concentrated solutions. The influence of the ion–dipole interactions between solvent molecules and the solute ions is increasing by dilution. In extremely dilute solutions the predominant weak dipole– dipole interaction is present. In diluted solutions exactly in the range of validity of the Debye–Hückel law, properties of the systems, such as conductivity [1], viscosity [2] and volumetric properties [3], were mostly calculated. Due to their commercial uses in many technological areas, the ion solvation process and equilibrium involved in many concentration sections in water and many nonaqueous media have been of indefinite importance. The existence of ions, solvated ions, and free solvent hang on the concentration area [4]. Hence, the investigation of volumetric properties in the wide electrolyte concentration range in different solvents is essential. The present work was assumed in order to investigate volumetric properties of copper sulfate in aqueous ethanol and to explain the nature of solute–solvent interactions in a diluted and concentrated copper sulfate solution. Copper sulfate (CuSO4) has been widely used for algal growth control and treatment of human copper deficiency. Ethanol is a colorless liquid at room temperature. It is a polar solvent, with the high relative permittivity of 24.4. This feature of ethanol allows the study of the volumetric properties in the solutions with high copper sulfate concentration. Ethanol is the major used commercially solvent in the pharmaceutical industry and many other organic syntheses. Because of the possibility of H-bonds formation, ethanol solutions are often used as model systems to study the interaction of peptides and proteins [5]. A varied range of dielectric constant (ε), viscosity (η) and a high degree of hydrogen bonding effect at different temperatures are showed by aqueous ethanol solutions. By the determination of conductivity, many interactions between water and ethanol by mixing them at varied
M
amounts may be studied over that mixing range. Suitable conductivity measurements offer a useful prediction of ion–solvent interaction, proton–anion and proton–solvent association, and solvent structure.
Ac ce p
te
d
2. Experimental
Copper sulfate with mass fraction > 99% obtained from the Shanghai Chemical Co., China and used without further purification. Ethanol was purchased from Aldrich, and the purity is better than 99%, which was dried under reduced pressure at 323 K before being used. Water is distilled two times before using it; all the investigated solutions were prepared newly. The weight of samples was determined by a Mettler AE 200 balance with a sensitivity of ±0.0002 g. ultrasonic waves are used to degas the prepared solutions that used within 12 hours of preparation. The solutions densities were determined within ± 0.00001 g·cm−3 with an Anton Paar DMA 55 digital densimeter (Austria). Two times distilled water and dried air are used to calibrate the used densimeter. The temperature was kept constant to ±0.05 K using a HAAKEC thermostatic bath (German). The conductance measurements of the prepared salt solutions were carried out using Jenway Conductivity Bridge of a cell constant value 1cm−1 and a deviation of ±0.12 µS cm−1. Potassium chloride solutions are used to accurately determine the cell constant of the used conductivity electrode. The Conductivity Bridge was connected to MLW 3230 ultra-thermostat to maintain the temperature constant at the required temperature (±0.006 °C). Ethanol–water mixed solvents with the alcohol mass fractions of 0%, 20%, and 40% were prepared by applying the following equation: Alcohol percentage = (V1 ρ1)100/ (V1 ρ1+V2 ρ2)
(1)
where ρ1 and ρ2 are the density of alcohol and water respectively. V1 is the volume of alcohol which will be added to the volume V2 of water to get the mixture of the required percentage. The salts under examination with a concentration of (5 × 10−2, 4 × 10-2, 3 × 10-2, 2 ×10-2, 1 × 10-2 mol·dm−1), were prepared by take a certain volume of the prepared standard solution of the salt and making a serial dilution to the necessary volume for measurements by the
1
Page 1 of 6
beforehand prepared mixed solvents [6]. The properties of used
solvents are supplied in Table S1 (Supplementary Materials)
Table 1 Densities and apparent molar volumes of solutions of copper sulfate in aqueous ethanol at different temperatures m solute (mol.dm-1)
298.15Kb ρ (g.cm-1)
303.15K Vϕ (cm3.mol-1
ρ (g.cm-1)
308.15K Vϕ (cm3.mol-1)
ρ (g.cm-1)
313.15K Vϕ (cm3.mol-1)
ρ (g.cm-1)
0 %( EtOH-H2O) 0.9964 0.9985 1.0005 1.0020 1.0039
0.01 0.02 0.03 0.04 0.05 40 %( EtOH-H2O)
0.9841 0.9861 0.9880 0.9893 0.9909
36.414±0.161 41.504±0.101 46.577±0.082 64.530±0.081 69.050±0.090
0.9811 0.9831 0.9851 0.9865 0.9879
0.01 0.02 0.03 0.04 0.05
0.9619 0.9638 0.9657 0.9670 0.9686
42.967±0.181 48.286±0.110 49.989±0.081 66.980±0.080 70.634±0.111
0.9600 0.9619 0.9639 0.9651 0.9668
a b
28.504±0.060 33.480±0.054 38.440±0.054 53.440±0.054 54.341±0.073
0.9939 0.9960 0.9980 1.0000 1.0016
35.858±0.086 40.980±0.077 42.625±0.060 58.958±0.076 68.698±0.078
0.9760 0.9780 0.9800 0.9819 0.9831
34.894±0.118 40.072±0.122 41.737±0.099 45.142±0.089 61.798±0.072
0.9750 0.9770 0.9791 0.9810 0.9822
34.703±0.153 39.892±0.117 38.057±0.091 42.349±0.062 59.564±0.038
0.9567 0.9587 0.9607 0.9625 0.9635
42.014±0.125 41.926±0.124 41.939±0.116 47.202±0.092 67.808±0.080
0.9550 0.9570 0.9590 0.9609 0.9619
41.697±0.179 41.610±0.141 41.523±0.108 44.171±0.078 65.398±0.044
42.621±0.097 47.963±0.078 46.058±0.062 66.732±0.078 68.234±0.089
28.014±0.044 33.017±0.059 38.003±0.058 40.448±0.047 49.947±0.052
0.9918 0.9939 0.9959 0.9979 0.9998
Standard uncertainty is 0.001 mol.dm-1. Uncertainty of temperature = 0.05K.
27.599±0.110 32.624±0.071 37.632±0.056 40.088±0.031 34.549±0.007
cr
29.027±0.140 38.989±0.080 45.582±0.071 58.829±0.070 60.717±0.080
us
0.9991 1.0011 1.0030 1.0045 1.0063
an
0.01 0.02 0.03 0.04 0.05 20 %( EtOH-H2O)
Vϕ (cm3.mol-1)
ip t
a
two groups and the adjacent groups. Table 2 show that the values of Vϕ0 increase with the increase of temperature, this observation indicates that the solute-solvent interactions are favored at higher
3. Results and discussion
temperatures. Vϕ0 increase with the addition of organic solvent and may be attributed due to low surface charge density as a result of which the electrostatic attraction is more in a medium of low relative permittivity. Therefore, ion - solvent interaction would also be more and subsequently will be larger.
M
3.1. Apparent molar volume
d
Table 1 is containing the densities (ρ) of copper sulfate solutions in water and in ethanol – water at different temperatures 298.15 K, 303.15 K, 308.15 K, and 313.15 K, where m solute is CuSO4 molarity in the EtOH-H2O solutions. The apparent molar volumes (Vϕ) of copper sulfate were calculated from the equation:
te
(2)
Ac ce p
where m is the molarity (mol·dm−1) of the solute (copper sulfate), M is the relative molar mass of solute (kg·mol−1), and ρ and ρ0 are the densities (g·cm−3) of solution and solvent, respectively. The uncertainty of m was ±0.001 mol·dm−1. The calculated values of Vϕ are also recorded in Table1. By using calculated Vϕ which is the function of molality of the solute, interactions between solute and solute can be predicted. Table 1 show that the values of Vϕ increase with the elevated concentration of solute.
Table 2 Limiting apparent molar volumes (Vϕ0) and experimental slopes (BV) of copper sulfate in water, and aqueous ethanol solutions at different temperatures Solvent
Vϕ0 (cm3·mol − 1)
BV x 10 3(cm3. mol−2. kg)
0 %( EtOH-H2O) 298.15 K 303.15 K 308.15 K 313.15 K
3.2. Limiting apparent molar volume
20 %( EtOH-H2O)
The limiting apparent molar volumes (Vϕ0) were obtained by least-squares fitting to Masson equation [7]:
298.15 K 303.15 K 308.15 K 313.15 K
(3)
1.175 3.108 10.385 14.696
2.711 2.298 1.640 1.288
4.559 5.386 13.947 15.996
2.806 2.626 1.836 1.605
40 %( EtOH-H2O) 298.15 K 303.15 K 308.15 K 313.15 K
where Vϕ0 is the intercept, that is free from solute–solute interactions by definition and therefore provides an indication about solute–solvent interactions, but the experimental slope, BV provides information regarding solute–solute interactions. The evaluated values of Vϕ0 and BV are listed in Table 2. The values of Vϕ0 as reported in Table 2 are positive for copper sulfate in water and in aqueous ethanol solutions indicating the presence of strong solute– solvent interactions in these systems. This trend of Vϕ0 values is due to their hydration behavior [8, 9], which comprises of following interactions in these system: (I) the two groups of the salt, Cu+2 and SO4−2 are hydrated in an electrostatic way and (ii) the volume change results from the overlap of hydrated co-spheres of
16.400 17.292 19.618 21.969
2.348 2.208 1.702 1.485
3.3. Transfer volume Transfer limiting apparent molar properties gives not only qualitative but also quantitative information about solute–solvent interactions without considering the impacts of solute–solute interactions. The standard partial molar volumes of transfer (∆trVϕ0) from water to aqueous ethanol solutions have been calculated by Eq. (4) [27, 28]:
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Page 2 of 6
40), the relation between the Van der Waals volumes and the partial molar volumes (the packing density) is found to be constant. Therefore, it is possible to calculate the Van der Waals volumes (Vw) of copper sulfate in (EtOH-H2O) mixtures at different temperatures (298.15, 303.15, 308.15 and 313.15 K) by applying Eq. (6)[24, 25]:
(4)
(6)
ip t
The volume of electrostriction (Ve) that is the volume of the solute compressed by the effect of electric field of solvent is calculated by using Eq. (7):
cr
(7)
The solvated radii [13] of the organic–aqueous mixtures (EtOHH2O) at different temperatures were calculated using Eq. 8 by allowing the spherical form of the solvated ions.
298 .1 5K 303 .15K 308 .1 5K 313 .1 5K
us
34 32 30 28 26 24 22 20 18 16 14 12 10 8 6 4 2 0 -2 0.00
0.05
0.10
0.15
(8)
The values of V, Vw, Ve, and solvated radii of copper sulfate in (EtOH-H2O) mixtures at different temperatures are listed in Table 3. In comparing the data of solvation of the substance used, it is observed that the values of the molar volume are increased by increasing the organic solvent content in the mixtures due to the increase in the volume of organic solvent [14] compared to water. Electrostriction volumes calculated for copper sulfate in (EtOHH2O) mixtures having negative values. The electrostriction volumes increase in negativity by increasing the percentages of the organic solvent, indicating the more work (energy) is done by the solvent on the solvation sheaths of the salts. The solvated radii are increased as the organic solvent content increase and as the temperature increase.
an
∆
tr
vΦ
o
Fig.1 shows the variation of ∆trVϕ0 of copper sulfate with the mole fraction of ethanol. The ∆trVϕ0 values of copper sulfate are positive and increase with increasing concentration of ethanol. The difference in the ∆trVϕ0 values in aqueous ethanol solutions primarily comes from the influence of organic solvent, which reflects the change in the structure of interaction between solute and [10, 11] solvent. The detected positive increasing of volumes of transfer for copper sulfate point out that in the ternary system (copper sulfate + ethanol + water), the ionic–hydrophilic interactions between the ethanol OH groups and CuSO4 ionic sphere, which lead to a positive contribution to ∆trVϕ0 is the predominate interaction over any other interaction.
0.20
M
XS
Fig.1. CuSO4 Partial molar volumes of transfer from H2O to EtOH – H2O solutions at different temperatures
V
VW
Ve
ro(AO)
Ac ce p
Solvent
te
d
Table 3 Molar volume (V), Van der Waals volume (Vw), electrostriction volume (Ve) in (Cm3.mol-1) and solvated radii (ro) of copper sulfate in (EtOH-H2O) mixed solvents at different temperatures
0 %( EtOH-H2O) 298.15 K 303.15 K 308.15 K 313.15 K
248.442 248.938 249.410 249.934
164.220 164.548 164.860 165.207
-84.222 -84.390 -84.550 -84.727
3.873 3.875 3.878 3.880
This may be due to the excess solvation processes, and the higher solvated radii of the organic solvent used than those of water and also due to the increasing in the electronic clouds around the solvated molecules as a result of the increase in their vibration and rotation motions with increasing the temperature. The solvated radii of copper sulfate in water and in aqueous ethanol solutions at different temperatures are given in Table 3 and are illustrated in Fig.2.
298.15K 303.15K 308.15K 313.15K
20 %( EtOH-H2O) 298.15 K 303.15 K 308.15 K 313.15 K
252.156 252.743 253.435 253.977
166.675 167.063 167.521 167.878
-85.480 -85.679 -85.914 -86.098
3.892 3.895 3.898 3.901
257.672 258.259 258.982 259.493
170.321 170.709 171.187 171.524
-87.351 -87.549 -87.795 -87.968
3.920 3.923 3.927 3.929
3.93
3.92
3.91
298.15 K 303.15 K 308.15 K 313.15 K
O
ro(A )
40 %( EtOH-H2O)
3.90
3.89
3.88
3.87 0.00
3.4. Calculation of the different Volumes
0.05
0.10
0.15
0.20
XS
From density of copper sulfate in water and aqueous ethanol the molar volumes [12] have been calculated by Eq. (5):
Fig.2. Copper sulfate solvated radii in H2O and EtOH-H2O at different temperatures
(5)
3.5. Limiting molar conductance
where the molar mass of used salt is symbolized by M, and the density of the solution by d. For quite big molecules (more than
3
Page 3 of 6
The specific conductance of solutions of copper sulfate with a concentration range of (0.001 –0.01) mol·L−1 in 0%, 20%, and 40% (EtOH – H2O) at 298, 303, 308 and 313K was measured. The molar conductance for all the studied systems was calculated using Eq. (9). (9) Where C is the ordinary concentration and Ks is the measured specific conductance of the used solution from which the specific conductance of the used solvent was deducted. The experimental molar conductivities were analyzed as per Kraus–Bray conductivity equation [15].
Kraus-Bray
(10) The limiting molar conductance, and dissociation constant, Kc was obtained from the intercept and slope of the plot 1/ϕm vs ϕmC. However, this model does not include any correction for inter-ionic effects or for the activities of the ions. Therefore, Shedlovsky [16] relation was used to evaluate the absolute limiting molar conductance and association constant KA.
20 %( EtOH-H2O)
an
298.15 K 303.15 K 308.15 K 313.15 K
(11)
121.50±0.12 123.01±0.12 132.97±0.13 140.25±0.14
122.90±0.12 124.28±0.12 134.75±0.13 142.76±0.14
70.67±0.07 72.67±0.07 76.56±0.07 82.03±0.08
71.59±0.07 72.55±0.07 77.99±0.07 83.22±0.08
58.68±0.05 64.02±0.06 65.44±0.06 69.73±0.06
60.23±0.06 66.04±0.06 67.56±0.06 71.01±0.07
us
0 %( EtOH-H2O) 298.15 K 303.15 K 308.15 K 313.15 K
ϕmo
Shedlovsky
cr
Solvent
ip t
Table 4 Limiting molar conductance (ϕm0) for copper sulfate in aqueous ethanol from T=298.15K to 313.15K.
40 %( EtOH-H2O)
ϕmo
298.15 K 303.15 K 308.15 K 313.15 K
M
The γ is the activity coefficient of the electrolyte. and KA were obtained from the intercept and slopes of the plot of 1/Sϕm vs CϕmSγ2. The values of limiting molar conductance at used temperatures are estimated by conductivity models of Kraus–Bray and Shedlovsky and presented in Table 4.
3.7. Walden product
te
d
Limiting molar conductance (ϕmo) was found to be higher in water and then decreased by adding ethanol to it. This behavior may be due to the formation of hydrogen bond between ethanol and water molecules resulting in the association of ethanol and water molecules, which lead to a decrease in the mobility of solvated ions and reduces the limiting molar conductance values by increasing the percentage of organic solvent in the solvent medium. The difference in viscosity (η) is not only the factor controlling the ionic mobility, which is shown by the Walden product. The limiting molar conductance of copper sulfate increased with increase in temperature from 298.15K to 313.15K for all percentages of mixed solvent as a result of the increase in ionic mobility. Hydrogen bonding of water is broken by increasing in thermal energy lead to smaller solvated ionic size and hence increases the mobility of the ions.
According to the Stokes' law, the ionic mobility depends on bulk viscosity, so the Walden products [17, 22] would appear reciprocal to the ionic radius. The differences in Walden product with solvent composition and temperature might then be discussed through variations in ion solvation alone.
Ac ce p
(12) Where the value of electronic charge is symbolized by eο, Faraday constant by F; and the ionic charge by Z and the effective Stokes molecular (ionic radius) is symbolized by r. Table 5 Association constant Ka and changes in Gibb's energy (∆G°A) for used salt in water + EtOH at different temperatures Solvent
KA
∆G°A (kJ.mol-1)
3.6. Association constant
0 %( EtOH-H2O)
The calculated values of association constant existed in Table 5. The values of KA of the studied salt at the same temperature were found to increase as the fraction of solvent ethanol increase with water. The extent of ion association depends on the nature of ion–ion interaction in the solution, the dielectric constant of the medium and also intermolecular hydrogen bonding between the solvent molecules. This introduces the fact that the values of KA increased with the increase of EtOH in water. The association constant for the studied salt was found to decrease with the increase in temperature; increased thermal motion probably breaks many bonds between ions that make a large distance between each other, where it gets solvated. Therefore the movements of ions have to increase. This may account for the decrease in KA for the increased temperature.
298.15 K 303.15 K 308.15 K 313.15 K
56.98 48.55 45.54 44.78
-4.596 -4.489 -4.488 -4.541
59.43 50.23 49.34 47.67
-4.645 -4.529 -4.582 -4.616
61.23 60.12 58.88 57.44
-4.679 -4.737 -4.790 -4.610
20 %( EtOH-H2O) 298.15 K 303.15 K 308.15 K 313.15 K 40 %( EtOH-H2O) 298.15 K 303.15 K 308.15 K 313.15 K
4
Page 4 of 6
The negative ∆G°A values indicate that the association processes in all studied systems are spontaneous processes. The negative estimation of (∆H°A) demonstrating that the association processes is exothermic in nature. Many concepts in numerous solvents [20, 21] are in a decent concurrence with the values of (∆H°A) and (∆S°A). Small values of the entropy of association (∆S°A) in all the studied systems suggesting less disorderliness of the system is required for the formation of ion-association of all the thermodynamic functions describing the ion association and solvation process.
The most satisfactory interpretation of the Walden products is based on the structure of H2O–ethanol mixtures and the effect of ions on this structure. The thermodynamic, kinetic, ultrasonic and transport data indicate that addition of simple alcohols to water initially, enhances the structure of the solvent water [18]. 298.15 303.15 308.15 313.15
ip t
0.10
Table 6 Entropy change of association (∆S°A) and enthalpy change of association (∆H°A) for copper sulfate in used solvents at different temperature
0.09
0.08
0.07
cr
0.06
(∆S°A)(J.mol-1)
Solvent
m
o
2
Λ ηo/(S·cm mol
-1
kg·m
-1
-1
s )
0.11
0.05 0.1
0.2
0.3
0.4
0 %( EtOH-H2O)
Volume fraction of ethanol
298.15 K 303.15 K 308.15 K 313.15 K
Fig.3. Plots of Walden product ϕmo ηo /(S·cm2 mol− 1 kg·m− 1 s− 1) against volume fraction φv for copper sulfate in water+ ethanol from T=298.15 K to 313.15 K.
an
20 %( EtOH-H2O)
us
0.0
298.15 K 303.15 K 308.15 K 313.15 K
The values of the Walden product are clearly decreased by elevation of the temperatures. This Walden product negative temperature coefficient might be related to the expansion in the size of solvated ions in the solutions as temperature elevates as a consequence of the difference of the proportion of the organic solvent and H2O molecules in the sheath of solvation with temperature [19]. Limiting molar conductance and the viscosity are two compelling variables on the Walden product, in which the viscosity is contrarily relative to temperature while the limiting molar conductance is specifically corresponding to the temperature. This opinion indicates that the involvement of the viscosity value is the most effective variable on the contrarily relative behavior of the Walden product with the temperature. The values of the Walden product were found to decrease as the proportion of ethanol solvent increases in the following order: 0% > 20% > 40%, which might be related to a drop in the molar conductance at infinite dilution in the same bearing. This implies that the impact of an elevation in the limiting molar conductance is higher than the impact of a drop in the viscosity of the medium.
40 %( EtOH-H2O)
M
Walden products should decrease with increase in temperature. This prediction is in agreement with the Walden products as depicted in Fig. 3.
Ac ce p
te
d
298.15 K 303.15 K 308.15 K 313.15 K
-12.213 -12.213 -12.213 -12.213
20.02 20.07 19.57 19.15
-10.615 -10.615 -10.615 -10.615
24.91 24.31 23.74 23.94
-12.108 -12.108 -12.108 -12.108
3.9. Activation energy of the transfer process Since the conductance of an ion depends on its mobility [22, 23], it is quite reasonable to treat the rating process proceeding with the disparity of temperature on the basis of Eq. (14) [26]; (14)
where A is the frequency factor, R is the gas constant and Ea. is the Arrhenius activation energy of the transfer process. The Ea. values can be assessed from the plot of (logΛ0) vs. (1/T). The estimations of Arrhenius activation energy of the transfer process of the CuSO4 in the utilized solvents are considered in Table 7. The behavior of activation energy change is inverse that of Λ0. On the other hand, there is no definite order of the activation energy of transfer, which may be due to the effect of many interfered factors on the association processes and consequently on the activation energy of transfer.
The standard free energy of association (∆G°A) was calculated for salt under study using Eq. (13) and its values were listed in Table 5.
Table 7 Activation energy (Ea.) for copper sulfate in EtOH-H2O solvents
(13)
The values of the standard enthalpy (∆H0A) and the standard entropy (∆S0A) of association process were calculated from van't Hoff equation (
25.54 25.47 25.06 24.50
Λ0 =A e-Ea/RT
3.8. Thermodynamic parameters
∆GA = - RT ln KA
(∆H°A) (kJ.mol-1)
Solvent
Ea. (kJ mol-1)
0% EtOH-H2O
8.216
20% EtOH-H2O
8.115
40% EtOH-H2O
8.053
by the plots of (log KA) versus (1/T), where
the slope is equal the value of (-∆H°A/2.303R) while the entropies of association (∆S°A) for the electrolytes were calculated by the use of Gibbs-Helmholtz equation ∆G°A = ∆H°A - T∆S°A The values of the standard enthalpy (∆H0A) and the standard entropy (∆S0A) of association process were tabulated in Table 6.
4. Conclusions
5
Page 5 of 6
ip t
Copper sulfate volumetric properties in EtOH-H2O solvents have been described. The standard partial molar volumes of transfer for copper sulfate are determined. The different solvation volumes are determined. The difference of volumetric properties reflects the significant influence of solvent and temperature on the salt behavior. The nature of the ion-solvent interaction taking place in the solution is controlling the extent of ion-pairing in salt solutions under study. Additionally, it hangs on the dielectric constant and the different properties of the medium. The association decreases as the temperature increases and increases in the proportion of organic solvent increases.
References
Ac ce p
te
d
M
an
us
cr
[1] J.F. Castel; E.S. Amis; J. Chem. Eng. Data 17 (1972) 55–59. [2] D. Feakins, D.J. Freemantle, K.G. Lawrence, J. Chem. Soc. Faraday Trans. I 70 (1974)795–806. [3] I.Y. Klugman, J. Electrochem. 38 (2002) 415–420. [4] Y. Marcus, Ion Solvation, John Wiley & Sons, Chichester, UK, 1986. [5] A. Wahab, S. Mahiuddin, Can. J. Chem. 79 (2001) 1207–1212. [6] E.A. Gomaa, M.A. Tahoon, J. Mol. Liq. 214 (2016) 19–23. [7] T.S. Banipal, G. Singh, J. Solut. Chem. 32 (2003) 997–1015. [8] D.P. Kharakoz, J. Phys. Chem. 95 (1991) 5634–5642. [9] C. Zhao, P. Ma, J. Li, J. Chem. Thermodyn. 37 (2005) 37–42. [10] J.E. Desnoyers, M. Aerl, G. Perron, C. Jolicoeur, J. Phys. Chem. 73 (1969) 3346–3351. [11] C. Visser, G. Perron, J.E. Desnoyers, J. Am. Chem. Soc. 99 (1977) 5894–5900 [12] F. J. Millero, J. Phys. Chem., 72(9), 3209-3214 (1968). [13] J. Padova, and I. Abrahamer, J. Phys. Chem., 71(7), 2112-2116 (1967) [14] E.A. Gomaa, Thermochimica Acta, 91(1985)235-241. [15] C.A. Kraus, W.C. Bray, J. Am. Chem. Soc. 35 (1913) 1315–1434. [16] T. Shedlovsky, J. Franklin Inst. 225 (1938) 739–743. [17] P. Walden, Z. Anorg. Allg. Chem. 113 (1) (1920) 85-97. [18] F. Franks, D.J.G. Ives, Q. Rev. London 20 (1966) 1 –44. [19] R.A. Robinson, R.H. Stokes, Electrolyte Solutions, 2nd ed. Butterworth, London, 1965. [20] G.H. Nacollas, Interactions in Electrolyte Solutions, 1st ed. Elsevier, Amsterdam, 1966. [21] T. Hashitami, T.R. Tamamushi, Thermodynamic of electrolyte solutions in ions and solvents, Kagaku Sosetsu, Chem. Soc. of Japan, Tokyo, 1976. [22] J.I. Bhat, M.K. Shetty, J. Mol. Liq. 160 (2011) 140–143. [23] F.I. El-Dossoki, N.E.Y. Abdallh, S.E.T. Elmasly J. Mol. Liq. 163 (2011) 135–140. [24] E.J .King, J. Phys. Chem., 73, 1220 (1969). [25] J.I.Kim and E.A.Gomaa, Bull.Soci.Chim.Belg.,90(1981)391. [26] Esam A. Gomaa , Mohamed A. Tahoon , A. Shokr , Ionic association and solvation study of CoSO4 in aqueous - organic solvents at different temperatures, Chemical Data Collections (2016), doi: 10.1016/j.cdc.2016.06.005. [27] Milan Vranes, Sanja Dozic, Vesna Djeric, Slobodan Gadzuric, J. Chem. Thermodynamics, 54, 2012, 245-249. [28] Xu Wang, Ranran Fu, Yuhua Guo, Ruisen Lin, J. Mol. Liq, 197, 2014, 73-76.
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S1658-3655(16)30060-7 http://dx.doi.org/doi:10.1016/j.jtusci.2016.08.007 JTUSCI 327
To appear in: Received date: Revised date: Accepted date:
8-3-2016 26-8-2016 28-8-2016
Please cite this article as: E.A. Gomaa, A. Negm, M.A. Tahoon, Conductometric and volumetric study of copper sulfate in aqueous ethanol solutions at different temperatures, Journal of Taibah University for Science (2016), http://dx.doi.org/10.1016/j.jtusci.2016.08.007 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.
Conductometric and volumetric study of copper sulfate in aqueous ethanol solutions at different temperatures Esam A. Gomaa, Amr Negm, Mohamed A. Tahoon* Chemistry Department, Faculty of Science, Mansoura University, 35516-Mansoura, Egypt
ABSTRACT
cr
ip t
An Anton Par Model 55 densimeter is used to measure the densities at 298.15 K, 303.15 K, 308.15 K, and 313.15 K of copper sulfate solutions in H 2O and in EtOH-H 2O. The acquired information was utilized to ascertain the apparent molar volumes, limiting partial molar volumes, and transfer partial molar volumes, for copper sulfate. These computed parameters are utilized to decipher the solute–solute and solute–solvent interactions of copper sulfate in aqueous ethanol solution. The ion solvation behavior of copper sulfate in water and aqueous ethanol in the scope of 298.15 to 313.15K, using electrical conductivity principle has been studied. Kraus–Bray and Shedlovsky models of conductivity were used to analyze obtained conductance data. The limiting molar conductance λmo, association constant KA, the energy of activation of the rating process (Ea), and related thermodynamic parameters have been determined. Walden product (λmoη0) has been determined. Standard thermodynamic parameters of association (∆G°A, ∆H°A) were calculated and discussed. Increased ion–solvent and solvent–solvent interactions is suggested by increasing the amount of ethanol which indicated by limiting molar conductance values. The negative ∆G°A values indicate that the association processes in all studied systems are spontaneous processes. The negative estimation of (∆H°A) demonstrating that the association processes is exothermic in nature.
us
Keywords: Partial molar volume; Copper sulfate; Binary mixtures; Transfer volumes
an
* Corresponding author. Tel.: +201098351007.
E-mail address: [email protected] (M. A. Tahoon).
1. Introduction Significant data provided from the physicochemical properties of salts in aqueous solutions explain (solute + solute) and (solute + solvent) interactions that imperative in comprehension the dependability of these systems and are ensnared in a few biochemical and physiological procedures in a living cell. Due to the existence of many interactions, the determination of the physical and chemical properties of organic solvents + inorganic salts solutions (partially solvated melts) in the wide concentration range is very complex. Strong ion–ion interactions are dominant in concentrated solutions. The influence of the ion–dipole interactions between solvent molecules and the solute ions is increasing by dilution. In extremely dilute solutions the predominant weak dipole– dipole interaction is present. In diluted solutions exactly in the range of validity of the Debye–Hückel law, properties of the systems, such as conductivity [1], viscosity [2] and volumetric properties [3], were mostly calculated. Due to their commercial uses in many technological areas, the ion solvation process and equilibrium involved in many concentration sections in water and many nonaqueous media have been of indefinite importance. The existence of ions, solvated ions, and free solvent hang on the concentration area [4]. Hence, the investigation of volumetric properties in the wide electrolyte concentration range in different solvents is essential. The present work was assumed in order to investigate volumetric properties of copper sulfate in aqueous ethanol and to explain the nature of solute–solvent interactions in a diluted and concentrated copper sulfate solution. Copper sulfate (CuSO4) has been widely used for algal growth control and treatment of human copper deficiency. Ethanol is a colorless liquid at room temperature. It is a polar solvent, with the high relative permittivity of 24.4. This feature of ethanol allows the study of the volumetric properties in the solutions with high copper sulfate concentration. Ethanol is the major used commercially solvent in the pharmaceutical industry and many other organic syntheses. Because of the possibility of H-bonds formation, ethanol solutions are often used as model systems to study the interaction of peptides and proteins [5]. A varied range of dielectric constant (ε), viscosity (η) and a high degree of hydrogen bonding effect at different temperatures are showed by aqueous ethanol solutions. By the determination of conductivity, many interactions between water and ethanol by mixing them at varied
M
amounts may be studied over that mixing range. Suitable conductivity measurements offer a useful prediction of ion–solvent interaction, proton–anion and proton–solvent association, and solvent structure.
Ac ce p
te
d
2. Experimental
Copper sulfate with mass fraction > 99% obtained from the Shanghai Chemical Co., China and used without further purification. Ethanol was purchased from Aldrich, and the purity is better than 99%, which was dried under reduced pressure at 323 K before being used. Water is distilled two times before using it; all the investigated solutions were prepared newly. The weight of samples was determined by a Mettler AE 200 balance with a sensitivity of ±0.0002 g. ultrasonic waves are used to degas the prepared solutions that used within 12 hours of preparation. The solutions densities were determined within ± 0.00001 g·cm−3 with an Anton Paar DMA 55 digital densimeter (Austria). Two times distilled water and dried air are used to calibrate the used densimeter. The temperature was kept constant to ±0.05 K using a HAAKEC thermostatic bath (German). The conductance measurements of the prepared salt solutions were carried out using Jenway Conductivity Bridge of a cell constant value 1cm−1 and a deviation of ±0.12 µS cm−1. Potassium chloride solutions are used to accurately determine the cell constant of the used conductivity electrode. The Conductivity Bridge was connected to MLW 3230 ultra-thermostat to maintain the temperature constant at the required temperature (±0.006 °C). Ethanol–water mixed solvents with the alcohol mass fractions of 0%, 20%, and 40% were prepared by applying the following equation: Alcohol percentage = (V1 ρ1)100/ (V1 ρ1+V2 ρ2)
(1)
where ρ1 and ρ2 are the density of alcohol and water respectively. V1 is the volume of alcohol which will be added to the volume V2 of water to get the mixture of the required percentage. The salts under examination with a concentration of (5 × 10−2, 4 × 10-2, 3 × 10-2, 2 ×10-2, 1 × 10-2 mol·dm−1), were prepared by take a certain volume of the prepared standard solution of the salt and making a serial dilution to the necessary volume for measurements by the
1
Page 1 of 6
beforehand prepared mixed solvents [6]. The properties of used
solvents are supplied in Table S1 (Supplementary Materials)
Table 1 Densities and apparent molar volumes of solutions of copper sulfate in aqueous ethanol at different temperatures m solute (mol.dm-1)
298.15Kb ρ (g.cm-1)
303.15K Vϕ (cm3.mol-1
ρ (g.cm-1)
308.15K Vϕ (cm3.mol-1)
ρ (g.cm-1)
313.15K Vϕ (cm3.mol-1)
ρ (g.cm-1)
0 %( EtOH-H2O) 0.9964 0.9985 1.0005 1.0020 1.0039
0.01 0.02 0.03 0.04 0.05 40 %( EtOH-H2O)
0.9841 0.9861 0.9880 0.9893 0.9909
36.414±0.161 41.504±0.101 46.577±0.082 64.530±0.081 69.050±0.090
0.9811 0.9831 0.9851 0.9865 0.9879
0.01 0.02 0.03 0.04 0.05
0.9619 0.9638 0.9657 0.9670 0.9686
42.967±0.181 48.286±0.110 49.989±0.081 66.980±0.080 70.634±0.111
0.9600 0.9619 0.9639 0.9651 0.9668
a b
28.504±0.060 33.480±0.054 38.440±0.054 53.440±0.054 54.341±0.073
0.9939 0.9960 0.9980 1.0000 1.0016
35.858±0.086 40.980±0.077 42.625±0.060 58.958±0.076 68.698±0.078
0.9760 0.9780 0.9800 0.9819 0.9831
34.894±0.118 40.072±0.122 41.737±0.099 45.142±0.089 61.798±0.072
0.9750 0.9770 0.9791 0.9810 0.9822
34.703±0.153 39.892±0.117 38.057±0.091 42.349±0.062 59.564±0.038
0.9567 0.9587 0.9607 0.9625 0.9635
42.014±0.125 41.926±0.124 41.939±0.116 47.202±0.092 67.808±0.080
0.9550 0.9570 0.9590 0.9609 0.9619
41.697±0.179 41.610±0.141 41.523±0.108 44.171±0.078 65.398±0.044
42.621±0.097 47.963±0.078 46.058±0.062 66.732±0.078 68.234±0.089
28.014±0.044 33.017±0.059 38.003±0.058 40.448±0.047 49.947±0.052
0.9918 0.9939 0.9959 0.9979 0.9998
Standard uncertainty is 0.001 mol.dm-1. Uncertainty of temperature = 0.05K.
27.599±0.110 32.624±0.071 37.632±0.056 40.088±0.031 34.549±0.007
cr
29.027±0.140 38.989±0.080 45.582±0.071 58.829±0.070 60.717±0.080
us
0.9991 1.0011 1.0030 1.0045 1.0063
an
0.01 0.02 0.03 0.04 0.05 20 %( EtOH-H2O)
Vϕ (cm3.mol-1)
ip t
a
two groups and the adjacent groups. Table 2 show that the values of Vϕ0 increase with the increase of temperature, this observation indicates that the solute-solvent interactions are favored at higher
3. Results and discussion
temperatures. Vϕ0 increase with the addition of organic solvent and may be attributed due to low surface charge density as a result of which the electrostatic attraction is more in a medium of low relative permittivity. Therefore, ion - solvent interaction would also be more and subsequently will be larger.
M
3.1. Apparent molar volume
d
Table 1 is containing the densities (ρ) of copper sulfate solutions in water and in ethanol – water at different temperatures 298.15 K, 303.15 K, 308.15 K, and 313.15 K, where m solute is CuSO4 molarity in the EtOH-H2O solutions. The apparent molar volumes (Vϕ) of copper sulfate were calculated from the equation:
te
(2)
Ac ce p
where m is the molarity (mol·dm−1) of the solute (copper sulfate), M is the relative molar mass of solute (kg·mol−1), and ρ and ρ0 are the densities (g·cm−3) of solution and solvent, respectively. The uncertainty of m was ±0.001 mol·dm−1. The calculated values of Vϕ are also recorded in Table1. By using calculated Vϕ which is the function of molality of the solute, interactions between solute and solute can be predicted. Table 1 show that the values of Vϕ increase with the elevated concentration of solute.
Table 2 Limiting apparent molar volumes (Vϕ0) and experimental slopes (BV) of copper sulfate in water, and aqueous ethanol solutions at different temperatures Solvent
Vϕ0 (cm3·mol − 1)
BV x 10 3(cm3. mol−2. kg)
0 %( EtOH-H2O) 298.15 K 303.15 K 308.15 K 313.15 K
3.2. Limiting apparent molar volume
20 %( EtOH-H2O)
The limiting apparent molar volumes (Vϕ0) were obtained by least-squares fitting to Masson equation [7]:
298.15 K 303.15 K 308.15 K 313.15 K
(3)
1.175 3.108 10.385 14.696
2.711 2.298 1.640 1.288
4.559 5.386 13.947 15.996
2.806 2.626 1.836 1.605
40 %( EtOH-H2O) 298.15 K 303.15 K 308.15 K 313.15 K
where Vϕ0 is the intercept, that is free from solute–solute interactions by definition and therefore provides an indication about solute–solvent interactions, but the experimental slope, BV provides information regarding solute–solute interactions. The evaluated values of Vϕ0 and BV are listed in Table 2. The values of Vϕ0 as reported in Table 2 are positive for copper sulfate in water and in aqueous ethanol solutions indicating the presence of strong solute– solvent interactions in these systems. This trend of Vϕ0 values is due to their hydration behavior [8, 9], which comprises of following interactions in these system: (I) the two groups of the salt, Cu+2 and SO4−2 are hydrated in an electrostatic way and (ii) the volume change results from the overlap of hydrated co-spheres of
16.400 17.292 19.618 21.969
2.348 2.208 1.702 1.485
3.3. Transfer volume Transfer limiting apparent molar properties gives not only qualitative but also quantitative information about solute–solvent interactions without considering the impacts of solute–solute interactions. The standard partial molar volumes of transfer (∆trVϕ0) from water to aqueous ethanol solutions have been calculated by Eq. (4) [27, 28]:
2
Page 2 of 6
40), the relation between the Van der Waals volumes and the partial molar volumes (the packing density) is found to be constant. Therefore, it is possible to calculate the Van der Waals volumes (Vw) of copper sulfate in (EtOH-H2O) mixtures at different temperatures (298.15, 303.15, 308.15 and 313.15 K) by applying Eq. (6)[24, 25]:
(4)
(6)
ip t
The volume of electrostriction (Ve) that is the volume of the solute compressed by the effect of electric field of solvent is calculated by using Eq. (7):
cr
(7)
The solvated radii [13] of the organic–aqueous mixtures (EtOHH2O) at different temperatures were calculated using Eq. 8 by allowing the spherical form of the solvated ions.
298 .1 5K 303 .15K 308 .1 5K 313 .1 5K
us
34 32 30 28 26 24 22 20 18 16 14 12 10 8 6 4 2 0 -2 0.00
0.05
0.10
0.15
(8)
The values of V, Vw, Ve, and solvated radii of copper sulfate in (EtOH-H2O) mixtures at different temperatures are listed in Table 3. In comparing the data of solvation of the substance used, it is observed that the values of the molar volume are increased by increasing the organic solvent content in the mixtures due to the increase in the volume of organic solvent [14] compared to water. Electrostriction volumes calculated for copper sulfate in (EtOHH2O) mixtures having negative values. The electrostriction volumes increase in negativity by increasing the percentages of the organic solvent, indicating the more work (energy) is done by the solvent on the solvation sheaths of the salts. The solvated radii are increased as the organic solvent content increase and as the temperature increase.
an
∆
tr
vΦ
o
Fig.1 shows the variation of ∆trVϕ0 of copper sulfate with the mole fraction of ethanol. The ∆trVϕ0 values of copper sulfate are positive and increase with increasing concentration of ethanol. The difference in the ∆trVϕ0 values in aqueous ethanol solutions primarily comes from the influence of organic solvent, which reflects the change in the structure of interaction between solute and [10, 11] solvent. The detected positive increasing of volumes of transfer for copper sulfate point out that in the ternary system (copper sulfate + ethanol + water), the ionic–hydrophilic interactions between the ethanol OH groups and CuSO4 ionic sphere, which lead to a positive contribution to ∆trVϕ0 is the predominate interaction over any other interaction.
0.20
M
XS
Fig.1. CuSO4 Partial molar volumes of transfer from H2O to EtOH – H2O solutions at different temperatures
V
VW
Ve
ro(AO)
Ac ce p
Solvent
te
d
Table 3 Molar volume (V), Van der Waals volume (Vw), electrostriction volume (Ve) in (Cm3.mol-1) and solvated radii (ro) of copper sulfate in (EtOH-H2O) mixed solvents at different temperatures
0 %( EtOH-H2O) 298.15 K 303.15 K 308.15 K 313.15 K
248.442 248.938 249.410 249.934
164.220 164.548 164.860 165.207
-84.222 -84.390 -84.550 -84.727
3.873 3.875 3.878 3.880
This may be due to the excess solvation processes, and the higher solvated radii of the organic solvent used than those of water and also due to the increasing in the electronic clouds around the solvated molecules as a result of the increase in their vibration and rotation motions with increasing the temperature. The solvated radii of copper sulfate in water and in aqueous ethanol solutions at different temperatures are given in Table 3 and are illustrated in Fig.2.
298.15K 303.15K 308.15K 313.15K
20 %( EtOH-H2O) 298.15 K 303.15 K 308.15 K 313.15 K
252.156 252.743 253.435 253.977
166.675 167.063 167.521 167.878
-85.480 -85.679 -85.914 -86.098
3.892 3.895 3.898 3.901
257.672 258.259 258.982 259.493
170.321 170.709 171.187 171.524
-87.351 -87.549 -87.795 -87.968
3.920 3.923 3.927 3.929
3.93
3.92
3.91
298.15 K 303.15 K 308.15 K 313.15 K
O
ro(A )
40 %( EtOH-H2O)
3.90
3.89
3.88
3.87 0.00
3.4. Calculation of the different Volumes
0.05
0.10
0.15
0.20
XS
From density of copper sulfate in water and aqueous ethanol the molar volumes [12] have been calculated by Eq. (5):
Fig.2. Copper sulfate solvated radii in H2O and EtOH-H2O at different temperatures
(5)
3.5. Limiting molar conductance
where the molar mass of used salt is symbolized by M, and the density of the solution by d. For quite big molecules (more than
3
Page 3 of 6
The specific conductance of solutions of copper sulfate with a concentration range of (0.001 –0.01) mol·L−1 in 0%, 20%, and 40% (EtOH – H2O) at 298, 303, 308 and 313K was measured. The molar conductance for all the studied systems was calculated using Eq. (9). (9) Where C is the ordinary concentration and Ks is the measured specific conductance of the used solution from which the specific conductance of the used solvent was deducted. The experimental molar conductivities were analyzed as per Kraus–Bray conductivity equation [15].
Kraus-Bray
(10) The limiting molar conductance, and dissociation constant, Kc was obtained from the intercept and slope of the plot 1/ϕm vs ϕmC. However, this model does not include any correction for inter-ionic effects or for the activities of the ions. Therefore, Shedlovsky [16] relation was used to evaluate the absolute limiting molar conductance and association constant KA.
20 %( EtOH-H2O)
an
298.15 K 303.15 K 308.15 K 313.15 K
(11)
121.50±0.12 123.01±0.12 132.97±0.13 140.25±0.14
122.90±0.12 124.28±0.12 134.75±0.13 142.76±0.14
70.67±0.07 72.67±0.07 76.56±0.07 82.03±0.08
71.59±0.07 72.55±0.07 77.99±0.07 83.22±0.08
58.68±0.05 64.02±0.06 65.44±0.06 69.73±0.06
60.23±0.06 66.04±0.06 67.56±0.06 71.01±0.07
us
0 %( EtOH-H2O) 298.15 K 303.15 K 308.15 K 313.15 K
ϕmo
Shedlovsky
cr
Solvent
ip t
Table 4 Limiting molar conductance (ϕm0) for copper sulfate in aqueous ethanol from T=298.15K to 313.15K.
40 %( EtOH-H2O)
ϕmo
298.15 K 303.15 K 308.15 K 313.15 K
M
The γ is the activity coefficient of the electrolyte. and KA were obtained from the intercept and slopes of the plot of 1/Sϕm vs CϕmSγ2. The values of limiting molar conductance at used temperatures are estimated by conductivity models of Kraus–Bray and Shedlovsky and presented in Table 4.
3.7. Walden product
te
d
Limiting molar conductance (ϕmo) was found to be higher in water and then decreased by adding ethanol to it. This behavior may be due to the formation of hydrogen bond between ethanol and water molecules resulting in the association of ethanol and water molecules, which lead to a decrease in the mobility of solvated ions and reduces the limiting molar conductance values by increasing the percentage of organic solvent in the solvent medium. The difference in viscosity (η) is not only the factor controlling the ionic mobility, which is shown by the Walden product. The limiting molar conductance of copper sulfate increased with increase in temperature from 298.15K to 313.15K for all percentages of mixed solvent as a result of the increase in ionic mobility. Hydrogen bonding of water is broken by increasing in thermal energy lead to smaller solvated ionic size and hence increases the mobility of the ions.
According to the Stokes' law, the ionic mobility depends on bulk viscosity, so the Walden products [17, 22] would appear reciprocal to the ionic radius. The differences in Walden product with solvent composition and temperature might then be discussed through variations in ion solvation alone.
Ac ce p
(12) Where the value of electronic charge is symbolized by eο, Faraday constant by F; and the ionic charge by Z and the effective Stokes molecular (ionic radius) is symbolized by r. Table 5 Association constant Ka and changes in Gibb's energy (∆G°A) for used salt in water + EtOH at different temperatures Solvent
KA
∆G°A (kJ.mol-1)
3.6. Association constant
0 %( EtOH-H2O)
The calculated values of association constant existed in Table 5. The values of KA of the studied salt at the same temperature were found to increase as the fraction of solvent ethanol increase with water. The extent of ion association depends on the nature of ion–ion interaction in the solution, the dielectric constant of the medium and also intermolecular hydrogen bonding between the solvent molecules. This introduces the fact that the values of KA increased with the increase of EtOH in water. The association constant for the studied salt was found to decrease with the increase in temperature; increased thermal motion probably breaks many bonds between ions that make a large distance between each other, where it gets solvated. Therefore the movements of ions have to increase. This may account for the decrease in KA for the increased temperature.
298.15 K 303.15 K 308.15 K 313.15 K
56.98 48.55 45.54 44.78
-4.596 -4.489 -4.488 -4.541
59.43 50.23 49.34 47.67
-4.645 -4.529 -4.582 -4.616
61.23 60.12 58.88 57.44
-4.679 -4.737 -4.790 -4.610
20 %( EtOH-H2O) 298.15 K 303.15 K 308.15 K 313.15 K 40 %( EtOH-H2O) 298.15 K 303.15 K 308.15 K 313.15 K
4
Page 4 of 6
The negative ∆G°A values indicate that the association processes in all studied systems are spontaneous processes. The negative estimation of (∆H°A) demonstrating that the association processes is exothermic in nature. Many concepts in numerous solvents [20, 21] are in a decent concurrence with the values of (∆H°A) and (∆S°A). Small values of the entropy of association (∆S°A) in all the studied systems suggesting less disorderliness of the system is required for the formation of ion-association of all the thermodynamic functions describing the ion association and solvation process.
The most satisfactory interpretation of the Walden products is based on the structure of H2O–ethanol mixtures and the effect of ions on this structure. The thermodynamic, kinetic, ultrasonic and transport data indicate that addition of simple alcohols to water initially, enhances the structure of the solvent water [18]. 298.15 303.15 308.15 313.15
ip t
0.10
Table 6 Entropy change of association (∆S°A) and enthalpy change of association (∆H°A) for copper sulfate in used solvents at different temperature
0.09
0.08
0.07
cr
0.06
(∆S°A)(J.mol-1)
Solvent
m
o
2
Λ ηo/(S·cm mol
-1
kg·m
-1
-1
s )
0.11
0.05 0.1
0.2
0.3
0.4
0 %( EtOH-H2O)
Volume fraction of ethanol
298.15 K 303.15 K 308.15 K 313.15 K
Fig.3. Plots of Walden product ϕmo ηo /(S·cm2 mol− 1 kg·m− 1 s− 1) against volume fraction φv for copper sulfate in water+ ethanol from T=298.15 K to 313.15 K.
an
20 %( EtOH-H2O)
us
0.0
298.15 K 303.15 K 308.15 K 313.15 K
The values of the Walden product are clearly decreased by elevation of the temperatures. This Walden product negative temperature coefficient might be related to the expansion in the size of solvated ions in the solutions as temperature elevates as a consequence of the difference of the proportion of the organic solvent and H2O molecules in the sheath of solvation with temperature [19]. Limiting molar conductance and the viscosity are two compelling variables on the Walden product, in which the viscosity is contrarily relative to temperature while the limiting molar conductance is specifically corresponding to the temperature. This opinion indicates that the involvement of the viscosity value is the most effective variable on the contrarily relative behavior of the Walden product with the temperature. The values of the Walden product were found to decrease as the proportion of ethanol solvent increases in the following order: 0% > 20% > 40%, which might be related to a drop in the molar conductance at infinite dilution in the same bearing. This implies that the impact of an elevation in the limiting molar conductance is higher than the impact of a drop in the viscosity of the medium.
40 %( EtOH-H2O)
M
Walden products should decrease with increase in temperature. This prediction is in agreement with the Walden products as depicted in Fig. 3.
Ac ce p
te
d
298.15 K 303.15 K 308.15 K 313.15 K
-12.213 -12.213 -12.213 -12.213
20.02 20.07 19.57 19.15
-10.615 -10.615 -10.615 -10.615
24.91 24.31 23.74 23.94
-12.108 -12.108 -12.108 -12.108
3.9. Activation energy of the transfer process Since the conductance of an ion depends on its mobility [22, 23], it is quite reasonable to treat the rating process proceeding with the disparity of temperature on the basis of Eq. (14) [26]; (14)
where A is the frequency factor, R is the gas constant and Ea. is the Arrhenius activation energy of the transfer process. The Ea. values can be assessed from the plot of (logΛ0) vs. (1/T). The estimations of Arrhenius activation energy of the transfer process of the CuSO4 in the utilized solvents are considered in Table 7. The behavior of activation energy change is inverse that of Λ0. On the other hand, there is no definite order of the activation energy of transfer, which may be due to the effect of many interfered factors on the association processes and consequently on the activation energy of transfer.
The standard free energy of association (∆G°A) was calculated for salt under study using Eq. (13) and its values were listed in Table 5.
Table 7 Activation energy (Ea.) for copper sulfate in EtOH-H2O solvents
(13)
The values of the standard enthalpy (∆H0A) and the standard entropy (∆S0A) of association process were calculated from van't Hoff equation (
25.54 25.47 25.06 24.50
Λ0 =A e-Ea/RT
3.8. Thermodynamic parameters
∆GA = - RT ln KA
(∆H°A) (kJ.mol-1)
Solvent
Ea. (kJ mol-1)
0% EtOH-H2O
8.216
20% EtOH-H2O
8.115
40% EtOH-H2O
8.053
by the plots of (log KA) versus (1/T), where
the slope is equal the value of (-∆H°A/2.303R) while the entropies of association (∆S°A) for the electrolytes were calculated by the use of Gibbs-Helmholtz equation ∆G°A = ∆H°A - T∆S°A The values of the standard enthalpy (∆H0A) and the standard entropy (∆S0A) of association process were tabulated in Table 6.
4. Conclusions
5
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ip t
Copper sulfate volumetric properties in EtOH-H2O solvents have been described. The standard partial molar volumes of transfer for copper sulfate are determined. The different solvation volumes are determined. The difference of volumetric properties reflects the significant influence of solvent and temperature on the salt behavior. The nature of the ion-solvent interaction taking place in the solution is controlling the extent of ion-pairing in salt solutions under study. Additionally, it hangs on the dielectric constant and the different properties of the medium. The association decreases as the temperature increases and increases in the proportion of organic solvent increases.
References
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