AASCIT Communications
Volume 2, Issue 4
May 10, 2015 online
ISSN: 2375-3803
Accurate Solvent –Solvent Densities, Dielectric
Constants and Volumes of Mixed N-Methyl
Pyrrolidone (NMPy) – Water Solvents at 298.15K
Esam A. Gomaa
Chemistry Department, Faculty of Science, Mansoura University, Mansoura, Egypt
Mohamed A. Tahoon Chemistry Department, Faculty of Science, Mansoura University, Mansoura, Egypt
Hadeer A. Fawzi
Chemistry Department, Faculty of Science, Mansoura University, Mansoura, Egypt
Keywords
Densities, Dielectric Constant, Molar Volume, Van der Waals Volume, Electrostriction Volume, Crystal Volume,
(NMPy) – Water Mixtures
T
he present paper reports the study of binary mixture N-Methyl Pyrrolidone(NMPy) – Water Solventsand their properties
over the entire range of composition at 298.15K.The densities and dielectric constants for mixed NMPy – water solvents
at 298.15K were accurately measured using densimeter DMA-58 and decameter DK-300 respectively. Different volumes
(molar volume VM, Van der Waals volume VW, electrostriction volume Ve and crystal volume VC ) for mixed NMPy – H2O
solvents were evaluated from density measurements .The results are discussed in the light of intermolecular interactions
occurring in the binary mixture.
Introduction
Study of dielectric behavior of polar and nonpolar molecules and their mixtures under varying conditions of compositions
has evoked considerable interest. There have been several investigations on the dielectric behavior of solvent mixtures in
which dielectric spectra were used to examine molecular orientations, hydrogen bonded networks and microdynamics of these
systems. Excess properties depend on the composition and temperature, are of great importance for the study of the interaction
between mixing components. Density measurements of solvent mixtures are expected to shed some light on the solvent-solvent
interaction and configuration of their mixtures .When a binary mixture is formed, the excess properties like dielectric
parameters do not vary linearly with composition. The deviation from linearity of these parameters is termed as excess
parameters and is helpful to understand the nature of intermolecular interactions and bonding between the two liquids [112].When a binary mixture is formed, the excess properties like refractive index and dielectric parameters do not vary linearly
with composition. The deviation from linearity of these parameters is termed as excess parameters and is helpful to understand
the nature of intermolecular interactions and bonding between the two liquids. As a result many workers [13-16] have studied
the excess parameters in liquid mixtures. Solvents miscible in water has important role on the effect of hydrogen bonds of
water which plays vital role in chemical, physical and biological processes.
The aim of this work is to measure accurately the density and dielectric constants of mixed (NMPy-H2O) solvents which are
necessary for further thermodynamic calculations.
The increase in densities, decrease of volumes and decrease of dielectric constants with decrease of mole fraction of NMePy
in the mixture were discussed in view of the relation between dipole moment and square diameter of solvent parameter.
94
2015; 2(4): 93-98
Experimental Details
(NMPy) is obtained from Merk co. It was used without further purification as the supplier claims their purity is more than
99%. The solutions are prepared with different volume fractions of respective chemicals
All the glassware were left in chromic mixture for one day, and then washed several times with water, distilled water, finally
with bidistilled water . And they were dried in an electric oven.
These volume fractions are converted to mole fractions for further calculations.
Double distilled water was used for preparation of solution mixtures (with conductivity less than 5 µs/cm).
Densimeter DMA-58 and decameter DK-300 were used for measuring both density and dielectric constant respectively.
The density meter is based on the measurement of the period of harmonic oscillation of a quartz U-tube. The sample fluid is
injected into the U-tube and its density alters the oscillation period. The U-tube can be described as undamped oscillation of a
mass suspended from a spring.
The temperature was maintained constant using a thermostat (INSREF-India make) with an accuracy of ± 0.1K to maintain
the temperature at 298.15K.
It is important to mention that at least three separate determinations were performed and the mean absolute value of density
and dielectric constant was then reported.
Results and Discussion
The densities of mixed NMPy- H2O at 298.15K were evaluated from the measured oscillation parameter (T) and β parameter
as given in equations (1-3).
=
(1)
−
=
=
(2)
(3)
−
here (T) is the oscillation period measured by densimeter , d H2O is the density of water and dL is the density of air(d H2O at
298.15K = 0.99707, dL at 298.15 =0.001185 measured at 760 Torr).
The densities of mixed NMPy – H2O are given in Table (1) and Fig. 1 , with calculated molecular weights for used mixtures
from equation (4).
=
.
Where (M) is the molecular weight of the mixed solvent, X
organic solvent, M
is the molecular weight of water and M
+
.
.
(4)
is the mole fraction of water, X . is the mole fraction of
is the molecular weight of organic solvent.
The molar volumes (VM) were obtained from density measurements. The VM as calculated by dividing the molecular weight
by exact solution densities.
The packing density (ρ) as explained by Kim [6- 8] the relation between Van der Waals volumes (VW) and the molar
volumes (VM) for relatively large molecules was found to be constant [9-20] and equal to 0.661.
ρ = VW / VM = 0.661 ± 0.017
(5)
The electrostriction volumes (Ve) which is the volume compressed by the solvent can be calculated by using equation (6) as
follows:
Ve = VW – VM
(6)
The solvated radii of the organic–aqueous mixtures (NMPy-H2O) were calculated using equation (7) by considering the
ISSN: 2375-3803
95
spherical form of the solvated molecules.
V =
1
π Nσ 3
6
(7)
Where V is the molar volume calculated from the densities as described before and σ is the solvated diameter.
The molar volume (VM), Van der Waals volume (VW), and electrostriction volume (Ve) for mixed NMPy-H2O solvents at
298.15K are tabulated in Table 2.
The packing density for crystal (Pc) was evaluated from the mean values of many readings and found to be 0.6482.
Dividing the Van der Waals volume (VW)[20-28] by crystal volume(VC) equation (8):
"# =
$%
$&
= 0.6482
(8)
The calculated crystal volumes for mixed NMPy-H2O mixtures are listed in table 2.
The dipole moments evaluated from the literature values of pure solvent dipole moments by applying equation (9):
μ =
- μ-
+
(9)
μ
Whereμ- , μ are the dipole moments for both NMPy and water at 298.15K, and X1, X2 are the mole fractions of both
mixtures.
Relaxation μ /σ were evaluated and tabulated in table 3. The dipole moments and diameters (σ) for mixed NMPy-H2O
were estimated by the sum of the dipole moments (ref.7) as explained in equation 9 for each solvent multiplied by their mole
fractions. The estimated dipole moments together with the ratio µs/ σ2 are also cited in Table 3.
Most values in Table 3 and Fig.2 .are increased with decrease of NMPy mole fractions indicating more solvation.
From results It is observed that density increases with increase in mole fraction of NMPy in the mixture.
Also it is observed that all different volumes are increasing by the addition of NMPy solvent.
Table 1. Oscillation period (T) and density (D) values for (NMPy-H2O) mixtures at 298.15K.
vol. %
XS(FA)
T
D (g/cm3)
M.Wt
100
1
3.9231
1.0285
99.13
95
0.7804
3.9288
1.0339
81.3
90
0.6273
3.9336
1.0387
68.89
85
0.5145
3.9373
1.0421
59.79
80
0.4379
3.9394
1.0451
52.72
75
0.3594
3.9443
1.0468
47.16
70
0.3038
3.9495
1.0466
42.65
65
0.2578
3.9400
1.0457
38.92
60
0.2191
3.9383
1.0439
35.78
Table 2. Different volumes of mixed (NMPy – H2O) solvents at 298.15K.
XS(FA)
VM(cm3/mole)
VW(cm3/mole)
Ve(cm3/mole)
VC(cm3/mole)
1
96.38
63.70
-32.68
98.27
0.7804
95.87
63.37
-32.5
97.76
0.6273
95.93
63.07
-32.36
97.30
0.5145
95.12
62.87
-32.25
96.99
0.4379
94.85
62.69
-32.15
96.71
0.3594
94.69
62.59
-32.1
96.55
0.3038
94.70
62.59
-32.11
96.55
0.2578
94.79
62.65
-32.14
96.65
0.2191
94.95
62.76
-32.19
96.82
96
2015; 2(4): 93-98
Fig 1. Relation between mole fraction of NMPy(XS) and density at 298.15K.
Table 3. Diameter (σ), dipole moment (µs), (µs/σ2) and dielectric constant (є) of mixed (NMPy – H2O) solvents at 298.15K.
XS(FA)
σ (A0)
µs (1018esu)
µs/ σ2
є
1
2.84
4.08
0.505
32.0
0.7804
2.83
3.59
0.448
35.7
0.6273
2.839
3.25
0.404
39.5
0.5145
2.831
3.00
0.379
43.0
0.4379
2.829
2.80
0.349
45.9
0.3594
2.827
2.65
0.331
49.2
0.3038
2.827
2.53
0.316
51.7
0.2578
2.828
2.43
0.303
54.4
0.2191
2.830
2.39
0.292
56.5
Fig 2. Relaltion between mole fraction of NMPy (XS) and molecular radius of binary mixture at 298.15K.
ISSN: 2375-3803
97
Conclusion
The density of NMPy-H2O solutions have been measured experimentally at 298.15K. From density data the different
volumes, molar, Van der Waals, electrostriction and crystal volumes are determined. The dielectric parameter shows systematic
changes with concentration conclude that these mixtures have intermolecular interactions.The evaluated values of different
volumes indicate the presence of intermolecular interaction between mixtures components.
Abbreviations
N-Methyl Pyrrolidone (NMPy), Density (D), Dielectric Constant (є), Molar Volume (VM), Van der Waals Volume (VW),
Electrostriction Volume (Ve), Crystal Volume (VC), Mole Fraction (XS), Molecular Weight (M.Wt), Dipole Moment (µs),
Diameter (σ).
Prof. Dr. Esam A. Gomaa
Prof. of Physical Chemistry, Faculty of Science, Mansoura University.
Email Address: [email protected]
Special area, Chemical Thermodynamics and Solution Chemistry. Dr. Rer. Nat.. from Muich
Technical University , Germany on 1982.Got Prof. degree on 1994.Has more than 140 published
paper in international journals in Chemistry, Physics and Environment. Participates in more than 20
international conferences. Has scientific school consists of about twenty scientists.
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