Indian Journal of Chemistry
Vol. 48A, December 2009, pp. 1667-1672
Effect of temperature on the partial molar
volumes of some bivalent transition metal
nitrates and magnesium nitrate in the
water-rich region of binary aqueous
mixtures of dimethyl acetamide
M L Parmar* & D S Banyal
Department of Chemistry, Himachal Pradesh University
Summer Hill, Shimla 171 005, Himachal Pradesh, India
Email: [email protected]
Received 8 July 2009; revised and accepted 17 November 2009
Partial molar volumes of some bivalent transition metal
nitrates, viz., manganese nitrate, cobalt nitrate, nickel nitrate,
copper nitrate, zinc nitrate and magnesium nitrate have been
determined in binary aqueous mixtures of N,N-dimethylacetamide
(DMA) in the water-rich region (5, 10, 15, 20 and 25% by weight)
of DMA from solution density measurements at 303.15 K, and in
5% w/w DMA + H2O at five equidistant temperatures (298.15,
303.15, 308.15, 313.15 and 318.15 K). The density data have been
analysed by Masson’s equation. The partial molar volumes and
experimental slopes have been interpreted in terms of
ion-solvent and ion-ion interactions, respectively. The partial
molar volumes vary with temperature as a power series of
temperature. Structure making/breaking capacities of electrolytes
have been inferred from the sign of the second derivative of
partial molar volumes with respect to temperature at constant
pressure. All the electrolytes have been found to act as structure
breakers in binary aqueous mixtures of dimethyl acetamide.
Keywords:
Solution chemistry, Partial molar volumes,
Electrolytes, Ion solvent interactions, Ion-ion
interactions, Structure breakers
Partial molar volumes of electrolytes provide
valuable information about ion-ion, ion-solvent and
solvent-solvent interactions1-15. This information is of
fundamental importance for understanding the
reaction rates and equilibria involving dissolved
electrolytes. The addition of organic solvent to an
aqueous solution of electrolyte brings about a change
in solvation of ions that often results in a large change
in the reactivity of dissolved electrolyte16,17.
Aqueous mixtures of aliphatic amides are used in
many investigations of self-aggregation, peptide
properties and solubility of drugs18. Some biological
processes are also known to prefer “amide-like”
environment to “water-like” environment19. The aim
of the present study is to generate new information on
the interactions in dimethyl acetamide + water
systems that are interesting from the chemistry and
biological point of view.
Experimental
The reagents, manganese nitrate, cobalt nitrate,
nickel nitrate, copper nitrate, zinc nitrate and
magnesium nitrate, were of analytical reagent grade.
The reagents were used as such, without further
purification, after drying over P2O5 in a desiccator.
These reagents were always placed in the desiccator
over P2O5 to keep them in dry atmosphere. Freshly
distilled conductivity water (sp. cond.~ 10-6 Ω-1 cm-1)
was used for preparing binary DMA + water mixtures
as well as standard liquid. N,N-Dimethyl acetamide
(AR grade) was shaken with barium oxide for several
days and refluxed with barium oxide for one hour and
then fractionally distilled under reduced pressure.
Only the middle fraction was used for the present
study. The density and viscosity of DMA were found
to be 0.9365 g cm-3 and 0.8764 cP, respectively at
298.15 K and are in good agreement with the
literature values20 (0.9366 g cm-3 and 0.8800 cP).
All the binary aqueous mixtures of DMA as well
solutions of nitrate salts were made by weight and the
conversion of molality, (m) into molar concentration
(c) was done by using the standard expression,
c = 1000 d m/(1000 + m M2) where d is the solution
density and M2 the moleculate weight of nitrate salt.
For density measurements, an apparatus similar to
the one reported earlier21-23 was used. The accuracy in
density measurement was 1 x 10-4 g cm-3. The
apparent molar volumes, (φv), were calculated from
density data by using the standard expression,
M 2 10 3  d − d 0 
φv =
−

 where d0 and d are the
d0
c  d0 
densities of solvent (DMA + water) and solution,
respectively, c is the molar concentration of nitrate
salt and M2 is its molecular weight. The density
measurements were carried out in a well-stirred
water-bath whose temperature was controlled to
± 0.01 K.
Results and discussion
The densities measured for the solutions of
transition metal nitrates, viz., manganese nitrate,
1668
INDIAN J CHEM, SEC A, DECEMBER 2009
cobalt nitrate, nickel nitrate, copper nitrate, zinc
nitrate and magnesium nitrate in DMA + water (5, 10,
15, 20 and 25% by weight of DMA) at 303.15 K have
been used to calculate the apparent molar volumes
(φv) of nitrates. The plots of φv against the
square-root of molar concentration (c½) at 303.15 K
were found to be linear without scatter and with
negative slopes, for all the transition metal nitrates
and magnesium nitrate in the different compositions
of DMA + water, reported here. A representative plot
for magnesium nitrate in different compositions of
DMA + water at 303.15 K is shown in Fig. 1. The
partial molar volumes (φ0v) were calculated using
least square fits to the linear plots of experimental
values of φv versus square root of molar
concentration (c½) using Masson relation relationship,
φv = φ0v + Sv c½, where φ0v = V
͞ 02 is the partial
molar volume and Sv the experimental slope. The
values of φ0v and Sv, along with standard errors,
obtained in different compositions of DMA + water at
303.15 K, are recorded in Table 1.
Fig. 1 —Plots of φv versus c½ for magnesium nitrate in different
compositions of DMA + water at 303.15 K. [1, 5% DMA + water;
2, 10% DMA + water; 3, 15% DMA + water; 4, 20% DMA +
water; 5, 25% DMA + water].
It is evident from Table 1, that the values of Sv are
negative for all the bivalent transition metal nitrates
and magnesium nitrate in water as well as in different
compositions of DMA + water mixtures at 303.15 K,
thereby showing the presence of weak ion-ion interactions in both the systems. It is also clear from Table 1
that the value of Sv, for an individual nitrate,
decreases in magnitude with the increase of DMA
content in water, thereby suggesting that ion-ion
interactions are further weakened with the increase of
DMA content. In other words, it may be said that the
solvation of ions improves with the increase of DMA
in water.
A comparison of results obtained in DMA + water
with those obtained in water only, suggests a possible
explanation for the presence of negative Sv values
(i.e., negative slopes) for all the nitrates. Although, at
infinite dilution, all the nitrates are completely
dissociated in the different compositions of DMA +
water, the situation would have been different at
higher concentrations of these electrolytes. Due to the
moderate dielectric constant of DMA + water
mixtures, these salts remain completely ionized even
at fairly high concentrations in DMA + water
mixtures. Therefore, an appreciable inter-ionic
penetration occurs and this gives rise to negative
slopes in the φv versus c½ curves for these salts.
These negative values of Sv in different compositions
of DMA + water also suggest the presence of
cation-anion penetration24 and this happens due to the
competition between the ions to occupy the void
space of large solvent molecules.
It is also clear from Table 1, that the values of φ0v
are positive and large for all the nitrates, in water as
well as over the entire composition range of DMA +
water mixture at 303.15 K, thereby showing the presence of strong ion-solvent interactions. It is also clear
from this table that the value of φ0v increases regularly
with the increase of DMA composition for an
individual salt, showing that ion-solvent interactions
improve on the addition of DMA in water. A quantitative comparison of the magnitude of values of φ0v and
Sv shows that φ0v values are much larger in magnitude
than those of Sv values, for all the nitrates, suggesting
that ion-solvent interactions dominate over the ion-ion
interactions in water as well as in DMA + water
mixtures at 303.15 K.
The volumes of transfer (∆ ͞V02,tr) were calculated
using the standard, ∆ ͞V02,tr = φ0v (M S) - φ0v (W), and
are recorded in Table 1. Here φ0v (M S) and φ0v (W)
NOTES
are the partial molar volumes of nitrates in mixed
solvent (DMA + water) and water, respectively. The
increase in φ0v and ∆͞V02,tr (cf. Table 1), for all the
bivalent transition metal nitrates and magnesium
nitrate, may be attributed to the decrease in
electrostriction in the presence of DMA. Thus,
the electrostriction effect, which brings about the
1669
shrinkage in the volume of solvent, decreases in the
mixed solvent as compared with that in pure water.
From the values of ∆͞V02,tr, it may also be inferred that
the solvation of ions of a particular nitrate increases
with the increase of DMA content in water, thereby
reducing the strong25 solvent-solvent interactions, i.e.,
interactions between DMA and water.
0
Table 1 — Partial molar volumes (φ v), experimental slopes (Sv) and partial molar volumes of transfer (∆
transition metal nitrates and magnesium nitrate in DMA + water mixtures at 303.15 Ka
DMA + water (% w/w)
φ0v (cm3 mol-1)
0 (water)
5
10
15
20
25
194.62 (± 0.32)a
230.03 (± 0.06)
240.84 (± 0.09)
246.03 (± 0.01)
250.88 (± 0.01)
255.82 (± 0.01)
0 (water)
5
10
15
20
25
140.61 (± 0.04)
214.67 (± 0.03)
227.23 (± 0.06)
240.00 (± 0.04)
255.29 (± 0.13)
265.08 (± 0.11)
0 (water)
5
10
15
20
25
180.10 (± 0.25)
194.98 (± 0.07)
200.16 (± 0.05)
205.16 (± 0.07)
216.08 (± 0.05)
230.36 (± 0.06)
0 (water)
5
10
15
20
25
129.55 (± 0.04)
218.68 (± 0.00)
231.34 (± 0.82)
242.78 (± 0.34)
245.25 (± 0.18)
251.32 (± 0.30)
0 (water)
5
10
15
20
25
153.24 (± 0.04)
233.50 (± 0.28)
251.66 (± 0.18)
261.67 (± 0.17)
291.65 (± 0.18)
301.72 (± 0.40)
0 (water)
172.04 (± 0.00)
5
199.45 (± 0.00)
10
222.38 (± 0.10)
15
243.20 (± 0.07)
20
257.41 (± 0.08)
25
264.28 (± 0.10)
a
Standard errors are given in parentheses.
Sv (cm3 dm3/2 mol-3/2)
Manganese nitrate
-239.77 (± 0.02)a
-201.29 (± 0.01)
-225.74 (± 0.01)
-234.50 (± 0.01)
-238.05 (± 0.01)
-240.27 (± 0.01)
Cobalt nitrate
-22.12 (± 0.01)
-193.13 (± 0.01)
-198.48 (± 0.01)
-228.90 (± 0.01)
-268.99 (± 0.01)
-280.48 (± 0.01)
Nickel nitrate
-105.78 (± 0.01)
-172.95 (± 0.01)
-176.09 (± 0.01)
-184.73 (± 0.01)
-200.41 (± 0.01)
-217.49 (± 0.01)
Copper nitrate
-104.66 (± 0.01)
-240.95 (± 0.06)
-257.50 (± 0.09)
-277.03 (± 0.02)
-279.87 (± 0.01)
-292.82 (± 0.02)
Zinc nitrate
-68.54 (± 0.01)
-249.68 (± 0.01)
-260.88 (± 0.01)
-270.54 (± 0.01)
-339.62 (± 0.01)
-357.49 (± 0.02)
Magnesium nitrate
-72.76 (± 0.00)
-102.92 (± 0.01)
-149.42 (± 0.01)
-189.15 (± 0.01)
-196.93 (± 0.01)
-212.51 (± 0.01)
∆
͞V02,tr) for
͞V02,tr (cm3 mol-1)
——
35.41
46.22
51.41
56.26
61.20
——
74.06
86.62
99.39
114.68
124.47
——
14.88
20.06
25.06
35.98
50.26
——
89.13
101.79
113.23
115.70
121.77
——
80.26
98.42
108.43
138.41
148.48
——
27.41
50.34
71.16
85.37
92.24
1670
INDIAN J CHEM, SEC A, DECEMBER 2009
Since NO͞3 ion is common in all the bivalent
transition metal nitrates and magnesium nitrate,
therefore from the values of ͞V02,tr, it may also be
inferred that in a particular composition of binary
aqueous mixtures of dimethyl acetamide, the
electrostriction for these cations follows the order:
Zn2+ > Cu2+ > Co2+ > Mg2+ > Mn2+ > Ni2+.
Thus, it may be concluded that the order of
solvation of these cations by DMA + water is just the
reverse. Further, since the value of ͞V02,tr, for an
individual salt, increases with increase in composition
of DMA in water, therefore the extent of preferential
solvation, for a particular cation also increases with
the increase of DMA in water, which may be
attributed to the decrease in solvent-solvent
interactions between DMA and water.
Since the behaviour of an individual nitrate salt
was found to be linear and identical in different
compositions of DMA + water at 303.15 K, only one
system (5% w/w DMA + water) has been selected for
studying the effect of temperature. The densities were
determined for different concentrations of nitrate salts
in 5% w/w DMA + water at different temperatures
(298.15, 303.15, 308.15, 313.15 and 318.15 K). The
linear plots of φv versus c½ have been obtained at
different temperatures for individual salt. A sample
plot for zinc nitrate is shown in Fig. 2.
The values of limiting apparent molar volumes
(φ0v) and the experimental slopes (Sv) at different
temperatures have been obtained by using
least-square fits to the linear plots of φv versus c½ and
these values along with standard errors are given in
Table 2.
It is evident from Table 2, that the values of Sv are
negative for all the nitrate salts in DMA + water
system at all temperatures, which reflects that the
ion-ion interactions are very weak over the entire
temperature range, studied here. Further, it is also
clear from Table 2 that the value of Sv, for an
individual nitrate salt decreases in magnitude with the
rise in temperature in 5% w/w DMA + water mixture.
This suggests that ion-ion interactions further weaken
with the increase in temperature, which may be
attributed to the increase in solvation of ions of the
individual nitrate salt.
The values of φ0v, for all the nitrate salts in DMA +
water increase with the increase in temperature
(Table 2), showing that ion-solvent interactions are
further strengthened with the increase in temperature.
The increase in φ0v may be attributed to the increase in
solvation of the ions of individual electrolyte in
DMA + water system.
The temperature dependence of φ0v in DMA +
water for bivalent transition metal nitrates and magnesium nitrate can be represented by the following
expressions:
φ0v = - 1099.99 + 7.21 T – 0.009 T2 for maganese
nitrate, φ0v = - 3211.36 + 20.10 T – 0.029 T2 for
cobalt nitrate, φ0v = - 4214.80 + 26.58 T – 0.040 T2 for
nickel nitrate, φ0v = -7210.28 + 46.39 T – 0.072 T2 for
copper nitrate, φ0v =- 9894.48 + 63.19 T – 0.098 T2 for
zinc nitrate, and, φ0v = - 1578.24 + 9.35 T – 0.011 T2
for magnesium nitrate. The temperature T is
expressed in Kelvin.
The partial molar volume expansibilities, φ0E =
[∂φ0v/∂T]p, calculated using the above expressions for
different nitrates in 5% w/w DMA + water system are
also recorded in Table 2. The value of φ0E decreases
with the increase of temperature, for all the bivalent
transition metal nitrates and magnesium nitrate, in
5% w/w DMA + water (Table 2) indicating that the
Fig. 2 — Plots of φv versus c½ for zinc nitrate in 5% DMA + water mixture at different temperatures. [1, 298.15 K; 2, 303.15 K; 3,
308.15 K; 4, 313.15 K; 5, 318.15 K].
NOTES
0
1671
0
Table 2 — Partial molar volumes (φ v), experimental slopes (Sv) and partial molar volume expansibilities (φ E) for bivalent transition
metal nitrates and magnesium nitrate in 5% w/w DMA + water at different temperaturesa
Temp.
Sv
φ0v
φ0E
3
3/2
-3/2
3
-1
3
(K)
(cm
dm
mol
)
(cm mol )
(cm mol-1 K-1)
298.15
303.15
308.15
313.15
318.15
226.49 (± 0.04)a
230.03 (± 0.06)
241.64 (± 0.05)
244.25 (± 0.63)
256.43 (± 0.04)
298.15
303.15
308.15
313.15
318.15
200.94 (± 0.12)
214.67 (± 0.03)
241.96 (± 0.16)
252.80 (± 0.09)
262.24 (± 0.15)
298.15
303.15
308.15
313.15
318.15
181.52 (± 0.05)
194.98 (± 0.07)
207.55 (± 0.04)
217.03 (± 0.09)
219.95 (± 0.14)
298.15
303.15
308.15
313.15
318.15
203.59 (± 0.39)
218.68 (± 0.00)
232.22 (± 0.20)
240.10 (± 0.43)
248.11 (± 0.23)
298.15
303.15
308.15
313.15
318.15
212.99 (± 0.09)
233.50 (± 0.28)
247.15 (± 0.25)
252.53 (± 0.32)
263.22 (± 0.04)
298.15
303.15
308.15
313.15
318.15
195.90 (± 0.05)
199.45 (± 0.03)
210.88 (± 0.41)
213.30 (± 0.06)
241.90 (± 0.24)
a
Standard errors are given in parentheses.
Manganese nitrate
-200.68 (± 0.00)a
-201.28 (± 0.00)
-209.96 (± 0.00)
-210.32 (± 0.00)
-232.99 (± 0.00)
Cobalt nitrate
-175.20 (± 0.01)
-193.13 (± 0.00)
-279.55 (± 0.01)
-308.90 (± 0.00)
-329.18 (± 0.01)
Nickel nitrate
-144.92 (± 0.00)
-172.95 (± 0.00)
-203.29 (± 0.00)
-206.28 (± 0.00)
-207.18 (± 0.01)
Copper nitrate
-208.36 (± 0.02)
-240.95 (± 0.06)
-254.02 (± 0.01)
-270.74 (± 0.02)
-289.34 (± 0.01)
Zinc nitrate
-203.51 (± 0.00)
-249.68 (± 0.01)
-250.14 (± 0.01)
-252.15 (± 0.02)
-269.58 (± 0.00)
Magnesium nitrate
-93.32 (± 0.00)
-102.92 (± 0.00)
-128.30 (± 0.02)
-126.39 (± 0.00)
-198.49 (± 0.01)
behaviour of these nitrate salts is just like common
electrolytes; in the case of common electrolytes the
partial molar volume expansibilities decrease with
the rise in temperature. The variation of φ0E with
temperature, for all the transition metal nitrates
and magnesium nitrate, has been found to be linear in
5% w/w DMA + water as shown in Fig. 3. The decrease in φ0E for an individual nitrate salt, may be ascribed to the absence of “caging or packing effect”25.
During the past few years, it has been emphasized
by a number of workers that Sv is not the sole criteria
1.689
1.596
1.503
1.411
1.318
2.890
2.601
2.312
2.024
1.735
2.890
2.493
2.096
1.698
1.301
3.380
2.659
1.937
1.216
0.495
4.594
3.611
2.629
1.646
0.663
2.551
2.437
2.323
2.209
2.095
for determining the structure making or breaking
nature of any solute. Hepler26 has developed a technique of examining the sign of [∂2φ0v/∂T2]p for various electrolytes in terms of long range structure
making or breaking capacities of the electrolytes in
aqueous solutions using the general thermodynamic
expression: [∂ Cp/∂ P]p = – [∂2 φ0v /∂ T2]p.
On the basis of this expression, it has been deduced
that the structure making electrolytes should have
positive values and the structure breaking electrolytes
negative values. In the present study, it is observed
INDIAN J CHEM, SEC A, DECEMBER 2009
1672
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2
3
4
5
6
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8
9
10
11
12
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17
18
0
Fig. 3—Variation of φ E with temperature for some transition
metal nitrates and magnesium nitrate in 5% DMA + water.
[1, manganese nitrate; 2, cobalt nitrate; 3, nickel nitrate; 4, copper
nitrate; 5, zinc nitrate; 6, magnesium nitrate].
19
20
that [∂2φ0v/∂T2]p, for the solutions of bivalent transition metal nitrates and magnesium nitrate, is negative,
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