The heat capacity and density of solutions of barium and tetrabutylammonium iodides in N-methylpyrrolidone at 298.15 K

Article abstract of DOI:10.1134/S0036024409030121

The heat capacity and density of solutions of barium and tetrabutylammonium iodides in N-methylpyrrolidone (MP) were studied at 298.15 K by calorimetry and densimetry. The standard partial molar heat capacities and volumes (Cp2 and V2) of the electrolytes

Full text of DOI:10.1134/S0036024409030121

ISSN 0036-0244, Russian Journal of Physical Chemistry A, 2009, Vol. 83, No. 3, pp. 392–395. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © A.N. Novikov, O.F. Lenina, V.A. Vasilev, 2009, published in Zhurnal Fizicheskoi Khimii, 2009, Vol. 83, No. 3, pp. 473–476.
PHYSICAL CHEMISTRY
OF SOLUTIONS
The Heat Capacity and Density of Solutions of Barium
and Tetrabutylammonium Iodides
in N-Methylpyrrolidone at 298.15 K
A. N. Novikova, O. F. Leninaa, and V. A. Vasilevb
a Novomoskovsk Institute, Mendeleev University of Chemical Technology, Novomoskovsk, Russia
b Mendeleev University of Chemical Technology, Miusskaya pl. 9, Moscow, 125190 Russia
e-mail: uroboros@newmsk.tula.net
Received March 17, 2008
Abstract—The heat capacity and density of solutions of barium and tetrabutylammonium iodides in N-meth-
ylpyrrolidone (MP) were studied at 298.15 K by calorimetry and densimetry. The standard partial molar heat
°
°
capacities and volumes (Cp2 and V2 ) of the electrolytes in MP were calculated. The standard heat capacities
Cpi and volumes Vi of the Ba2+ and (C4H9)4N+ ions in solution in MP at 298.15 K were determined. With the
°
°
tetrabutylammonium ion, these values were in agreement with those calculated on the basis of the tetrapheny-
larsonium–tetraphenyl borate and tetraphenylphosphonium–tetraphenyl borate assumptions. The results are
discussed in relation to the special features of solvation in solutions of the salts studied.
DOI: 10.1134/S0036024409030121
INTRODUCTION
1 × 10–3 J/(g K). The densities of solutions (ρ) were
measured on a precision pycnometric unit [6]. The
errors in density measurements were 2 × 10–5 g/cm3.
This work continues systematic studies of solutions
of electrolytes and nonelectrolytes in the aprotic dipo-
lar solvent N-methylpyrrolidone (MP). We studied the
heat capacities and volume properties of 1–1 electro-
lytes in MP in [1–4]. Studies of electrolytes of another
valence type and salts containing organic ions, such as
tetraalkylammonium ions, which differ from typical
inorganic ions by large sizes and small electric charge
surface densities, are of certain interest. We selected
barium and tetrabutylammonium iodides as objects of
study. These salts are fairly well soluble in MP.
RESULTS AND DISCUSSION
The results of Cp and ρ measurements are listed in
Table 1. The concentration dependences of Cp and spe-
cific volumes V of solutions of LJI2 and (ë4H9)4NI in
MP and a 1–1 electrolyte (RbI) in MP (for comparison,
according to [1]) are shown in Fig. 1. It follows from
these plots that Cp and V decrease as the concentration
increases for these electrolytes, as for the majority of
inorganic salts. The Cp(V) = f(m) dependences, how-
ever, have special features for each type of electrolytes.
Compared with solutions of RbI, the properties of solu-
tions of (ë4H9)4NI change to a much lesser extent, and
those of solutions of LJI2, to a greater extent as the con-
centration varies. Two effects influence the properties
of solutions. On the one hand, bonds between solvent
molecules get broken under the action of the electro-
static field of ions, which increases the heat capacity
and volume of solutions. On the other hand, solvent
molecules become oriented around ions, and solvation
sheaths are formed, which is accompanied by a
decrease in heat capacity and volume [7–9] and elec-
trostriction, that is, solvent compression, which also
decreases volume [9–11]. The second effect predomi-
nates in solutions of LJI2, because the doubly charged
EXPERIMENTAL
MP of ch. (pure) grade was dried over molecular
sieves 4A and doubly distilled in a vacuum. The content
of water in MP determined by titration according to Fis-
cher did not exceed 0.02 wt %. Anhydrous LJI2 was
prepared from barium iodide dehydrate of kh. ch.
(chemically pure) grade. It was doubly recrystallized
from doubly distilled water and dried at 383–413 K for
24 h. Tetrabutylammonium iodide of ch. d. a. (pure for
analysis) grade was doubly recrystallized from acetone
and dried at 353–363 K in a vacuum for 10–12 h. Solu-
tions were prepared in a dry box, which completely
excluded contact between substances and air moisture.
The heat capacities of solutions (Cp) were measured
on a hermetic isothermic-shell calorimeter with a plati-
num resistance thermometer as a temperature sensor
[5]. The errors in Cp measurements were no more than Ba2+ ion, first, is in our view capable of forming the sec-
392

THE HEAT CAPACITY AND DENSITY OF SOLUTIONS
393
Table 1. Mean heat capacity (Cp, J/(g K)) and density (ρ, g/cm3)
values for solutions of barium and tetrabutylammonium iodides
in MP at 298.15 K and various concentrations (m, mol/kg MP)
nitrogen with alkyl groups result in the formation of
one solvation shell and weak electrostriction.
The experimental Cp and ρ values were used to cal-
culate the apparent molar heat capacities ΦC and vol-
umes ΦV of barium and tetrabutylammonium iodides in
MP. The corresponding concentration dependences are
shown in Fig. 2. The ΦC(LJI2) values are described by
a linear dependence on the root of the molal solution
concentration m. For (ë4H9)4NI, the ΦC = f(m1/2)
dependence has a noticeable bend at m . 0.5. The
ΦV = f(m1/2) dependences of the electrolytes are close
to linear, but, similarly to the related V = f(m) depen-
dences considered above, have different slopes.
m
Cp
m
ρ
BaI2
0.0000
0.0998
0.2000
0.2999
0.4999
0.7001
0.8502
1.0004
1.753
1.708
1.667
1.630
1.561
1.504
1.465
1.429
0.0000
0.1019
0.2000
0.2999
0.5004
0.7508
0.9011
1.0002
1.02802
1.06206
1.09406
1.12584
1.18758
1.26109
1.30330
1.33046
°
To determine the standard partial molar values Cp2
=
°
°
°
ΦC and V2 = ΦV corresponding to the state of infi-
(C4H9)4NI
1.753
nitely dilute solutions, the ΦV = f(m1/2) dependence for
(ë4H9)4NI was approximated by the equation
0.0000
0.0997
0.1502
0.2000
0.2500
0.3000
0.4002
0.5001
0.5501
0.7501
0.8107
1.0004
0.0000
0.0999
0.1502
0.1999
0.2505
0.3001
0.4008
0.4996
0.5501
0.7504
0.8100
1.0004
1.02802
1.03280
1.03565
1.03754
1.04021
1.04193
1.04645
1.04973
1.05204
1.05823
1.06048
1.06562
1.745
1.742
1.740
1.736
1.735
1.729
1.724
1.721
1.712
1.709
1.699
Φ = Φ° + am1/2 + bm,
(1)
where a and b are empirical coefficients, and the
ΦC(ΦV) = f(m1/2) dependences for LJI2 and the linear
portion of the ΦC = f(m1/2) dependence for (ë4H9)4NI,
by a linear regression equation taking into account the
statistical weights of values depending on errors in ∆Φ.
°
°
The Cp2 and V2 values of barium and tetrabutylammo-
nium iodides in MP are listed in Table 2. It is not sur-
prising that the results do not correspond to the equa-
tions
°
°
C
p2(i)(åP) = –0.602Cp2(i)(H2O),
(2)
(3)
ond solvation shell, and, secondly, causes stronger sol-
vent electrostriction. Calculations of the standard entro-
pies of the barium and rubidium ions in MP at 298.15 K
° °
2(i)(åP) = 0.784V2(i)(H2O),
V
obtained in [2] for 1–1 electrolytes and simple ions.
°
°
°
( Si(åP) ) from the thermodynamic functions of transfer
Here, Cp2(i) and V2(i) are the standard partial molar
heat capacities and volumes of electrolytes and ions in
MP and water. This is also evidence of the special fea-
tures of the solutions under consideration (see above).
°
°
∆trGi and ∆trHi [12] and the standard entropies of the
°
°
Ba2+(åP)
ions in aqueous solution (Si(H O) ) [13] give S
=
2
°
–300.3 J/(mol K) and SRb+(åP) = –35.5 J/(mol K), which
°
°
The separation of the Cp2 and V2 values into ionic
is evidence of stronger solvent ordering in the solvation
sheath of the barium ion.
°
components was performed on the basis of the Cpi (MP)
°
and Vi (MP) values for the iodide ion in MP [2, 3] and
These effects are much less pronounced in solutions
of (ë4H9)4NI. The large size of the (ë4H9)4N+ ion and using the condition of the additivity of partial molar
strong screening of the positive charge localized on values. The results are listed in Table 2.
Table 2. Standard partial molar heat capacities (Cp2(i) , J/(mol K)) and volumes (V2(i) , cm3/mol) of barium and tetrabutyl-
°
°
ammonium iodides and ions in MP at 298.15 K
Value
BaI2
214
56.9 0.3
(C4H9)4NI
558 10
Ba2+
126
8.5 0.3
(C4H9)4N+
514 10
I–
°
Cp2(i)
5
5
44 2 [3]
24.2 0.2 [2]
°
V2(i)
306.7 0.3
282.5 0.3
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 83 No. 3 2009

394
NOVIKOV et al.
580
2
560
240
1.7
3
~
~
1
2
1
220
315
1.5
1.0
~
~
~
~
2
3
305
70
~
~
1
0.9
0.8
2
1
60
0
0.5
1.0
0
0.5
1.0
m
m1/2
Fig. 1. Concentration dependences of the specific heat
capacities and volumes of (1) barium, (2) rubidium, and
(3) tetrabutylammonium iodides in MP at 298.15 K.
Fig. 2. Concentration dependences of the apparent molar
heat capacities and volumes of (1) barium and (2) tetrabutyl-
ammonium iodides in MP at 298.15 K.
According to [14–17], the standard partial molar tetrabutylammonium iodide into ionic components.
heat capacities and volumes of large-sized tetraalky-
°
°
The Cpi and Vi values (Table 3) were calculated
lammonium ions in various nonaqueous solvents are
close to each other. Table 3 contains the literature data
according to the tetraphenylarsonium–tetraphenyl borate
(TATB) and tetraphenylphosphonium–tetraphenyl
borate (TPTB) assumptions extensively used for non-
°
°
on Cpi [12] and Vi [16] of the tetrabutylammonium
cation in aprotic solvents whose properties are similar
to those of MP, namely, dimethylformamide (DMFA),
dimethylsulfoxide (DMSO), propylene carbonate (PC),
acetonitrile (AN), and dimethylacetamide (DMAA).
°
°
aqueous solutions [14–20]. The scale of Cpi and Vi val-
ues in MP is based on dependences (2) and (3) [2–4].
Agreement between the values obtained for the
(ë4H9)4N+ ion in various nonaqueous solvents is in our
°
°
Note that the Cpi and Vi values for MP closely agree
°
view evidence that the scale of ionic components Cpi
with those for the other solvents, especially considering
that these values were obtained using different methods
°
and Vi developed by us is close to the scale based on
°
°
for the division of the Cp2 and V2 values obtained for
the TATB–TPTB approach.
3
°
°
Table 3. Standard partial molar heat capacities (Cp i , J/(mol K)) and volumes (Vi , cm /mol) of the tetrabutylammonium
cation in aprotic dipolar solvents at 298.15 K
Value
MP
DMSO
DMFA
PC
AN
DMAA
°
Cp i
514
–
517
281
496
283
513
276
–
°
Vi
282.5
282
278
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 83 No. 3 2009

THE HEAT CAPACITY AND DENSITY OF SOLUTIONS
395
11. Problems of Solution Chemistry: Ionic Solvation, Ed. by
G. A. Krestov, N. P. Novoselov, I. S. Perelygin, et al.
(Nauka, Moscow, 1987) [in Russian].
REFERENCES
1. V. A. Vasilev and A. N. Novikov, Zh. Fiz. Khim. 67 (7),
1387 (1993).
12. Advances and Problems in the Theory of Solvation:
Structural and Thermodynamic Aspects, Ed. by
V. K. Abrosimov, G. A. Krestov, G. A. Al’per, et al.
(Nauka, Moscow, 1998) [in Russian].
2. V. A. Vasilev and A. N. Novikov, Zh. Fiz. Khim. 67 (7),
1391 (1993).
3. A. N. Novikov and V. A. Vasilev, Zh. Fiz. Khim. 80 (4),
598 (2006) [Russ. J. Phys. Chem. 80 (4), 505 (2006)].
13. Thermal Constants of Substances: A Handbook, Ed. by
V. P. Glushko (VINITI, Moscow, 1965–1981), Vols. 1–
10 [in Russian].
4. A. N. Novikov, V. A. Vasilev, and O. F. Lenina, Zh. Fiz.
Khim. 81 (11), 1947 (2007) [Russ. J. Phys. Chem. A 81
(11), 1743 (2007)].
5. B. V. Mikhailin, A. F. Vorob’ev, and V. A. Vasilev, Zh.
14. Y. Marcus, Ion Solvation (Wiley, Chichester, 1985).
Fiz. Khim. 56 (8), 1937 (1982).
15. Y. Marcus and G. Hefter, J. Chem. Soc., Faraday Trans.
6. A. F. Kapustinskii, M. S. Stakhanova, and V. A. Vasilev,
Izv. Akad. Nauk SSSR, Otd. Khim. Nauk, No. 12, 2082
(1960).
1 92 (5), 757 (1996).
16. Y. Marcus and G. Hefter, Chem. Rev. 104, 3405 (2004).
7. K. P. Mishchenko and G. M. Poltoratskii, Thermody-
namics and Structure of Aqueous and Nonaqueous Solu-
tions of Electrolytes (Khimiya, Leningrad, 1976) [in
Russian].
17. L. P. Safonova, A. N. Kinchin, andA. M. Kolker, Zh. Fiz.
Khim. 73 (12), 2154 (1999) [Russ. J. Phys. Chem. 73
(12), 1943 (1999)].
18. R. Alexander and A. J. Parker, J. Am. Chem. Soc. 89,
8. V. A. Vasilev, Izv. Vyssh. Uchebn. Zaved., Khim. Khim.
5539 (1967).
Tekhnol. 22 (12), 1458 (1979).
19. M. R. Dack, K. J. Bird, and A. J. Parker, Aust. J. Chem.
9. V. A. Vasilev, Zh. Fiz. Khim. 54 (3), 796 (1980).
10. V. A. Latysheva, Saline Aqueous Solutions: A Systematic
28, 955 (1975).
Approach (S.-Peterb. Univ., St. Petersburg, 1998) [in 20. B. S. Krumgalz, J. Chem. Soc., Faraday Trans. 1 76,
Russian].
1887 (1980).
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 83 No. 3 2009