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Thermodynamics of NaCl, NaBr and NaNO3 in dioxane—water mixtures from conductance measurements
Thermochimica Acfa, 41(1980) Elsevier Scientific
247-252
Publishing Company,
Amsterdam
-
Printed in Belgium
247
NOtt?
THERMODYNAMICS OF NaCl, NaBr AND NaN03 IN DIOXANE-WATER MIXTURES FROM CONDUCTANCE MEASUREMENTS
N.C. DAS AND
P.B. DAS
*
Department of Chemistry, Ravenshaw College. Cuffack 753003 (Received
(India)
21 March 1980)
Studies of electrolytic conductance in dioxane-water mixtures containing 10, 20 and 30% dioxane have been reported [ 11. The variation in the Walden product with solvent composition and temperature was described and discussed with respect to theories concerning solvent structure and ionsolvent interaction. In the present work, attempts have been made to evaluate the thermodynamic functions for the transfer of NaCl, NaRr and NaN03 from water to the respective dioxane-water media, which would give some information regarding solute-solvent interaction.
MATERIALS
AND
METHODS
The salts and dioxane used were of the Merck Extra Pure grade. Purification of dioxane, preparation of solvents, solutions and measurement of conductance have been reported earlier [l] . The conductance measurement was of an accuracy of &2 in 1000 and the concentration range was from 0.01 to 0.001 mole 1-l.
RESULTS
AND
DISCUSSIONS
plot of A vs. C112 was found to be linear and A0 has been obtained from the extrapolated values at zero concentration. The Walden product is almost constant at all temperatures and at all solvent compositions [ 11. This constancy is presumably due to the contribution of the positive temperature coefficient of the conductivity with the negative temperature coefficient of the viscosity of the solvent. Hence, it is very difficult to predict whether the solvent will h&e a positive or negative effect within the temperature range studied presently (i.e. from 30 to 45°C). Since the dielectric constant of the medium is less, the dissociation constants, H were calculated by both the Fuoss and Krauss [2] and the ShedThe
* To whom
correspondence
~0040-6031/80/0000-0000/$02.25
should be addressed. @ 1980
Elsevier Scientific
Publishing Company
614 743 749 1211
442 552 1030 808
446 504 ?02 903
NuBr 30 35 40 45
NaNOs 30 36 40 45
10% dioxane
900 952 1455 1507
832 871 1109 1672
1313 1723 2074 2019
20% dioxane
AG: (J mole-’ )
NaCl 30 35 40 45
Temp. (“C)
Free energy, enthalpy and entropy of hnsfer
TABLE 1
1403 1573 2099 2309
1414 1681 2083 2287
2073 2373 2618 3181
30% dioxane
7.0 314 742 112
113 314 408 613
312 310 620 870
572 513 628 1280
312 413 452 814
512 713 788 1342
20% dioxane
(J mole-’ )
10% dioxane
-All:
614 873 1050 1614
640 873 1050 1614
1022 1225 1302 2223
30% dioxane
of NaCl, NaBr and NaN03 from water to dioxane-water
1.49 2.66 3.97 3.19
1.96 2.81 4.59 4.46
3.06 3.39 4.09 6.54
4.86 4.77 6.65 9.67
3.78 4.17 5.30 7.99
6.02 7.94 9.13 10.57
20% dioxane
(J K-l mole-’ )
10% dioxane
-A$
6.66 7.95 8.70 12.32
6.78 8.38 9.83 12.23
10.21 11.67 12.61 16.99
30% dioxane
mixtures at different temperatures
249
lovsky [ 33 methods. The results obtained by the two methods were found to be the same. The standard thermodynamic parameters, AGO, A.@ and AS’, have been calculated 141. The plots of AGO, AH’ and ASo vs. solvent composition were found to be linear. The extrapolated values give the thermodynamic parameters for water. The standard thermodynamic quantities (AGO,, m and Ag) for the transfer process from water to 10, 20 and 30% dioxanewater mixtures could be calculated from the values in water and the different dioxane-water mixtures [4] by using the Feakins and Turner method [ 51. These are tabulated in Table 1. The probable uncertainties in AGT are *15 J mole”, in A@ are +18 J mole-’ and in A@ are k0.5 J K-’ mole-’ in all solvent compositions. The standard Gibb’s free energy of transfer, AGO,, is observed to be positive at all solvent compositions and at all temperatures. The positive values indicate that the salts NaCl, NaBr and NaN03 are in a higher free energy state in dioxane-water mixtures than in water, suggesting that water has more affinity for the salts than for dioxane-water mixtures. The values of a and Ae are negative for all the solvent mixtures. So the entropies in dioxane-water mixtures is less than in pure water and hence the net amount of order created by the salts in dioxane-water mixtures is more than in pure water. Since single ion values of tiee energies are not available presently for the solvent mixtures studied, the method adopted by Khoo and Chan I61 was followed to study ion-solvent interaction. Considering that AG& -) are mostly positive, this is qualitatively AG&r -1 and AG& -1 - AG&oj, in agreement with the Born theory, which predicts that bromide ion should be in a lower free energy state than the chloride ion and nitrate lower than bromide in mixed solvents of lower dielectric constant than water. Therefore, the Born equation may be expected to fit increasingly better as the dioxane content of the mixture is increased. The same observations were made by Fez&ins and Turner [ 51. It may be possible to split the AG: values into two parts as Roy et al. [7] have done, i.e. a “non-electrostatic” or “chemical” contribution, denoted in their terminology by AGO,,. h ), and an electrostatic contribution, AGO,,, 1j, which has been calculated from the Born equation.
where r+ and r- are the crystallographic radii of the cation and anion, and E, and E, are the dielectric constants of the mixed solvent and water, respectively. To calculate the electrostatic part of the entropy of transfer, eqn. (1) on differentiation and algebraic manipulation yields
(2) where the values of dlne,/dT
and dlne,/dT
can be evaluated from the simple
250 TABLE
2
Electrical and chemical part of the thermodynamic of salts from water to dioxanmater mixtures Temp.
(“0
AG:‘,,)
(J mole-’
quantities accompanying
AG&cn)
)
(J mole-’
the transfer
)
10% dioxane
20% dioxane
30% dioxane
10% dioxane
1260 970 1157 315
2173 2023 2225 1991
3593 3462 3704 3490
-646 -227 -408 396
2118 1972 2169 1940
3501 3373 3606 3400
-786 -393 -97 14
-1286 -1109 -1059 -368
-2087
40 45
1228 945 1127 794
NuNOs 30 35 40 45
1211 932 1112 784
2089 1945 2139 2139
3454 3328 3557 3355
-765 -438 -410 119
-1189 -993 -684 -632
-2051 -1755 -1458 -1046
Temp.
-W(,I)
(J mole-’
20% dioxane
30% dioxane
NaCl 30 35 40 45
NaBr 30 35
(“C)
@(cn)(J
)
-860 -290 -151 28
-1520 -1089 -1086 -309
-1692 -1523 -1113
mole-‘)
10% dioxane
20% dioxane
30% dioxane
10% dioxane
20% dioxane
30% dioxane
1294 1215 499 1258
2211 2219 2479 2493
3546 3577 3521 4063
982
1699
905
1506
-21 388
1691 1151
2524 2352 2428 1840
NaBr 30 35 40 45
1263 1220 488 1324
2155 2233 2418 2430
3317 3600 3478 3958
1150 906 78 711
1843 1820 1976 1616
2677 2722 2478 2349
NaNOs 30 35 40 45
1243 1202 481 1306
2125 2200 2384 2170
3409
1236 888 -261 1194
1553 1687 1756 886
%795 2677 2764 3194
Temp.
-A&,1)
(“C)
(J K mole-’
550 3814 4803
AL&n,
)
(J K-l
mole-‘)
10% dioxane
20% dioxane
30% dioxane
10% dioxane
29% dioxane
30% dioxane
8.43 7.21 5.29 6.84
14.47 14.00 15.03 14.10
23;56 23.23 24.50 23.75
5.37 3.82 1.24 0.34
6.45 6.06 5.90 3.53
13.35 11.56 11.99 6.76
N&l 30 35 40 45
251 TABLE 2 (continued) Temp. (“0
-&:(,I)
(J K mole-‘)
&$ch)
10% dioxane
20% dioxane
8.22 7.03 5.16 6.66
14.10 13.65 14.65 13.74
22.95
8.10 6.93 5.09 6.57
13.91 13.46 14.45 13.55
22.65 22.33 23.55 25.67
30% dioxane
(J K-l mole-l)
10% dioxane
20% dioxane
30% dioxane
NaBr 30 35 40 45
22.64 22.63 23.34
6.26 4.22 -0.57 2.20
10.32 8.48 9.35 5.75
16.17 14.26 12.80 10.91
6.69
9.05 8.69
15.99 14.38 14.75 13.35
NaN03
30 35 40 45
4.27 2.12 3.38
8.80 3.98
empirical equation -dine = -- 1 dT 8
(3)
in which 0 is a constant written as
S&I) = --
iVe2
characteristic
of the medium.
So eqn. (2) may be
1
--‘)(;L) 2 ( es& &Jew
F’rom a knowledge of AGO, and ASO,,,,, , the electrostatic part of the enthalpy change has been computed. The chemical contribution of the free energy of transfer, AGttCh), entropy of transfer, ASO,(chj, and enthalpy of transfer, m(,,, can then be obtained by subtracting the respective electrostatic contribution values from the molar quantities. These values are presented in Table 2. It is evident from an examination of the Table 2 that the chemical contribution of the free energy of transfer is negative in almost all cases and hence is thermodynamically favourable as far as the chemical interactions are con. cemed. Smce AGO,,. 1j is positive, the lower the value, the greater is the ionsolvent interaction. Hence, from Table 2 it can be said that the ionsolvent interaction is in the order NO; > Br- > Cl-, which is in accordance with our viscosity and apparent molar volume results [ 81. Al?&.,, is negative, whereas is positive, and both increase with increase in dioxane content. ~W.0 is negative in all cases and becomes more negative with increase in AZ,.,, dioxane content, indicating the order in the solvent structure. With a few exceptions, @, Ch) is positive and is almost independent of temperature. It increases with increase in dioxane content, indicating the chemical interaction.
252
REFERENCES 1 N.C. Das and P.B. Das, Electrochim. Acta, 23 (1978) 191. 2 R.M. Fuoss and CA. Krause, J. Am. Chem. Sot., 55 (1933)
476. 3 T. Shedlovsky, J. Franklin Inst., 225 (1938) 439. 4 N.C. Das, P.P. Mima and P.B. Das, Acta Ciencia Indica, Vc (1979)
136.
5 D. Feakins and D.J. Turner, J. Chem. Sot., (1965) 4986. 6 K.H. Khoo and C.Y. Chan, Aust. J. Chem., 28 (1973) 721.
7 R.N. Roy, W. Vernon and A.L.M. Bothwell, Electrochim. Acta, 17 (1972) 8 N.C. Das and P.B. Das, Ind. J. Chem., 15A (1977) 826.
5.
247-252
Publishing Company,
Amsterdam
-
Printed in Belgium
247
NOtt?
THERMODYNAMICS OF NaCl, NaBr AND NaN03 IN DIOXANE-WATER MIXTURES FROM CONDUCTANCE MEASUREMENTS
N.C. DAS AND
P.B. DAS
*
Department of Chemistry, Ravenshaw College. Cuffack 753003 (Received
(India)
21 March 1980)
Studies of electrolytic conductance in dioxane-water mixtures containing 10, 20 and 30% dioxane have been reported [ 11. The variation in the Walden product with solvent composition and temperature was described and discussed with respect to theories concerning solvent structure and ionsolvent interaction. In the present work, attempts have been made to evaluate the thermodynamic functions for the transfer of NaCl, NaRr and NaN03 from water to the respective dioxane-water media, which would give some information regarding solute-solvent interaction.
MATERIALS
AND
METHODS
The salts and dioxane used were of the Merck Extra Pure grade. Purification of dioxane, preparation of solvents, solutions and measurement of conductance have been reported earlier [l] . The conductance measurement was of an accuracy of &2 in 1000 and the concentration range was from 0.01 to 0.001 mole 1-l.
RESULTS
AND
DISCUSSIONS
plot of A vs. C112 was found to be linear and A0 has been obtained from the extrapolated values at zero concentration. The Walden product is almost constant at all temperatures and at all solvent compositions [ 11. This constancy is presumably due to the contribution of the positive temperature coefficient of the conductivity with the negative temperature coefficient of the viscosity of the solvent. Hence, it is very difficult to predict whether the solvent will h&e a positive or negative effect within the temperature range studied presently (i.e. from 30 to 45°C). Since the dielectric constant of the medium is less, the dissociation constants, H were calculated by both the Fuoss and Krauss [2] and the ShedThe
* To whom
correspondence
~0040-6031/80/0000-0000/$02.25
should be addressed. @ 1980
Elsevier Scientific
Publishing Company
614 743 749 1211
442 552 1030 808
446 504 ?02 903
NuBr 30 35 40 45
NaNOs 30 36 40 45
10% dioxane
900 952 1455 1507
832 871 1109 1672
1313 1723 2074 2019
20% dioxane
AG: (J mole-’ )
NaCl 30 35 40 45
Temp. (“C)
Free energy, enthalpy and entropy of hnsfer
TABLE 1
1403 1573 2099 2309
1414 1681 2083 2287
2073 2373 2618 3181
30% dioxane
7.0 314 742 112
113 314 408 613
312 310 620 870
572 513 628 1280
312 413 452 814
512 713 788 1342
20% dioxane
(J mole-’ )
10% dioxane
-All:
614 873 1050 1614
640 873 1050 1614
1022 1225 1302 2223
30% dioxane
of NaCl, NaBr and NaN03 from water to dioxane-water
1.49 2.66 3.97 3.19
1.96 2.81 4.59 4.46
3.06 3.39 4.09 6.54
4.86 4.77 6.65 9.67
3.78 4.17 5.30 7.99
6.02 7.94 9.13 10.57
20% dioxane
(J K-l mole-’ )
10% dioxane
-A$
6.66 7.95 8.70 12.32
6.78 8.38 9.83 12.23
10.21 11.67 12.61 16.99
30% dioxane
mixtures at different temperatures
249
lovsky [ 33 methods. The results obtained by the two methods were found to be the same. The standard thermodynamic parameters, AGO, A.@ and AS’, have been calculated 141. The plots of AGO, AH’ and ASo vs. solvent composition were found to be linear. The extrapolated values give the thermodynamic parameters for water. The standard thermodynamic quantities (AGO,, m and Ag) for the transfer process from water to 10, 20 and 30% dioxanewater mixtures could be calculated from the values in water and the different dioxane-water mixtures [4] by using the Feakins and Turner method [ 51. These are tabulated in Table 1. The probable uncertainties in AGT are *15 J mole”, in A@ are +18 J mole-’ and in A@ are k0.5 J K-’ mole-’ in all solvent compositions. The standard Gibb’s free energy of transfer, AGO,, is observed to be positive at all solvent compositions and at all temperatures. The positive values indicate that the salts NaCl, NaBr and NaN03 are in a higher free energy state in dioxane-water mixtures than in water, suggesting that water has more affinity for the salts than for dioxane-water mixtures. The values of a and Ae are negative for all the solvent mixtures. So the entropies in dioxane-water mixtures is less than in pure water and hence the net amount of order created by the salts in dioxane-water mixtures is more than in pure water. Since single ion values of tiee energies are not available presently for the solvent mixtures studied, the method adopted by Khoo and Chan I61 was followed to study ion-solvent interaction. Considering that AG& -) are mostly positive, this is qualitatively AG&r -1 and AG& -1 - AG&oj, in agreement with the Born theory, which predicts that bromide ion should be in a lower free energy state than the chloride ion and nitrate lower than bromide in mixed solvents of lower dielectric constant than water. Therefore, the Born equation may be expected to fit increasingly better as the dioxane content of the mixture is increased. The same observations were made by Fez&ins and Turner [ 51. It may be possible to split the AG: values into two parts as Roy et al. [7] have done, i.e. a “non-electrostatic” or “chemical” contribution, denoted in their terminology by AGO,,. h ), and an electrostatic contribution, AGO,,, 1j, which has been calculated from the Born equation.
where r+ and r- are the crystallographic radii of the cation and anion, and E, and E, are the dielectric constants of the mixed solvent and water, respectively. To calculate the electrostatic part of the entropy of transfer, eqn. (1) on differentiation and algebraic manipulation yields
(2) where the values of dlne,/dT
and dlne,/dT
can be evaluated from the simple
250 TABLE
2
Electrical and chemical part of the thermodynamic of salts from water to dioxanmater mixtures Temp.
(“0
AG:‘,,)
(J mole-’
quantities accompanying
AG&cn)
)
(J mole-’
the transfer
)
10% dioxane
20% dioxane
30% dioxane
10% dioxane
1260 970 1157 315
2173 2023 2225 1991
3593 3462 3704 3490
-646 -227 -408 396
2118 1972 2169 1940
3501 3373 3606 3400
-786 -393 -97 14
-1286 -1109 -1059 -368
-2087
40 45
1228 945 1127 794
NuNOs 30 35 40 45
1211 932 1112 784
2089 1945 2139 2139
3454 3328 3557 3355
-765 -438 -410 119
-1189 -993 -684 -632
-2051 -1755 -1458 -1046
Temp.
-W(,I)
(J mole-’
20% dioxane
30% dioxane
NaCl 30 35 40 45
NaBr 30 35
(“C)
@(cn)(J
)
-860 -290 -151 28
-1520 -1089 -1086 -309
-1692 -1523 -1113
mole-‘)
10% dioxane
20% dioxane
30% dioxane
10% dioxane
20% dioxane
30% dioxane
1294 1215 499 1258
2211 2219 2479 2493
3546 3577 3521 4063
982
1699
905
1506
-21 388
1691 1151
2524 2352 2428 1840
NaBr 30 35 40 45
1263 1220 488 1324
2155 2233 2418 2430
3317 3600 3478 3958
1150 906 78 711
1843 1820 1976 1616
2677 2722 2478 2349
NaNOs 30 35 40 45
1243 1202 481 1306
2125 2200 2384 2170
3409
1236 888 -261 1194
1553 1687 1756 886
%795 2677 2764 3194
Temp.
-A&,1)
(“C)
(J K mole-’
550 3814 4803
AL&n,
)
(J K-l
mole-‘)
10% dioxane
20% dioxane
30% dioxane
10% dioxane
29% dioxane
30% dioxane
8.43 7.21 5.29 6.84
14.47 14.00 15.03 14.10
23;56 23.23 24.50 23.75
5.37 3.82 1.24 0.34
6.45 6.06 5.90 3.53
13.35 11.56 11.99 6.76
N&l 30 35 40 45
251 TABLE 2 (continued) Temp. (“0
-&:(,I)
(J K mole-‘)
&$ch)
10% dioxane
20% dioxane
8.22 7.03 5.16 6.66
14.10 13.65 14.65 13.74
22.95
8.10 6.93 5.09 6.57
13.91 13.46 14.45 13.55
22.65 22.33 23.55 25.67
30% dioxane
(J K-l mole-l)
10% dioxane
20% dioxane
30% dioxane
NaBr 30 35 40 45
22.64 22.63 23.34
6.26 4.22 -0.57 2.20
10.32 8.48 9.35 5.75
16.17 14.26 12.80 10.91
6.69
9.05 8.69
15.99 14.38 14.75 13.35
NaN03
30 35 40 45
4.27 2.12 3.38
8.80 3.98
empirical equation -dine = -- 1 dT 8
(3)
in which 0 is a constant written as
S&I) = --
iVe2
characteristic
of the medium.
So eqn. (2) may be
1
--‘)(;L) 2 ( es& &Jew
F’rom a knowledge of AGO, and ASO,,,,, , the electrostatic part of the enthalpy change has been computed. The chemical contribution of the free energy of transfer, AGttCh), entropy of transfer, ASO,(chj, and enthalpy of transfer, m(,,, can then be obtained by subtracting the respective electrostatic contribution values from the molar quantities. These values are presented in Table 2. It is evident from an examination of the Table 2 that the chemical contribution of the free energy of transfer is negative in almost all cases and hence is thermodynamically favourable as far as the chemical interactions are con. cemed. Smce AGO,,. 1j is positive, the lower the value, the greater is the ionsolvent interaction. Hence, from Table 2 it can be said that the ionsolvent interaction is in the order NO; > Br- > Cl-, which is in accordance with our viscosity and apparent molar volume results [ 81. Al?&.,, is negative, whereas is positive, and both increase with increase in dioxane content. ~W.0 is negative in all cases and becomes more negative with increase in AZ,.,, dioxane content, indicating the order in the solvent structure. With a few exceptions, @, Ch) is positive and is almost independent of temperature. It increases with increase in dioxane content, indicating the chemical interaction.
252
REFERENCES 1 N.C. Das and P.B. Das, Electrochim. Acta, 23 (1978) 191. 2 R.M. Fuoss and CA. Krause, J. Am. Chem. Sot., 55 (1933)
476. 3 T. Shedlovsky, J. Franklin Inst., 225 (1938) 439. 4 N.C. Das, P.P. Mima and P.B. Das, Acta Ciencia Indica, Vc (1979)
136.
5 D. Feakins and D.J. Turner, J. Chem. Sot., (1965) 4986. 6 K.H. Khoo and C.Y. Chan, Aust. J. Chem., 28 (1973) 721.
7 R.N. Roy, W. Vernon and A.L.M. Bothwell, Electrochim. Acta, 17 (1972) 8 N.C. Das and P.B. Das, Ind. J. Chem., 15A (1977) 826.
5.