72
J. Chem. Eng. Data 1987, 32, 72-76
Me$. A very similar signal was observed by Shuppert and Angell (5)in the case of mixtures of hydrogen chloride and pyridinium chloride and was attributed to the HCI,- ions. The authors report that this sharp line disappears at high temperature (>338 K) because a rapid exchange occurs in this case between N-H+ and HCI,- protons. I n our case, the N-substitution of the pyridinium ion allows thus the observation of HCI,- ions at higher temperature. Figures 1 and 2 show that some other process occurs for the dissolution of hydrogen chloride since a solubility of about 0.25 mol/L was measured for XZm, 2 0.33. Our experimental results do not allow any interpretation of this extra solubility. Assuming that this extra solubility remains constant in all the concentration range and particularly for the pure N-alkylpyridinium salt, it can be found that the solubility is somewhat lower than the analytical concentration of the N-alkylpyridinium halide. I n the case of N-ethylpyridinium bromide, the solubility of HCI through HX,- formation is 6.25 mol/L when the analytical concentration of bromide ions is 7.34 mol/L. For N-methylpyridinium chloride, the solubility as HCI,- is 7.5 mol/L, the
analytical concentration of chloride ions yielding 8.31 mol/L. The complexation reaction of hydrogen chloride by halide ions is thus not quite quantitative and a competition exists between N-alkylpyridinium cations and hydrogen chloride for the halide ions. Reglstry No. EtPyBr, 1906-79-2; MePyCI, 7680-73-1; ZnCI,, 7646-85-7; HCI, 7647-01-0.
Literature Cited (1) Simonis. L.: Come. . . C.: Glibert. J.: Claes, P. Thermochim. Acta 1986. 99, 223. Claes, P.; Simonis, L.;Glibert, J. Electrochim, Acta, in press. Vedel, J.; Tremillon, B. Bull. Soc. Chim. h.1986, 220. (4) Goffman, M.; Harrington, G. W.J. Phys. Chem. 1983- 6 7 , 1877. Shuppert, J. W.;Angell, C. A. J. Chem. Phys. 1977, 6 7 , 3050 , , Easteal. A. J.; Angell, C. A. J. Phys. Chem. 1970, 7 4 , 3987. (7) Bues, W.;Brockner, W.2.Phys. Chem. 1974, 88, 290. (8) Itoh, M.; Sakal, K.; Nakamura, T. Inorg. Chem. 1982, 27, 3552. (9) Takagi, Y.; Nakamura, T. J. Chem. Soc., Faraday Trans. 7 , 1985, 87, 1901.
12
Received for review March 25, 1986. Accepted September 15, 1986
Apparent Molar Heat Capacities and Volumes of Aqueous Solutions of MgCI2, CaCI,, and SrCI, at Elevated Temperaturest Preet P. S. SaluJa"and Jacques C. LeBlanc Research Chemistry Branch, Atomic Energy of Canada Limited, Whiteshell Nuclear Research Establishment, Pina wa, Manitoba, Canada ROE 7L0
Heat capacity (C,) and density ( d ) data at 0.6 MPa and in the temperature range 298.15-373.15 K are presented for aqueous MgCI,, CaCI,, and SrCI,. Data were obtained over the concentration ( m )ranges 0.1-0.53 moiekg-' for MgCI,, 0.03-0.98 mobkg-' for CaCI,, and 0.03-2.0 mol-kg-' for SrCI,. The values of C, and d of a solution relative to that of water were measured wlth a preclsion of fO.l mJ.K-'.g-' and f5 ~ g c m - respectlvely, ~, at ail temperatures. The Cp and d results were used to calculate the apparent molar heat capacities ( 4Cp) and volumes ( @ V I ,respectively. Our @c,resuits at room temperature are In good agreement wlth available literature data; however, our @CP values at 348.15 and 373.15 K differ considerably from the high-temperature literature data avaliable only for MgCI,, because of the much lower precision (f2 to f13 mJ-K-'.g-') of the C, measurements reported in the literature.
While @C, and @Vdata for aqueous 2:l electrolytes are available at 298.15 K (5-B), very few values are available at higher temperatures (9-72).This is because both heat capacity, C,, and density, d , were difficuit to measure at elevated temperatures before the recent development of flow microcalorimeters ( 7 , 73- 75)and flow densimeters ( I , 76, 77) able to withstand higher operating temperatures and pressures. I n this paper, we present measured values of C, and d along with calculated @C,and @Vvalues for aqueous MgCI,, CaCI,, and SrCI, (a fission product electrolyte) from 298.15 to 373.15 K, at a constant pressure of 0.6 MPa. I n an accompanying paper ( 78),we apply Pitzer's ion-interaction model ( 7 , 4) to our data, combined with some literature data of comparable precision (5-72),to obtain partial molar heat capacity, CO,,,(T), and volume, Po2( T ) , functions, and to generate temperature-dependent equations for calculating other thermodynamic properties (such as the enthalpy, Gibbs energy, and osmotic coefficient) of these electrolytes at higher temperatures.
Introduction
Experlmental Section
The present work is part of a continuing effort from this laboratory to obtain thermodynamic data for aqueous species at elevated temperatures. The importance of this work for modeling applications in the nuclear industry (e.g., waste management and safety) and in nonnuclear areas has been discussed in our earlier papers ( 7-4). We have recently reported apparent molar heat capacities, @C,, and volumes, @ V ,up to 373 K for a number of 1:l aqueous electrolytes (3). I n this paper, we extend our studies to the 2:1 aqueous electrolytes, MgCI,, CaCI,, and SrCI,.
To apply the ion-interaction model ( 4 ) , a large number of high-precision Cp(T , m )and d( T , m )measurements are required over a wide range of T and m . This approach yields reliable temperature-dependent (, T) and Vo,(T ) functlons, along with ion-interaction parameters (4). The flow C, microcalorimeter and flow vibrating-tube densimeter system, and the operating procedure used for all the measurements, were similar to those described in detail elsewhere ( 7 ) . The chemicals used for this study were obtained from Fisher (MgC12)and Alfa Products, Ventron Division (CaCI, and SrCI,). Details of sample handling and solution preparation were similar to those described earlier ( 7 ) . Simultaneous
Issued as AECL-9036. 0021-9568/87/ 1732-0072$01.50/0
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0 1987 American Chemical
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Journal of Chemical and Engineering Data, Vol. 32, No. 1, 1987 73
Table I. Apparent Molar Heat Capacities, #CP, and Heat Capacities, C,,of MgC12, CaC12, and S&12 i n Aqueous Solutions as a Function of Temperature, at 0.6 bfPa molality, m/(mol.kg-') C,/(J*K-'.g-') W,/(J.K-'.mol-') molality, m/(mol.kg-') C,/(J.K-'-g-') V P(/ J.K-l-mol-l) MgC12, 298.15 K CaCl,, 348.15 K (75.50)" (75.26)" water (4.1911)' water (4.1779)" 4.1111 4.0590 4.0115 3.9533 3.8807
0.10844 0.19711 0.28186 0.38842 0.52775
-224.6 -216.7 -208.4 -201.8 -193.6
0.05108 0.10015 0.20271 0.49449 0.98452
(75.28)' -198.4 -189.2 -181.7 -175.0 -165.9
water
MgCl,, 323.15 K water
0.02976 0.09940 0.10213 0.19769 0.21060 0.21251 0.42541 0.46990 0.66613 0.88035
MgC12, 348.15 K water
(75.50Y' -205.6 -192.7 -184.9 -177.6 -172.3
(4,1911)" 4.1262 4.0766 4.0308 3.9751 3.9040
0.10844 0.1971 1 0.28186 0.38842 0.52775
(4.2143)" 4.1462 4.0946 4.0469 3.9894 3.9182
0.10844 0.19711 0.28186 0.38842 0.52775
0.02747 0.10044 0.20459 0.68309 1.00093
(75.92)" -233.2 -217.4 -208.6 -199.1 -188.0
0.02747 0.10044 0.20459 0.68309 1.00093
(75.26)O -240.9 -230.0 -225.5 -214.5 -214.7 -198.5 -181.3 -168.6
(4.1779)" 4.1570 4.1097 4.1083 4.0467 4.03705 3.9089 3.7778 3.6708
0.02976 0.09940 0.10213 0.19769 0.21251 0.42541 0.66613 0.88035
(4.1790)" 4.1592 4.1144 4.1129 4.0544 4.0455 3.9242 3.7982 3.6956
0.02976 0.09940 0.10213 0.19769 0.21251 0.42541 0.66613 0.88035
(4.1779)" 4.1527 4.0882 4.0028 3.6567 3.4709
(75.26)" -259.0 -245.0 -221.3 -183.3 -156.1
(4.1790)" 4.1549 4.0937 4.0126 3.6817 3.5017
(75.28)" -219.0 -200.3 -177.2 -144.4 -121.6
SrCl,, 348.15 K water 0.02747 0.10044 0.20459 0.68309 1.00093
CaCl,, 323.15 K water
(75.92)' -243.6 -216.8 -215.5 -196.0 -195.1 -194.5 -172.3 -175.8 -153.3 -138.1
SrC12, 323.15 K water
CaCl,, 298.15 K water
(4.2143)" 4.1932 4.1470 4.1453 4.0859 4.0779 4.0768 3.9543 3.9269 3.8291 3.7284
SrCl,, 298.15 K water
MgC12, 373.15 K water
-198.3 -185.0 -163.8 -149.0 -117.6
CaCl,, 373.15 K
(4.1790)' 4.1150 4.0654 4.0199 3.9644 3.8957
0.10844 0.19711 0.28186 0.38842 0.52775
4.1574 4.1267 4.0664 3.9032 3.6739
(75.28)" -203.7 -193.2 -190.7 -180.3 -179.2 -163.4 -150.1 -138.9
(4.1911)" 4.1670 4.1061 4.0257 3.6995 3.5227
(75.50)' -216.7 -195.3 -170.3 -133.2 -109.3
SrCl,, 373.15 K water 0.0468 0.0998 0.2058 0.5013 1.0454
(4.2143)" 4.1737 4.1293 4.0456 3.8322 3.5096
(75.92)" -206.0 -197.0 -178.4 -154.7 -117.7
for pure solvent (water) taken from compilations of Kell et al. (19, 20) and Raznjevic
"Values in parentheses are heat capacities (21).
measurements of d ( T,m) and volumetric heat capacities at nearly the same temperature and pressure provided the Cp(T,m) in J.K-'.g-'. Thus, both @Cp(J-K-'.mol-') and @V(cm3. mol-') were determined in a single experiment. The overall precisions in the Cpand d determinations were estimated to be f0.1 mJ.K-l.g-' and f5 p g . ~ m - ~respectively , (3). Results and Dlscussion
Pr/mary Results. The C,(T,m) and d ( T , m ) values for aqueous MgCI,, CaCI,, and SrCI, were used to calculate the @ C p ( T , mand ) @ V ( T , mvalues ) from the following equations: @Cp(T,m) = M,C,(T,m) M,
+
@ v =-dum)
iooo[c,,(r,m) -
I n the above equations, M, is the molecular weight of the dissolved solute. C o p , ,and do1 are, respectively, the heat capacity and density of the pure solvent (water) at the operating temperature and pressure. The reference Cop,,values for pure water, as a function of temperature, were obtained from the tables of Kell et al. (19, 20). The Cop,,values as a function of pressure were obtalned from the Handbook of Thermodynamic Tables and Charts (27). The reference d o , values for pure water were calculated by using the equations of Fine and Miller0 (22). The Cp(T,m)and @Cp(T,m) values are given in Table I, and the d ( T , m )and @ V ( T , mvalues ) are given in Table 11.
coP,,(~)i
m
(1)
Comparlson wlth Literature Heat Capacity Data
(2)
Room-Temperature @Cp(m) Values. Our @Cp(m) values at 298.15 K and 0.6 MPa for aqueous MgCI,, CaCI,, and SrCI, were compared with existing literature data (5-8).The room-
1000[d(T,m)- d o l ( T ) ]
mdol(r)d v m
74 Journal of Chemical and Engineering Data, Vol. 32. No. 1, 1987 I801
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Reference 5 Reference 8 Present W o r k
348 15 K, 0 373 15 K [Present W o r k ]
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Flgure 1. Apparent molar heat capacities, @C ( m ) ,as a function of molality, m, for aqueous solutions of (a, upper) &GIz, (b, middle) CaCI,, and (c, lower) SrCI,; a comparison with 298.15 K data of Perron et al. (5, 6, 8) and Spitzer et al. (7).
temperature literature values for these electrolytes were obtained at atmospheric pressure (0.1MPa), and thus should be extrapolated to 0.6 MPa. However, pressure corrections ( 10 J.K-'.mol-' at tower concentrations (
