s o v . , 1961
A C T I V I T Y C O E F F I C I E N T S O F KITRATES I N L k W O N - E X C H A N G E
charge Z of the polymer can be obtained from the concentration coefficient B and the extrapolated molecular weight. This is a modification of the method given by Johnson, et al. A comparison of equations 16 and 24 or equations 33 and 38 suggests that the assumption d In C/d(r2) = d In [dClr dr]/d(r2) made by-Johnso_n, et a1.,2is equivalent to the assumption: illw= M,. Equations for charged heterogeneous polymers (equations 16, 24, 33, 34, 38 and 39) were derived by assuming that certain values of B and B 2 and higher terms can be considered negligible and that all partial specific volumes are equal. The equations are readily applicable to data obtained from the interference or schlieren optical system. It should be emphasized that equation 33 for Mw of all species from the meniscus to the bottom of the cell was not derived rigorously with regard to the concentration dependent term B. On the other hand, equation 38 was derived using no assumptions with regard to the integration of the B
RESIX
2039
term, Thus, the concentration dependent term for M , can be considered to be more reliable. -4 compgrison of t_he concentration dependent term for Mw,Land Mz,r(equations 16 and 24) or for Ll?f,5. or Mz (equations 33 and 38) igdicates that this coefficient for Mz,ror XZis 2 ( M W / M 2 )times as large as that for the corresponding MW,r or XI\. This statement is in agreement with the results of Van Holde and Baldwin'O for a single species. From equations 25 an> 27 it & seen that the extrapolated values of Mw and 11.1, are functions of (Z'/Xp'), the charge of a monomer unit divided by its molecular weight. The quantity (d ln G ' dC), in the coefficient B is most likely a constant only if the temperature and pressure are not varied and thus may he considered as a partial derivative. It also might be added that all of the above equations appear to be valid for the ,Irchibald approach-to-equilibrium method since the meniscus and bottom of a cell can be considered as being at equilibrium at all times (ref. 4, p. 780).
ACTIVITY COEFFICIEYTS OF LiN03, HNO, -4YD YH,;\'03 IN DOWEX-I AKION-EXCHANGE RESIN BYJ. DANON Centro Brasileiro de Pesquisas Fisicas, Av. Wenceslau Braz 71, Ria de Janeiro, Brazil Receaved May ZS, 1961
Activity coefficients of LiN03, HNO, and ",NO3 in the resin phase were measured with Dowex-l,S% DVB. The results obtained with the nitrates suggest that the internal medium of the exchanger behaves like a concentrated aqueous solution without notable interaction between the various ionic species inside the resin phase. The large uptake of HNOJ by the resin is attributed to an interaction of this acid with the exchanger.
When an ion exchange resin is immersed in an electrolytic solution, a given amount of electrolyte penetrates the resin phase. The difference in ionic composition between the two phases depends on the type of resin, its degree of cross-linking and on the activity of the ions of the aqueous solution. These systems can be treated by thermodynamic met'hods by considering a two-phase equilibrium and it is thus possible to calculate the activity coefficients of the electrolyte in the resin phase. Wit,h anion-exchange resins such measurements were made mostly with chloride systems . l - 3 In the present work we have extended thcse studies to the nitrat]e systems. Anion-exchange resins have been wed for the investigat)ion of nitrat'e complexes and the quantitative t,rea.tment of these results depends on the knowledge of the act,ivities of the electrolytes in the resin p h a ~ e . ~ ? ~ We assume with Xelson and Kraus2 t'hat, J is an electrolyte of the M,+X,- where y + and v- are t'he number of positive ions (M) and negative ions (X). The equilibrium distribut,ion of J is described by the equality of t'he thermodynamic activities in the two phases (1) K. A. Kraus and G. E. hloore, J . Am. Chem. Soc., 76, 1439 (1953). (2) F. Nelstin and K. A. Kraus, i b i d . , 80, 4154(1958). (3) D. H. Freeman, J . Phus. Chem., 6 4 , 1048 (1960). (4) Y . Maruuu and C. D. Coryell, Bull. Research Council Israel, SA, 1, 17 (1959). ( 5 ) J. Danon, J . Inorg. & Nuclear Chem., 13, 112 (1960).
aJ =
aJ(r)
(1)
where the subscript (r) denotes the resin phase. Equality 1 implies that the same standard states are selected for J in the two phases. Relation 1 can be written as a function of data on electrolyte invasion O,J = m w+.mxu- r: = ~ M ( ~ ) v + . v z x ( ~7 ):Y -( r ) (2) where m represent the molal concentration of the ions and y + the mean activity coefficients.
Experimental The amount of electrolyte in the resin was measured b~ the volumetric method.' Dowex-1 resin, 87, DVB, 50-100 mesh was washed with 4 M HCl in order to remove inipurities and converted to the nitrate form with dilute HPiOj. After being washed with mater the resin was dried over Xnhydrone a t 60" to constant weight. About 1 g. of resin was placed in a emall sintered glass funnel. Xitrate solutions of known composition were passed through the funnel until partition equilibrium was attained. The fiinnel next was centrifuged to constant weight and the resin was washed with water in ortier to remove the imbibed electrolyte. HN03 was titrated with standard XaOH. LiNO, !\as determined by flame photometry in an ElectroSelenium photometer n-hich was previously calibrated u i t h solution8 of known concentrations of LiNO, prepared from standard Li2C0,. SH4NO3was determined by displacing KH,OH with concentrated S a O H in a distillation apparatus and the products were collected over HsSOa of known molaritv. All determinations were made a t least twice. i l n a l ~ t i c a l reagents were used throughout. The determination of the interstitial volume of the resin bed was made with spherical glass beads of the Sam? mesh.
J. DANON
2040
Vol. 65
0.5
TABLEI" ms
0 077 0 736 1 506 2 922 4 14 5 97 8 50 11 38 12 84
lo
i
m J(r)
mwr)
0 010 333 .993 2 006 3 54 5 79 9 00 12 61 14 15
LiN03 6 434 G 712 7 513 8 720 10 55 13 25 17.07 21 38 23 21
r 0.298
.'192 ,551 ,697 .68 .68 .69
.io
. 70
Yr(r)
0.261 .359 ,432 .668 .78 1.02 1.42 1.94 2.24
pljH4n'03
-1
I 0
5
10
15
na J (I). Fig. 1. The value obtained, 0.0345 1. per 1. of bed, is slightly higher than that found for 200-230 mesh Dowex-1 (0.033 l./l.). This difference is probably a consequence of the difference in mesh of the two batches. The water content of the resin was determined by the difference in weight of the dry resin and the resin equilibrated with 1%-aterafter Centrifugation and corrected for the interstitial water. The value obtained, 1.465 f 0.005 kg. of wet resin per kg. of dry resin, gives a water content of the wet resin of 31 35%. The volume of the resin bed in the several media investigated was determined by measuring with a cathetometer the height of the bed after centrifugation in a calibrated sintered funqel. The value found averaged 2.12 f 0.08 1. per kg. of dry resin. The changes of this observed value with the various electrolytes are within the experiniental error in the measurement of the volumes. The capacity of the resin for nitrate ions was measured by two different procedures. The resin was converted to the chloride form with NaCl solution and the chloride ion was ne\t eluted with NaC104 and titrated with AgN03 solution of known molarity. Other measurements were made by eluting the nitrate ion with NaC104. The nitrate was next reduced with Devarda's alloy and NaOH and the SH,OH formed were distilled over HzSOI of known molarity. The average value obtained in ten determinations was 2.952 =t0.005 moles per kg. of dry resin. This yields a molality of the nitrate functional group of the resin of 6.325 equivalents per kg. of resin water. All determinations were made at room temperature (25 f 3 " ) .
Results and Discussion The results obtained are summarized in Table I. The results obtained for the nitrate systems show a close similarity with other systems. For LiSO, the relation between the activity coefficients in the resin and the aqueous solution remains essentially constant and close to 0.7 as mJ changes from 3 to 13. The value of J? is notably close to that found for LiC12 (-0.8). The values of for ",NO3 are also constant in the molality range 1 to 23. Although the value of r increases it remains close to unity until very high molalities of the aqueous phase. The constancy of r a t values not, far from unity confirms the conclusions of previous studies1,2that the internal media of the exchanger behaves like a concentrated aqueous solution without, a notable interaction between the imbibed electrolyte and the "resin-electrolyte."
1 2 4 6 10 22
05 85
45 52 70 43 5 11 9 21
6 92 0.59 0.30 .60 .no 8 32 no .!I6 .2n 9 86 1.on .29 10 82 6.5 1 23 . '77 09 12 95 1.74 80 18 43 .25 "OB 0 031 6 360 0.147 0.121 0 068 ,254 ,186 0 317 0 235 6 615 2 743 .2i5 ,354 1 816 9 582 360 ,313 2 684 11 880 4 664 362 5 491 12 850 ,330 3 043 11 62 36 ... 5 504 20 23 41 77 .29 10 28 29 00 ... .'Lo 15 06 63 35 85 36 ... Values of mean activity coefficients in aqueous solutions were taken from Robinson and Stokes "Electrolytic Solutions," Butterworths Publications, Londoii, 1955. 0 1 2 3
TABLE11" Electrolyte LiNOa
mxo, 6 3 1 20 mLl(r) 6 3 1 22 mH(r) HNOa NHhNOa 6 3 4- 1 31 mNHi(r)
+ +
log
+ +
-0 26 .A3 .52 -
-
ms range 0 013 r n ~ , ( ~ ) 3-13 .03 ma(r) -1-3 0119 mNHd(r) 1-22 Ygr)
The small number of determinations of y f ( p ) a t low values did not permit the calculation of t h e corrections It has been possible, according to the methods of however, to verify that the fractional retrntion for L B O 3 is less than 0.1. a
WLJ
With HN03 as well as for HC1 and HzS04,2a strong interaction between the electrolyte and the resin is demonstrated by the excess uptake of acid even a t moderate concentrations of the esternal electrolyte. This is reflected on the values of I' which are quite below unity for 1 he all range of mJ values. A comparison between the values of r obtained for the three acids shows that for a given molality of the aqueous phase we h a w rHNos
< rHzSOa < r H C l
This decrease of the value of r follows the increase in reactivity of these acids with the aromatic groups of the resin, suggesting that the large uptake of acids from the aqueous solution is probably due to this type of acid-base reaction. It has been shown recently3 that the theory of specific interactions for concentrated solutions leads to the following relation hetween activity coefficients Y*(,.) and internal concentration of electrolytes in the resin phase log
Y*-(r)
=
P1VLJ(r.,
+ Bzmxc.,
(3)
where PI and pz represent the sums of coefficients
AN ULTRASENSITIVE THERMISTOR JIICROCALORIMETER
Xov., 1961
which are independent of the concentrations. If rnxcr) is linearly dependent on VZJ(,), relation (3) becomes log
=u
+b
m
~
~
(4)
‘Yhe chloride systems were found to vary according to relation (4) a t external electrolyte concentrations above about one molal.3 Below this concentration negative deviations of linearity occur. The devia-
2041
tions are due to the relatively low values of ?i(r) a t low external electrolyte concentrations which has been attributed to consistent experimental errors and the influence of impurities of the resin phase.3 A similar behavior was observed with the nitrate systems as is illustrated in Fig. 1. The results of applying relations 3 and 4 are given in Table 11.
,4W ULTRASENSITIVE THERMISTOR MICROCALORIMETER AND HEATS
OF SOLUTION OF NEPTUNIUM, URANIUM AND URANIUX TETRACHLORIDE1 BY G. R. ARGUE,^ E. E. MERCER^
AND
J. W. COBBLE
Department of Chemistry, Purdue University, Lafayette, Indiana Received M a y Z4. 1961
A sensitive solution microcalorimeter using a thermistor-amplifier bridge and automatic recording has been constructed with magnesium, heats of solution in 1 M HCl have been and evaluated. The sensitivity of the instrument is 1 x measured to =k0.2’3&with samples as small as 19.51 fig. The device has been designed primarily for use in determining the thermodynamic functions of actinide elements and their compounds. The heats of formation of U(1V) in 1 M HCl, U+4(aq.) and UClp(c) have been redetermined and new values are reported for Np( IV), Np( 111)in 1M HCl and N ~ + ~ ( a q .Np+S(aq.). ),
Introduction sensitivity; such instruments probably qualify to be called ultramicrocalorimeters. Microcalorimeters suitable for carrying out heats The calorimeter has been used in redetermining of solution and reaction of actinide and other scarce elements have been reported and described the heats of formation of U(1V) and Np(1V) in by Westrum and E ~ r i n gGunn , ~ and C ~ n n i n g h a m , ~acid solutions, and the heat of formation of UCld(c). and White and Salman.6 In general, these in- Kew measurements on the heats of solution of struments have sensitivities such that precise heat UCI4(c)in perchloric acid solutions, and neptunium data for some reactions can be obtained with in HC1 solutions, allows accurate estimations of samples of a few milligrams. However, still more the heats of formation of U+4(aq) and K ~ + ~ ( a q ) sensitive calorimeters will be required to extend a t infinite dilution. Finally, a new method has heat measurements on the actinides and their eom- been used to directly determine the heat of formapounds beyond the transcurium elements. There tion of n ’ ~ + ~ ( a q ) . are a number of ways in which the sensitivity of Experimental small microcalorimeters can be improved, but Calorimeter.-The microcalorimeter body was a modithe most feasible method appears to be the sub- fication of the design of Westrum and E ~ r i n g . It ~ was constitution of thermistors as the temperature sensing structed from a small tantalum beaker having a volume of 7 cc., being about 4 cm. in length. The element. Such applications are not ne^,^!^ but approximately top was fitted with a tantalum lid which could be fastened the current availability of extremely stable thermis- to make a vacuum tight seal and was suspended by a Kel-F tors with high temperature coefficients makes plastics hanger from the top of a “submarine jacket” their application to microcalorimetry extremely (Fig. 1). A 40 mil diameter Pyrex stirring rod running the center of this hanger and a glass thermistor probe desirable; in addition, such use further lends itself down piercing the lid through a vacuum tight seal provided the t o automatic recording devices. This latter fea- essential parts of the device. An aluminum radiation ture in itself increases the accuracy of micro- shield supported on lucite legs was used. This submarine calorimetry, and this communication reports the type of calorimeter also has been used by otherss.4; the principal advantages of this arrangement have been studied details of an automatic recording thermistor and summarized recently el~ewhere.~ microcalorimeter approximately four times more A synchronous 288 r.p.m. motor was mounted directly sensitive than any yet described. Further, ex- above the stirring rod on a guided spring suspension. A perience with this device has led to recommenda- slight vertical movement of the suspension broke the bulb fastened to the end of the stirring rod.lo The tions for future microcalorimeters of even higher sample whole stirring apparatus could be covered by a plastic bag (1) Supported by the U. S. Atomic Energy Commission. (2) From th
