Aug., 1951
AQUEOUS TERNARY SYSTEMS INVOLVING UNIVALENT IODATES
3613
[CONTRIBUTION FROM THE DEPARTMENT OF CHEWSTRY, NEW YORK UNIVERSITY ]
Some Aqueous Ternary Systems Involving Univalent Iodates BY JOHN E. RICCIAND IRVING AMRON The aqueous ternary systems of AgI03 with each of the following salts were found to be simple a t 25': LiIOa, NaIO1, KI03, x H r I 0 3 ,AgN03. The solubility of AglOa was determined at 25 and 45'. The solubility curve of a form of LIIOS stable above -~50-60" is reported, from 10 t o 95", as also the solubility, a t 25', of a form probably stable at that temperature. The system AgIO~-IzO~-HzOforms the incongruently soluble pyro-iodate AgIOa.12Os a t both temperatures studied, 25 and 4 5 O . . Similarities in the formulas of double compounds of iodates with iodic acid or with iodine pentoxide are discussed, and it is suggested that the compound previously described as KI08.2HIOa is probably anhydrous, with the formula KI03.1z06. The system LiIOa-HI03-Hz0 was studied at 25'. Unlike the other univalent iodates LiIo3does not form distinct compounds with HIOa or Iz06a t this temperature, but a solid solution. The limits of this solid solution do not extend t o the simple components LiI03 and HI03, which are present as pure solid phases, but they do include the molar ratios of possible compounds of LiIo3 with either HI03 or 1 2 0 6 .
The k s t phase d e investigations on the solid compounds of iodic acid and the iodates were reported by Meerburg,' who determined the 300 isotherms of the ternary systems involving NaI03, K I 0 3 and "*IO3, respectively. In extension of this work we have studied the system~ ~ 1 H103-H20 (more the system Ag103IzOS-HZO)a t 25 and 45', and the system LiIOsHI03-H20 a t 25'. At the same time some aqueous systems of AgI08 and other related salts were examined a t 25', and certain solubilities were determined, particularly that of one form of LiI03 from 10 to 95'. the univalent iodates studied form solid with H103 Or h 0 5 at room Both "acid iodates" or compounds of a salt with "HI03," and "pyro-iodates," compounds of salt are reported. ~ ~has1now 0been~found and a pyro-compound, with the to form AnI03*IzOs. LiIO3 Seems to be exceptional in forming, at 2 3 O , a solid solution rather- than any definite compound. Since the composition of the solid solution does not extend to the individual components, however, it is not possible to say whether it involves H I 0 3 or LO6, and it is possible that it may represent solid miscibility on the part of two or more actual compounds. Materials and Analytical Methods.-Two samples of pure silver iodate were obtained by washing commercial preparations with warm, dilute nitric acid and water, followed by drying at 100'. A third sample was purified by recrystallization of commercial material together with solubility residues from an ammoniacal solution with nitric aci$ followed by washing with water and drying at 100 The purity of the samples, determined iodometrically, was 99.9-100.0%. Because of the low solubility of AgI03 and because of further difficulties from precipitation of AgI on undecomposed AgI03, the samples for analysis were dissolved completely in 50% aq. K I before treatment with dil. H2SOn. After the instant reduction of all the iodate in this manner, the liberated iodine was titrated with standard thiosulfate. The silver content of the first sample was also determined gravimetrically, with a result of 99.9% purity. For this purpose the sample, again first dissolved in a small volume of 50% aq. K I , was reduced to iodide with SOz; after a hundredfold dilution of the solution, the precipitated AgI was filtered after boiling with some nitric acid. Commercial NHlIOa was recrystallized and vacuum-dried a t 60-70". Iodometric analysis with &&Oa gave 99.9% purity. C.P. samples of NaIOs, KIO, and AgNOa w q e dried and used without further purification. The lodlc acid used was ground to fine powder and dried a t room temperature over anhydrone for one week. It was found 100.0% pure both alkalimetrically with NaOH (standard-
.
(1) P. A. Meerburg, Z . onorg. Chcm., 46, 324 (1905); also Chem. Weckblad, 1, 474 (19041,
ized with KIO8.HIOa prepared according to Shaffer and Hartman2) and iodometrically with standard NazSlOa. A second method used for determination of iodate, which will be referred t o as iodometry with standard H&O4, was the procedure, described in most analytical texts, in which the sample is titrated with standard acid in presence of excess 0 ~ of- K I and Na&Oa, with methyl red as indicator. Since the equivalent weight of iodate is here six times that in respect to thiosulfate, this method was used for the analysis of the concentrated solutions of the system LiI03HIOrH20. Both methods are very accurate, agreeing withinl/lOOO. Some of the lithium iodate used was made by purscation of two samples of commercial c.p,material, which assayed -97% LiIOs. One sample contained insoluble Ba(I0a)z and gave an acid reaction. Part of it was simply recrystallized twice and part was neutralized with Kahlbaum LiOH before the second crystallization. The other sample contained insoluble LizCOS and gave an alkaline reaction; this was neutralized with iodic acid, followed by LiOH, before two recrystallizations. The rest of the salt used was made from Kahlbaum Li2COa and C.P. iodic acid, with linal neutralization with some LiOH. Various turbidities appearing during the process were removed by filtration when possible and bv boilinrc with activated carbon. The final product was obtained by slow evaporation with stirring on a hot-plate. After decantation the crystals were filtered by suction and washed with water. Ground and dried at 110-180°, the product was found to be 99.9 to 100.1% pure by determination of lithium as LizS04after reduction with SOz, and by determination of iodate by titration with Na2SlOs and with HzS04. The determinations of solubilities, both binary and ternary, were made according to procedures usually followed in similar investigations, and a few minor variations will be indicated in connection with particular systems.
Solubility of AgIOa, 25 and 45'.-These solubilities were determined by rotation of excess of solid with freshly boiled, distilled water in 250-ml. Pyrex bottles (glass-stoppered without grease) in large constant temperature water-baths. The solid used was first freed of very fine particles through warming and stirring with successive for an hour, followed by portions of concd. "03 repeated washing and decantation with water. After rotation and settling of the solid, the liquid was sampled by means of calibrated 50-ml. delivery pipets fitted with filter paper tips. Samples showing any appreciable Tyndall effect gave high results and were therefore discarded. The solution was analyzed by determination of iodate with 0.01 N NazSz03. In one experiment, rotation for 5 months gave, a t 25O, 0.0506 g./l. (U, from unsaturation) and 0.0506 (S, from supersaturation); a second independent set of runs gave 0.512 and 0.0511 (2) P. A. Shaffer and A. F. Hartman, J . B i d . Chcm., 45, 376 (1920); I. M. Kolthoff and L. H. van Berk, THISJOURNAL. c(I, 2799
see also
(1926).
3814
JOHN
E. RICCIAND IRVING AMRON
(U), 0.0507 and 0.0509 (S) after 7 days. At 45" the results, after 2 days of stirring, were 0.0995 g./L (U) and 0.0997 (S). Average values may be taken as 0.0508 g./l. a t 25" and 0.0996 at 45", or 0.00510 and 0.01006% by weight, respectively. With corrections for ionic strength neglected, the solubility product values would be 3.23 X and 1.24 X lo-', respectively. The solubility at 25' agrees well with the most recent literature ~ a l u e s which ,~ range from 0.0501 to 0.0507 g./l. a t 25". By interpolation, the literature values give -0.10 g./L at 45'. Salt Systems at 25'.-The following five systems were studied a t 25': (1) AgI03-LiI03HzO ; (2) AgI03-NaI03-HzO; (3) AgI03-KI03H2O; (4) AgI03-NHJO3-H20 ; (5) AgIOa-AgNO3H2O. The isotherms are all of the simplest type, with the individual salts, hydrated only for NaI03. H20, as the sole solid phases; there is no evidence of either compound formation or solid solution. In systems 1-4 the concentration of AgI03 in the solutions containing the second salt was not detectable, all qualitative tests for silver in the solution being negative; hence the second salt was determined either through evaporation for total solid or through titration of total iodate. In system 5, total solid was determined by evaporation to dryness after addition of a drop of concd. "03, which, apparently by preventing reduction of silver, always gave pure white residues. The final weighed residue was taken up in water for determination of RgI03, whereupon AgN03 was calculated by difference. For iodate determination the solution of the residue was treated with HCl to precipitate AgCl and the filtrate was titrated with 0.01 N Na2Sz03. Preliminary test of the procedure showed it to be dependable, leading to an uncertainty of about 0.003 in the final percentage of AgI03. The solubility of AgIOB was depressed to 0.009% a t 22.65% AgN03, 0.008P; a t 48.47%, 0.035% at 70.43%, and 0.040-0.043~~ a t 7 1.84% (saturation). The solubility of LiI03is 43.86% (density 1.55s) ; other densities are 1.227 at 23.25% and 1.553 at 43.3iyo. Although the average value found for the solubility of KIOB agrees with the average literature value, the individual determinations showed considerable scattering (8.428 to 8.504), a frequent observation with this salt, possibly attributable4 to some colloidal b e h a ~ i o r . ~The solubility found for NaI03.H20, 8.34%, is lower than the most recent determination, 8.49Yo6 (which was itself distinctly lower than all previously reported values, averaging -8.6%). The present determination was made with monohydrate as the actual starting solid, with long periods of stirring, with both directions of equilibration, and, in some experiments, with special precautions, involving discarding of successive portions of saturated solution, to avoid colloidal particles. (3) W. B. Baxter, THISJOUBNAL, 43, 615 (192l), 1. M Kolthoff and
J. J. Lingane, J . Phys. Chcm., 43,133 (1938); N. C. C. Li and Ying-Tu Lo, THISJOURNAL, 68, 894 (1941); R M. Reefer and H. G. Reiber, ibid., 68,689 (1941); P.I?. Derr, R h l . Stockdale and W. C. Vosburgh, {bid.. 68, 2670 (1941). (4) A. E. Hill and J. E. Rteci, tbrd., 68, 4305 (1931). ( 5 ) J. W. McBain and S. S. Kistler. J. Phyr C h . ,86. 130 (1931) (1))
J 1,
R i c c ~dnrl
n
I
J
iiiht
1111-
I(a1 k \ \ I
6 9 , llJ80 (1'117)
VOl. 73
The solubility of NHJO, was found to be 3 . 6 8 ~ 7 ~ (density 1.026) a t 25", and 5.992y0 (density 1.037) a t 45". Solubilities a t these temperatures have not previously been reported ; however, the present values fall on a smooth curve with those reported at 30" (4.20%) by Meerburgl and a t 15" (2.5%) and 101" (12.7%) by Ramrnel~berg.~ System AgI03-IzO6-HzO; 25" and 4S0.The complexes in this system were made up from AgIo3, HIO, and water. The liquids were sampled with delivery pipets a t low concentration and with specific gravity pipets for high concentration. They were found to contain no significantly detectable concentration of AgI03 and hence the determination of acid with standard NaOH was calculated directly as either H I 0 3 or 1206.The determination, in a number of samples, both of acid and of iodate gave agreement within 1/1000, so that to this extent, at any rate, the absence of AgIO3 in solution was confirmed. The densities obtained, many of them not listed in the table, may therefore be taken as those of solutions of iodic acid. They agree well, a t 25", with the values reported by Randall and Taylor8 for the range 0-61% 1206; those a t higher concentrations are not considered as dependable as these. Equilibrium was in general proved by repeated analysis after further stirring following an initial period of about a week. The data, in terms of weight percentage of AgI03 and 1 2 0 5 as components, are listed in Table I for the two temperatures studied, 25 and 45". The stable relations a t 25" are plotted, in the same units, in Fig. 1, from which the formation of a 1: 1 compound is clear. The diagram for 45" is very similar to Fig. 1. The compound formed more rapidly, and equilibrium was more easily attained, near the point b, the solution congruently saturated with compound and H I 0 3 (or I2O6.H20),than near point a, the solution incongruently saturated with AgI03 and the compound. This difference would be expected if the formation of the compound depends on poly-iodate ions whose concentration would increase with that of iodic acid. At any rate, it was not possible to obtain equilibrium (except for one experiment a t 4.5') for complexes with compositions in the invariant region A-aX . H as prepared from water, solid HI03 and solid 9gIO3, even though they were seeded with thc compound and some were agitated a t 100' for a few hours before being brought to 23 or 43". The resulting metastable values have been omitted from both the table and the diagram. The invariant point a a t both temperatures was finally obtained by direct equilibration of the actual solid phases, AgI03 and double compound, with solutions. Since the double compound was added 3s a wet residue from other experiments the total complex compositions for these points are estimated. When the data were originally plotted in terms of HI03 as a component the tie-lines did not converge sharply at a point on the base of the triangle, ( 7 ) C. I' Kammelsberg, .'t7111 P h p z ~ n d Chon (Pogn ), 44, 5;; (1878) ihr 11 I< i i i i r i l l d u d \1 1) 1 a ) l o r , i P l i j i C t i e r i ~, 45, '359 (1911,
AQUEOUS TERNARY SYSTEMS INVOLVING UNIVALENT IODATES
Aug., 1951
3615
TABLEI SYSTEMAgIO3 ( =A)-I206 ( = B)-H20 ( =: W) Saturated solution %B Density
Total complex %A %B
Solid phase
At 25' 3.03 18.96 9.99 33.17 2.99 47.21 45 22 46 20 54.06 14.96 1.864 5.00 55.02 1.999 8.00 58.81 2.12 5.01 62.15 10.01 61.67 2.18 5.00 63.57 2.22 5.00 64.48 66.39 5.00 67.35 5.00 68.29 5.00 2.45 5.00 69.24 5.50 69.25 2.48; point b, average of four 0.00
A A A A, A.B A, A.B A.B A.B A*B A.B A-B A*B A-B A-B A*B A*B A.B A*B A.B, B.U7 B.W
At 45" 20.01 19.97 20.00 10.00 8.99 5.00 21 22 5.01 5.01 5.00 5.00 15.00 5.00 5.00 5.01 5.01 15.01 15.00 5.01 4.98 14.95 5.00 2.00 0.00
A A A A A A A, A.B A, A.B A, A.B A.B A.B A*B A.B A.B A.B A*B A.B A*B A.B A.B A.B A.B A*B A.B, B.W B*W
19.51 36.89 48.64 52.11 52.09 54.12 55.20 59.78 63.04 63.72 64.69 65.70 07.82 68.85 69.86 71.00 71.42 71.54 71.55
1.203 1.455
34.55 40.40 46.43 47.44 48.42 49.53 49.95 49.94 49.94 50.45 50.99 51.55 52.73 54.24 55.30 56.29 57.44 61.10 66.74 70.64 71.69 72.05 73.24 74.02 73.89
1.410 1.512 1.637 1.653 1.681 1,702
. ..
1.727 1,737
1.820 1.849
1.911 2.42 2.47 2.54 2.58
27.53 32.21 36.98 42.68 44.10 46.96 44 42 49.81 50.75 51.24 51.71 53.11 54.08 55.03 55.98 56.93 58.82 62.59 68.76 69.71 66.21 71.14 74.00
...
A
Fig. 1.-System
AgIOa(A)-1206(B)-H20 (W) at 25".
Fig. 1 and to the line connecting the points A and A.W, or "HI03." On the base line the twelve tie-lines a t 25' give 54.57 * 0.68% 1 2 0 5 (0.68 being the average deviation from the mean) while the thirteen tie-lines a t 45" give 53.39 * 0.48% 1 2 0 5 . The theoretical value for AgI03. 1 2 0 5 is 54.14%. The extrapolations to the line A-A.W give 55.47 =t0.91% 1 2 0 5 a t 25' and 54.11 1.02 a t 45', but the theoretical value for AgI03. 2HI03, or AgIO3~I20~.H20, is 52.60% 1 ~ 0 ~The . agreement with the anhydrous formula is clearly so much better that we may take the compound to be the pyroiodate AgIOa.1205. Other Pyro- or Po1yiodates.-The following is a list of apparently all the compounds between iodic acid or iodine pentoxide and other iodates reported in the literature : f
Compound
Reference no.
2~dI03~1205 NaI03.2HI03( NaIO3.I2O5.H20)
1 1 K I ~ ~ . H I ~ ~ ( ~ K I ~ ~ ~ I1,9, ~ ~10,K11, ~ 12 H~O) 1, 9, 11, 12, 13 KI03.2HI03 (KI03.1205.H20) 13,14 K103.1206 RbI03.HIOa (2RbI03.IzOs.HzO) 15 RbI0~~2HI0~(RbI0~~IzOs~H~0) 13,15 RbIOs.InOj 13 2C~I03.1206 15 CSI~~~IZ~K~'/ZHZ~ 15 NH4103.2HIO3(KHaIO3.1206.HzO) 1, 1G
In addition to these involving univalent iodates, we have also Ba(103)2.1205.17 but fell, with some spreading, slightly to the right The formation of these solid compounds may be of the 1:2 molar ratio. (A 1:2 molar ratio of taken as in a sense confirming the formation. of AgI03 to H I 0 3 corresponds to a 1: 1 ratio of AgI03 poly-acid ions or of condensation in general in to 1 2 0 5 . ) Although the discrepancy from the aqueous iodic acid, inferred from studies of its compound composition ''Ag1O3~2HIO3'' was small, (9) A. Ditte, Ann. chim. p h y s . , [41 21, 47 (1870). the analytical accuracy involved gave it sig(10) J. C. G . de Marignac, Ann. Mines, [a] 9, 32 (185G); [ 5 ] 19, 66 nificance. Since the tie-lines for the compound (1857); reported in J. W. Mellor, "A Comprehensive Treatise on Inorappeared, a t both temperatures, to converge ganic and Theoretical Chemistry," Longmans, Green, London, 1922, p. 335. below the base of the diagram, with a negative VOl.(11)11,N. A. E. Millon, A n n . chim. phys., 131 9, 400 (1843). percentage of water, the compound was suspected (12) S. B. Smith, THISJOURNAL, 69,2285 (1947); for details, Docuto involve IZO5 rather than HI03, and the data ment 2389, Amer. Documentation Inst. (13) U. Croatto and 0. Bryk, C w . chim. it& 71, 690 (1941). were therefore recalculated in the terms here pre(14) G. S. Serullas, Ann. chim. p h y s . , 121 43, 117 (1830). sented. These tie-lines, fixed by compositions (1.5) H. L. Wheeler, A m . J . Sci., [3] 44, 123 (1802). of liquid and total complex, were extrapolated (16) A. Ditte, Ann. chim. phys.. [61 21, 145 (1880). algebraically4 both to the base of the triangle of (17) A. J. Freedman, Dissertation, New York University, 19.18.
3616
JOHX
freezing point lowering, molecular conductivity, and ionic mobilities.ls From this point of view the compound AgIOa.IzOs might be considered as a triiodate, AgIsOa, and KI03.HIOa as either a biiodate, KHIz06, or a tetraiodate, K2I4OI1"20. But it is not possible, of course, to reason specifically from the formulas of the solids to probable formulas of condensed ions. In this connection we may note, for example, that in the case of the fairly soluble salt KI03, the familiar compound "KI03.HI03" is precipitated from aqueous solution a t 25" at a concentration as low as 0.38% HIOd and 7.77% KI03,19while no "poly-iodate" of silver appears until the iodic acid concentration reaches 54.9% (point a a t 25', in terms of HI08 as solute). The greatest regularity in the formulas of the solid compounds is, in fact, seen not from the point of view of possible ions of condensed acids, but on the basis of simple ratios of MI03 to IzOS,in compounds which may or may not be hydrated. All the formulas fall into two groups: R/IIO~.I~OS and 2MI03.1206, in each case with or without one (onehalf for the cesiuin compound) mole of water. These observations suggest the question whether the compounds reported as NaI03~2HIOn, NHJ03. 2HI03 and KI03.2HI03 were correctly identified. For the first of these Meerburg reported direct analyses of the solid phase, but the other two were based on tie-lines which do not permit significant distinction between such formulas and the anhydrous pyroiodates, since the tie-lines did not originate in solutions of sufficiently high iodic acid content. In Table 11, Smith's data for tie-lines originating from the two most concentrated solutions a t each temperature are given, recalculated in terms of KIOa, 1 2 0 6 and H2O as the components. 'rABLB
C.
0 25
50
Solution %A r/oR
0 29 .30 .38 .34 83 .99
44.83 61 14 53 84 64 24 55.36 66 17
Wet residue % A yo B
31 90 32 41 29 94 29.24 29 80 28 39
System LiIOa-HIOg-HzO at 25'.--For the analysis of the solutions the iodic acid content was determined by titration with standard NaOH, and the neutralized sample was then used for the determination of total iodate, either with standard NagSzOa after suitable aliquoting or directly with standard HzS04. The second, faster method was used €or most of the work. The data are listed in Table I11 and plotted in Fig. 2. TABLE
(A =
58.19 60 45 59.32 62 48 59.20 62.60
7 0 HIO dt 1 A I B
-0 62 .YO
+ -
.11
-1 48 -0 01 - 42
These tie-lines were then extrapolated algebraically to their intersections with the line 1KI03:11206; the result, in terms of %HzO a t the intersection, is given in the last column of the table. The average value is - 0.28( * 0.57)% HzO. Since the formula KIOs.2HI03 or KIOa-IzO6.H20requires 3.18% HzO, it is clear that these tie-lines, which are the significant ones for the distinction, indicate the composition KI03.1206. The solids in the system KI03--120~-H20in the temperature range 0-50' axe therefore probably KI03, KI03.HI03 (congruently soluble), KI03.1206 (incongruently soluble) and H103.20 (18) See, for example, N. V. Sidgwick, "The Chemical Elements and Their Compounds,'' Oxford University Press,1950, pp. 1228-1229. (19) From the data of S. B. Smith, ref. 12 (on microfilm service). (20) Prof. S. B. Smith has commented, in a private communication, that even if KIO~IPOS is the solid phase in the region involved in Table 11, i t is still possible that the solid is KIO1.2HIOs at lower concentrations of 120s.
111
SYSTEM LiI03-H10~-H~0AT 25' LiIOa; B = HIOl; S.S. = solid solution)
Saturated solution %A % B Density
43.86 43.96 43.96 43.83 43.56 43.08 42.49 41.48 40.81 40.42 40.16 40.25 40.16 (40.19
0.00 1.03 3.13 6.67 11.18 16.65 20.89 26.56 28.80 30.78 31.40 31.30 31.30 31.33
39.7.5 39.57 38.84 38.53 37.21 37 1.7 36.28 :!5.35 34.70 8 4 09 3.7.62 33.48 32.88 32.81 29.86 27.25 (26.84
32.46 32.65 34.58 35.42 38.25 38.52 40.29 40.38 42.23 43.54 44.79 45.60 46.00 47.02 47.25 52.74 57.45 58.16
26.70 26.95 26.82 25.91 21.08 16.48 10.20 7.23 3.50 1.24 0.00
58.19 58.10 58.15 58.56 61.25 63.91 68.09 70.19 72.92 74.62 75.40
:16.18
11
PARTOF SYSTEM KIOJ (,4)-IL0, (B)-t120 (LV),FROM L)ATA OF S.B. SMITH^^ T',"p.,
Vol. 73
E. RICCIAND IRVINGAMRON
1.558 1.579 1.620 1.697 1.797 1.923 2.027
Total complex %A %B
...
0.00 1.00 2.93 6.00 10.00 15.00 20.00 24.99 22.00 29.98 23.99 26.27 26.50
49.99 48.80 50.01 50.00 49.00 44.99 44.98 2.237 55.00 2.300 41.99 2.312 54.96 2.310 52.50 2.311 54.99 2.311) -aver. ( a ) ; point (c) 2.334 50.54 29.46 2.340 52.98 28.99 2.385 47.96 31.98 39.94 34.98 2.475 46.99 35.00 2.476 47.49 35.00 2.525 36.97 39.98 47.00 36.50 2.567 46.50 38.00 2.602 46.00 39.01 2.636 45.50 40.00 35.00 44.99 44.99 41.00 2.695 42.00 43.00 2.702 44.48 42.00 2.848 35.00 49.99 2.979 32.88 54.09 2.995) -av.(b);point
-.
(4 2.993 2.993 2.998 2.961 2.827 2.609 2.514 2.487
-
31.89 27.99 25.99 19.99 18.99 14.00 9.00 6.00 3.00 1.00 0.00
55.11 58.96 60.96 67.97 04.97 68.97 71.97 75.00 76.97 77.93
Solid phase
%
LiIOa In
solid
A A A A A A A A A A A S.S A S.S. A + S.S. 8 2 . 4
+ +
A
+ S.S.
S.S. S.S. S.S. S.S.
S.S. S.S. S.S.
S.S. S.S.
S.S. S.S. S.S. S.S.
S.S. S.S. S.S. S.S. S.S. S.S. S.S. S.S. B B B B B B B
+B
+B +B +B
(78.7) 78.2 77.8 76.0 76 74.0 74.0 74 72.9 71.5 71.0 70.5 71 69.8 68.9 69.0 67.3 65.2 (65.0) 64.4
... B The liquids were sampled with 1-ml. specific gravity pipets. Solutions with at least 20% HzO could still be pulled through filter paper tips for separation from solid. Those with less water were too viscous for such filtration, and were sampled only after sufficient settling. When the
Aug., 1951
3617
AQUEOUS TERNARY SYSTEMS INVOLVING UNIVALENT IODATES
' 1 8.0
Fig. 2.-Systern
c
LiIO,-HIO~H~O a t 25".
crystals were not too fine, one or two days of settling suiliced. So much time was otherwise required for settling that the solid-liquid mixture was alternately centrifuged for one minute and replaced in the water-bath for five minutes, until sufficient clear supernatant liquid was available for sampling. The viscosity was so high that even without filtration the withdrawal of a 1-ml. sample required up to 30 minutes. The densities are plotted against the iodic acid concentration in Fig. 3. The relative values of these densities are significant even though the accuracy of the determinations of the highest values is probably not high. Equilibrium was reached in 2 to 8 weeks depending on the composition and the amount of solid involved; equilibrium was checked on a few representative complexes, including the most viscous, in each series prepared, before the whole series was analyzed. For saturation with the solid solution equilibrium was checked on each solution, the agreement being 1/1000. In most cases equilibrium was approached presumably from supersaturation because it was necessary to heat the complex to break up the solid cake formed on mixing the components. Since the caking depended somewhat on the order of mixing, some of the points were obtained from undersaturation by variation of this order. Supersaturation in respect to HI03 as solid phase was always very persistent, and the solutions on the solubility curve of HIOs were all seeded with the solid before stirring a t 25'. In some cases in which the preheating of the complexes led to such marked supersaturation the solutions were so viscous that the liquid barely flowed when the tubes were inverted. For a few of the worst cases the rotation of the tubes was started at -45", where the liquids were less viscous, and the temperature of the water-bath was slowly lowered to 25" over a period of 30 hours, the tubes being seeded with HIO, at -36'. The solid phases are seen from Fig. 2 to be pure LiIO:, a solid solution of intermediate composition, and pure HIOa. The tie-lines converge with satisfactory sharpness a t the compositions of the simple solids LiIOa and HIOI. The break in the liquid
1.5
;
Fig. 3.-Density
I PO
I
I 40
I
I
I
60
Wt. % ' HI08 +. of saturated solution, system LiI08-HI08H20 a t 25".
curve a t point a, for twofold saturation with LiIOa and the limiting solid solution c, is vague in the plot of Fig. 2, but it is brought out in the density plot of Fig. 3. The limiting compositions of the solid solution, points c and d, may be estimated from a Roozeboom type of distribution diagram, in which the weight ratio of the salts in the liquid phase is plotted against the ratio in the solid phase. Extrapolation of the curve for saturation with solid solution to the compositions a and b in the liquid phase gives 78.7% LiIOa a t point c and 65.0y0 LiI03 a t point d. This solid solution is of the unusual type noted in the system Na2SOcNaBr03-H207 studied from 37.5 to 52O2I; with point "d" containing only -10% NaBrOa a t 37.5" it would be difficult to attribute that solid solution to solid miscibility of binary compounds of reasonable formulas. In the present case the limits c and d are such that it is more probable that the solid solution is formed between definite compounds, although whether they would be compounds of LiIOs with HIOa or with 1206cannot be determined from the data. The limits c and d cover approximately the ratios 1.8 to 3.6 LiI03/HIOa; in terms of LiI03, 1 2 0 5 and H20 as components, the corresponding limits cover the ratios 4.8to 9.1 LiIo3/1~06. Under microscopic examination the crystals of the solid solution appeared as long hexagonal rods similar to those of the form of LiIOs stable at 25O, as observed on samples both from binary and from ternary solubility experiments. The solid solution crystals differed only in that their ratio of length to width was usually about twice that of the LiIOs crystals. Solubility of Li1Oa.-Many measurements were made in an attempt to determine the stable solubility curves of the forms of LiIO, from 10 to 95". The crystallization of the form or f o m stabk in (21) J. E. P.M,
TBIDJOURNAL, 17, 80,s (1~3s).
JOHN E. RICCIAND JOHN A.
3618
SKARULIS
Vol. 7 3
the lower range (10 to -50") is so slow, however, that all that could be reasonably read from the results is a curve attributable to a form stable above -50-60". This form, crystallizing in small octahedra, persists metastably evidently down to lo", and its solubility curve, with some points approached from undersaturation, some from supersaturation, and a few from both directions, was determined from 10 to 9.5". For each point the solid phase was examined microscopically and found to be always the same. The values, listed in Table IV, fall on a smooth curve with a minimum solubility near 85". These values represent measurements agreeing on repeated analysis with continued stirring at each temperature. The density of the solution a t 24.95', with 45.33% LiIo3, was 1.587. Many widely scattered and unreproducible "solubilities" lower than the values on this curve were observed a t temperatures below 5 5 O , and one higher than the curve a t 60" but none
below the curve a t temperatures above 50". It is probable, therefore, that the form involved is stable above and unstable below -50-60". Most attention was giver1 to 25", where a longconstant value of 43.86y0 was obtained with several different samples of starting material. This is lower than the value in Table IV, and therefore must pertain to a form stable (relatively) a t 25". Whether it is the most stable form a t 25", however, cannot be said, although its solubility does agree ~) fairly well with the value ( ~ 4 4 . 0 7 extrapolated from the solubility curve of LiIOs in the system LiIOs-HIO3-H20 as presented in Table 111 and Fig. 2. It also agreed in crystalline appearance with the LiIOs solid phase obtained in the ternary system, in the form of long hexagonal rods, as already mentioned. It is probably the form studied crystallographically by Zachariasen and Barta. 22 Since this solid is definitely anhydrous according to Fig. 2, we may infer that the higher temperature form involved in Table IV must also be anhydrous. TABLE IV For comparison, we note that the solubility SOLUBILITY OF ONE FORM OF LiI08 (OCTAHEDRAL CRYSTALS) values in the literature are few, a t scattered U, undersaturation; S , supersaturation; m , metastable temperatures, and sometimes with no information Temp Solubility Approach concerning the purity of the salt and the attainOC. wt. ?& LiIOa from ment of equilibrium. LUhden~ann~~ reported 9.93 47.19 ( m ) u 42.18% a t 10'; H e y d ~ e i l e r gave ~ ~ values of 23.5 20.24 45.86 (m) S and 38.3%, for two forms, at 18"; G r i i n e i ~ e n ~ ~ 24.95 45.33 (m) U&S reported 38% a t 18"; Mylius and Funkz6reported 29.94 44.89 (m) U 44.6% a t 18". Ira addition a hydrate of the salt 34 * 95 44.45 ( m ) U was also reported (LiIOa.Hz0, at -60") by Ditte,lG 40.00 44.12 (m) U although it has not again been mentioned. 45.00 43.84 (m) U h S (22) W.H.Zachariasen and F. A . Barta, Phys. Rev., 36, 1693 (1930); 50.06 43.51 (m) S 37, 1326 (1931). 55.1 43.35 (?) U I
60 2 65 3 75.5 85 5 99 1
43 43 42 42 42
10 00
U U
82 76 85
S U
u
[CONTRIBUTION FROM
(23) R. Liihdemann, 2. physik. Chon., BSQ, 133 (1935). (24) A. Heydweiler, Ann. Physik, ST, 741 (1912). (25) E. Griineisen, Wmensch. Abh. PhyS.-Teihn. Rcichsansl., 4, 246 (1905). (26) F. Mylius and R . Funk, Bcr.. 30, 1716 (1897).
NEW YORK,N. Y.
RECEIVED NOVEMBER 29, 1950
DEPARTMENT OF CHEMISTRY, NEWYORK UNIVERSITY ]
Some Aqueous Salt Systems Involving Fluosilicates BY JOHN E. RICCIAND JOHN A. SKARULIS The solubility relations in several aqueous systems, some ternary and one quaternary, involving fluosilicates are reported for 25'. The isotherm of the system KsSiFs-KBr-HnO shows the saturating solid KlSiFs to be anhydrous. The three ternary systems involving the salt pairs ( NH4)&iiFpMgSiF6,SrCl&rSiFs, and (NH4)tSiFarSiFs were studied with 0.5% aqueous HoSiFs as solvent, to prevent hydrolytic precipitations. The first two are simple, with (NHI)~W~, MgSiF143H20, SrClt.6H~0and SrSiFe2HeO as sole solid phases. The third pair forms a congruently soluble double salt the formula of which seems to be (NH4)tSiF&SrSiF@. In connection with these systems the solubilities of (NH4)BSiF6and SrSiF~2Hs0in presence of H&iFs, up to -30%, were also determined. The three systems containing the pairs NH&-NH4CI,NH4CI(NH&SiF6, and NH4F-(NH4)2SiF& were studied with pure water as solvent. The first two are simple, the only solids being the anhydrous salts. The third involves the already known incongruently soluble double salt NHnF-(NH4)2SiFs. The 25" isotherm of the quaternarysystem NH4F-NHrCI-( NH&3iF&-HtOhas two solutions of threefold saturation. One is a transition point in isothermal evaporation, with the phase reaction (NH4)aiFs liquid F? NH&l NHIF.(NH&~F~ H t G , and the other is the congruent drying-up point for the solids NH4F NH&I NHIF.(NH&~IF~.
+ + +
The literature contains little information on solubility equilibria of the fluosilicates. Solubilities of a number of fluosilicates, some of them of uncertain dependability, are cited in Mellor's "Treatise,"l in Seidell's "Solubilities,"2 and in a compila(1) J. W. Mellor, "A Comprehensive Treatise on Inorganic and Theoretical Chemistry," Longmans, Green & Co , New York, N. Y . , 1025, Vol. VI, pp. 944-958. (2) A. Seidell, "Solubilities of Inorganic and Organic Substances," D. Van Nostrand Co., New York, N, X.'1940, Vol. I, pp. 810, 970,
+
+
tion by Carter of values known to 1930.3 Carter also reported some further measurements, in particular the solubilities of the sodium, potassium and No double salts of barium salts from 0 to -80'. the fluosilicates are mentioned other than the compound NHdF. (NH&SiFO. This was first prepared 1098. A few further individual solubilties have since been reported in the literature. 13) R. H. Carter, Ind. Eng. Chrm., U, 886 (1980).
