5038
K. H. GAYERAND H. LEIDER
Vol. 76
a t approximately 1300" by interpolation between radius from 1.79 k a f o r thorium to 1.G3 k . for prothe melting points of thorium and uranium. The tactinium to 1.54 A. for uranium is analogous to metal, in common with other members of the 5f that in the series Zr-Nb-Mo rather than to that of series, forms hydrides by direct union of the ele- the 4f-metals. Accordingly, it may be concluded that there are no 5f-electrons in the metal strucments. The compounds which were identified were tures of the heavy elements thorium to uranium. found generally to be isostructural with the corAcknowledgment.-The authors are grateful to responding uranium compounds. However, the Miss H. Anne Plettinger for her assistance with crystal structure of the metal was tetragonal and X-ray diffraction analyses reported in this paper. We would also like to thank Mr. Irving Sheft for unlike any of the other 5f elements. If an electron is added to an f-shell, there isea his assistance in the early phases of the protacsmall contraction in metallic radius of 0.01-0.02 A. tinium fluoride experiments, and Dr. lliartin H. as evidenced by the observed metallic radii for the Studier for his help in many ways. -if series of elements. The large decrease in metallic LEMONT, ILLINOIS [COXTRIRUTION PROM
THE
CHEMISTRY DEPARTMENT, WAYNE UXIVERSITY]
The Solubility of Thorium Hydroxide in Solutions of Sodium Hydroxide and Perchloric Acid at 2S01 BY K. H. GAYERAND H. LEIDER RECEIVED JUNE 17, 1954 The solubility of thorium hydroxide has been studied in perchloric acid and sodium hydroxide solutions at '75 '. The hvdroxide reacts mainly as a base, the chief reaction in acid solution being ThO(OH)2 2H+ % T h o + 2H20. The reaction constant, Kg, is 5.5 X l o 4 and Apso = -6500 cal./mole. K., = 5.5 X for the reaction ThO(0H)Z % T h o + + SOH-.
+
The purpose of this investigation was to obtain information regarding the reactions of thorium hydroxide toward perchloric acid and sodium hydroxide solutions, to determine ionic species involved, and to evaluate free energies and equilibrium constants for such reactions. The results indicate that thorium hydroxide reacts predominantly as a base. Procedure.-The general procedure is similar to that described by Garrett and Heiks.* An all-glass apparatus was used. Water.-Conductivity water was prepared in a Barnstead conductivity still, degassed by boiling with nitrogen bubbling through it, and then stored under nitrogen. Perchloric Acid Solutions.-Approximately one molar acid solutions were prepared from 70% G. F. Smith Chemical Co. purified perchloric acid with degassed conductivity water, and then stored under nitrogen. Standard acid solutions were also prepared with conductivity water and standardized against standard sodium hydroxide solution. Sodium Hydroxide Solutions.-ilpprosimately one molar solutions of bases were prepared under nitrogen by dissolving Baker and Adamson reagent pellets in degassed conductivity water in a paraffined flask. Barium hydroxide was added to just precipitate any carbonate. Following this, the solutions were stored under nitrogen. Standard base solutions were also prepared with conductivity water and standardized against potassium acid phthalate usiiig~. phenolphthalein indicator. Thorium Perchlorate Solutions.-Thorium hydroxide was precipitated from a solution of Baker and Adamson reagent grade thorium nitrate by addition of excess sodium hydroxide solution. The precipitate was washed by decantation with large volumes of conductivity water until the absence of a sodium flame test in the supernatant liquid was noted. The hydroxide was dissolved in perchloric acid, diluted to a final concentration of approximately one molar with degassed conductivity water, and stored under nitrogen. Colorimetric Reagents.-A standard thorium solution was prepared by dissolving recrystallized J. T. Baker reagent (1) From a dissertation submitted by Herman Leider in partial fulfillment of t h e requirements for t h e Doctor of Philosophy degree a t Wayne University. (2) A. B. Garrett and R. E. Heiks, THISJOURNAL, 63, 562 (1941).
+
+
thorium nitrate in conductivity water. Aliquot portions of this solution were used to prepare the color standards. Eastman Kodak disodium salt of l-(o-arsenopheiylazo)-2naphthol-3,6-disulfonic acid and Baker and Adamson A. C. S. standard hydrochloric acid were used to develop the color. Thorium Hydroxide.-Thorium hydroxide was prepared by addition of excess sodium hydroxide solutiou to a solution of thorium perchlorate. The precipitate was washed with degassed conductivity water. Absence of the sodium flame test indicated comoleted washing. The solid phase was unchanged after equilibration with acid or base. Equilibration.-Pairs of 100-ml. samples of the hydroxide in acid or base were collected in 12.5-ml. sample flasks under nitrogen. One of each pair was agitated in a 35' thermostat for five to seven days followed by agitation in a 25" thermostat for the same period of time. They were then allowed to settle for three to five days in the 25O thermostat. other member of each pair was directly agitated in the Thz 25 thermostat for a t least seven days aiid allowed to settle for three to five days. Determination of pH (-log A H + ).-The flask necks were broken while enclosed in a rubber membrane and samples were taken using a Beckman 290-78 hypodermic type glass electrode. Measurements were made with a Beckman Model G meter which was calibrated a t pH 4 with 0.05 ;If potassium acid phthalate buffer and a t PH 7 with Beckman 3581 buffer Thorium Analysis.-The thorium analysis was made with a Beckman Model B spectrophotometer using the method of Thomason, Perry and Byerlya3
.
The Data.-The data are presented in Tables I, I1 and 111 and are represented graphically in Figs. 1 and 2. The slope of the curve of Fig. 1 is very nearly 0.5, indicating that a divalent ion is produced by the reaction T h o + + 4-3H20 or preferably Th(OH)4 + 2 H + ThO(OH)2
+ 2H+ 1 ' T h o + + + 2H20
Figure 2 , the solubility curve for ThO(OH)2 (or Th(OH)4)in base, does not seem to show a solubility minimum, but rather seems t o extrapolate di(3) P. F. Thomason, M. A. Perry and W. M. Byerly, A n d . Chern.. 21, 1239 (1949).
SOLUBILITY OF THORIUM HYDROXIDE IN BASEAND ACID
Dec. 5, 1954
5939
rectly t o a water solubility of the order of 5 X moles thorium/1000 g HzO. TABLEI SOLUBILITY OF THORIUM HYDROXIDE IN NaOH SOLUTIONS AT 25' Initial moles NaOH/ 1000 g. HtO
Moles thorium/1000 g. HnO
Ka
Kb
1.08 x 1 0 4 . ....... . . . . . . ... 3000 X 102.42 390 X 8 . 8 5 X 1075 190 3.66 23 38 0.2 0.4 0.6 0.8 18 3.79 21 Initial moles NaOH/1000 g. H20. 4.93 x 10-7 1.3 1.6 5.94 1.5 1.9 Fig. I.-Solubility curve for thorium hydroxide in NaOH at 13.8 3.2 3.5 25'. 1.8 9.88 1.9 4.93 0.9 0.9 1.1 8.92 1.4 9.86 1.4 0.9 0.8 12.9 1.5 TABLE I1 SOLUBILITY OF THORIUM HYDROXIDE IN HClO4 SOLUTIONS AT 25" 0.0098 .0765 .1595 .2220 .3022 ,3842 .3950 .4342 .5081 .5257 .6307 .7023 .8650
Initial moles
Moles thorium/1000 g. HzO
HC10'/1000 g. HIO
2.03 X 4.06 X 1.01 x 2.03 X 4.06 x 8.11 x
6.48 X 1.48 X 4.04 X 9.80 x 2.00 x 3.62 X
IO-' lo-' IO-' 10-1
lo-*
IO+ 10-2
0
0.2 0.4 0.6 0.8 Initial moles HC10,/1000 g. HzO. Fig. 2.--Solubility curve for thorium hydroxide in HCIOl TABLE I11 at 25". SOLUBILITY OF THORIUM HYDROXIDE IN HCIOl SOLUTIONS AT 25" constant ionic strength ( p = 1.00), concluded that Moles thorium/ 1000 g. HnO
9.79 x 10.3 X 9.92 x 9.32 x 9.40 x 1.72 x 2.00 x 3.15 X 3.83 x
AH
10-3
lo-' IO-s
10-3 10-3 10-2 10-2
10-2
3.63 x 3.89 X 3.98 x 4.17 x 4.47 x 5.13 x 5.62 x 6.61 X 7.59 x
K6
+
10-4
lo-'
10-4 10-4 10-4 10-4 10-4 10-4
2 . 7 x 101 2 . 7 X 10' 2 . 5 x IO' 2 . 2 x 101 2 . 1 x 101 3 . 4 x 101 3 . 6 x IO' 4 . 8 X 10' 5 . 0 x io1
lo-' 10-1
6.5 x 5.9 X 5.4 x 5.2 x 4.2 x 5.5 x 5.3 x 5.8 X 5.3 x
104 104 104 104 104 104 104
+
Tht4 f 3H20 2Thf4
A later work5 supported this conclusion. In more recent studies617it is reported that a Th404+8, is formed over a considerable concentration range, and that there is no other simple species, but rather increasing polymerization O C C U ~ S . ~ Kraus and Holmberg,8 working with solutions of thorium perchlorate in excess perchloric acid a t (4) E. Chauvenet and J. Tonnet, Bull. SOC. chim. France, 14) 47, 701 (1930). (5) E. Chauvenet and Souteyrand-Franck, ibid., 47, 1128 (1930). ( 6 ) P. Schall and J. Paucherre, i b i d . , 14, 937 (1947). (7) P. Souchay, ibid., 16, 143 (1948). (8) K . A. Kraus and R . W. Holmberg, A. E. C.D., 2919, August 29, 1950 (date declassified).
+
u = Th+4
m = d = ThtO+6 h = equilibrium acidity
104
Th(OH)z'+ f 3Hs0' T h o C + f 2Ha0+
+
T h o + + 2H80+ and ThzO+S 2H30+
+ 3H20
explained their hydrolysis data. Also, their reaction constants were given as Km = mh2/u = 3.1 X and Kd = dh2/u2= 2.7 X where
lo4
Chauvenet and Tonnet4 reported that the hydrolysis of thorium proceeds by one of two mechanisms Th+' 4H20 or Th+' -I- 3H20
__
a monovalent hydrolysis product, Th(OH)3+, is unimportant and the reactions
KO
Latirnerg gives a solubility product for the reaction Th(0H)r
Th+'
+ 40H-
1.0 X calculated from heats of forniation and estimated entropy values. Latimer also gives values for titanium'O TiO(0H)z J_ TiO++ 2 0 H - K = ca. 10-29 for zirconium"
K
=
+
ZrOf+
ZrO(0H)z
and for hafniurnl2 HfO(0H)z
_____
HfO++
+ 20H-
+ 20H-
K =3X
10-28
K = 4 X 10-26
(9) W. M. Latimer, "Oxidation Potentials," Prentice-Hall Inc., New York, N. Y., 1952, p. 299. (10) Ref. 9 , p. 2fi6. (11) Ref. 9, p. 271. (12) Ref. 9 , p. 273.
K. H. GAYERAND H. LEIDER
5940
The constant calculated in this work for the reaction ThO(OH)l(s)
Tho+-
+ 20H-
K1
=
5.5 X 10-24
falls into correct sequence if thorium is considered to be a member of the titanium subgroup. This indicates that thorium is the most basic member of the subgroup, as would be expected. General Equilibria.-The possible equilibria of Th(OH)4 in acid, base and water solution may be represented by equations 1 to S
+ 20HThO(OH)z(s)J_ ThO(0H)- + OHThO(OH)t(s) + OH- J_ HTh03- + H2O ThO(OH)2(s) + 2 0 H - zTho3= + 2H20 ThO(OH)*(s)+ H + JJ ThO(0H)' $- HIO ThO(OH)z(s) + 2 H ' z T h o + - + 2H20 ThO(OH)z(s)zHTh03- + H + ThO(OH)p(s) ThOa' + 2H' ThO(OH)z(s)
ThoTi
+ OH-=
HTh03-
+ H20
K?
= KaK," = 1.6 X lo-" AF;O = 27,000 cal./mole
Similarly for Kg,using Kq and K , ThO(OH)z(s)
(4) (5) (6)
+ 20H-
ThdO'
+ H20
(8,
AFso = 46,000 cal./mole
+
(7) (8)
(3)
AFso = -6500 cal./mole
The assumption was made that Y?.hO++ = Y ? H + , where YH + was calculated from the Debye-Huckel equation. For reaction 5 ThO(OH)t(s)
+H
' S ThO(0H)-
+ H20
(3)
AFjo = -2100 cal./mole
It has been assumed that YThO(OH) "/YH+ = 1. Using K Sand KFV, K2 is evaluated for thc reaction
+
(2)
+ 20H-
(I)
ThO(OH)z(s) = ThO(OH)+ OHK~ = K ~ K ,= 3.2 x 10-13 LFZO = 17,000 cal./mole
Likewise, for the reaction ThO(OH)s(s)
ThO(OH):(s)
+
Equilibrium in Acid Solutions.-The data presented in Table I11 indicate that the principal reaction of Th(0H)c in acid medium is given by equation 6. For reaction 6 ThO(OH)z(s) 2" J_ T h o + + f 21320
AF~O= 7900 cal./mole
and K4for reaction 4
Jr Th08= + 2H
Kg = K4Kw2 = 1 6 X lova4
(2)
-%pparently,the reaction ThO(OH)n(s) G ThO(OH)2(aq) is unimportant, since the solubility curve does not show a solubility minimum but extrapolates upward to what can be assumed to be the water solubility. Direct measurement of the water solubility was not possible. Very erratic results were obtained. Equilibria in Basic Solutions.-The values of K 3 and K 4 in Table I indicate that in concentrated base, above 0.38 molar sodium hydroxide, the important reactions of Th(0H)d are (3) and (4), and that these reactions occur to about the same extent. Reactions appear to be more involved in dilute sodium hydroxide. K 3 for reaction 3 was calculated ThO(OH),(s)
Hiickel theory. The values of Y N ~ O Hwere interpolated from the data of Robinson and Stol;es.l3 Combining Ka and the ionization constant for water K,,Ki was calculated for the reaction ThO(OH)s(s) JJ HThOi- f H (7)
(1)
(3)
Vol. 76
Tho++
K1 = K C K , ,= ~ ~5.5 X lopz4 AFl0 = 32,000 cal./mole (4)
Acknowledgment.-The authors gratefully wish to acknowledge the support of the U. S. -1tomic Energy Commission, Project #AT(11-1)-214, in sponsoring this work. DETROIT,?vfIC€iIGAX (13) R. A . Robinson and R. H . Stokes, z'ruiis. F u i a d o y S o r , 4 5 , 0 1 2 (1949).
