T H E SOLUBILITY O F YTTRIUM S A L T S BY M . C. CREW, HILDUR EDITH STEINERT AND B. S. HOPKINS
The solubility of salts of the rare earth metals is of special importance because their separation depends so largely upon slight differences in solubility. In spite of this fact there is very little accurate information available in regard to the solubility of individual salts of this group of elements. This investigation was undertaken for the purpose cf determining the solubility in water of yttrium chloride, bromide, nitrate and sulfate. The yttrium material used was a part of that purified in the determination of the atomic weight of this elementa2 The fractions used for determining the solubility were only slightly short of atomic weight purity. They contained traces of both holmium and erbium but no other known impurity. The yttrium material was twice precipitated as the oxalate and twice as the hydroxide. The final precipitation was as the oxalate, which was dried and ignited in platinum to the oxide. This was then dissolved in either hydrochloric, nitric or sulfuric acid and the solution evaporated to crystallization. After standing the crystals were filtered off and thoroly drained from the mother liquor in a high-powered centrifuge. The crystals were washed and whirled again. In preparing the bromide it was found to be more satisfactory to dissolve yttrium hydroxide in hydrobromic acid because this acid dissolves Yz03only slowly. By keeping the Y(OH)S in excess, a salt was obtained free from occluded acid. The reagents used were carefully purified. The water was newly distilled conductivity water which was carefully protected from the air. Kitric and hydrochloric acids were freshly redistilled from quartz apparatus; oxalic acid was recrystallized until jt left no weighable residue on ignition. Hydrobromic acid was made by the hydrolysis of phosphorus tribromide. The gas was dissolved in water and this solution was distilled before using. For the purpose of obtaining a saturated solution a t a definite temperature a thermostat was used. This wae equipped with a stirring device, an electric heating coil and a sensitive heat regulator. In order to obtain a saturated solution an Erlenmeyer flask containing both solute and solvent was immersed in the thermostat. On account of the small quantity of material with which it was necessary to work a stirring device within the flask wa? impossible. To enable the solution to reach the mturation point promptly the flask was vigorously shaken a t intervals. The flask was kept at a constant temperature for at least five hours before the samples for the determination were with1 This paper is No. I 7 of the series “Observations on the Rare Earths” from the laboratory of the University of Illinois. ZEgan and Balke: J. Am. Chem. SOC. 35, 365 (1913); Hopkins and Balke: 38, 2332 (1916); Xremers and Hopkins: 41, 718 (1919).
T H E SOLUBILITY O F YTTRIUM SALTS
35
drawn. An occasional test was made in which a much longer period of time was allowed for the solution to reach the saturation point, but in no case was any change observed after the elapse of five hours. Since the chloride, bromide and nitrate are more soluble in hot water than in cold it was found that the point of saturation could be more quickly reached by first holding these salts for a time at a temperature somewhat above that desired for the determination, then gradually lowering to the required point. In the case of the sulfate saturation was best obtained at a lower temperature, then raising to the required point, since the solubility of Y2(SO4)3 decreases as the temperature rises. Danger of supersaturation was avoided by vigorous shaking in the presence of an excess of the solute. The method used in making a determination was to place a convenient quantity of the pulverized salt in the flask and add to it a quantity of water insufficient to dissolve all the salt at the temperature under consideration. After it was certain that a saturated solution had been obtained in the thermostat duplicate samples were drawn off for analysis. For this purpose a cylindrical separatory funnel was used by which the solution could be drawn up into the stem and held by turning the stop cock. To prevent drawing up fine particles of the undissolved solute, the end of the funnel was covered with a strainer consisting of a double thickness of fine mesh silk cloth, held in place by a rubber band. A new strainer was used for each determination. Before the solution was drawn into the funnel the latter was brought to a temperature as closely as possible to that of the solution in order that the solution might not be exposed to a sudden change of temperature with consequent change in its condition. After filling the stem of the funnel with the solution, the strainer was quickly removed and the solution at once poured into a tared platinum crucible. This was immediately covered and dropped into a wide weighing bottle whose tightly fitting stopper was adjusted quickly. Then the weighing bottle, crucible, cover and solution were weighed and the actual weight of the solution was determined. In the case of the nitrate and sulfate, these solutions were then evaporated to dryness and ignited directly to the oxide in the same platinum dish. The oxide was then weighed and its weight gave the weight of the anhydrous ( YZO3 1 The factor 2.0596 was used for converting the
multiplied by the factor 2.43
2Y(N03)3
nitrate in the solution. weight of oxide to that of the sulfate. From the data so obtained, the weight of solute in solution in I O O grams of water was determined. Since the halogens are not converted to the oxide on ignition, the solutions of the chloride and of the bromide were diluted, pure oxalic acid added, the precipitate filtered, washed, dried and ignited to the oxide. The factor 1-73 was used for converting the oxide to chloride and the factor 2.9043 for converting the oxide to chloride and the factor 2.9043 for converting the oxide to bromide. Duplicates of all determinations were made and where the results failed to check closely or, where there was doubt concerning any value additional checks were made. The values obtained are shown in the tables and summarized in the accompanying curve.
M. C. CREW, HILDUR EDITH STEINERT AND E. S. HOPKINS
36
TABLEI Solubility of Y(N03)3in Temperature Wt. Solution 0'
22.5'
I .3078 I . 2234
I.2721
35O 60.2' 66.5'
7403 '5738 ' 7974 ' 9248 '
Wt. Oxide
IOO
grams of water
w t . Y(T\'Os)s
Wt. HzO
,6308
'2596 ,2888 ,2988 I853 ,1561 ,2193 '2585
'
.6770 '5184 ,5481 '2893 . 1934 ,2624 ,2968
7050
7240 '4510 ' 3804 '53.50 ,6280 '
'
Solubilitv in IOO grams H20
93.1 136 133 155
197 203. I 211
TABLE I1 Solubility of YC13 in Temperature
Wt. Solution W t . Oxide
IOO
grams of water
Wt. Chloride
Wt. HzO
Solubility in 100 grams
HnO 0'
16'
'7788 .4919 2.5405 2.7712
25.1'
45 ' 60 '
80
I . 2507
,6352 ,5140 .9599 I . 5632 3.0338 .7082 I ,0225
. I 9 17 ' 119.5 ' 63 7 0 ,6861 ,3354 . I552 ' I392 ' 2405 ,3924 ,7664 . I798 ' 2593
1880
4469 ,2850 1,4395 I . 5832
,5800
.7707
'2694 ,2410 '4164 .6800 I . 3270 ,3120 ,4499
,3658 ' 3 130 ' 543 5 ,8832 I . 7068 .3962 ' 5756
'3319 .2069 I. IO10 I.
'
74.3 72.7 76.6 75.1 75.4 75.3 77.0 76.3 77. 77.6 78. I 78. I
TABLEI11 Solubility of YBr3 in roo grams of water Temperature Wt. Solution 0'
30° SO0
7 5 O
95'
2.0425 I . 7876 4.557= 2.4427 ' 9094 I . 2197 .6816 I . 8688 2.5979
Wt. Oxide
.2686 .2452 ,7187 ' 3 793 ' I533 ' 2059 .1236 ,361I ,5078
Wt. YBrj
.7802 .7122
2.0874 I . IO17
'4453 ' 5981 .3591 I . 0488 1,4749
Wt.Hn0 I . 2823
1.0754 ' 4697 I . 3410 ,4641 ,6216 ,3225
2
.8200
I.
1230
Solubility in IOO grams
HzO 61.81 66.23 84.52 82.15
95.95 96.21 111.32 127.91 131.33
THE SOLUBILITY O F YTTRIUM SALTS
37
TABLEIT' Solubility of Y2(SOI)B in I O O grams of water Temperature Wt. Solution
3.6' 15.8'
,1766 I729 . I921 ,1287 ,1729 1673 . I189 '0704 ,0289 ,0766 044 .0333
4,9015 4.8791 5.7067 3 7850
25'
5.3215
5 . I094 50'
75" 95O
'
'
'
'
I
U 0-0-0
I
I
''
II
j.3110
3.5199 4.9654 4.7648 4.645 2.650 1.8344 4.9234 4.3934 3,4179
'
'
4 8899 2,7950 1 8939 5.0812 4.484 3.4865
4,5378 4,5230
3637 .3561 .3957 .2651 .356I 3446 2449 .14jo ,0595 .I578 ,0906 ,0686 '
'
'
Wt. H10
Wt. Y2(SO4)3
Wt. Oxide
O
40
T€/Y/?€/+I TUK€
! 60
c,
I
I
- 0
80
Solubility in I 00 grams €120
8.016 7.873 7,450 7.531 7.172
7.232 5.272
5,472 3 245 3,2045 2.063 '
2.007
I
1 100
FIG I
This method of determining the amount of solute in solution was selected because of the difficulty in getting salts of a definite degree of hydration'. The accuracy of the results obtained was decreased by the fact that in the final calculations the experimental error was multiplied in some cases by 2 0 0 on account of the small quantities of material with which we were compelled 1
Hopkins and Balke J Am Chem Sac 38, 2343 (1916)
38
M. C. CREW, HILDUR EDITH STEINERT AND B. S. HOPKINS
to work. Duplicates which checked within 1.5% were accepted as satisfactory if the mean of these determinations gave a point within 1% of a smooth curve joining all the points obtained. In determining the value of Y(NOs)a a t 0" the duplicate determination was lost. Since the one value obtained gave a point exactly in line with the other values, it was accepted because of the difficulty of working a t that temperature. I n order to test the degree of hydration of the eolute about one gram of each of the hydrated salts was placed in a dilatometer and enough nujol added to fill the tube. This apparatus was mounted on a meter stick which served as a scale and was then immersed in a thermostat. The temperature was raised gradually from room temperature to 95" and a t regular intervals the height of the nujol column and the temperature were recorded. When these results were plotted, in every case a smooth curve was obtained. This was interpreted as indicating that there were no changes in the hydration of these salts between 25' and 9 5 O , since if any change took place a break in the temperature-pressure curve could be expected. Urbana, Illinois, June 26, 1,924
