NOTES
Sept., 1951 bidity developed during the titration) the solutions a t the end-point were always perfectly clear, and remained so on boiling. After considerable dilution, however, white precipitates of copper(1) thiocyanate formed: such precipitates could not be secured from copper(I1) thiocyanate solutions even after long standing. TABLE I MILLICOULOMETRIC ELECTROLYSIS OF COPPER(II)IN 1 F THIOCYANATE The solution initially contained 0.500 micromole of copper(11) in 0.497 ml. of 1.00 F potassium thiocyanate. &+ = -0.90 v. The blank counting rate of the millicoulometer was 0.2960 i 0.0001 count/sec., including the contribution from the residual current, and the sensitivity was 4.537 X 10-4 microfaraday/count Galvanometer deflections have been corrected for the residual current.
.
Time
0 1000 2000 3000 4000 5000 8000 12000
Counts, MicroRegister Counts cor. faraday
11745 12178 12602 13019 13430 13834 14993 16472
d, cm.
0 0 0 30.27 433 137 0.062 28.40 857 265 .120 26.69 1274 386 .I75 25.08 1685 501 .227 23.56 2089 609 .276 21.80 3248 880 .399 18.01 4727 1175 .533 14.36 Mean:
Micromole reduced
n
0 .. 0.0312 1.99 ,0593 2.02 .OS59 2.04 .111 2.05 .140 1.97 .203 1.97 .263 2.03 2.01 i 0.03
As it is not uncommon to find reducing impurities in ammonium thiocyanate preparations, it seems probable that the copper(I1) in the solutions of Korshunov and Malyugina was reduced to the 1state by some adventitious contaminant. Acknowledgment.-This work was supported by Contract Number AT (30-1)-842 between the U. S. Atomic Energy Commission and Yale University.
+
STERLING CHEMISTRY LABORATORY YALEUNIVERSITY SEW HAVEN,CONN.
4481
studies on solutions containing the non-complexing perchlorate ion. Experimental Materials Used.-The majority of the rare earths employed were either the same as those used previously%or of the same degrees of purity. With praseodymium (PR-43, 99% PreOrl), europium (EU-5, 92.7% EusO:, 6.7% SmrOt), and erbium (ER-1-2s, 98% ErtO:, 2% YpOs), materials of slightly different compositions were used. Approximately 0.1 M (0.02 M with europium) perchlorate solutions were prepared by treating slight excesses of the oxides with 72% perchloric acid, atering, and diluting to volume. Such solutions were standardized by the usual oxalate-oxide procedure. Carbonate-free sodium hydroxide solutions were standardized against potassium hydrogen phthalate. Titration Procedure.-Titrations were carried out at 25 i 0.5' exactly as previously described.* All solutions were stirred with nitrogen to minimize carbon dioxide interference. Measurements of PH were made immediately after each addition of alkali and at three-minute intervals until constant values were obtained.
Results Numerical data characterizing these titrations are summarized in Table I. It is apparent that TABLE I ELECTROMETRIC TITRATION DATAFOR PERCHLORATE SOLUTIONS
Ion
La+++ Pr+++ Nd+++ Sm+++ ELI+++ Gd+++ y+++ Er+++ yb+++
LU+++
Precipitation pH At preAt Average solubility cipitation OH-/ product incidence R + + + = 0.4 constant
8.10 7.40 7.30 7.13 6.91 6.84 6.81 6.61 6.45 6.45
8.18 7.43 7.34 7.17 6.99 6.90 6.88 6.68 6.55 6.55
1.7 x 6.7 X 3.2 x 8.4 x 0.9 x 1.8, x 1.6 x
10-19 10-22 10-22
x x
10-24 10-2'
10-23
10-25
10-48 10-23
4.1 x 10-24 2.5 1.9
Average water solubility (X 1 y mole/liter
8.8 2.2 1.9 1.3 0.8 .9 .9 .6 .5 .5
data for perchlorate solutions are closely comparable with those already reported2 for nitrate solutions. The differences in basicity between ions of adjacent elements are somewhat better defined, Observations on the Rare Earths. LXI. Pre- and the well-known excessively high basicity of cipitation of Hydrous Oxides or Hydroxides from the lanthanum ion is somewhat more apparent for perchlorate solutions. In addition the prePerchlorate Solutions1 cipitation ranges for all of the cations were found BY THERALD MOELLERAND NORMAN FOGEL to embrace smaller PH intervals than with the The utilities of data obtained from electrometric nitrate solutions. The apparently anomalous betitrations of salt solutions with alkalies in establish- havior of praseodymium shown in previous studies2 ing the relative basicities of the tripositive rare was also resolved, and the titration curve for praseoearth metal ions are well known.21a Both precipi- dymium perchlorate lay close to and above that tation PH values and solubility product constants for the neodymium salt and uniformly considerably calculated for the hydrous hydroxides indicate below that for the lanthanum salt. Use of a more basicity decreases paralleling decreases in ionic nearly pure praseodymium sample doubtless acradii, but there are sufficient differences among counts for the difference. Titration data for perchlorate solutions support data for nitrate, chloride, sulfate and acefate solutions of comparable concentrationsa to suggest the theoretical basicity order for these cations and that cation-anion interactions are of some im- place yttrium in its logical place between gadolinportance. Although such interactions would prob- ium and erbium. That precipitation was complete ably be of least consequence in nitrate solutions, in all cases a t OH-:R+++ mole ratios of 2.60it was deemed advisable to carry out parallel 2.75 suggests basic salt formation to be a t a minimum in perchlorate solutions. (1) For the preceding communication in this series, see T. Moeller and F. A. J. Moss, T ~ l JOURNAL, s 18, 3149 (1961). Noms CHEMICAL LABORATORY RECEIVED MARCH1, 1951
(2) T.Moella and H. E. Kremers. J . Phys. Cham.. 48, 395 (1944). (3) T . Moellc w d 8. 8. K:erpps, Chcm. &us., 37, 97 (1945).
UNIVERSITY OF ILLINOIS ILLINOIS URB~NA ,
RECEIVE^ APRIL 23, 1951
