compiexing strength to the copper(I1) a t the acidic pH of this titration. If the ratio of ytterbium or lutetium to scandium exceeds 1, niore copper(I1) than usual should be added to obtain a titration curre n-ith a favorable slope. However, the curve also becomes more V-shaped with additional copper(I1) (Figure 41. This is because copper(I1) absorbs at the same wave length as coppw(I1)-EDTA. Khile the original absorbance is blocked out b y the initial instrument setting, dilution occurs during the formation of the nonabsorbing scandium-EDTA complex causing a decrease in copper(I1) absorbance.
Figure 4. Effect of additional copper(l1) on titration curve 1.
2.
1 : 1 Yb to Sc ratio with 4 ml. of Cu(NO& os indicator 10 : 1 Yb to Sc ratio with 1 1 ml. of Cu(NOslz os indicator
DATA AND INTERFERENCES
Data for titration of individual synthetic scandium samples are presented in Table I. The accuracy with n-hich scandium can be titrated is limited somen-hat by the necessity for graphical location of the end point; i t also depends on the quantity and type of foreign cations present. The average error for all titrations reported is h0.5%. The principal interfering cations arc bisinuth(III), thorium(IV), hafnium, and zirconium(1T’). However, the sum of scandium and tl orium can be detcrmined by this method and it may also be possible to titrai e bismuth quantitatively (12). Slow quilibrium prevents accurate analysis TT lien hafnium and/or zirconium are prwent. The tolerance for iron is limited 3ecause some oxidation of iron(I1) occurs in adjusting the pH and during the titration. Ascorbic acid prevents this oxidation but Fill interfere in the titration unless the concentration is lie it low. lip to 0.1M sod urn acetate, chloroacetate, nitrate, chloride, or perchlorate mas added m-ithoui interference. Sulfate (0.1M) interfues, as does fluoride.
ml. EDTA
Table 1.
Titration of Scandium in Presence of Other Metal Ions Theory MetalMetalTheory Metal Scandium EDTA, EDTA. ?*letal Scandium EDT.1, EDTA, Rl! hli. Ratio Ratio JII. Present MI. Present 4: 1 4 . 71 4 (i!J 3.65 3.67 Ln ... 10: 1 4.70 ... 4.60 Lu 1: 1 Fe(I1 5.41 5.40 il 5 :1 ... 9.72 0.72 20: 1 -11 16: 1 5.51 5.51 Y 4.66 4.69 33: 1 5.50 5.51 40: 1 .\1 Y 4.66 4.69 A1 47: 1 5.56 5.51 Y 60: 1 4.68 4.69 20: 1 4.3ti 4.32 La 4.66 CO 20: 1 4.69 40: 1 4 65 4.69 20: 1 co Ce(II1) 4.68 4.69 ‘0: 1 4 32 4.3‘1 40: 1 Ctl 4.74 4.69 Ce(111) 4.66 4.69 Pr 3: 1 5.50 40: 1 Cd 5.51 4.22 4 32 16: 1 5.52 20: 1 Pr Zn 5.51 40: 1 4.64 4.ti!i 33: 1 5.50 5.51 Zn Pr 15:l 4.70 4.Li!l 47: 1 ..49 i 5.51 Pba Pr 4.77 4.69 Nib 1:l 4.72 4.69 Nd 40: 1 4 66 4.69 47: 1 L1n 10: 1 .5.48 5.51 Sm “0: 1 4.31 4 32 5.53 UO:(II 5: 1 5.51 4.21 4.32 16: I 10: 1 5.53 5.51 1:02( I1 I 33:1 7 3 :1 4.64 4.6!) 3.53 5.51 Dy UO*(II (io: 1 4.68 4.6:) 47: 1 F, . 5 2 5.51 Ca Dy 60 : 1 1:l 5.42 4.68 4.6!) Yb 5.40 R k 4.66 4.69 4.32 Yb 4: 1 4.32 Generalr 4.68 4 ti9 10: 1 4.35 4.32 Generalc Yb 1: 1 4.74 4.69 Lu a For higher ratio, increase Cu concentration. * Interferes in higher rntios. e Mixture of all metals escept Fe(II1) and S i : i i i I : 1 i : i t i o of each rnr+il to :TcI ml. Cu(N03)?as indicator.
.
:; LITERATLIRE CITED
Bjerrrini, J., Schrvarzenbach, G., Sillen, I,. G., “Sta ility Constants, Part, I, Organic Ligaad 3 , ’ ’ pp. 56-8, Burlington House. London. 1957. ( 2 ) Cheng, I-dipropionitrile, used in the text beginning in the third column of page 11 and in Table 11, should have been written 3,3’oxydipropionitrile. VOL. 31, NO. 7,JULY 1959
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