N o tizen 1493 Solvent Deuterium Isotope Effect on Hydrolysis
of Nd3+ Ion
Ma s t jn o b u Ma e d a*, To sh ih ik o Am a y a, and Hid e t a k e Ka k ih a n a
*Department of Applid Chemistry, N agoya In stitu te of Technology, Gokiso, Showa-ku, Nagoya 466, Japan Research Laboratory for Nuclear Reactors,
Tokyo In stitute of Technology, O-okayama, Meguro-ku, Tokyo 152, Japan (Z. Naturforsch. 32 b, 1493-1495 [1977]; received August 30, 1977)
Deuterium Isotope Effect, Formation Constant, H eavy W ater, Hydrolysis, Neodymium Ion
The hydrolysis equilibria of N d3+ ion in light- and heavy-water solutions containing 3 mol dm-3 (Li)C104 as an ionic medium were studied at 25 °C by measuring the lyonium- ion concentration with a glass electrode.
Analysis o f the em f data indicated the forma
tion o f only the mononuclear com plex Nd(OL)2+ in both light and heavy water. The form ation constant was smaller in D2O (log */?2,i = -— 16.54 ± 0.04) than in H2O (log *ß2,i = — 15.90 ± 0.06). The formation constant K<z,\ for the heavy-water system (log i?2,i = 12.28) had a larger value than th at for the light-water system (log K%t1 =
1 1 . 8 6 ).
Introduction
As was reported in previous papers1-7, the authors studied the hydrolytic reactions of various metal ions in both light and heavy water. The composi
tions of complexes formed by hydrolysis in heavy water were found to be analogous to those in light water, and the formation constant */?P,q of the complexes in D2O were smaller than those in H2O.
In a previous w ork7 the authors measured the ionic product of D2O containing 3 mol dm-3 LiC104 and examined th e deuterium isotope effect on formation constants i£p,q for hydrolysis species of boric acid.
I t was found th a t the K v<ri values in heavy water were slightly larger than those in light water. The deuterium isotope effect on i£P,q values for other hydrolysis species was not reported.
In the present work, potentiometric measure
ments of the hydrolysis of N d3+ ion were carried out in heavy w ater as well as in light water in order to elucidate the deuterium isotope effect. These experi
ments used 3 mol dm-3 (Li)C104 as an ionic medium, because the ionic product of D2O in this system is available7.
R equests for reprints should be sent to Dr. M . Ma e d a, D epartm ent of Applied Chemistry, Nagoya Institute of Technology, Gokiso, Showa-ku, Nagoya 466, Japan.
A neodymium perchlorate sample solution and other reagents used were prepared and analyzed according to the same procedures as those in the previous papers5-6.
All the apparatus employed were the same as those in Ref. 7.
Preparation of a test solution
A test solution was prepared as follows. A slightly acidic neodymium perchlorate solution, which had been freed from CO2 by passing purified N2 gas, was electrolyzed to reduce L+ ions by using a d. c. power supply until precipitates appeared. In order to saturate the solution with Nd(OL)3 precipi
tates the m ixture was stirred with a magnetic rod for two days. The precipitates of Nd(OL)3 were removed by filtration with G 4 glass filters. All the procedures were carried out under an atmosphere of N2 gas in a room kept a t 25 ± 1 °C.
Emf measurements
A test solution thus prepared, in which the total concentration of perchlorate ions was kept a t 3 mol dm-3 by addition of LiC10 4, was acidified in small steps by constant-current coulometry, and the lyonium-ion concentration was measured by means of a glass electrode8. The same cell assembly as described in Ref. 9 was used for emf measure
m ents and coulometric titrations.
All the measurements were performed a t 25,00 ± 0,02 °C in a parrafin oil therm ostat in a room therm ostated a t 25 ± 1 °C.
Results and Discussion
The values of Z (log d)s for the heavy-water system are graphically shown in Fig. 1.
Experimental R ea g en ts a n d a p p a r a tu s
Fig. 1. Average number, Z, of OD bound per N d 3+ as a function of log d. The drawn curve was calculated w ith the formation constant of log *ßz.i = — 16.54.
1494 N o tizen I t is seen th a t the plot is a function of only d and independent of B. The plot analogous to th a t in Fig. 1 was obtained in the light-w^ater system. This indicates th a t only mononuclear complexes are formed in both light and heavy water.
On the basis of these d ata the compositions and formation constants of the hydrolysis species were estim ated by graphical procedures. The concentra
tion of the lyonium ion set free by hydrolysis, BZ, is given by the following form,
BZ = 2 p *jffPlibl-P (1)
Since the values of Z do not exceed 0.02 in the solutions studied, the graphical calculations can be simplified by using the approxim ation b = B. Thus, equation (1) gives
Z = £ p * f t , , l - p (2)
According to Eq. (2), 1/2 Z l2 values were plotted as a function of — log 1. The data for the heavy water system are shown in Fig. 2. I t is apparent th a t 1/2 z d2 values are independent of d values, which means p = 2. The same result was obtained for the light water system. Thus, it is concluded th a t the hydrolysis species formed in light and heavy water is Nd(OL)2+. The formation constants read from the intercepts were — 16.54 ± 0 .0 4 (in D2O) and — 15.90 ± 0 .0 6 (in H2O) in log *ß unit.
The presence of the Nd(OH)2+ species was not reported previously. All the previous investiga
to rs10-12 found only N dO H 2+ as a mononuclear species. This complex was not detected in the present work, although its possibility was examined by a least squares m ethod with an electronic
Fig. 2. 1/2 Zd2 as a function of — log d. The straight line was calculated with the formation constant of
log *ß2.i = — 16.54.
computer. One possible explanation for this in consistency m ay be th at the maxium Z values reached in the present work is much larger th an those in the previous studies and th a t the low-Z region, where the NdOH2+ complex was probably formed, was not measured in the present work.
Bu r k o v et a l. 12 reported th a t the main hydrolytic reaction of N d3+ ion in 3 mol dm-3 (Na)C104 aqueous solution is the formation of the dimer N d2(OH)24+.
They titrated an acidic neodymium perchlorate solution with an alkali, and their maximum Z value did not exceed 0.005. The authors titrated a solution saturated with Nd(OH)3 precipitates with an acid and obtained the maximum Z value of 0.02. Such differences in experimental procedure m ight cause the inconsistency in composition of hydrolysis species, if the attainm ent of hydrolysis equilibria is slow.
The formation constant *ß2.i of the Nd(OL)2+ species in D2O was smaller than th a t in H2O. This trend is consistent with th a t for other m etal ion hydrolysis species1-7. The formation constants K 2,i wTere calculated using the *^2,1 values and the values of K w for H2O (pKw) = 13.88) and D2 0(pÜLW = 14.41)7.Theiip,q values for hydrolysis species of Y 3+
and lanthanoid ions were also calculated by use of the *ßp,q values in 3 mol dm-3 (Li)C104 solution reported previously5*6. The calculated ifp.q values are summarized in Table I. The K Pt(l values in the heavy water system are larger than those in the light water system. This means th a t there are some isotope effects in hydrolysis other th an th a t ascribed to the difference between the ionic products of light and heavy water.
Notation L: lyon, H or D,
d : concentration of the free deuterium ion,
1: concentration of the free lyonium ion, B : total concentration of N d3+,
b : concentration of free N d3+,
*/?p>q: formation constant for the reaction qM>+ + P L2O = Mq(OL)p(«i- pH -f- p L +, Zp,q formation constant for the reaction
qMz+ - f pO L- = Mq(OL)p(M-P)+,
Z = (1— L — K w/1)/B, the average num ber of lyonium ions split off per N d3+,
Kw: ionic product of water.
Table I. i£p,q values for hydrolysis of Y 3+ and lanthanoid ions in H2O and D2O containing 3 mol dm-3 (Li)C104-
Y 3+ La3+ N d 3+ Gd3+ Er3+
h2o d2o h2o d2o h2o d2o h2o d2o h2o d2o
log K \,\ - - 3.84 4.06 - - 5.68 6.07
log K 2,i 1 0.96 I I.82 - - 11 .8 6 12.28 - - 10.56 11.42
log-K:22 13.72 14.07 _______- __________ - ________- _________ - _________ 14.04 14.53 1 H. Ka k i h a n a and M . Ma e d a, Bull. Chem. Soc.
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