Article pubs.acs.org/jced
Solubility of Tellurites of Rare Earth Elements Lubka G. Atanasova*,† and Ginka N. Baikusheva-Dimitrova‡ †
Inorganic Chemical Technology Department, University “Prof. Dr. Asen Zlatarov”-Burgas, Prof. Yakimov str. 1, Burgas 8010, Bulgaria ‡ Inorganic and Analytic Chemistry Department, University “Prof. Dr. Asen Zlatarov”-Burgas, Prof. Yakimov str. 1, Burgas 8010, Bulgaria ABSTRACT: The solubility product is an important value characterizing the properties of slightly soluble compounds and is widely used in chemistry practices. It is a special case of the equilibrium constant for reactions of solid substance solution, which allows calculating a number of other thermodynamic parameters of the process. The present paper studies for the first time the effect of solution acidity in hydrochloric and perchloric acids on the solubility product of the following tellurites of rare earth elements: La2(TeO3)3, Y2(TeO3)3, and Sc2(TeO3)3. It is proven that the solubility product and the solubility itself of La2(TeO3)3 have higher values, followed by Sc2(TeO3)3 and Y2(TeO3)3. The values of the La2(TeO3)3 solubility product are closer to those of tellurites of the lanthanides Ce, Pr, and Nd compared to those of Y2(TeO3)3 and Sc2(TeO3)3. The close values indicate that they are analogues to the IIIb group of the Periodic Table.
2. EXPERIMENTAL SECTION The metal tellurites La2(TeO3)3, Y2(TeO3)3, Sc2(TeO3)3, Ce2(TeO3)3, Pr2(TeO3)3, and Nd2(TeO3)3 are synthesized from TeO2, oxides of rare earth elements La2O3, Y2O3, and Sc2O3, and oxides of lanthanides Ce2O3, Pr2O3, and Nd2O3 of high purity (99.999 %) using a high vacuum ampule synthesis in the solid state. Stoichiometric quantities of the initial ingredients are well-homogenized and heated to a temperature 50 degrees lower than the melting temperature of the initial oxides and the tellurites to be obtained. The compositions of the metal tellurites of the elements studied are determined by chemical analysis while their purity was determined by X-ray analysis. The chemical analysis involved complexonometric determination of the metal component8 and gravimetric for the tellurite ion.9 For higher precision, three measurements were made for every tellurite, and the results were used to calculate the mass percent content of metal oxides and tellurium dioxide in the corresponding tellurite. The data obtained were averaged. The results obtained from the chemical analyses of the compounds studied were compared to the theoretically calculated content in the corresponding tellurite. The absolute and relative errors were determined. The absolute error is the difference between the mass percent content obtained experimentally μexp and the corresponding theoretically calculated values μT: Δμ = |μexp − μT | (1)
1. INTRODUCTION Recently, with the development of high technology and the search for new materials with practically interesting properties, the tellurites of rare earth elements attract increased attention. Three main application fields can be outlined. The first one is related to their use in glass and ceramics industries; the second one is pharmaceutics and the third, agriculture. There are a number of authors carrying out studies on various properties of rare earth tellurites and their applications. Gospodinov and Baikusheva-Dimitrova1 studied the structure and thermodynamics of rare earth tellurites from the cerium group. The authors synthesized and characterized these compounds using chemical, X-ray structural, and thermal analyses to determine the melting temperature and the changes of enthalpy and entropy for the phase transition during melting. Furthermore, the temperatures and the changes of enthalpies and entropies of the phase transitions of rare earth tellurites from the yttrium group were studied.2 The authors3−5 analyzed some optical properties of rare earth tellurites. It can be seen from the literary survey that there are no publications on studies on the solubility product and the solubility of the tellurites of rare earth elements. There are data on solubility product and solubility of selenites and the other compounds published.6,7 The aim of the studies reported in the present paper is to determine the effect of solution acidity in solutions of hydrochloric and perchloric acids on the solubility product and solubility of tellurites of rare earth elements: La2(TeO3)3, Y2(TeO3)3, Sc2(TeO3)3, and tellurites of the lanthanides: Ce2(TeO3)3, Pr2(TeO3)3, Nd2(TeO3)3, as well as a comparison of the results obtained. © XXXX American Chemical Society
The relative error was calculated by the formula:
ε = Δμ/μT ·100 %
(2)
Received: January 17, 2012 Accepted: May 31, 2012
A
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The results obtained are presented in Tables 1 and 2. The coincidence between the values determined by chemical
Table 3. Experimental Data on the Concentration of the Metal Ions in HCl and HClO4, pH, and Solubility Product at Temperature of 25 °C
Table 1. Chemical Analysis of the Metal Oxides of the Tellurites of the Type Ln2(TeO3)3
CMe3+ in HCl compound
theoretically calculated, determined by chemical analysis, mass % mass % metal oxide
La2(TeO3)3 Y2(TeO3)3 Sc2(TeO3)3 Ce2(TeO3)3 Nd2(TeO3)3 Pr2(TeO3)3
average value
metal oxide
compound
μT/%
1
2
3
μEXP/%
Δμ
ε/%
Sc2(TeO3)3 Y2(TeO3)3 La2(TeO3)3 Ce2(TeO3)3 Pr2(TeO3)3 Nd2(TeO3)3
22.36 32.04 40.49 40.67 40.79 41.27
22.4 32.13 40.53 40.6 40.81 41.25
22.23 32.11 40.44 40.66 40.77 41.28
22.37 32.06 40.49 40.68 40.8 41.27
22.33 32.1 40.486 40.65 40.793 41.267
0.07 0.06 0.003 0.02 0.003 0.003
0.3 0.2 0.01 0.06 0.01 0.01
mol·kg
−1
−4
2.6·10 5.1·10−5 9.2·10−5 2.39·10−3 2.11·10−3 2.30·10−3
CMe3+ in HClO4
K0s pH 2.05 2.10 1.89 1.50 1.50 1.51
−1 5
(mol·kg )
−38
2.59·10 2.88·10−41 3.90·10−41 2.40·10−37 1.30·10−37 2.00·10−37
mol·kg
−1
−3
1.4·10 9.2·10−5 2.4·10−4 3.6·10−4 3.21·10−4 3.92·10−4
K0s pH
(mol·kg−1)5
1.50 1.84 1.54 2.05 2.18 2.10
1.69·10−38 1.16·10−41 9.45·10−42 2.30·10−37 1.20·10−37 1.50·10−37
Table 2. Chemical Analysis of Tellurium Dioxide for the Tellurites of the Type Ln2(TeO3)3 theoretically calculated, determined by chemical analysis, mass % mass % tellurium dioxide
tellurium dioxide
average value
compound
μT/%
1
2
3
μEXP/%
Δμ
ε/%
Sc2(TeO3)3 Y2(TeO3)3 La2(TeO3)3 Ce2(TeO3)3 Pr2(TeO3)3 Nd2(TeO3)3
77.64 67.96 59.51 59.33 59.21 58.73
77.7 68.6 59.49 59.3 59.2 58.77
77.62 67.95 59.53 59.41 59.19 58.74
77.64 67.92 59.57 59.35 59.25 58.7
77.65 68.16 59.53 59.35 59.21 58.74
0.01 0.19 0.02 0.02 0.003 0.007
0.02 0.28 0.03 0.04 0.006 0.01
Figure 1. Comparison between the solubility products log(K0s / (mol·kg−1)5) of La2(TeO3)3, Y2(TeO3)3, and Sc2(TeO3)3 in hydrochloric acid at different solution pH values and 25 °C. ■, La2(TeO3)3; ◆, Y2(TeO3)3; ▲, Sc2(TeO3)3.
analyses and theoretically calculated ones was found to be very good. All of the reflections registered by the X-ray phase analysis were referred to pure phases of the corresponding tellurites. Peaks for the initial compounds and impurities were not observed. The results from the X-ray studies of the compounds synthesized have been presented by the author in another publication.10 The X-ray phase studies are carried out on URD-6 apparatus (Germany) under a regime of diffractometric recording and Cu-cathode Kα radiation with the Ni-filter for the β-radiation.
Figure 2. Comparison between the solubility products log(K0s / (mol·kg−1)5) of La2(TeO3)3, Y2(TeO3)3, and Sc2(TeO3)3 in perchloric acid at different solution pH values and 25 °C. ■, La2(TeO3)3; ◆, Y2(TeO3)3; ▲, Sc2(TeO3)3.
The solubility of precipitates of low solubility products, such as La 2 (TeO 3 ) 3 , Y 2 (TeO 3 ) 3 , Sc 2 (TeO 3 ) 3 , Ce 2 (TeO 3 ) 3 , Pr2(TeO3)3, and Nd2(TeO3)3, can be reliably determined only in acidic medium where the values of the degree of dissociation and the concentrations of metal ion compounds are high enough to be determined analytically.12 The cations of La, Y, Sc, Ce, Pr, and Nd do not form hydrocomplexes in acidic media.13 To determine the solubility of La2(TeO3)3,Y2(TeO3)3, Sc2(TeO3), Ce2(TeO3)3, Pr2(TeO3)3, and Nd2(TeO3)3, their saturated solutions in diluted mineral acids, 0.1 M hydrochloric (HCl) and 0.1 M perchloric (HClO4), are used. The metal ions of the compounds and the solvent anion should not form complexes. There are no data in the literature on the existence of perchlorate complexes of lanthanum, scandium, yttrium, cerium, praseodymium, and neodymium, and the stability constant of the chloride complex of lanthanum is comparatively low (pK1 = −0.15).14 Besides, the solvent should be properly selected with regards to the spectrophotometric determination of the metal ion concentrations in the solution.14 The colored reagents used in the
3. CALCULATION PROCEDURE It has been reported in the literature11 that the tellurites of lanthanum, scandium, yttrium, cerium, praseodymium and neodymium are slightly soluble compounds and their solubility products which are important values for both theory and practical purposes are unknown. The present work suggests a semiempirical method for determination of solubility (S/mol·kg−1) and solubility product (K0s /(mol·kg−1)5) of the slightly soluble tellurites: La2(TeO3)3, Y 2 (TeO 3 ) 3 , Sc 2 (TeO 3 ) 3 , Ce 2 (TeO 3 ) 3 , Pr 2 (TeO 3 ) 3 , and Nd2(TeO3)3. It is well-known that the following equilibrium exists in saturated solutions of the tellurites studied:11 Me2(TeO3)3 ⇔ 2Me3 + + 3TeO32 −
(3) B
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concentrations of the cations and anions of the compound studied in the solution. The concentration of [TeO32−] can be expressed stoichiometrically using the concentration of [Me3+]: [TeO32 −] = 1.5[Me3 +]
(5)
The ionic powers of the solutions μ were calculated according to the Debye−Hückel equation:11 μ = 0.5 ∑ Zi 2·Ci
Figure 3. Comparison between the solubility log(S/mol·kg−1) of La2(TeO3)3, Y2(TeO3)3, and Sc2(TeO3)3 in hydrochloric acid at different solution pH values and 25 °C. ■, La2(TeO3)3; ◆, Y2(TeO3)3; ▲, Sc2(TeO3)3.
(6)
i
where Zi is the charge of each ion in the solution; Ci/mol·kg−1 is the concentration of each ion in the solution (Table 3). The activity coefficients were calculated according to the extended equation of Debye−Hückel:11 log f± = − 0.512ZA ·Z B· μ /(1 + 0.328a · μ )
where ZA and ZB are charges of the metal and tellurite ion, respectively; a is an empirical parameter which, to a first approximation, can be assumed to account for the size of the solvated ions in angstroms. When determining the solubility of slightly soluble compounds, it is necessary to take into account the possibility of the occurrence of side reactions due to the complex-forming interactions of the metal cation from the precipitate. In analytical practice, the coefficients α are known as the measure of side reactions, and the value used to calculate the solubility is called the solubility product, Ks01, given by the expression:
Figure 4. Comparison between the solubility log(S/mol·kg−1) of La2(TeO3)3, Y2(TeO3)3, and Sc2(TeO3)3 in perchloric acid at different solution pH values and 25 °C. ■, La2(TeO3)3; ◆, Y2(TeO3)3; ▲, Sc2(TeO3)3.
spectrophotometric method should form a stable complex with the metals studied in acidic medium. The color reagent used was Arsenazo III, and the acidic media was created with HCl and HClO4. Taking into account eq 3 for the solubility product, we obtain: K s0 = [Me3 +]2 · [TeO32 −]3 · (fMe3+ )2 · (fTeO 2− )3 3
(7)
3 2 K s01 = K s0·αMe 3 +· α TeO 2 −·(H O)+ 3
(8)
3
α, the coefficient for the metal ion, is assumed to be unity since, as described above, complexes between metal ions and solvent anions (HCl or HClO4) are not practically formed. The αcoefficient of the tellurite ion accounts only for its protonation, and it can be regarded as the conjugated base of the weak telluric acid with power constants of acidity (Ka1 = 2·10−8 and Ka2 = 3·10−3).11,14
(4)
where f is the activity coefficient of the corresponding ions in the saturated solution; [Me3+] and [TeO32−] are the
Table 4. Solubility Products log(K0s /(mol·kg−1)5) and Solubility log(S/mol·kg−1) of La2(TeO3)3, Y2(TeO3)3, and Sc2(TeO3)3 in Hydrochloric Acid at Different Solution pH Values at 25 °C log(K0s /(mol·kg−1)5)
log(S/mol·kg−1)
pH
La2(TeO3)3
Y2(TeO3)3
Sc2(TeO3)3
La2(TeO3)3
Y2(TeO3)3
Sc2(TeO3)3
1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3.0
−41.35 −40.58 −39.82 −39.08 −38.35 −37.64 −36.94 −36.26 −35.58 −34.92 −34.27 −33.62 −32.98 −32.35 −31.72 −31.10
−44.55 −43.85 −43.10 −42.36 −41.64 −40.92 −40.21 −39.51 −38.82 −38.14 −37.46 −36.80 −36.14 −35.50 −34.85 −34.22
−43.32 −42.57 −41.83 −41.10 −40.37 −39.66 −38.96 −38.26 −37.58 −36.91 −36.24 −35.59 −34.94 −34.30 −33.66 −33.03
−16.61 −16.35 −16.11 −15.86 −15.63 −15.39 −15.16 −14.94 −14.72 −14.50 −14.28 −14.07 −13.86 −13.65 −13.44 −13.23
−18.26 −18.04 −17.80 −17.56 −17.32 −17.08 −16.85 −16.62 −16.39 −16.17 −15.95 −15.73 −15.51 −15.30 −15.08 −14.87
−17.65 −17.40 −17.16 −16.92 −16.68 −16.45 −16.22 −15.99 −15.77 −15.55 −15.33 −15.11 −14.89 −14.68 −14.47 −14.26
C
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Table 5. Solubility Products log(K0s /(mol·kg−1)5) and Solubility log(S/mol·kg−1) of La2(TeO3)3, Y2(TeO3)3, and Sc2(TeO3)3 in Perchloric Acid at Different Solution pH Values at 25 °C log(K0s /(mol·kg−1)5)
log(S/mol·kg−1)
pH
La2(TeO3)3
Y2(TeO3)3
Sc2(TeO3)3
La2(TeO3)3
Y2(TeO3)3
Sc2(TeO3)3
1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3.0
−37.75 −37.06 −36.38 −35.72 −35.06 −34.41 −33.76 −33.13 −32.50 −31.88 −31.26 −30.64 −30.03 −29.42 −28.81 −28.21
−43.35 −42.59 −41.84 −41.11 −40.38 −39.67 −38.97 −38.27 −37.59 −36.92 −36.25 −35.59 −34.94 −34.30 −33.66 −33.00
−41.30 −4055 −39.82 −39.10 −38.39 −37.69 −37.01 −36.33 −35.66 −35.00 −34.35 −33.71 −33.08 −32.45 −31.82 −31.20
−14.80 −14.57 −14.35 −14.12 −13.91 −13.69 −13.48 −13.27 −13.06 −12.85 −12.65 −12.44 −12.24 −12.04 −11.83 −11.63
−17.66 −17.41 −17.17 −16.93 −16.69 −16.45 −16.22 −15.99 −15.77 15.55 −15.33 −15.11 −14.90 −14.68 −14.47 −14.26
−16.62 −16.38 −16.14 −15.91 −15.67 −15.44 −15.22 −14.99 −14.77 −14.56 −14.34 −14.13 −13.92 −13.71 −13.50 −13.30
Figure 5. Comparison between the solubility products log(K0s / (mol·kg −1 ) 5 ) of La 2 (TeO 3 ) 3 , Y 2 (TeO 3 ) 3 , Sc 2 (TeO 3 ) 3 and Ce2(TeO3)3, Pr2(TeO3)3, Nd2(TeO3)3 in hydrochloric acid at different solution pH values and 25 °C. ■, La2(TeO3)3; ◆, Y2(TeO3)3; ▲, Sc2(TeO3)3; ●, Nd2(TeO3)3; thin line, Ce2(TeO3)3; thick line, Pr2(TeO3)3.
Figure 7. Comparison between the solubility products log(K0s / (mol·kg −1 ) 5 ) of La 2 (TeO 3 ) 3 , Y 2 (TeO 3 ) 3 , Sc 2 (TeO 3 ) 3 and Ce2(TeO3)3, Pr2(TeO3)3, Nd2(TeO3)3 in perchloric acid at different solution pH values and 25 °C. ■, La2(TeO3)3; ◆, Y2(TeO3)3; ▲, Sc2(TeO3)3; ●, Nd2(TeO3)3; thin line, Ce2(TeO3)3; thick line, Pr2(TeO3)3.
Figure 6. Comparison between the solubilities log(S/mol·kg−1) of La2(TeO3)3, Y2(TeO3)3, Sc2(TeO3)3 and Ce2(TeO3)3, Pr2(TeO3)3, Nd2(TeO3)3 in hydrochloric acid at different solution pH values and 25 °C. ■, La2(TeO3)3; ◆, Y 2(TeO 3)3; ▲, Sc2(TeO3)3; ●, Nd2(TeO3)3; thin line, Ce2(TeO3)3; thick line, Pr2(TeO3)3.
Figure 8. Comparison between the solubilities log(S/mol·kg−1) of La2(TeO3)3, Y2(TeO3)3, Sc2(TeO3)3 and Ce2(TeO3)3, Pr2(TeO3)3, Nd2(TeO3)3 in perchloric acid at different solution pH values and 25 °C. ■, La2(TeO3)3; ◆, Y2(TeO3)3; ▲, Sc2(TeO3)3; ●, Nd2(TeO3)3; thin line, Ce2(TeO3)3; thick line, Pr2(TeO3)3.
2 +)/(K · K ) αTeO32−·(H3O)+ = 1 + (α(H3O)+)/(K a2) + (α(H a 2 a1 3O)
The mole solubility (S) of Me2(TeO3)3 in acidic medium is determined by the expression:11,12
(9)
Based on eqs 3 to 9, the following expression was derived for the solubility product of the slightly soluble tellurites of the type Me2(TeO3)3: 2 3 3 2 K s0 = (27/8[Me3 +]5 ·f Me )/(αMe ) 3+ ·f 3 +· α TeO 2 − TeO 2 − 3
3
S=
K s0 ·αA /(f± )
(11)
where αA is the subsidiary function and is determined by the expression:11 αA = 1 + [H+]/K a2 + [H+]2 /(K a1·K a2)
(10) D
(12)
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Table 6. Solubility Products log(K0s /(mol·kg−1)5) and Solubility log(S/mol·kg−1) of Ce2(TeO3)3, Pr2(TeO3)3, and Nd2(TeO3)3 in Hydrochloric Acid at Different Solution pH Values at 25 °C log(K0s /(mol·kg−1)5)
log(S/mol·kg−1)
pH
Ce2(TeO3)3
Pr2(TeO3)3
Nd2(TeO3)3
Ce2(TeO3)3
Pr2(TeO3)3
Nd2(TeO3)3
1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3.0
−36.63 −35.96 −35.31 −34.67 −34.03 −33.40 −32.77 −32.15 −31.53 −30.92 −30.31 −29.70 −29.09 −28.49 −27.88 −27.28
−36.70 −36.04 −35.38 −34.74 −34.10 −33.46 −32.84 −32.22 −31.60 −30.98 −30.37 −29.76 −29.16 −28.55 −27.94 −27.34
−36.86 −36.20 −35.54 −34.89 −34.25 −33.61 −32.98 −32.36 −31.74 −31.13 −30.51 −29.90 −29.30 −28.69 −28.08 −27.48
−14.23 −14.01 −13.79 −13.58 −13.37 −13.16 −12.95 −12.74 −12.54 −12.33 −12.13 −11.93 −11.72 −11.52 −11.32 −11.12
−14.26 −14.04 −13.83 −13.62 −13.40 −13.19 −12.99 −12.78 −12.57 −12.37 −12.17 −11.96 −11.76 −11.56 −11.36 −11.16
−14.35 −14.13 −13.91 −13.70 −13.49 −13.28 −13.07 −12.86 −12.66 −12.45 −12.25 −12.04 −11.84 −11.64 −11.44 −11.24
Table 7. Solubility Products log(K0s /(mol·kg−1)5) and Solubility log(S/mol·kg−1) of Ce2(TeO3)3, Pr2(TeO3)3, and Nd2(TeO3)3 in Perchloric Acid at Different Solution pH Values at 25 °C log(K0s /(mol·kg−1)5)
log(S/mol·kg−1)
pH
Ce2(TeO3)3
Pr2(TeO3)3
Nd2(TeO3)3
Ce2(TeO3)3
Pr2(TeO3)3
Nd2(TeO3)3
1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3.0
−40.29 −39.58 −38.87 −38.17 −37.48 −36.81 −36.14 −35.47 −34.82 −34.18 −33.54 −32.91 −32.28 −31.66 −31.04 −30.42
−39.99 −39.29 −38.60 −37.91 −37.24 −36.56 −35.90 −35.25 −34.60 −33.96 −33.33 −32.70 −32.08 −31.46 −30.84 −30.23
−40.57 −39.85 −39.13 −38.43 −37.74 −37.05 −36.38 −35.71 −35.06 −34.41 −33.77 −33.13 −32.50 −31.88 −31.26 −30.64
−16.15 −15.91 −15.68 −15.45 −15.22 −15.00 −14.78 −14.56 −14.35 −14.13 −13.92 −13.71 −13.50 −13.30 −13.09 −12.89
−16.02 −15.79 −15.56 −15.34 −15.11 −14.89 −14.67 −14.46 −14.24 −14.03 −13.82 −13.61 −13.41 −13.20 −13.00 −12.79
−16.28 −16.04 −15.81 −15.58 −15.35 −15.13 −14.90 −14.68 −14.47 −14.25 −14.04 −13.83 −13.62 −13.41 −13.21 −13.00
4. RESULTS AND DISCUSSION
The results obtained for Ce2(TeO3)3, Pr2(TeO3)3, and Nd2(TeO3)3 are presented in Figures 5 to 8 and Tables 6 and 7. The solubility products of Ce2(TeO3)3, Pr2(TeO3)3, and Nd2(TeO3)3, as well as their solubilities, coincided in the same straight line. This is due to the fact that they are of the same periodic group as cerium. The same figures show also the comparison between the solubility products and the solubilities of these tellurites and La2(TeO3)3, Y2(TeO3)3, and Sc2(TeO3)3. As can be seen, the values of the solubility product and solubility of La2(TeO3)3 are closer to these of the lanthanides Ce, Pr, and Nd compared to those of Y2(TeO3)3 and Sc2(TeO3)3. The close values indicate that they are analogues of the group IIIb. The studies carried out and the results obtained on the solubility product and solubility on the tellurites of rare earth elements can be used to fill in missing data in an important field of inorganic chemistry which is the chemistry of tellurium. The semiempirical method suggested for the determination of the
Using the method described above, the solubility products and solubilities of La 2 (TeO 3 ) 3 , Y 2 (TeO 3 ) 3 , Sc 2 (TeO 3 ) 3 , Ce2(TeO3)3, Pr2(TeO3)3, and Nd2(TeO3)3 in hydrochloric and perchloric acids were calculated at different solution acidities (pH from 1.5 to 3.0). The results obtained for La2(TeO3)3, Y2(TeO3)3, and Sc2(TeO3)3 are presented in Figures 1 to 4 and Tables 4 and 5. The calculated values coincide with the experimentally determined ones shown in Table 3. The solubility product and solubility of these three tellurites increased with the increase of pH in both hydrochloric and perchloric acids. Comparing the values of solubility product and solubility of La2(TeO3)3, Y2(TeO3)3, and Sc2(TeO3)3, at the same pH of the acidic solution, it can be seen that they are higher with perchloric acid. In both hydrochloric and perchloric acids, the highest solubility product and solubility has La2(TeO3)3 followed by Sc2(TeO3)3 and Y2(TeO3)3. E
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(10) Baikusheva-Dimitrova, G. Investigation on the content of the rare earth tellurites. Proceedings of the International Science Conference, Stara Zagora, Bulgaria, Trakia University, June 4-5, 2009; pp 49−53. (11) Encyclopedia of Analytical Chemistry; John Wiley & Sons: New York, 2010. (12) Douglas, A.; Donald, W.; James, H. Fundamentals of Analytical Chemistry; Brooks Cole: New York, 2003. (13) Gospodinov, G.; Stamov, S.; Baikusheva-Dimitrova, G. Solubility product of III B Group metal tellurites. Bulg. Chem. Ind. 1999, 70, 91−93. (14) Lurie, U. Manual in Analytical Chemistry; Khimiya: Moscow, 1971.
solubility product of tellurites of rare earth elements can be used in studies on other compounds.
5. CONCLUSION The effect of solution acidity on the solubility product and solubility of tellurites of rare earth elements La2(TeO3)3, Y2(TeO3)3, and Sc2(TeO3)3 and lanthanides Ce2(TeO3)3, Pr2(TeO3)3, and Nd2(TeO3)3 was determined in solutions of hydrochloric and perchloric acids. The results obtained were compared. The solubility products and solubilities of the tellurites studied were found to increase with the increase of solution pH in both hydrochloric and perchloric acids. Comparing the values of solubility product and solubility for La2(TeO3)3, Y2(TeO3)3, and Sc2(TeO3)3 at the same pH of the acidic solution, they were found to be higher in solutions of perchloric acid. In both hydrochloric and perchloric acid, the highest values of solubility product and solubility had La2(TeO3)3 followed by Sc2(TeO3)3 and Y2(TeO3)3. The solubility product values for Ce2(TeO3)3, Pr2(TeO3)3, and Nd2(TeO3)3 are very close to each other and almost coincide in a straight line. The same was observed for the solubilities of these tellurites. The solubility products and solubilities of Ce2(TeO3)3, Pr2(TeO3)3, and Nd2(TeO3)3 were compared to these of La2(TeO3)3, Y2(TeO3)3, and Sc2(TeO3)3. The values of solubility product and solubility of La2(TeO3)3 were closer to these of Ce2(TeO3)3, Pr2(TeO3)3, and Nd2(TeO3)3. The close values indicate that they are analogues of the group IIIb of the Periodic Table.
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[email protected] (L.A.). Notes
The authors declare no competing financial interest.
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REFERENCES
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dx.doi.org/10.1021/je300079v | J. Chem. Eng. Data XXXX, XXX, XXX−XXX
