This work has been digitalized and published in 2013 by Verlag Zeitschrift für Naturforschung in cooperation with the Max Planck Society for the Advancement of Science under a Creative Commons Attribution 4.0 International License. Dieses Werk wurde im Jahr 2013 vom Verlag Zeitschrift für Naturforschung in Zusammenarbeit mit der Max-Planck-Gesellschaft zur Förderung der Wissenschaften e.V. digitalisiert und unter folgender Lizenz veröffentlicht: Creative Commons Namensnennung 4.0 Lizenz. BAND 24 b ZEITSCHRIFT FÜR NATURFORSCHUNG HEFT 7 Electrometric Studies on Thorium Arsenates as a Function of pH R. S. S axena and S hiva P rasad Department of Chemistry, Malaviya Regional Engineering College, Jaipur (India) (Z. Naturforschg. 24 b, 795—799 [1969] ; eingegangen am 24. Oktober 1968) The formation and composition of thorium arsenates obtained by the interaction of thorium nitrate and different alkali arsenates (meta, pyro and ortho) at specific pH levels 7.2, 8.3 and 11.1 have been studied by employing electrometric techniques involving amperometric, pH, potentio- metric and conductometric titrations. The results provide cogent evidence for the formation of three thorium arsenates having the molecular formulae ThO,-2 As20 5 , Th02-As20 5 and 3 T h 0 2-2A s20 5 in the vicinity of pH 4.2, 4.9 and 5.6 respectively. Analytical investigations of the compounds have also been carried out which substantiate the results of electrometric study. A survey of literature reveals that there are meagre references on the study of thorium ar senates. B arbieri 1 treated aq. arsenic acid (40%) with boiling solution of thorium nitrate ( 2% thoria) to get thorium mono hydrogen ortho arsenate Th (HAs04) 2• 6 HoO as a crystalline precipitate; whereas he obtained thorium-di-hydrogen ortho arsenate, Th(H 2 As04)4'4 H 2 0, by using 50 % of aq. arsenic acid and thorium nitrate solution containing 5% thoria. He further reported that more dilute solutions of reagents give gelatinous precipitates of variable composition. P ierre Castel 2 obtained crystals of Th(H 2 As0 4) 4 6 H20 and Th(HAs0 4) 2 • 5 H20 by mixing Th0 2 /As 2 0 5 in the ratios 0.05 to 0.14 and 1.63 —2.80, respectively. Gilles L e F lem, Jacques Lamic and P aul H agenmuller 3 prepared two allotropic form of Th(As0 3) 4 by tem perature treatment of mixtures of As 2 0 5 —T h 0 2 gel and arsenic acid. They observed that the products of heating the gel strongly were two forms of the pyro arsenate ThAs 2 0 7; the hexa arsenate Th 4 As 6 0 23 and the ortho arsenate Th 3 (As04) 4 . In view of the insufficient and conflicting reports of ealrier workers on the composition of thorium arsenates, and in the absence of any electrometric 1 B arbieri, Atti. Reale Accad. naz. Lincei 19, ii, 462 [1910], (5). 2 P ierre Castel, C. R. hebd. Seances Acad. Sei. 208, 37 [1939]. 3 Gilles Le F lem, J acques Lamic, and P aul H agen Muller (C.N.R.S., Bordeaux, France), Bull. Soc. chim. France 6, 188 [1966]. 4 R. S. S axena and M. L. Mittal, Z. physik. Chem. (N.F.) 34, 319 [1962]. 5 R. S. S axena and M. L. Mittal, J. inorg. nuclear Chem. 27,2553 [1965]. 6 R. S. S axena and G. P. S axena, Bull. chem. Soc. Japan 35,22 [1962]. 7 R. S. Saxena and G. P. S axena, Z. physik. Chem. (N.F.) 28, 220 [1961]. data on the subject, it was considered worthwhile to study the formation and composition of thorium ar senates obtained by the interaction of thorium ni trate and alkali arsenates at different pH levels, by means of electro-metric techniques which have pro vided more conclusive evidences on the composition of such and allied compounds 4~13. Experimental Merck’s guaranteed extra pure reagents, As2 05, Th(N03)4, NaOH and Quinhydrone were used. Air- free conductivity water was used in the preparation of solutions. A s 20 5 solution was further estimated as silver arsenate 14 and thorium as Th0 2 via its oxalate 14. Solu tions of different arsenates were prepared by adding calculated amounts of NaOH to boiling solution of As2 0 5 of the required strength. A manual polarograph with scalamp galvanometer as current recorder was employed for performing amperometric titrations. A capillary having the fol lowing characteristics, m = 2.416 mg/Sec, t = 3.58 sec, and m2/3 —2.226 mg2/3 esc-1 ^2 was used in conjunc tion with a saturated calomel electrode connected to the cell by a low resistance salt bidge. Twenty ml. of titre solution was taken in the cell each time and hydro gen was used for deaeration and stirring of solutions. Amperometric titrations were carried out at a potential 8 R. S. S axena and C. S. B hatnagar, J. inorg. nuclear Chem. 12,38 [1959]. 9 R. S. S axena and C. S. B hatnagar, Z. anorg. allg. Chem. 303, 12 [I960]. 10 R. S. S axena and C. M. Gupta, Z. Naturforschg. 13 b, 557 [1958]. 11 R. S. S axena, Z. analyt. Chem. 160, 194 [1958]. 12 R. S. S axena. Z. anorg. allg. Chem. 297, 146 [1958]. 13 R. S. S axena and O. P. S harma, J. Indian chem. Soc. 43, 209 [1966]. 14 A text book of quantitative inorganic analysis by A. I. Vogel. The English Book Society and Longmans Green and Co. Ltd., London 1962, p. 270, 541 and 367.
Transcript
This work has been digitalized and published in 2013 by Verlag Zeitschrift für Naturforschung in cooperation with the Max Planck Society for the Advancement of Science under a Creative Commons Attribution4.0 International License.
Dieses Werk wurde im Jahr 2013 vom Verlag Zeitschrift für Naturforschungin Zusammenarbeit mit der Max-Planck-Gesellschaft zur Förderung derWissenschaften e.V. digitalisiert und unter folgender Lizenz veröffentlicht:Creative Commons Namensnennung 4.0 Lizenz.
B A ND 24 b ZEITSCHRIFT FÜR NATURFORSCHUNG HEFT 7
Electrometric Studies on Thorium Arsenates as a Function of pHR. S. Sa x e n a and Sh iv a P r a sa d
Department of Chemistry, Malaviya Regional Engineering College, Jaipur (India)
(Z. Naturforschg. 24 b, 795—799 [1969] ; eingegangen am 24. Oktober 1968)
The formation and composition of thorium arsenates obtained by the interaction of thorium nitrate and different alkali arsenates (meta, pyro and ortho) at specific pH levels 7.2, 8.3 and 11.1 have been studied by employing electrometric techniques involving amperometric, pH, potentio- metric and conductometric titrations. The results provide cogent evidence for the formation of three thorium arsenates having the molecular formulae ThO,-2 As20 5 , T h02-As20 5 and 3 T h 0 2-2 A s20 5 in the vicinity of pH 4.2, 4.9 and 5.6 respectively. Analytical investigations of the compounds have also been carried out which substantiate the results of electrometric study.
A survey of literature reveals that there are m eagre references on the study of thorium a r senates. B arbieri 1 treated aq. arsenic acid (40%) w ith boiling solution of thorium n itra te (2% thoria) to get thorium mono hydrogen ortho arsenate T h (H A s04) 2 • 6 HoO as a crystalline precipitate; whereas he obtained thorium -di-hydrogen o rtho arsenate, T h (H 2A s0 4) 4'4 H20 , by using 50% of aq. arsenic acid and thorium nitrate solution containing 5% thoria . He further reported that more dilute solutions of reagents give gelatinous precipitates of variable com position. P ierre Ca stel 2 obtained crystals of T h (H 2A s0 4) 4 6 H20 and T h (H A s0 4) 2• 5 H 20 by m ixing T h 0 2/A s20 5 in the ratios 0.05 to 0 .14 and 1.63 — 2.80, respectively. Gilles Le F lem , Jacques Lam ic and P a u l H a g e n m u l l e r 3 prepared two allotropic form of T h (A s0 3) 4 by tem peratu re treatm ent of mixtures of A s20 5 — T h 0 2 gel and arsenic acid. They observed that the products of heating the gel strongly were two form s of the pyro arsenate ThAs20 7; the hexa arsenate Th4As60 23 and the ortho arsenate T h3 (A s04) 4 .
In view of the insufficient and conflicting reports of ealrier workers on the com position of thorium arsenates, and in the absence of any electrom etric
2 P ierre Castel, C. R. hebd. Seances Acad. Sei. 208, 37 [1939].
3 G illes Le Flem, Jacques Lamic, and P aul H agen Muller (C.N.R.S., Bordeaux, France), Bull. Soc. chim. France 6, 188 [1966].
4 R. S. Saxena and M. L. Mittal, Z. physik. Chem. (N.F.) 34, 319 [1962].
5 R. S. S axena and M. L. Mittal, J. inorg. nuclear Chem. 27,2553 [1965].
6 R. S. S axena and G. P. Saxena, Bull. chem. Soc. Japan 35 ,22 [1962].
7 R. S. Saxena and G. P. Saxena, Z. physik. Chem. (N.F.) 28, 220 [1961].
data on the subject, it was considered worthwhile to study the form ation and com position of thorium a rsenates obtained by the interaction of thorium n itrate and alkali arsenates at different pH levels, by means of electro-m etric techniques which have p ro vided m ore conclusive evidences on the com position of such and allied com pounds 4~ 13.
Experim ental
Merck’s guaranteed extra pure reagents, As20 5 , T h (N 0 3) 4 , NaOH and Quinhydrone were used. Air- free conductivity water was used in the preparation of solutions. A s20 5 solution was further estimated as silver arsenate 14 and thorium as T h 0 2 via its oxalate 14. Solutions of different arsenates were prepared by adding calculated amounts of NaOH to boiling solution of As20 5 of the required strength.
A manual polarograph with scalamp galvanometer as current recorder was employed for performing amperometric titrations. A capillary having the following characteristics, m = 2.416 mg/Sec, t = 3.58 sec, and m2/3 — 2.226 mg2/3 esc-1 2̂ was used in conjunction with a saturated calomel electrode connected to the cell by a low resistance salt bidge. Twenty ml. of titre solution was taken in the cell each time and hydrogen was used for deaeration and stirring of solutions. Amperometric titrations were carried out at a potential
8 R. S. S axena and C. S. Bhatnag ar , J. inorg. nuclear Chem. 1 2 ,3 8 [1959].
9 R. S. S axena and C. S. B hatnag ar , Z. anorg. allg. Chem. 303, 12 [I9 6 0 ].
10 R. S. Saxena and C. M. Gupta , Z. Naturforschg. 13 b, 557 [1958].
11 R. S. S a x ena , Z. analyt. Chem. 160, 194 [1958].12 R. S. S axena . Z. anorg. allg. Chem. 297, 146 [1958].13 R. S. S axena and O. P. S harma, J. Indian chem. Soc. 43,
209 [1 9 6 6 ].14 A text book of quantitative inorganic analysis by A. I.
Vogel. The English Book Society and Longmans Green and Co. Ltd., London 1962, p. 270, 541 and 367.
7 9 6 R. S. SAXENA UND SHIVA PRASAD
of —1.6 volts (vs. S.C.E.) using 0.001% Triton x 100 as a maximum suppressor. The pH and e.m.f. values were measured on a Cambridge null deflection type pH meter, using a wide range glass electrode and a quin- hydrone indicator electrode respectively, in conjunction with S.C.E. Conductance measurements were performed on LBR type conductometer (W Germany). 25 ml of titre solution was taken in the cell each time.
Using different concentrations of the reactants, a series of amperometric pH, e.m.f. and conductometric titrations were performed in aqueous and aqueous alcoholic media. Four representative graphs illustrating amperometric (fig. 1), pH (fig. 2), e.m.f. (fig. 3), and conductometric (fig. 4) titrations of meta, pyro, and ortho arsenates have been given and the electrometric results summarised in tables I and II.
Fig. 1. Amerometri titrations between T h(N 03) 4 and Sodium pyro- and ortho-arsenates.
The different arsenates were prepared by p rogressive additions of NaOH solution to boiling solution of As20 5 in the m olecular ratio 2 : 1 , 4 :1 and 6 : 1 , the corresponding com pounds form ed were:
and their pH was found to be 7.2, 8.3 and 11.1 re spectively.
Sodium meta-arsenate titrations: Fig. 2 (curves 1 and 4) illustrates the changes occurring in H® concentration when thorium n itra te solution (pH 3.6) is treated with NaAsOa solution (pH 7 .2 ). In direct titrations, curve 1, when T h (N 0 3) 4 solution was added from the m icroburette to NaAsO;} solution, a gradual change in pH was observed till at the stoichiometric end point (the stage at which the re action ends if simple double decom position takes
p lace ), a sharp fall in pH was noted with the in flection corresponding to the m olar ratio of T h 0 2: As20 5 as 1 :2 , suggesting the form ation of thorium m eta-arsenate T h 0 2 * 2 A s0 5 in the vicinity of pH 4.2 . In the case of reverse titrations, (curve 4 ) , when N aA s0 3 solution was used as the titran t, the pH first increases slowly but at the stoichiom etric end point a m arked jum p in pH was observed, suggesting the form ation of the same com pound according to the equation
Th (N 03) 4 + 4 N aA s03 = T h0 2 ■ 2 As20 5 + 4 N aN 03 .
7 9 8 R. S. SAXENA UND SHIVA PRASAD
Molarity of Calc. Equivalence points [ml] solutions observed from
pH e.m.f. conductance
Th(N 03 )4XaAs03
[M/]
Meta-arsenate titrations Direct titrations. Figs. 2, 3 and 4. Curve 1
Table I. Summary of the results of pH, e.m.f. and conducto- metric titrations.
Em ploying sim ilar concentrations of the reactants, potentiom etric (fig. 3, curves 1 and 4 ) , and con- ductom etric, (fig. 4, curves 1 and 4) titra tions were carried out. Well defined inflections and breaks are obtained at the stoichiometric end points corresponding to the m olar ratio of T h 0 2:As20 5 as 1 :2 and confirm the form ation of the identical com pound, thorium meta-arsenate T h 0 2-2 A s20 5 . Ampero- metric titrations were also tried but they were found unsuccessful.
Sodium pyro-arsenate titrations: Sodium pyro- arsenate solution (pH 8.3) was prepared as described earlier and a series of direct, (fig. 1 , curve 1 ), and reverse, (fig. 1, curve 3 ) , am perom etric titra-
Molarity of solutions
Calc. Equivalence points [ml] Observed in presence of 0 % ale. 20% ale.
T h ( X 0 3)4 N a 4 A s20 7 [M/]
Pyro-arsenate titrations Direct titrations. Fig. 1, Curve 1
100150
8001000
2.53.0
2.55 2.5 3.0 3.0
Reserve titrations. Fig. 1. Curve 3
6001000
100140
3.332.8
3.35 3.35 2.85 2.85
T h ( N 0 3)4 N a 3A s 0 4
Ortho-arsenate titrations Direct titrations. Fig. 1. Curve 2
6080
350500
2.572.4
2.6 2.55 2.45 2.4
Reserve titrations. Fig. 1. Curve 4
400600
4050
2.662.22
2.7 2.65 2.2 2.25
Table II. Summary of the results of amperometric titrations.
tions were perform ed at = — 1.6 V (vs. S.C.B.) at which T h40 yields a well defined reduction wave while arsenates ions do not produce any diffusion current. The titra tion curves provide well defined breaks at a point (see table I I ) , where the molecular ratio of T h 0 2 and As20 5 is as 1 :1 , suggesting the precip itation of thorium pyro-arsenate, T h 0 2'A s20 5 , in the neighbourhood of pH 4.9. The reaction can be represented as follows:
Na4As20 7 + Th (N 03) 4 = T h 0 2 • As20 5 + 4 N aN 03 .
Several d irect and reverse pH (fig. 2 , curves 2 and 5 ) , e.m .f. (fig. 3, curves 2 and 5 ), and con- ductom etric (fig. 4, curves 2 and 5) titrations of sodium pyro-arsenate were carried out with thorium n itra te solution. The end points obtained from the curves (see table I) indicated the reacting ratio of T h 0 2:As20 5 as 1 :1 , confirm ing the form ation of thorium pyro-arsenate.
Sodium ortho-arsenate titrations: Amperometric (fig. 1, curves 2 and 4 ) , pH (fig. 2, curves 3 and 6 ), and conductom etric (fig. 4, curves 3 and 6) titra tions perform ed between thorium nitrate (pH 3.6) and sodium ortho-arsenate (pH 11.1) solution yield well defined inflections and breaks at a point where the m olar ratio of T h 0 2:As20 5 is as 3 :2 corresponding to the form ation of thorium ortho-arsenate, 3 T h 0 2-2 A s 20 5 at pH 5.6 according to the reac-
ÜBER PHOSPHAZENE XXX 7 9 9
t i o n :
3 Th (N 0 3) 4 + 4 Na3A s0 4 = 3 T h0 2 • 2 As20 5 + 1 2 N aN 03.
It is noted that after each addition of the titran t it taken a little tim e for the pH, e.m .f., and conductance values to become steady. A thorough stirring in the neighbourhood of the equivalence point has a favourable effect. Each titra tion takes about half an hour for com pletion. The presence of ethyl a lcohol slightly im proves the position of the end points and increases the m agnitude of the jum p in pH and e.m .f., as it decreases the solubility of the precipitates form ed and m inimises hydrolysis and adsorption .
A nalytical stu d y: Analytical investigations were also carried out w ith a view to substantiate the electrom etric results. Thorium meta-, pyro-, and ortho- arsenates were prepared by m ixing the stoichiometric am ounts of thorium n itra te and respective arsenates. The precipitate obtained in each case was washed
several times with 10% ethanolic w ater and dried completely by keeping it in an oven at 110 for 6 hours and then in vacuum dessicator for 24 hours. A known am ount of each (2 gms.) was dissolved in minim um quantity of dilute HC1 and then analysed quantitatively for thorium and arsenic. T horium was estimated as its oxide via thorium o x a la te 14 and arsenic iodom etrically 14. F rom the proportions of ThOo and As20 5 in the com pounds thus obtained, their com positions were established, which were found to be the same as obtained by electrom etric methods.
The above electrom etric and analytical studies confirm the form ation of three thorium arsenates, viz. ThO o' 2 A s20 5 , T h 0 2 • As20 5 and 3 T h 0 2' 2 As20 5 in the vicinity of pH 4.2, 4 .9 and 5.6 respectively.
Our thanks are due to Prof. R. M. A d v a n i , Principal, Malaviya Regional Engineering College, Jaipur for providing research facilities.
Ü ber Phosphazene, XXX 1
Zur Ammonolyse von ChlorphosphoranenThe ammonolysis of phosphorus (V) chlorides
A lfred S c h m id pe ter , Caspar W e in g a n d und Elke H a f n e r -Roll
Institut für Anorganische Chemie der Universität München
(Z. Naturforschg. 24 b, 799—810 [1969] ; eingegangen am 7. Februar 1969)
The ammonolysis of a chlorophosphorane is characterised by the side by side substitution and condensation competing with one another. The different results fit into one reaction model from which the determining factors may be derived. Within the normal temperature range condensation proceeds only as long as both Cl and NH2 functions at the phosphorus are present.
Presubstitution by dialkylamines reduces condensation. Thus the partially alkylsubstituted tetraamino phosphonium and hexaamino diphosphorus nitride salts P (NR2) 2 (NH2) 2® > N [P (N R 2) (NH2) 2] 2® and N [P (N R 2) 2(NH2) ] 2® are synthesised.
Die A m m onolyse von Phosphorpentachlorid
Sie darf als die klassische Reaktion der Phospha- zenchemie gelten. Ih r schenkte schon 1811 D a v y - seine A ufm erksam keit und ihre detaillierte K lärung beansprucht auch noch das Interesse unserer Tage. Ohne besondere V orkehrungen durchgeführt, liefert die Um setzung von PC15 m it N H 3 ein weißes Reak-
1 XXIX. Mitt.: A. S c h m id p e t e r u . N. S c h in d l e r , Chem. Ber. 102, 2201 [1969].
2 H. D a v y , Ann. Physik 39, 3 [1811] ; Schweiggers J. ehem. Physics 3 ,7 9 [1811].
3 J. L ie b ig , Brief an F. W ö h l e r vom 12. 11. 1832.
tionsprodukt, das sich m it W asser auftrennen läßt. L iebig 3 schreibt 1832 dazu an W ö h l e r : „Das W asser enthielt n u r Salm iak und keine Spur von Phosphorsäure; der P hosphor muß also in die Zusam mensetzung des weißen K örpers eingegangen sein“ 4. D ieser K örper hat die idealisierte Zusam mensetzung PNoH 3-7, entsteht nach
PC15 + 7 NH3 5 NH4C1 + PN2H
4 J. L iebig u . F. W ö h le r , Liebigs Ann. Chem. 11, 139 [1834].
5 H. Schiff, Liebigs Ann. Chem. 101, 299 [1857].6 W. Co uldridge, J. chem. Soc. [London] 53, 398 [1888].7 A. B esson, C. R. hebd. Seances Acad. Sei. 114, 1264
