Atlas of Metal-ligand Equilibria in Aqueous Solution
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ELLIS HORWOOD SERI ES IN ANAL YTICAL CHEMISTRY
Editors: Dr. R. A. CHALMERS and Dr. MARY MASSON, University of Aberdeen Founded as a Jibrary of fund~ent_al bo_oks on impo~tan~ a~d gro~ing subject areas in analytical chemistry, this senes w1ll serve chem1sts m mdustnal work and in teaching or advanced study. l-:.research, .:. :. . _ _:_and ______________________ _ Published or in active preparation: APPLICATIONS OF ION-SELECTIVE MEMBRANE ELECTRODES IN ORGANIC ANALY SIS F. BAIULESCU & V. V. COSOFRET, Polytechnic Institute, Bucharest HANDBOOK OF PROCESS STREAM ANAL YSIS K. J. CLEVETT, Cresi Engineering (U . K.) Inc. AUTOMATIC METHODS IN CHEMICAL ANAL YSIS J . K. FOREMAN & P. B. STOCKWELL, Laboratory of lhe Governmenl Chemist, London THEORETICAL FOUNDATIONS OF CHEMICAL ELECTROANAL YSIS Z. GALUS, Warsaw University LABORATORY HANDBOOK OF THIN LAYER AND PAPER CHROMATOGRAPHY J. GASPARIC & J. CHURACEK, University of Chemical Technology, Pardubice HANDBOOK OF ORGANIC REAGENTS IN INORGANIC ANAL YSIS z. HOLZBECHER et al., Institute of Chemical Technology, Prague
ANAL YTICAL APPLICATIONS OF COMPLEX EQUI LIBRIA J. INCZÉDY, University of Chemical Engineering, Veszprém PARTICLE SIZE ANAL YSIS z. K. JELINEK, Organic Synthesis Research Institute, Pardubice OPERATIONAL AMPLIFIERS IN CHEMICAL INSTRUMENTATION ROBERT KALVODA, J. Heyrovsky Institute of Physical Chemistry and Electrochemistry, Prague ATLAS OF METAL-LIGAND EQUILIBRIA IN AOUEOUS SOLUTION J. KRAGTEN, University of Amsterdam GRADIENT LIQUID CHROMATOGRAPHY C. LITEANU & S. GOCAN, University of Cluj
SPECTROPHOTOMETRIC DETERMINATION OF ELEMENTS Z. MARCZENKO, Warsaw 'fechnical University
ÀNAL
HANÒBOOK OF vsis OF ORGANIC SOLVENTS V. SEDIVEC & J. F~E,K, Institute of Hygiene and Epidemiology, Prague METHODS OF CATALYTIC ANALYSIS .. G. SVEHLA, Queen's U_niv_ersity of Belfast H. THOMPSON, University of New York HANDBOOK OF ANAL YSIS OF SYNTHETIC POL YMERS AND PLASTICS J . URBANSKI et al., Warsaw Technical University ELECTROCHEMICAL STRIPPING ANAL YSIS F. VYDR,A, J. Heyrovsky Institut~ of Physic al Chemistry and Electrochemistry, Prague K. STU!,,IK, C~arles University, Prague E. JULAKOVA, The State lnstitute for Contro! of Drugs, Prague
Published by ELLIS HORWOOD LIMITED , Coll House, Westergate, Chichester, Sussex. Distributed world-wide by JOHN WI LEY & SONS Baffins Lane, Chichester, Sussex (and New Yo rk, Sydney, Toronto)
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Atlas of Metal-Ligand Equilibria in Aqueous Solution J. KRAGTEN
Chemical Department, Natuurkundig Laboratorium, Universiteit van Amsterdam
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Translation Editor: Dr. Mary Masson, Univers ity of Aberdeen
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ELLIS HORWOOD LIMITED Publisher
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JOHN WILEY & SONS New York • Lonaon · Sydney· Toronto
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. t u:arket Cross Chichester anc1en 1w ' First published in 1978 by
ELLIS HORWOOD LIMITED Coll House, Westergate, Chichester, Sussex, England this being the 50th book published by Ellis Horw?od in his 50th year of publishing
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To Coby Edith Annelies
Put it before them briefly so they wi/1 read it clearly so they wi/1 appreciate it, picturesquely so they wi/1 remember it and, above al/, accurate/y so they wi/1 be guided by its light.
JOSEPH PULITZER
Table of Contents
Foreword .................... ... ... . ......... . ..... .. ................ 11 Author's Preface .............. . ........... .. . . . . ... . .... . .............. 13 Chapter 1 .... . ..... . ...... . ..... .. ................ ... ................ 15 1.1 The Plots: Theory ................................. . ............ .16 1.1.1 Hydroxides ......................... .. .................... 16 Hydroxide precipitation ............... . .... . .... ·. ........... 19 Polynuclear hydroxide complex formation . .... . ................. 21 Areas of predominance of mononuclear complexes . ...... . .. . ...... 22 1.1.2 Other ligands ............ . .... ... ....... . ........ ... .... ... 22 The side-reaction coefficient .................................. 22 Hydroxide precipitation ....................... . ............. 24 Polynuclear hydroxide formation .............. .. .............. 25 1.1.3 Air-saturated solutions ............. . ................. . ... . .. 25 The influence of CO 2 . . • . • • . . • • • • • . • . • . . • • . . . . • • • . • • . • • • • • • • 25 The influence of 0 2 • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 27 1.2 The Plots: Some Practical Points ................ . ................... 29 1.2.l Significance of the lines in the plots ............................ 29 1.2.2 Superposability of the plots ..................... .. ........... 29 1.2.3 The amount of ligand in solution .... . ......................... 30 1.2.4 Data sources and selection criteria ...... . ....................... 31 1.2.5 Constants and experimental conditions .... . .... . ....... . ........ 32 1.2.6 Interpretation . . . . ............... ... . . ................ . .... 33 1.3 Some Practical Applications . .. . ..... . .... . ...... • ................ .34 1.3 .1 Conditional constants .... . ........ . . . .................. . .... 34 1.3.2 Manipulations of solutions ....... . ........................... 34 Dilution ................. . .......... . • • . • • . • • . • .. • . . ...... 34 Neutralization . . .......... . ...... . • . • • • • • • • • • • • • • • • • • .. • .. .36 1.4 Arrangement of the plots .. .. . . .... .. .. .. • . • • • • • • • • • • • • • • • • • • • • • • .39
Table of Contents
suver(IJ . ...... . . . . . . . ... . . . .............. . .... . ....... . .
Chapter 32 Chapter · · · · · · · · -40 · · · · • .s2 A]UJlliniUJD(ill) . .... . . .. .......... . ...... .. ..... . ........ .
BariUJll(JI) - including the carbonate system .. . ........... . .. _
Chapter 4 Chapter 5
· · · · · · · •70
Beryllium(II) . . ... . ........... . ............ . ....... . · · · · · · · · · · · · · · .80 Chapter 6 Bismuth(III) .. .......... . ........................ . · · · · · · · · · · · · · · · .94 Chapter 7 Calcium(II) - including the carbonate system .... . ...... . . . . . . . . . ... · · · · . I04 Chapter 8 Cadmium(II) - including the carbonate system ..... . .. . · · · · · · · · · · · · · · ••.I 14 Chapter 9 Chapter 10 Cerium(III) .... . .... . ........... .. . . .. .. .. . · · · · · · · · · · · · · · · · · · · • . .I 60
Cobalt(II) - including the carbonate system ....... . · · · · · · · · · · · · · · · · · • • . . Chapter 11
172
Chapter 12 Chromium(III) ............... . . · · · · · · · · · · · · · · · · · · · · · · · · · · · · · • . .. .214 Chapter 13 Coppe~II) ........... . · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · • .. ..... 222 Chapter 14 · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · • • . . . .... . .. .246 Dysprosium(III) Chapter 15 Erbmm(III) .... . ... . . . . . . . . . . . . _- . . . . . . . . . . . .. : . .
....... . .
· · · . . .258
Chapter 16 .............. . . . . . .. . .......... . Europium(III) Cha~:;~~I) - including the carbonate system. . . . . . . . .
Iron(III) ... _
. ...... . .. . ...... . .272 · · · · · · · · · · · · · · · · • • ... .284
Chapter 18 Gallium(III) . ..· _· .· · · · · · · · · · · · · • ....... . . . . . . . . . . . . . . · · · · · · · · · · · · · · .3 22 Chapter 19 Gadolinium(III).
· · · · · · · · · • ...... . .. . . . . .. . .... · · · · · · · · · · · · · . .. .. .344
..... . . . . . . . . . . . . . . . . . · · · · · · · · · · .. . . . ...... .358 Chapter 20
···
Hafnium(IV) .. . Chapter 21 ............. .. . . . . . . · · · · · · · · · · · · • • . .. . . . . . . . . ... .372 Mercury(II)
Chapter 22 lndium(III) .· .· · · · · · · • .... . ... . . . . . · · · · · · · · · · · · • . . . . . . . . . . . . . . . . . . .382 Chapter 23 · Lanthanum(III)
.
..... . . · · · · · · · · · · · · · · · • • . . . . . . . . . . . . .. ... . . . .400
- mcluding th e carbonate system
. . . . ..... . . .. . . . . .. . . . .416
Table of Contents
chapter 24 Magnesium(II) ................................................... .436 Chapter 25 Manganese(II) - including the carbonate system ......................... .452 chapter 26 Neodymium(III) ................................................. .496 chapter 27 Nl.ckel(II) ....... . . · · . . . . . . . . . . .......... . .......................508 chapter 28 Lead(II) ........ · · . · ............................................. 534 Chapter 29 Palladium(II) ............. '. ....................................... 576 chapter 30 Scandium(III) .................................................... 586 Chapter 31 samarium(III) .................................................... 600 Chapter 32 Tin(II) ............................................... . .......... 612 Chapter 33 Tin(IV) ......................................................... 622 Chapter 34 Strontium(II) - including the carbonate system .......................... 626 Chapter 35 63 6 Terbium(III) .......... · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · Chapter 36 648 Thorium(IV) .......... . .. ·. · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · Chapt~:!1,Ti(IV) ......... ...........................................660 Chapter 38 670 Thallium(III) ............. · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · Chapter 39 ............682 Uranium(IV) ........... • • • • · · · · · · · · · · · · · · · · · · · · · · · · · · Chapter 40 ..... . ................... 688 Uranyl,U(VI) .......... · · · · · · · · · · · · · · · · · · Chapter 41 .. . ....... 700 Vanadium(III) .......... • • • • · · · · · · · · · · · · · · · · · · · · · · · · · · · · Chapter 42 704 Vanadyl,V(IV) . ... ...... · · · · · · · · · · · · · · · · · . . ......... . .......... . . Chapter 43 . .. .... . ... . ...... 720 Yttrium(III) .. . ..... • • • · · · · · · · · · · · · · · · · · · · · · · · · Chapter 44 · . .. . . . . ... . .... . ... 730 Ytterbium(III) ... .. .. • • · · · · · · · · · · · · · · · · · · · · · · · · Chapter 45 . . . . . . . . . . . . .. 74 2 Zinc(l1) .... .. ..... • · · · · · · · · · · · · · · · · · · · · · · · · · · · · .. .
Chapter 46
Zirconium(IV) ......................... . .......... . Appendix · · · · · · · · · · · · · · .766 Stability Constants for Proton-Ligand Complexes ....... . . . . . . . Tabular Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . · · · · · · · ·799 ..... · · · .780
Foreword
Present-day theoretical treatments of metal-ligand equilibria owe much to Ringbom's Complexation in Analytical Chemistry. Since this book was published in 1963, many authors have found it useful to follow Professor Ringbom in his use of 'conditional constants' and 'side-reaction coefficients'. However, until now, in order to work with conditional constants it has been necessary to consult tables or carry out tedious calculations. I believe, therefore, that Dr. Kragten has done a great service for analytical chemists in producing this collection of plots of side-reaction coefficients for 45 metals in combination with 29 ligands, which give the necessary. information at a glance. Tue accompanying plots of pM' against pH, which illustrate directly the areas of predominance of the various species and indicate the conditions under which hydroxides will precipitate and polynuclear hydroxo-complexes will form, also provide valuable information for the analyst. It is a great pleasure to be associated with the publication of this most useful addition to the analytical literature.
2 August 1977
M. R. MASSON University of Aberdeen
Author's Preface
There is increasing interest at the present time in making critica! compilations of the equilibrium consta~ts for metal-ligand_ complexes. Without such a compilation, the chemist is faced w1th a mass of confusmg and possibly imprecise data. Origina! papers often contain insufficient information about the experimental set-up, the temperature, the ionie strength, the age and exact nature of any solid phase, etc., and the reader may not be able to criticize the data adequately. Thus, critica! compilations satisfy an important need in analytical and coordination chemistry. Nevertheless, only limited use is made of these critica! compilations. The complexity of the equilibrium systems means that it is not easy to obtain - directly from the constants - a clear insight into the behaviour of the metal ions under the various experimental conditions possible. Usually, an intermediate graphical representation is used as an aid to understanding, but the extensive calculations and plotting of graphs necessary for each metal-ligand combination are tedious and time-consuming. Moreover, if someone does perform the necessary calculations, he will restrict himself to his own particular problem, and this in turn means that the few results available in the literature are not generally useful. Thus we can see that a gap exists between the data in the literature and daily laboratory practice, and that it should be filled in such a way that the information is readily available in an easily accessible and generally applicable form. In compiling this Atlas, my aim has been to fill this gap and to help the chemist working in industria! and research laboratories to solve everyday problems. Although the greatest care has been taken in selecting the constants to be used, it was impossible to check each one for reliability. Specialists in a particular field may well be able to detect errors in the plots relating to their own speciality, and I hope that anyone who does detect such an error will not hesitate to contact me, so that I can incorporate the necessary correction in any future edition. I am grateful to the copyright-holders, John Wiley and Sons, and to the authors, Dr. C. F. Baes Jr. and Dr. R. E. Mesmer, for permission to make use of data in The Hydrolysis of Cations.
14
Author's Preface
I am greatly indebted to Mr Steven Arlman for his assistance in prepafing th computer program, his stimulating input of ideas, his painstaking plot administration an~ his assistance in plot-scanning. Without him, the book could not have appeared for som years. I am grateful to the staff of the Physical Laboratory for giving me the opportunit e to prepare this Atlas by allowing Mr Arlman and myself to have sufficient free tim[ and by supporting the work with a considerable proportion of the computer budget' I thank Mr Joop van Loenen and the production staff of SARA (the Academi · Computer Centre, Amsterdam) for their pleasant cooperation during the production 0~ the computer plots, and for their patience in ensuring that the plots were of the high quality needed. , I wish to express my gratitidue to Mr A. Ph. Reynaert, whose practical experience achieved by meticulous observation, was the inspiration for the Atlas, to Prof. Gerri~ den Boef and Prof. Adam Hulanicki for their interest and encouragement, and to Mrs Mariet Molders and Mrs Tineke Koster for their assistance in typing. I am grateful to the Series Editors, Dr. R. A. Chalmers and Dr. Mary Masson, for their help in preparation of the manuscript, and my final thanks goto Felicity, Ellis and Clive , Horwood for their enthusiastic cooperation, and for being such a friendly publishing family.
14 August 1977
J. KRAGTEN Natuurkundig Laboratorium Universiteit van Amsterdam
•
CHAPTER 1
lntroduction
It is unthinkable that anyone should attempt to describe the properties of metal ions in aqueous solution without consi~ering hydrolysis reactions. Most cations hydrolyse in aqueous solution, because they form strong bonds with oxygen atoms, and because, as a result of the self-ionization of water, hydroxide ions are always present at concentrations which can vary over the unusually wide range of I 0-1 O-r 4 M. With some metals the bonds with oxygen are so strong that the species M(OH)r do not dissociate further even in concentrated strong acids. Such species are sometimes written as Mon+, particularly when their exact composition is not known. In the calculations, the species Mon+ was treated as if it were a metal ion of valency n. When other ligands are present in solution, there will be competition between the ligands, L, and the products of hydrolysis. A generai formula for the final product is M0 0b(OH)c(H 2 0)dLeHr. However, without forgetting the correct formula for the product, it is possible to express the reactions in simpler terms if hydroxide ions and hydrogen ions are considered to be the only ligands competing with L. (This is possible because 2 0 - and H2 0 can be expressed in terms of OH- and H+.) In all cases of interest, this representation is adeguate for our purposes. We have studied the reactions of 45 metals with 29 ligands, and about 600 of the combinations turned out to be of real interest. Different methods of graphical presentation are possible, but since most workers are not interested in detailed information about the exact distribution of metal ions between the various possible metal-ligand and metal-hydroxide species, but want to be able to find out such basic things as the pH at which a hydroxide precipitates, the conditions for formation of polynuclear complexes, and the conditional constant for reaction of the metal with EDTA or DCTA, I decided to present two types of plots. The concept of the side-reaction coefficient, first introduced by Schwarzenbach, was extensively used by Ringbom in his excellent monograph Complexation in Analytical Chemistry [I]. In the first type of plot, the side-reaction coefficient (a) for reaction of th e metal ion with hydroxide and Iigand is plotted against pH for various ligand con- \ centrations.
lntroduction
[Ch. 1
16
The second type of plot is of pM' vs pH. Such plots illustrate the influence of metalligand complex formation on the regions where polynucl~ar hydroxo-complexes fonn and where hydroxide precipitates. The materia! is presented m such a way that the graphs for the separate metal-ligand combinations are superposable; the graph ~or _a _system containing more than one ligand can be composed from the graphs for the md1v1dual metal-
ligand . In combinations. preparation of this Atlas, certain simplifying assumpt10ns had to _be m~de, and one of these was that the metal-ligand species are not polynuclear. In reality, bmuclear and polynuclear species are formed in c~ncentr~ted so_Iutions1 with some ~etal-li~an~ combinations. lf this is known to occur m solut1ons w1th pM < 2, a wammg, d, 1s given in the tabular index to indicate that the pM'-pH diagram may not be completely reliable when pM' < 2. (See, for example, DTPA and citrate.) lf such species are formed in more dilute solutions, no plots are given, or the ligand is not considered at ali (e.g. dimercaptopropanol, BAL). Some metal-ligand complexes have limited solubility. lf the metal-ligand complex precipitates only in concentrated solutions, a waming, P, is given in the tabular index. lf precipitation occurs in more dilute solutions, no plots are given (e.g. oxalates, fluorides) or the ligand is not considered at ali (phosphate). Another possibility that had to be neglected was the formation of mixed-ligand complexes. The greatest care was taken in selecting values for the constants from the literature, and the computer output (plots and print-out) was double-checked against the originai literature. Nevertheless, it must be realized that there is some uncertainty in the positions of the lines on the pJots, and that the accuracy of their positions depends on the accuracy of the data used. Only data which seemed obviously unreliable have been rejected; the relevant combinations are marked U in the tabular index. Where there was some doubt ' the data were still used to produce plots, in view of the likelihood of unsuspected errors in the rest of the data. It was impracticable to check the accuracy of the constants (there were more than two thousand) for all the metal-ligand combihations. However, in many cases, large errors in some of the constants lead to only relatively minor inaccuracies in the positions of the linès.
1.1
THE PLOTS: THEORY
1.1.1 Hydroxides Hydro~ide equilibria form the basis of all the plots, and in this section the formation of t~e vanous hydroxide species will be discussed . Th e influence of other Iigands will be cons1dered later. The reaction scheme for hydrox.ide fo rmation can be set out as below · for argument's sake the metal ion is supposed to be tervalent, M3+. '
The Plots: Theory
sec, 1.1]
M3+
M(OH)t
\~
M(OH)g
17 M(OH)4
M(OH)r · · · ·
Jf
Jf
(M(OHh.nH2oj . solid
M2 (0H)t
(1)
or (M20 3.mH 20) solid. Mp (OH)~3P - q)+
The system has two independent v~riables; the concentrations of the various species depend on both the total concentratio~ of M and the pH. If an additional constraint is t only one degree of freedom remams, a relationship exists between the metal-ion ~~~centration and pH, and a curve reflecting the particular constraint can be drawn on the pM'-pH plot. The borderline of the precipitation region is found by detennining the concentration at which M(OH)g just precipitates at various pH-values. By setting [M(OH);] = [M(OH)if- 1] for different values of i, we get the borderlines of the regions of predominance of the various mononuclear specieS. We can derive the borderline of the region of predominance of polynuclear complexes by setting x = I in the expression p.[Mp (OH)q) = x .~[M(OH)i] At this borderline, 50% of the metal will be present as polycomplexes, so it 1is not very useful to analytical chemists, who are more concerned to know where polycomplexation begins. A useful approximation to this is the borderline where only I% of the metal is present as polycomplex. It is this 1% borderline that appears in the plots; it is found by settingx = 0.01. According to Ringbom [ I ] , a system of co-existing equilibria can be divided into a main reaction and the compe!_it iv.e-~ ~actio_ns, covering all other reactions. The,_p~rameter [M'l, the tota! c9ncentration of theme~\i_on not involved in the main reaction, is much more useful tnan the the concentration [Mr ] of free metal ion, to which it is related by Ringbom'1 side-reaction coefficient a,M pHp a 45° (dilution) line through P0 will first be followed. At pM' = pM~. + (pCam - pHp a horizontal part starts. Near pH = pKac (4.7) a vertical jump occurs as a consequence of the buffer action as the acetic acid is neutralized. The height of the jump depends on Cac and Cam and can be approximated by (pCam - pCac), i.e. the logarithm of the dilution factor and hence the amount by which pM' increases. A further small addition of ammonia causes a horizontal jump through the 'equivalence' point at pH = 7.1 until pH ~ p*Kam (9.4 ), the ammonia 'half-titration' value. A further addition of ammonia largely dilutes the solution; the pH will slowly approach the value pH = ½(14 + p*Kam - pCam) fora pure ammonia solution. This example demonstrates how a pathway can be constructed in the pM'-pH diagram. lt also shows how pM'-jumps can be generated by the addition of weak acids and bases, jumps that can be used to create alternative pathways in order to prevent unwanted hydroxide reaction. An overshoot of pH during the neutralization of acids can be prevented by using buffer solutions with a pH 1 unìt higher than that of the equimolar buffer; 80% of the buffer capacity then remains available for neutralization. When even this procedure leads to too-high pH-values, use can be made of an acidified hexamethylenetetramine (hexamine) solution which releases ammonia on heating, thus neutralizing the solution homogeneously and controllably. The addition of solids should be avoided. In the vicinity of solids high locai concentrations will occur, and with salts .u of weak acids extreme pH-values may arise. When, during a manipulation, ions which form a complex with the metal concern;d are in solution or come into solution the manipulation locus has to be constructed in the relevant plot. 0
,
0
)
The Sn(IV)-Cl plots show that tin metal can be dissolved in concentrated hydrochloric acid without precipitation of SnO 2 ; point P0 near the origin stays outside the SnO 2 region for chloride concentrations > 2M. If a solution with [Cl] ~ 2M is diluted tenfold with IM perchloric or nitric acid, the pH remains about O, pM' becomes I and [Cl] will be about 0.2M. The result is that P now lies in the precipitation region as the borderline has shifted faster than P. If the solution is diluted with IM hydrochloric acid, [Cl] gradually changes from 2M asymptotically towards lM. Under these circumstances point P remains outside the precipitation region and no SnOi precipitates. Combinìng this with the diagram for Sn(IV)-EDTA, and knowing that EDTA can be used for a complexometric back-titration procedure, we can conclude that the EDTA solution to be added should be acidified to pH = O and have [C I ] = I M. (The concentration of EDT A
lntroduction
fCh. 1
3B f the limited solubility of H4 Y.) After addition of th -3M because o h t .d e X 10 has to be < 7 . h S t room temperature, we ave o cons1 er the EDTA EDTA which quicklY reacts w1t n a lines i~ the pM'-pH p~ot. th t ongly acidic Sn(IV)-EDTA solution should not b . b . e . 1· tion is that e s r The unp ica . h d 'de or ammonia solut10n. The est method 1s to add r d ·th a .sodmm'd'fYd roxi . . a to pH 5 _6 (to prevent crossmg the borderline during the neutra 1ze WI solution of hexamme ahc1 It iteh solution to raise the pH by hydrolysis of the hexamine · · ) d then to ea e · add1t!on a:e accurate tin determinations are possible. . . . In this way ry , H ct · m for Cu it is obvious that ne1ther a prec1p1tate nor a polyFrom the pM -p iagra . . · · · 'd . . f d h n a piece of copper 1s d1ssolved m mtnc ac1 and the solution omplex w11l be orme w e ) Wh d' h d · en so mm y rox1de is c . . . t (4 4) (see pp. 223 and 245 . · diluted with water up to pom ' . . . . . . 15 d' t th H to 5 5 for the complexometnc titrat10n w1th TAR as md1cator a added to a JUS eP · ' 4-5% error is found . . _2 · · 1 ·t· dilute ammonia solut10n (1 O M, p. 225) a so gives a penetrat1on of the Add 1 100 0 1 · " d Th dd' . • ·t at·10n re g1·on • In practice an error of about I% 1s 1oun . e a1· a 1bon prec1p1 · of • enough concentrated ammonia gives an error of only 0.3% because the neutr. 1~at1on line passes . e f g corresponding to ammine-formation. However, 1t 1s found experilt bt . d h over th e Imes ' , mentally that a few slips can still occur. Very accurate res~ s are o rune w en the solution is neutralized with a solution of acetate or hexamme of pH 6. It may also be mentioned that when an ammoniaca! solution of copper (I 0- 2 M) is titrated at pH9.5 with trien (triethylenetetramine) with an ion-selective electrode used for the end-point determination, the trien should also be made ammoniaca!. If not, then if the Cu-NH3 solution is diluted locally with titrant by a factor of I O the borderline shifts 4 log units upwards while point P at (2,9.5) shifts only I unit, and P is passed by the borderline This explains the poor response of the electrode after a few determinations, because of the nearly irreversible hydroxide precipitation at the electrode surface. The addition of EDTA to an almninium solution has already been discussed. The pH can be slowly increased on heating if hexamine is added. When the Al-EDTA complex is completely formed and a final pH-adjustment is needed, in nearly all cases of practical interest (CA1 < I 0- 2 M), the neutralization line lies above the precipitation line, so no precipitate will be formed. However, when the pH is raised so that the dotted pH limit is passed, more than 1% of the Al-EDTA will dissociate, forming Al(OH) 4, and this reverts only slowly to Al-EDT A when the pH is lowered. Thus, formation of the soluble tetrahydroxo-complex leads to irregular results in this case. Systematic errors can usually be expected with all metals when the dotted pH-limits are passed, because of low reversion velocities. . . W~en AI(?H)4- is formed as above, a decrease in pH can cause penetration of the precipi~atwn reg10n, because part of the system behaves as if EDTA were absent: It is obvious that the addition of a complexing ligand does not guarantee trouble-free manipulations. of this section has been to show how pM '-pH plots can be used to elucidate ~he specific pitfalls which may exist in the common operations of analytical chemistry, and ex~ples have be~n used to give some insight into manipulation errors and to show that a num er of small sms can easily be committed and are mostly overlooked as an origin of errors.
I
Sec. 1. 4] 1.4
Arrangement of the Plots
39
ARRANGEMENT OF THE PLOTS
Ali the plots for one oxidation state of a metal are arranged in one chapter. The chapters are arranged alphabetically according to the chemical symbols of the metals; Iower oxidation states come first. The introduction of each chapter gives the hydrolysis constants used throughout the chapter, and attempts to give the reader some idea of the reliability which should be attributed to the plots for the particular metal. The pM'-pH plot for the metal in the absence of complexing ligands other than OHions appears on the next page. In this plot, the regions of predominance of the various mononuclear complexes are indicated by the log *K; lines. (Note that 'out-of-order' log *K; lines do not indicate the true predominance borderlines; see p. 22). On the following pages, the plots for the various ligands appear. There is one page for each metal-ligand combination, the upper diagram being the plot of log a vs pH and the Iower one the pM'-pH plot. The values of [L'] and the stability constants for the particular metal-ligand combination given alongside the plot of log a vs pH hold for both plots. The formation constants of the proton-ligand complexes are tabulated at the end of the book (p. 799). Within each chapter, the metal-ligand combinations are arranged alphabetically according to the name of the ligand.
REFERENCES [1) A. Ringbom, Complexation in Analytical Chemistry, Interscience, New York, 1963. [2) J. Kragten, Talanta 1977, 24,483. [3) L. G. Sillén and A. E. Martell, Stability Constants of Metal-fon Complexes, Special Publication No. 17, The Chemical Society, London, 1964. [4) L. G. Sillén and A. E. Martell, Stability Constants of Metal-fon Complexes, Supplement No. J, Special Publication No. 25 , The Chernical Society, London, 1971 . [5] R. M. Srnith and E. E. Martell, Criticai Stability Constants, Vols. 1 and 2, Plenum Press, New York, 1975. [6] C. F. Baes and R. E. Mesmer, The Hydro/ysis o[ Cations, Wiley, New York, 1976. [7) J. Kragten and L. C. Decnop-Weever, Talanta, in the press.
----
CHAPTER 2
Ag
Silver (I)
Brown Ag O is precipitated on addition of alkali to silver ions in solution. The solid 2 hydroxide, AgOH, is unstable and exists only transiently. The following hydrolysis constants were selected for the calculation and construction of the plots in this chapter. log *{3 1 log *{32
= -I 1.9 = ~23.8
log
*Kso = 6.3
There is no reliable evidence about the formation of polynuclear silvery-hydroxide compounds. In air-saturated aqueous solution, silver carbonate never precipitates; an apparent constant log Kcarb = 10.6 can be deduced from the solubility product of silver carbonate (log K!O = -11. l) and this apparent constant is much higher than the value of Ag 20 (log *Kso = 6.3). A decrease in reduction potential may lead to separation of metallic silver. ,The potential should, preferably, remain above the value E= (799-59.1 p[Ag+]) mV.
Copper(I I )-Tartrate
241
c11l 5
B
7
6
9
IO
li 16
16 LOG BET A0 : 3, I O LOG.BETAIII.IOHI =- 23 .oo LOG BETA 0o=4 -~ O LOG BETA 000: 5 , 60
14
t' 12
12 IO
8
'-' O
6
6
....J
e 4
d
O :O M b : O. ODI M C :O . O! M d :O . I M e :0 . 3 M
2
6
7
8
9
6
7
B
pH
I
2
3
4
5
9
10
Il
12
13
14 8
B
7
7
6
o 5
5
.
pM ' 4
4
3
2
2
o
o 2
3
4
5
6
8
7
pH
9
IO
Il
12
13
14
Copper(l I )-Tetren
242
8
[Ch. 12 9
10
J__JLLl-L.J_.-L__L_.1.--1__JL-L-7-f-.f-i~~___..,
,s
1
16
LOG BE TA 0: 22 , 80 LOG BETR 1: ! 8.!5 LOG BETR 2: 12. 70
14 14 12 12
-,o a:
IO
I
a... _j a:
8
8
è)
o_j
6
6
4
4
11
O :O
b
:0.0001 11 C : O.ODI 11
2
2 a
o
o 3
2
I
5
4
6
7
8
9
IO
6
7
8
9
IO
d
:O.O!
e
: 0.1
11 11
pH I
2
3
4
5
Il
12
13
14
8
8
/;
I
7
7
o/,a
6
6
I 5
~!
5
l
pM • 4
I
3
I 2
.''
' 2 ' ': '' ' ''' ' ''' '' b:
I I
o
o I
2
3
4
5
6
7
8
9
IO
11
12
13
pH I
14
Copper( 11 )- Tiron
cul
243
• 16
7
8
9
10
li
12 13 __1._-1.----1___,'--~--7.---/r------::;~--:T-, 1s
L0G BETA 0:14,27 L0G BETA 1:5, 14 L0G.BETA"LDN=-7 ,20 L0G BETA 00: 25 , 44
14
12
12
,- 10
a:
10
J:
a.. ...J e a:
B
o O 6
6
...J
4
4
O :O
2
b
2
o 12
M
: 0.0001 M
e
: 0 . 001
M
d
:0.01
M
e
:0,1
M
13
'' '' ''' ''
7
'' '' '' ''
6
' '''
'' '' ''' ' ''' ' '' ' ' '' ' '' '
'
5
4
3
2
'' '' ' b:
o 9
10
Il
12
13
14
Copper(l 1)-Trien
244 5
6
e
7
10
9
li
[Ch. 12 12
13 16
14
14
12
12
~IO
10
a:
l.OG BE TA0 =20. 40 LOG BET A1=14.t O LOG• BETAnLon=-1 0-80
I
(L _j
a:
e
8
o o
_j
6
6
a
4
4
2
o b
2
o 4
5
6
7
B
IO
11
12
13
6
7
B
9
ID
e
:0.1
e
o
9
d
:Q M : O, 0001 M :0 . 001 M :0 . 01 M
M
pH
I
2
3
4
5
Il
12
13
14
8
8
/;
/
7
Ì,
7
a
a
6
6
I 5
pM '
~I
5
l
4
3
2
I
I
I
4
I
3
2
o
o I
2
3
4
5
6
B
7
pH
9
ID
11
12
13
1'
Cu-Carbonate
cul
245
cu -
carbonate system
'fhe occurrence of the stabl_e, soluble carbonate complexes cuco 3 and Cu(COhH~has . fluence on the low-pH s1de of the precipitation region in the pM' _ pH diagram no ~se Cu(OHh i~ still the less soluble solid in air-saturated water. At high pH, however'. beca er hydroxide d1ssolves t_o form Cu(CO 3H-: coP~he equation for the hig~-pH borderline of the precipitation region in air-saturated [log Pco2 = -3.52 (P m atmospheres)], derived from the stability constants log water - 9 8 . M' . == 6.1 and log ~oo - · , is P - (-2 pH + 26.3). Th1s corresponds to an apparent ~~ue of 35.1 for log ~4 (see page 26). The following set of constants have been used for ;he plots for air-saturated solutions.
= - 8.2
log *~ 1 log *~ 2 log *~ 3
= -17.5 = -35.1
log *~ 22
= -10.6
log *K~
= 8.85
Carbonate cannot be treated as a separate ligand here, because the concentration of carbonate is not constant in air-saturated water; it increases enormously at high pH. Tue pM'-pH plots for air-saturated solutions containing other ligands can be constructed from the corresponding plots for .CO 2-free solutions by moving the high-pH borderline of precipitation to the left by 2 pH units. 3
2
I
4
5
7
6
8
10
I.I
12
13
14
8
8
.,;_ e:,
o
..J
. /;
/,
7
7
6
6
I 5
~!
5
pM'
9_
J
4
I
3
3
I 2
2
I o
o I
2
3
4
5
6
e
7
pH
IO
11
12
13
14
CHAPTER 13
Dysprosium (lii)
Dy
Hydrolysis of the large Dy 3+ ion does not become appreciable until fairly high pH (>7). Hydrolysis studies are quite difficult, since, at ordinary concentrations, hydroxide invariably precipitates when the averàge number of OH- ions coordinated is small. There is no evidencè for polycomplexation. A limited amount of reliable information 2 suggests that Dy(OH) + is formed on the low-pH side of the precipitation region. The studJ of hydroxide precipitation is difficult because of supersaturation, colloid forma tion and dependence of *K50 on particle size, rapid partial recrystallization and carbonate formatìon. These phenomena make definition of a generally useful equilibrium state somewhat arbitrary. The following data adopted from the compilation of Baes and Mesmer [ 1] hold in principle for a one-hour-old precipitate prepared under inert gas to exclude CO , at room 2 temperature, and at ionie strength = O. I. log *~ 1 = - 8.0 log *~2 = -16.2 log *~ 3 = - 24. 7 log *~4 = -35
log *K50
= 17
There is limited information on carbonate formation. It is suggested that the apparent solubility product of the carbonate, Kcarb , is so close to *Ks0 that mixtures of carbonate and hydroxide are formed. This implies that the pM'-pH plot does not change for airsaturated sglutions.
(II C. F. Baes and R. E. Mesmer, The Hydrolysis of Cations, Wi ley , New Yo rk , 1976.
Dysprosium( 11 1)
ovl
e
I
2
3
4
5
6
7
8
247
9
IO
Il
12
13
14
8
7
7
6
5
6
5
pM • 4 3
2
3 2
oi-,--r-,;--T3-"7-T4----r~5r----,-L.6r---r77;--r-1e-,-I9----,-~\~0-,~l~l-,-~l2~~1~3:-7~1~.° 2 I pH
·~
248
Dysprosium (111 )-Acetate 3
5
6
7
B
9
16
10
11
[Ch. 13 12 16
14
14
12
12
-10
a: I a... _J a:
L0G L0G L0G L0G
BETR0:l , 70 BETR 00: 3 ,20 BE TR000: 3 , 90 BETR 0000 :3 ,90
10
B
B
o o
_J
6
6
4
d 2
o 3
6
7
B
9
10
11
2
a :o b :0 .0 3
11 11
o
d
C :0,1 :0. 3
11 11
12
pH I 2 3 4 5 6 7 B 9 10 11 12 13 14 B-J---L-L_L.._.J.....-L-L-L-L.._-'-----'-----'--1..-'---'-r----'--'---'------'-.._....__.___.______._.._...._+B
pH
249
Dysprosium ( 111 )-Acetylacetone
ovl 5
6
7
B
9
10
11
12
LOG- BETA 0:6 -03 LOG- BETA 00 =I O. 70 LOG- BETA 000:14 . 04
14
I4
12
12
10
,... IO
a: J:
o..
8
..J 8 a: _,
o a
_J
6
6
4
M O :O M b :0 . 0001 e :0 . 001 M M :0.01
2
2
d e 5
:0.1
M
6
pH
l
2
3
4
5
6
7
8
9
10
11
12
13
14 8
8 7 7 6 6
5 5
. pM
4
4
3 3 2 2
250
Dysprosium (111 )-DCT A 9
[Ch. 13
10
14
14
12
12
~10
10
a:
LOO BETA 0 =20, 40 LOO BETA 1=10. 70
I CL _l
a:
B
8
6
6
o
o_j
4 O :O
b
2
2
M
,0.0001 M
C :0,001
M
d
:O.O!
M
e
,0.1
M
pH 7
8
9
8~1L..1-_L2_L_j3_L~4L.1-~5L..1-_L6---L.._j__L_...L_l__j_
11
13
12
'' : t
7
'' ' '' '' '
6
pM'
10
14
_i__J__J__L__J...._-L~:::1!:1l,;l_._i8 :
7
' :' ': ''
6
''
5
5
4
4
3
3
2
2
pH
Dysprosium (111 )-DTPA
ovl 2
3
5
6
7
9
16
251 IO 16
I4
14
12
12
,.... 10
IO
a:
LOG BETA 0: 22 , 92 LOG BETA 1:1 4 ,5 6
J::
(l_
_J
a:
e
8
6
6
è) C)
_J
4
O :O ,0.0001 e ,0.001 d , 0.01
a
b
2
2
e
o 2
3
4
5
6
7
8
9
10
6
7
8
9
IO
:O.I
11 11 11 11 11
pH
2
3
4
5
ll
12
13
8
7
7
6 6 5 5
pM
.
4
4
3 3
2 2
1 o1-~-~---,----,-- r - - r - . - T-rL,- ,77' ' -r-8 2
3
5
5
--Y9-,-;i:1o::--•-:i1i;--1-r--;1t27
+-1~3;--rt
Dysprosium(lll)-EDTA
252 I
2
3
4
7
6
5
B
9 16
16
LOG BE TA LOG BETRo-1 8,30
14
t=l o ·OS
12 ~10
cr I
a... 8
_j
cr
o
o
6
_j
4
a :o
a
2
2
o
o I
2
3
5
6
B
7
9
b
:0 . 000 1 C :0.001 M :0 .01 M e :O,I M
d
1O
pH I 2 3 4 5 7 ___.l~8t_j_~SL..1-~l[O__J___jl~1 _1_,1 12~ ~i3 er__.1...____L____j_L__L__l__j__l_L_l6_J~.L
14
8
7
6
5
a
3
2
oT-r7"2'r-f31~4i ~ls~)-;6-r-,7-,--Te-,--Tg--i-1,0J l1J1IJ~12-..-1~3__,.J1.° pH
253
Dysprosium( 111 )-1 minodiacetate
py] 4
5
6
7
B
9
IO
11
12
13 16
16
LOG BETA 0=6 -BB LOG BETA 00 =12-31
14
14
12
12
,... IO
10
a:
:i:
o...
8
....J 8
a: ...., e,
6
. CJ 6
....J 4
a :o b :0 . 0001
2
2
e e
:0 . 001 :0 . 01 :0.1
12
13
d o
o 4
s
6
7
B
9
IO
Il
12
13
6
7
8
9
10
M M M M M
pH I
2
3
4
5
11
14
e -+-_.___JL_--'--_J_----1._,1__--'----1..-----1_L--1---1..-----1- L ---'----1..--,JL-..L,-_J_,......J.-L---'--_.___JL_--'---+-8
7
7
6
6
5
5
4
3
3
2
2
O-+----.-.-~-.---r--,.-.----.---.-++-,--l---r--ir--.--r-r--r-,--,---,--,-...------.---.-,--,--4-0 I
2
3
4
5
6
7
8
pH
9
10
11
12
13
14
r
L
Dysprosium(l 11 )-Pyridine-2,6-dicarboxylate
254
14
d
12
e
10 b
4
a
a :o
2 2
a 3
4
5
6
7
B
9
IO
o Il
12
b :0.00001 C :0, 000 1 d : 0. 001 e :0. 01
pH I 2 3 9r_.___.___.___J_
5 6 .L.._.l...._..L__j_.....J.._j___JL_L 7
M M M
___j__JB L1-19__j~lf0-1.~11~~'12,...J...__J_I3_
1
6
5
3
2
0
T1
~2r i-13~r-r4, 75:--rlr6--r-7r--r-~8~r-9l--r-l-.--J---.---.------.-----r--rJ.0 10 11 12 13 14 pH
d
Dysprosium( 111 )- 5- Sulphosalicylate
255
ovl 7
6
8
9
10
Il
12
LOG 8ETA 0 =8,29 LOG BETA 1=2, 42 LOG 8ETA 00 =14 , 89
14 I4
12 12
10
,.... 10
a:
J: 8
O-
.J 8
a:
,..J
c.')
6
O 6 .J 4
t1
O :O
2
2
b
,0 .001 t1 e ,0 . 01 t1 d ,0 . 1 t1
5
pH
I
2
3
4
5
6
7
8
9
10
Il
12
14
13
8
B
7 7
6 6 5 5
pM '
4
3
2
2
1 1r 1 ot-.-,-.-.------r-r---.,,JL.~+--r 5 I 2 3
pH
7 - • ; ç - , 7 ~ • ~· 7 1~3
1
~ 1~4°
·~
256
Dysprosium(l 11)-Tartrate 4
5
6
7
8
16
9
IO
Il
12
[Ch. 13 13 16
14
LOC, BETR 0:3 . 30
14
12
12
~,o
a:
IO
I
CL _j
a:
8 8
o
o_j
6 6
4
4
e
a :O
d
5
6
7
:0 . 00 1 e :0 . 01 d : 0 .1 e -:0 . 3
2
o 4
b
8
o
9
10
11
12
13
6
7
B
9
IO
M M M M M
pH
I
2
3
5
Il
12
13
14
8 -+--'---1-.,___.__._--J'--'---'---'-----"'-...__.__._...,.....--,-.._......__.____._.._......__.__._..._......__._-+-B
pH
'
'
.
CHAPTER 14
Er
Erbium (lii)
Hydrolysis of the rather large Er 3+ ion does not start until fairly high pH. At ordinary concentrations, hydroxide is always precipitated when the hydrolysis is being studied ; precipitation starts even when only small amounts of the ion are hydrolysed. There is conclusive evidence, however, from the limited amount of reliable information available ' that the polycomplex Erz(OH)t is formed. As with most rare earths, the study of hydroxide precipitation is difficult because of supersaturation, colloid formation and the dependence of *K50 on particle size, and rapid partial recrystallization. These phenomena make the definition of a generally useful equilibrium situation somewhat arbitrary. Tue following data adopted from the compilation of Baes and Mesmer [ 1] hold for a one-hour~ld precipitate. log log log log
*~ 1 *~2 *~ 3 *~4
= - 7.9 = -16.0 = - 24.2 = -33.0
log *~ 22 = -13.7
log *K50
=
16.0
Tue information available about carbonate formation suggests that it should not occur, and that CO 2 will not be absorbed.
I 1 I C.
F. Baes and R. E. Mesmer, The Hydrolysis of Cations, Wiley, New York , 1976.
Erbrum(II I)
eri
259
7
10
11
li'
I3
IO
11
IZ
13
6
6
o 5
1
8
pH
9
14
260
Erbium(l 11)- Acetate
3
5
7
6
B
9
IO
Il
[Ch. 14 12
16
16
1,
14
12
12
~ ID
LOG LOG LOG LOG
BE TA 0 : I • 60 BtTA 00 : 2 , 90 BE TA000 :3. 70 BETA 0000: 3 , 60
IO
a: I
CL ....J B
a:
B
ò
o
6
6
....J
4 d
2
O :O b :0 , 03 e : 0 .1 d :0.3
2 e
o 3
6
7
B
10
9
M M M M
Il
pH I
2
B- r ~ _ ._
3 4 5 6 7 B 9 IO 11 12 13· t4 _.____.___.__...__.____.___.__...__.____.___._-r-'..__.____.___.__...__.____.____.__.__._-'--L--+B
7
7
6
5
3
2
2
2
3
5
6
7
B
pH
9
ID
11
12
13
14
Erbium(l 11 )- Acetylacetone
erl
261 3
4
5
6
7
8
9
10
16
11
12 16
14
LOD BETA 0: 5 . 99 LOD BETA 00:1 0 -67 LOD BETA 000 : 14. 85
14
12 12 ,.... 10
a:
IO
:e
o..
..J
a: _,
e
8
a a
6
6
_j
4
4
O :O 2
b
: O. 0001 C :O.ODI :O . O! e :0.t
2
d o
2
3
4
5
M M M
12
pH I
M M
6
8
8
9
10
Il
12
13
14 8
7 7 6
6
5
5
pM' 4 3
2
2
o
o I
2
3
4
12
5
pH
13
14
262
fabium(lll)-DCTA 2
3
4
5
B
7
6
9
[Ch. 14 10
16
16
14
14
12
12
~,o a:
IO
LOG BETA 0 :2 1 ,40 LOG BETA 1:1 2 ,00
I
a... -1 a:
B
B
o
o
6
6
_j
4
4
O :O 2
2
o
o I
2
3
4
5
6
7
8
9
IO
6
7
8
9
10
M
e
,0.001
d
M
:O.O! :O.I
M
e
o
M
b :o . 0001
M
pH 2
3
4
5
Il
12
13
7
7
6
6
5
pM
5
4
3
3
2
2.
2
3
5
6
7
B
pH
9
IO
11
12
13
14
Erbium( 111 )-DTPA
~rl
263 5
6
7
B
9
16
10 16
14
14
12
12
,- 10
10
cr:
LOG BETR 0:2 2. B3 LOG BETR 1: l 4 -2B
:r::
o...
_j 8
8
cr: ...., à
O 6
6
_j
4
4
o
2
2
a :o b : 0.0001 e
d
I
2
3
4
5
6
7
o
8
9
10
8
9
10
e
:0.001 :O . O! :0. 1
M
M M M M
13
B
7
6
5
pM '
4
3
2
o
o 2
3
4
10
7
pH
264
Erbium(lll)-EDTA s
6
e
7
10
9
[Ch. 14
Il
1,
14
12
12
~IO
10
a:
LOO BETA 0: I B. 85 LOO BETR 1:I0,65
I
a.. .....J
a:
e
e
6
6
'
'
o o
.....J
2
2
O :O
M
b
M
e
d o
e
o
3
5
6
7
8
10
9
11
: O. 0001 :0.001 :0.01 :O.I
M M M
12
pH I 2 3 4 5 6 7 8 9 10 11 12 13 14 8 ~---'-----'--'-----'----'-----''---'-----'----'-----''--_._.....__.__~_._.....__.__~_._.....__--.-,-.....,_...._......__._-+ 8
7
7
6
6
5
3
2
O,+-- , - -,--,----,---,.-..---.---,--+-,-,-----,--r----,-,-----,--,-----,,---r1-----+----+r-+-r-.--.-----r-r--t-
l
2
3
4
5
6
7
8
pH
9
10
Il
12
13
14
Erbium( 111 )-(OH )-Ouinolinesulphonate
~rl 5
6
e
7
9
265
10
16 LOG BETAo=7 . 05 LOG BETAoo= 13 · 20 LOG BETAooo=IB.,S
14
12
10
,.- I O
a:
:i:
a... _i
a: ...,
e
e
6
6
c:J O _.J
a :O 2
,0.0001 11 e , 0.001 11
o
e
d 11
11
b
:O.O! :O.I
11
11
12
pH
l _L-j2~..L._l3_L_J__l~SL--L_JS~..L.~7L..L~/==~9~~~1:0:_ . ì111:_r_1L_ 2...l...._1_,_3_ _11' B e
7
6
o
6
5
3
3
2
2
Erbium(l 11 )-1 minodiacetate
266
[Ch. 14. 3
4
5
6
7
12
11
10
9
8
16
16
14
14
12
12
~IO
10
a: :r: a... _J a:
8
LOG BET A0: 7 , OS LOG BETAoo:12 . se
8
ò
o
6
_J
4
2
O :O
M
b
M
e
d e 5
4
7
6
8
9
10
:0.0001 : 0 . 001 : 0.0 1 :0. 1
M M M
11
pH 1 2 3 4 5 6 7 B 9 10 11 12 13 14 B-;-~-~~_._~_..___,___.__._....__._-'-___.'---.,__._-'-,-'--,-'-,.-'---'-.1_-L--1._JL._.L_~ B
7
6
6
5
5
3
3
2
2
0,-,--,,---,--,----,-,--,--,----tti-r--r--.-rr,---,--.-r--,---,--,-.--------,--,-- , - , -+o I
2
3
4
5
6
7
B
pH
9
IO
11
12
13
14
Erbium(III )-Oxalate
Erl 3
16
5
'
6
7
B
IO
9
li
267 12 16
IA
1A
12
12
,... 10
10
a: :r::
LOG BE TFl 0:4 ,BO LOG BETF1 00 =B. 20 LOG BETF1 000 =I O. 00
e
o..
8
..J B
a: _,
d
à
o ..J
6
6 e 4 b
2
2 o
o
3
4
5
6
7
B
10
9
11
12
o
O :O b :O.ODI C :O.DI d :O. I
11
e :0.3
11
11 11 11
pH ! 2 3 4 5 6 7 8 9 10 li 12 13 14 8-4-__._~-'-_._---'--'--'-..L....-'---'-_jL--'-...&...,__._~~ J-,.1-,...J...-1.--L--'-.J.__1.__JL--'-+ B
7
6
6
5
5
3
2
2
0- 1 - - - - - - - - - - - ~ J . . . - ~ 1 - . - ' - ~ ~ - ' - - - ~ - - - - ~ ~---~--+-0 11 12 13 10 14 7 9 B 6 l 5 2 3
pH
Erbium(l 11 )-Pyridine-2,6-dicarboxylate
268
,,
" 5
3
2
7
6
B
9
IO
!eh
li
16
16
14
14
12
·lq
Loo Btr 11 Loo Btr o-8.7s LOo Btr:00°15, 32 000=21 , 96
12
~ ,o
a:
IO
I CL _J
B
a:
B
ò
o_J
6
6
4
a
a :o
2
2
b =o -0000 1 e
o 2
3
4
5
6
o
7
B
9
IO
Il
6
7
B
9
IO
pH 2
3
5
4
8
d e
:0. 000 1 " :0.001 :0.01
" "
Il 14
e 7
6
5
s pM'
4
3
2
o+-r--r"-T---i-r--.-,---,-+,---,-~--,r-rl-,---,L---,-----,'L,~.L.,--,r-r-r,r--i~ I
2
3
4
5
G
7
B
pH
9
10
14
Erbium( 111 )-5-Sulphosalicylate
269 6
5
B
7
9
IO
11
12
_.L--'-~~--------__.___,__t- 16
16 LOO BETR 0 : B. 15 LOO BETR 1:2 - 12 LOO BETR 00 : t 4 . 45
O :O
b
2
3
4
5
B
7
9
10
Il
M
:0.001 M
C : O.O!
M
d
M
12
:O.I
13
I
14
B
7
7 6
6
5
5
. pM
4 4
3
3 2
2
o 11
o 2
3
4
5
pH
12
13
14
Erbium (111 )-Tartrate
270
3
5
6
B
7
9
IO
li
[Ch. 14 12 16
16
14
H
LOO BETA 0=3 .33
12
12
IO
~IO
a:: I
o... _j
a:
B
o o
_J
6
6
A
e d
2
2
e
o 5
6
B
7
IO
9
11
O :O :O . 001 C : O. O! : O. I e :o.3
b
M M
d
M
M M
12
pH I 2 3 4 5 6 7 B 9 IO 11 12 13 14 B-+---'------'-.._-'---'----'--'-..,__-'--'-----'--'----'--,--4----'-- ..._-'---'-----'--..._--'---'-----'-- .l--'--I-B
7
6
6
5
5
3
3
2
2
0 -+--r----r- . -. - - .--.~,---.-,H---f--T on particle size, and rapid recrystallization. These phenomena make it difficult to define a useful equilibrium situation. The following data have been adopted; the solubility product applies to a one-hourold precipitate. · Iog *P 1 log *P 2 Iog *P 3
= - 8.0 = -16.3 = -24.5
log *P4 log *P 22 log*K&>
= -36.0 = -13.9 = 18.7
There is evidence that a hydroxide-carbonate mixture is precipitated from air-saturated solutions, but this does not measurably influence the pM' -pH plot below pH 11.
NwtymhtmOIO
~l
0--+--------,-F-"-.--~1-=q~•q~+-,.-.----,,--,-,------,------,------,--,-~~~ - = - = - - . µ1 ' 4 I\
5
l'i
7
8
pH
10
ll
\~
Neodymium(l 11)-Acetate
498
e
7
6
5
3
9
!O
11
[Ch. 26 12 16
16 14 14
LO G BE H; 0: I •90 LOG BETA oo-_3 •SO LOG BETA ooo--s •Oo
12 12 IO ,.... I O
cr: I
CL __J
cr:
e
o
e:)
__J
6 6 4 4
d
e
2
2 b 4
5
6
o 8
7
9
IO
pH
7
pH
li
12
O :O
11 :0.01 11 C : O,! M d : 0.3 11
b
Neodymi u m ( 111 )-Acetylacetone
499
Nd] 4
5
6
7
9
8
10
11
12
13 16
J6 L0O BETA 0 =5 , 30 L0O BETA 00 =9. 40 L 0O BETA 000:12 .60
14
14
12
12
10
--10
a: :r:
a... _.l
a:
B
8
6
6
4
4
d O _J
O
b
2
2
C
o
o 4
5
6
7
B
9
10
11
12
13
6
7
B
9
10
M :O :O . 0001 M :O ,001 M
d
:0 . 01
M
e
:0.1
M
pH 2
3
4
B-+-___._ _,___.__ _._____.__ _._____.__
5_
11
12
13
14
_._____.__~___._-~~~-~~--L-r---'-------'--_._____.__~~~~ --a
7
7
6
6
pH
J
Neodymium(l 11)-DCTA
[Ch. 26
500 3
4
5
6
e
7
IO
9
li
12 16
16 LOG BETA 0: 18 , 40 LOG BETA, : 8 , BO
14 14
12 12 ID ~IO
:X:
o...
_J
a:
e e 6
a 4 4
O :O 2
2
o o
5
3
6
7
e
9
10
li
6
7
8
9
12
10
b
M :O , 0001 M
e
,0.001
M
d ,o.o ì
M
e
M
, 0.1
pH
3
2
4
5
11
12
14
8
6
7 7 6 6
5
5
a
pM '
4 4
3 3
2 2
~/2
al o 2
3
4
5
6
8
7
pH
9
10
11
12
13
Neodymium(lll)-DTPA
Nd]
501 6
2
7
e
9
10
11 16
16
L0G BETR 0:21,69 L0G BETR1:13 ,53
14
12
12
,.... 10
10
C[
:r:
o..
e
e
O 6 ...J
6
...J
C[
CJ a
4
a 10 2
b e
d o 9
10
e
:0.0001 :0.001 :0.01 :0.1
11 11 11 11 11
11
pH 2 al•_ _L__J_L_J3_L_j4_
7 10 8 9 13 11 12 .L__J5_.L__j6_L_l__L__j__L_l___j___:_[_J_L_..L__...,1-__._\001
7
6
5
3
2
2
3 2
o;;--' 711;--rt-t-~;--r-~ o PH
\
Neodymium( l 11 )-EDTA
502
4
5
6
7
9
B
11
10
12
[Ch. ~e 13 16
16
LOG BETAo=l6 . so L0G BETA,:B , ?o
·14
14
12
12
10
~10
a: I
CL _J
a:
B
B
è)
o_J
6
6
4
4
O :O b :0 . 0001 e :0.001 d :0.01 e :0 . 1
2
2
o
o 4
5
6
7
8
9
10
l!
12
13
6
7
8
9
10
M
11 11 11 11
pH
2
3
4
5
8
11
12
' ' '' '' ''
13
14
8
::
!'
7
pM'
7
6
6
5
5
4
4
3
3
2
2
pH
Neodymium(! 11 )-(OH )-Ouinolinesulphonate
503
Nd]
L0G BETA 0:6 ,07 L0G BETA 00: l l , 26 L0G BETA 000 =15 ,5B
14
12
,- 10
a:
X:
o.. _j
a:
8
,.J
é)
O 6 ...J 4 O :O
M
b
M
:0,0001 C :0,001 d : 0,01 e :0 , 1
2
o
M
M
6
5
4
M
PH
II I 7
7
6
6
5
5
pM '
4
4 3
3
I
'I
2
2
o-l-..,.........,.........,.........,......._ _.....-.....---,-l.J-,tl-r----r---::r"'~-r-r-+r-r-+r-r-r--:i:::--r---:i::--r--:t:" l
2
3
4
5
6
7
pH
.J
Neodymium(lll)-lminodiacetate
504
[Ch. 26 B
7
6
5
9
10
11
12
1'
14
12
12
- ,o
10
a:
LOG BE TA 0: 6 , SO LOG BETA 00 : 11 . 39
r
Q_
....J
a:
B
B
6
6
4
'
Cl
o
....J
O :O : O, 0001 e ,0.00 1 d : O. O! e ,0.1
b
2
o 5
4
6
7
B
9
10
11
12
6
7
B
9
M M M M M
pH 3
2
I
4
5
IO
Il
12
14 8
B
7
pM
.
6
6
5
s
' 3
3
2
2
o~ - - -- - - -- - ---+.--+...1---.,t.....- ---,+--~-~- --,.-~--.--,--.-,-To 4 1
2
3
4
5
6
7
8
pH
9
10
11
12
13
1
Neodymium( 111 )-Pyridine-2,6-dicarboxylate
505
Ndl 7 8 6 9 10 11 _.L__j'--r.L-...L-.-L.~---'--~~~~~___._...._....._, 1 6 16
L 0G BETA 0 =8-73 L0G BETA 00=15 . 40 L0G BETA 000=20. 4 1
14 14
12
12 10
8
6
4
a 2
1·1
2
3
4
5
6
7
8
9
10
11
6
7
8
9
10
t1
e
,0.00 1
t1
d
:0.01 ,0 .1
t1
e
o
o
a ,o b ,0 . 0001
t1
t1
pH
I
... I
2
3
4
5
11
12
13
14
8
8
7
7
6
6
5
5
pM' •
4
3
3
2
2
pH
Neodymium(l 11 )-5-Sulphosalicylate
506
[Ch. 26 2
3
4
5
7
6
8
9
IO
Il
16
16
14
14
12
12
,..... IO
LOG BETAo:7 .39 LOG BETA1=2 ,09 LOG BETA oo--13 •OI
10
C[
I
o.. _J
C[
8
8
ò
o
6
6
_J
4
2
a :o
b e
o 2
3
4
5
6
7
d 8
9
M : 0 . 001 M :0.0 1 M :o.i M
10
pH
7
6
6
5
5
3
2
o+---.-r----,r-.-,-----,----.----,c-T-1~'-h--l-r--,--.-----,---.-~----,--.-----,---.----r--,--r-,,o I
2
3
4
5
6
7
8
pH
9
10
li
12
13
Neodymium(l 11)-Tartrate
507
Ndl 7
6
5
4
3
8
9
10 16
L0G 8ETA 0 =3 -45
14 14
12 12
10 ,- 10
a: :r:
8
a..
....J 6
a:
6
e!)
a
6
_J
4 4
e d
2
e
2
o 1
2
I
2
3
4
5
6
7
B
9
6
7
B
9
a :O
t1
b ,0.001 e ,o .01 d ,0 .1
t1
e
t1
,0.3
t1 t1
II
pH
3
4
5
10
11
12
13
14
B
6 I I
7
7
6
6
5
I pM'
4
4
3
3
2
2
II
I'
L,
I
I
o
o 2
3
4
5
6
8
7
pH
9
, I,
CHAPTER 27
Nickel . (Il)
Ni
The first hydrolysis constant, log *(3 1, of Ni 2+ is accurately known. The other constants have been estimated from solubility studies, and are less certain. The polycomplex NiiOH)l+ is extensively reported in the literature; it has been found at moderate nickel concentrations at high ionie strengths, and it gives rise to a polycomplex line on the pM'-pH plot. The existence of Nii{OH) 3+ is assumed tentatively. Solid Ni(OH}i is more stable than NiO in aqueous medium. However, a wide range of values for the solubility product of Ni(OH}i has been reported because of uncertainty about the physical state of the solid. For active Ni(OHh, freshly precipitated from solution, log *~ = 13.3, but values down to 10.8 have been reported for the inactive aged form. The values used for construction of the plots are: log *(3 1 log *(3 2 log *(3 3 log */34
= -10.2 = -19.2
log *(3 12 log *(3 44
= -10.5 = -27.3
= -30 = -44
log *K&"O
=
13.3
The equilibrium between Ni 2+ and Ni(OH}i(s) can only be established in solutions with a redox potential below E = (897 - 59. I pH) m V. In air-saturated solutions, there is an equilibrium between Ni 2+ and Ni 3O4 ; a value of log *K&"O = 8.5 can be calculated for the solubility product of Ni 3O4 • Normally, the oxidation proceeds too slowly to be important, but its rate may be increased by catalysis. No carbonate formation occurs in air-saturated solutions (log Kcarb = 14.8).
Nickel(II)
509
Nil
7
6 6
5 5 4
3 3
2 2
o-+-~~-~-~-~----~-...-1--~-'---'-r-~---~---~-'---.,___-~o e 1
2
3
5
6
9
7
pH
IO
li
12
13
14
510
Nickel (11 )-Acetylacetone
[Ch. 2ì 5
4
6
7
8
9
IO
11
12
13
16
16
14
14
12
12
10
IO
LOG BETAo: 6 •06 LOG BETA 00 =l0,7? LOG BETA 000 : 13 ,
09
-
a: I a... _j a:
8
8
6
6
4
4
c.!)
o_J
O :O
b
2
e
d o
e
o 4
5
6
7
8
9
IO
11
12
13
6
7
8
9
10
H
:0.0001 M , 0.001 M , 0 . 01 M :0, 1 M
pH I
2
3
5
Il
12
5 -1----1...---1_L-..L_-'-----'-__J'----'----'---'-----'--'---'--_.___.____._.,___,...__._..,....,____,._,....-'--..J,...-.J__-L--.L.
7
6
6
5
3
2
o..!---.---,--,--,--,-----,--..-------r----,-----rc!L:--./4---,-----,----,.,.L,--,,-r-/--,--,--,L,-,-,-,:i:-o I
2
3
5
6
7
8
pH
9
10
11
Nickel ( 11 )-Ammonia
511
Nil 7
8
10
9
12
11
13
14 16
16
LOG LOG LOG L OG LOG LOG
14
14 12
12
BETR 0 :3 . oo BETR 00:5.28 BETR 000 =6. 82 BE TR0000:7.98 BETR 0 0000:8.60 BETR 000000 =8 . 60
10
,.- I O
a:
:i:
8
O-
_.l B
a:
6
cJ C) 6 _.J
4
o b
2
o 5
6
7
;O
M
e
;0.0 1 M ;O.I M
d
;!
M
8
pH
2
3
4
5
G
8
7
9
10
11
12
13
14
e
B
7 7 6 6 5
5
pM
1 •
I I I
3
I
2
2
pH
I
512
Nickel(l 1)-Citrate
[Ch. 27 16
z
3
4
5
7
6
e
9
10
Il
16
14
14
12
12
~IO
IO
a:
LOG BETRo=S . 40 LOG BETR 1=3 , 30 LOO BETA 1=1,?S Loo•eE TANLON=- 7 •90
I
o.. _J
a:
e
e
e!)
o
6
_,J
4
a ,o b :0 . 0001
2
e
d e 3
4
5
7
6
e
9
pH
pH
IO
:0.00 1 :0.01 : O,!
M
M M M M
r
Nickel(II) Cyanide
513
Nil 7
e
9
IO
11 __j__L__L.-J.-'7..___1_~r-~__.____.--r1s
16 14
LOO BETR 0000: 30.40
12 12
IO ,- 10
a:
:X:
0-
.J
a:
e
e
6
O :O
M
b
M
e
a
d o 10
e
: 0.0001 ,0.001 ,0 . 01 ,0 . 1
M
M
I
M
Il
111
pH
14 12 13 IO li 7 8 9 6 5 ej1_L-l2___J_L3.J.._J.___lL-L...L_j_-L-J_-L_j_1--...L-L_j__L-..1.._....1.....J.--'-:--'--~ 1 8
7
6
5 I
I
I
pH
I
Nickel(l 1)- DCTA
514
[Ch. i1
1'4
14
12
12
-10
10
a:
LOG BE TAo=20. 30 LOG BET A1 =1 l , 2Q
I
a... ....J B
B
a:
o o
....J
6
6
4
O :O
b
2
2
e
d e
o
o 2
3
4
5
6
7
8
9
10
Il
s
7
8
9
10
t1 : 0.0001 11 :0.001 11
:O.O! :O,!
M 11
pH
I
pM'
2
3
4
5
Il
12
13
14
8
8
7
7
s
6
5
5
4
a
3
2
2
pH
.P
,
Nickel(l I)-DTPA
Ni] 5
"
16
6
7
B
515
9
11 16
1-'
1"
12
12
. - !O
IO
cc
LOG BETA 0 :20 , 30 LOG BE TA. =15.-40 LOG BETA,:9 . 80
:I:
a,_
_J
cc
e
8
6
6
e)
O _J
4
2
2
o
o 5
2
O :O b ,0.0001 C :O.ODI d :O . O! e ,0.1
o
6
7
8
9
IO
11
6
7
B
9
10
M M M M M
pH I
2
3
4
5
11
12
13
14
B
8
7
7
6
6
5
5
I
pM '
4
4
o
I
3
2
2
2
3
5
6
7
B
pH
I
9
10
li
12
13
14
I
'
1'
Nickel(ll)-EOTA
516
[Ch. 27 10
2
3
16 LOG BETA 0: 1B , 60 LOG BET A, =1 1 ,60 LOG.BETA ftLON=-12 , 20
14
u 12 12 10
~ ,o a: I
a.... ....J
a:
e
è)
o
6
....J 4
'
O :O
2
b
2
a
e
d e
o
o 2
3
4
5
6
7
8
9
10
li
6
7
e
9
10
:0 . 0001 ,0 . 001 :O . O! : 0.1
n n n n n
pH
e
I
2
3
4
5
Il
12
13
14
e
7
7
6
6
5
5
pM' '
a
3
3
2
2
•/, o I
2
3
5
6
e
7
pH
o 9
IO
Il
12
13
14
Nickel{l 1)-EGTA 7
6
5
4
8
9
517 10
11
2
16
16 14
14
LOO BETA 0:13 .55 LOO 8ETA 1 : S . 18
12 12
10
,- 10
a:
:e o... _.I
a: '-' C)
8
e
6
6
_.I
4
a :O 2
b
2
a
e
d e
o 10
11
9
10
,0.0 0 01 , 0 . 001 ,0.01 ,0.1
11 11 11 11 11 I
II
pH I
2
3
4
7
6
5
8
12
13
14
\
8
8
7
7
6
6
5
5
p M'
11
4
a 3
2
2
3
4
5
6
7
pH
Nickel (11 )-Ethylenediamine
518 5
7
6
9
B
10
li
12
13
[Ch.27 14
16 -+-__J_........J_.L.......L-L........l-.L.......L-L__J~..L--'----'--~-'---'-----'--t- 16
14
14
12
12
~IO
10
a: I a... _J a:
LOG BETA 0:7 ,SO LOG BETAoo=l3,Bo ~DG BETAooo=IB. IO
B
o
o_J
6
4 O :O
:0,0001 M C :0,001 M d :0,01 M
2
2
e
o-4--,:;;,.::::::.,,-=::;,.:::::,....-,---._......-...,....:::::;..-.-......---.--,---.--,---.--,---+o
s
s
1
a
s
10
11
12
13
M
b
:O,!
M
14
pH 3
2
I
4
8 -+--'-__JL._..L-....L-'-__J-
e
IO 11 12 9 13 7 6 5 .L.......L__L----1-.J..._....L__L----1-.J..._....L----'-----1-.J..._....L,...J------1---,-.L.....L.,..L__j_
7
6
5
a
b
3
2
o+-,--,-,----,---,---,r-.-----.---.---,rr--nC.,.--,--,--,----.-----.--r---,-----rh--r---H'-r---i---t" I
2
3
5
6
B
7
pH
9
10
11
12
13
Nickel(ll)-Glycine
5 19
Nil
14
L0G BE TR0 = 5 . 7B L0G BETR 00 = 10 . 5B L0O BETR 000 : 14 .00
12
10
B
6
2
M
d
M
e
o 6
o :O b : 0 .0 0 01 e - :0. 0 01 :0.0 1 :O . l
M M M
II I
7
pH
2
5
3
6
B
7
9
10
11
12
13
14 B
6
7
7
6
6
5
5
pM' •
4
9
3
2
z
,1
1
o 2
3
4
5
6
B
7
pH
10
'j
Nickel (11 )-Hydroxylamine
520
2
5
3
IO
9
8
7
6
[Ch. 27 11
16
16
14
14
12
12
,.... IO
10
a:
LOO BE TR 0=1 , SO LOO BETR 00 =9 . 70 LOO BETRoaoo= 12 • SO LOO BETR000000=IB,S5
:e a... _J
a:
8
8
6
6
o o
_J
4
'
e
a .o b .o . 0001
b
2
a
o 7
8
9
10
M M
e
.0.001
M
d
. 0.01
e
; O.I
M M
11
pH
6
6
5
5
3
2
O-t--,-,- ,--,---,-r-.--,---,-,r-,-f--T----,i---r---l--,--.--/.----.-,-....---,---,-,r,----,-,-o 1
2
3
4
5
6
7
8
pH
9
IO
11
12
µ Titanyl
Ti(OH)~
-1
O
2
3
5
661
6
7
8
9
10
11
12
B+-J...~____l-.l.....--'--'--i-.1.....--'---1...-1_l_..L-1...-1_jL_.L..L-1.._J__L_..L_L......L_j_~B
•o
0 ..J
7
.
7
,e o
0 ..J
6
6
5
5
3 3
2
2
0-l--~-l-.--.-,--,--r--,,-,--,------r-,-~--,---.--r-ir-.----.--r--.-r--.--.--r-ir-~O 12 11 10 9 8 7 6 5 4 3 2 -1 o
pH
' Titanyl-EDTA
662
[Ch. 37 9
LOG BETA 0=17. 50
14 14
12
10 ~10
a: I
Q_
a:
B
e
ò
6
c:J 6
4
O :O
b e
2
d
M ,0.000 1 M ,0.00 1 M ,0.01 M
e :O, l 5
2
6
7
4
5
M
pH -1
O
2
3
6
7
8
9
10
11
12
B+---'----'--'---'---'----'--'---'---'----'--'---'---'---'--"------'-r----'--'-r---'----'-,-''----'--'----'-L-+B
7
6
6
a
5
5
pH
e
Il Titanyl-Fluoride
Ti(OH)~1
663
o
-1 16
LOG LOG LOG LOG
14
I4
12
12
BETA 0 :6 .60 BETA 00 : 11 • 70 BETA 000 : 16. 30 BETA 0000 : 2 0. 40
10
,-. I O
a:
X:
a.... _J
8
8
a: à
o
6
6
_J
4
4
O
b 2
2
o
o
e
d e
o
-1
2
3
4
5
6
7
8
4
5
6
7
8
r'
:O , 0.00001 ,0.000 1 ,0.0 0 1 :O.O! :O.I
11 11 11 M 11 M
pH -1
O
2
3
9
10
11
12
8-+--L-....L.--'---'--..L.----'-...L--'~-'-~ '---'-- L---'--~-'--'---- -'--'---~-'-- ' - --'--'-~-'----'----'-----'--+-8
7
7
6
6
5
5
-1
a
o
2
pH
[Ch , 37
Titanyl-Oxalate
664 -I
o
16 LOG BETA 0=6 ,60 LOG BETA 00=10,70
14 14
12
12
10
~ 10
a: :e a.. ...J e a: e,
o
6
...J
4
O :O
M
b ,0.001
M
d ,0.1
M M M
e ,0.01
2
e
o -I
o
2
3
4
5
6
7
4
5
6
7
,0.3
pH 2
3
8
9
10
Il
-I a,~---'----'-----'----'---..L._~----1._L-r-1-~~.1__L...JL__J___j____l___L...:..r____.1__1._J
12 8
7
7
6
6
5
5
4
3
2
2
o:_1;--"'6'-i'7-'73j'7T4-/-1s~'~sr--,7-,,-ir-,------.-.--,----~Jo 7 10 11 12 B 9
pH
I
Titanyl-Salicylate
1 i(OH)f) 2
o
3
4
5
6
7
665 8
9 16
16
14
14
12
12
,..... 10
IO
a: :r:
a...
6
8
CJ 6
6
__J
a:
LOG BETA 0 :!5.66 LOG BETA 00:2 4 .40
e, __J
4
2
d
:O M :0.001 M :O.O! M ,0.1 M
10
11
O
2
b C
o
o
2
3
4
5
6
4
5
8
pH -1
6
o
.1
2
3
6
7
8
9
12
8
7
7
6
6
5
5
pM' "
,1
3
3 2
2
pH
Titanyl-5-Sulphosalicylate
666 o
5
3
2
7
6
B
[Ch.37 9
16
16
14
14
12
12
~,o a:
10
LOG BETA,=3. I O LOG BETA 11 =5. 40 LOG BETA 110=1B,46
I
o... _J
a:
B
B
6
6
4
4
2
2
ò
o_J
O :O M b :O.O! M e :0 . 1 11 2
3
4
5
6
7
B
4
5
6
7
pH -I
O
2
3
B
9
IO
11
12
a +~-.__._---'--~-~~~~.__._---'--~-~~--+-.___._____.__.__.___.__.__.___,__---l-+-a
7
7
6
6
5
5 a
3
3
2
2
O--r,--r-,--~,---r--,--- ,--,-,--,-----,--,----,--,---r---,--,---,---,-- , - --,---,-----,-,----,--t-0 -l o 2 3 4 l2 5 6 7 li B 9 IO
pH
, Titanyl-Tartrate
2+1
667
r;(OH)2
5
3
2
6
7
B
9
16 16 LOG BETA 00:9 . 70
14
I4
12 12 10
,.... 10
cr:
J:
o..
B
....J
6
cr: Cl
6
O 6 ....J 4
2
2
o
O :O M :0.001 M e :0.01 d :0.1 M e :0-3
b
" "
-o 2
o
3
4
5
6
7
B
9
4
5
6
7
8
pH -I
O
2
3
9
IO
11
12
5--l---'---'----'---'-....L....._,__.,__.___,._+-_.__...._____,,....,_-.-''-....L....._,__-'---'---'---'---'--'---'----'---'---+-8
7
7
6
6
5
5
4
3
3
2
2
o-i--.1,-,--,---.---,. - ~-,-:::::;:_~~~--,-......----r---,.-.---.----.- , - . --.-,,--,--,--+ o -I
O
2
3
4
5
6
pH
7
8
9
10
11
12
-----... Titanyl-Tiron
668 2
3
4
[Ch.37
5
10
16
16
14
14
12
12
~10
10
L0G BET A _ L0G BET u-15.oo A110=32 , 3S
I
a... _J
a:
e
e
6
6
o o
_J
4
O :O 2
e
M , 0 .0 001 M ,0.001 M , 0.0 1 M :0-L M
10
11
b
2
e
d o
3
4
5
6
7
8
9
10
4
5
6
7
8
pH o
2
3
9
7
6
6 a
5
pM'
5
b 4
b:
e
3
3
2
2
o
o o
2
6
7
B
9
10
11
12
pH
E
CHAPTER 38
TI
Thallium (lii)
3
Thallium exists as T1 + and T1 3+ in aqueous solution ; the T1 + ion is easily reduced. In its +III state T1 should oxidize water, but the reaction does not proceed at a measureable rate. The +III state is stabilized by complexing ligands, because Tl + forms much weaker comp lexes than T1 3+_ The stability constants of Tl(OH) 2+, Tl(OH)'; and Tl(OHh(aq) have been deterrnined potentiometrically; the first two are known accurately. There is no evidence of polynuclear complex formation. A value for log *~4 could be estimated from the dependence of the solubility of T l 20 3 on pH. There is a slight tendency for supersaturation to occur, but the solubility of a precipitate, once it has been formed, changes little on aging. Tue following data were used for construction of the plots. log *~ 1 log *~2 log *~ 3
=-
·o.94
= - 2.09 = - 3.8
log*~ 4
=-15.3
log *K50
=-
3.35
11111 Thallium(l 11) TI]
671
7
6
6
5
5
4
3
3
2
2
01 +-r--.---r--.---r----.---.------.---.------,---.------,---.------,---r--.-----ir----r-,----,-----,-,-------,-,-------,-+ o -I O 2 3 4 5 6 7 8 9 10 11 12
pH
Thallium( 111 )- Acetate
672 o
2
3
4
5
6
[Ch. 38
7
8
16
14
14
12
12
,.._ IO
IO
a:
LO!r BETA 0=6 , 20 LO!r•BETA,._w- 1 , 80 LO!r.BETA"LIOHlr=-4, I O LO!r BETA 00 =11 ,30 LO!r BETA 10=8 , 00 LO!r BETA 000 ='15, I O LO!r BETA 0000 = 1B, 30
I
a... _J
a:
o _J
8
8
6
6
4
4
2
2
o
o
-1
o
2
3
4
7
8
7
8
O :O :0.01 C :0 , 03 d :0 . 1 e :0, 3
b
M M M M M
pH -I
O
2
3
4
5
6
9
10
11
12
8---r----~---~~---~--,__~.,...._--~---'---'----'---'--'--'---'-----"--L--+-8
6
pH
8
9
IO
11
12
Thallium(l 11)-Bromide
673
fl] -1
2
o
5
3
6
7
8
16 e
16
LOG LOG LOG LOG LOG LOG
14 14 12 12
BETA 0 :8.30 BETA 00:!4 .60 BETA 000:l 9 020 BETA 0000 =22 .30 BETA 00000 =24. 80 BETA 000000 =26. 50
d
10 ,-. 10
a:
:r: a... _l
a:
B
e
8
c.'.)
o
_l
6 6
b
a ,o
4
b
e ,0.0001
2
a
2
d e
F'
o
o -I
o
2
-I
o
2
3
4
5
6
7
B
4
5
6
7
0
M
: O .0000 1 M
,0.001 ,0. 0 1 , 0. 1
M M M M
pH 3
9
10
Il
12 B
0 7 7
6 6
5 5
pM'
4
3 3
2 2
o+----,r--,----,L~_J~~- 4--,r----,---_J~~---,-i-1----,-,--7- , , - - }6--,79:-------,----;-1 ~0--,~1~1:--r--;i12; 0 -!
O
2
3
4
pH
674
Thallium(l 11 )-Chloride
[Ch.38
-I O 2 3 4 5 6 7 8 15...L--1._L__j____l_L__j____i._L....L____L__JL.._j__L____J_...lr-.........---'-+16
14
14
12
12
~IO
e 8
B
a: ò
o_J
BETA 0:7, 50 BETA 00:12,00 BETA 000 : 14, BO BETA 0000:l 6. 70
IO
a: I a... _J
LOG LOG LOG LOG
d 6
6
e
4
4
O :O
b
b
e
2
2
d
a
e
f'.'
o..L~-.-=:;::::::--r--,-,----,--r----r-r-.------.----.-.--.-----.--,- o 7 4 5 6 B 3 -I 2 o
:0.00001 :0.0001 :0.001 :O.O! :O.I
11 11 11
11 11 11
pH . 5 4 7 2 6 o 3 B 9 10 Il 12 ...L--1.-L....L.----...i..____J~.J.__~----1.-J..,-...L..-'--,-~~-'----'---'--'----'--'---'-----'--'-----'-----'--'------+-8
7
6
6
5
5
3
3
2
-+--r-'-.-+--.--+--,,--f.r---.--.+-.---.--,.-.---.---,--.---,--r--,.---.--r-.-~-,----.-.--+o
o
2
3
5
6
pH
7
8
9
10
11
12
:a:
111111 Thallium( 111 )-DCTA
il] 2
"
3
s
6
7
675 B
14
14
12
12
~10
10
a: :r:
LO!, BETA 0 ::3B, 30
CL
.....J B
B
a
a:
è)
6
O 6 .....J
2
2
O
:O
b
:0.0001 M
M
C
:0.001
d
:O.O!
M
M
e
:O.I
M
pH
B
10 11 12 _t__--1._.,___..__iÌ0
7
7
7 B 9 2 -1 o :l-1_1--1._.L-1._L-1._.L-1._i"_..L_j_s_J__6_i___L_L_-1..._JL..._L_-----1_
6
s pM'" 3
2
pH
-......._ 676
Thallium(l 11 )-DTPA o
2
3
'
6
5
7
[Ch. 38 e 16
1'
14
12
12
-10 CI:
10
L0C. BETA 0: , 6 ,00
:e
CL _J
CI:
a
8
8
ò
o _J
6
6
' 2
2
O :O
M
b
M
e
d o -1
o
e
o 2
3
5
6
7
8
5
6
7
8
,0.0001 , 0.001 ,0.01 ,0.1
M M M
pH -1 8
pM
.
o
2
3
'
9
10
11
12 8
7
7
6
6
5
5
' 3
3
2
2
pH
Thallium(ll 1)-EDTA
677
111
'
3
6
5
7
B 16
16
.,
LOG BETA 0 : 36.00 LOG•BETR,._.,.=-6 .oo
1'
12 12 10 ,... 10
a:
B
:X: 0-_.J
a: _,
6
6 C)
6
_.J
'
O :O ,0.0001 e , 0.001 d , 0 . 01 e :O.I
b
2 2
o
o
-I
o
2
-I
o
2
3
pH 3
'
5
6
7
8
4
5
6
7
8
9
IO
Il
"
" " "
li
"
12
8
8 7
6 6
5 5
pM
.
'
4
3
3
2
2
pH
6
4
7
8 16
14
14
~,o a:
IO
_j
8
8
6
6
I CL
o o
_j
LOG BETA 0 =1 1 , 57 LOG BETA 00 = I B. 30 LOG BE TA 000 =2 4 . 30
12
12
a:
'
[Ch. 38
Thallium ( 111 )-1,10-Phenanthrol ine
678
4
4
2
2
o
o -I
o
2
3
4
6
5
pH
pH
7
8
O
:O
M
b
:O.ODO !
M
C
:O . ODI
M
d
: O.O!
M
e
:O . I
M
..... Thallium( 111 )-Sulphate
679
fl ) 2
4
3
6
5
7
8 16
L 0G L0G L0G L0G L 0G
14 14 12
8E TA 0 = I , 95 8ETA 1:I ,23 BETR 00:3, H BETFl 11 =2, 12 BETA 10:3 ,00
12 10
,- 10
a:
:e:
8
a..
..J 8
a:
6
e)
O 6 ..J
b
2
o o
o
5
6
7
8
5
6
7
8
M
O :O
2
e
,o . o3 M ,o.3 M
d
:1
M
11
pH 2
3
4
9
10
11
12 8
7 7
6
_/6
5 5
pM' ' 3 3
2 2
pH
Thallium(lll)-Tartrate
680
-I O l6 r---'---1-L_l__J___j2~ LJ3L_.1_~4LL~SL..1_~6L +i 7....-1_
18
16
L0G BETA L0G B o-11, 57
14
ETA -12
L0G BE
12
oo,81 lAooo= 13 , 34
12
~IO
10
I
a... 8
_J
a:
B
ò
o_J
6
6
' a :o
b e d
2
o o
3
2
e :o.3
o
4
5
6
7
8
'
s
6
7
B
M
: 0.001 M :0 .01 M , 0.1 M M
pH o
-1
3
2
8
9
IO
Il
12
8
7
7
a
6
6
s
pM ' ,
•
3
3
2
o
o
2
3
•
o
s
6
pH
7
8
9
IO
11
12
CHAPTER 39
Uranium (IV)
u
In the absence of complexing ligands, quadrivalent uranium can exist in aqueous solutions of redox potentials below E= (270 - 118 pH) mV. Under these conditions, it may exist in equilibrium with UO 3, but at potentials below (204 - 59 pH) mV the trioxide is reduced, and hydrolysed uranium(IV) solutions occur in equilibrium with hydrated UO 2• Polynuclear complex formation interferes in the study of the mononuclear species. In acid, the hydrolysis of u4 + is explained adequately by log *~ 1 = -1.6 and log *~1s,6 = -17.2. Log *~ 5 = -17.6 can be estimated from solubility measurements at high pH. The values log *~2 = -3, log *~ 3 = -7.3, and log *~4 = -11.8 (at ionie strength = 2) can be estima ted by assuming that, at infinite dilution, the stepwise constants form a regular progression. As commonly occurs with multivalent metals, uranium(IV) solutions can be supersaturated with Ì-espect to precipitation of UO 2.xH 2O. Log *Ks0 = 5 can be estimated for the solubility product of the freshly precipitated hydrated precipitate. This value approaches zero after aging of the precipitate for several hours. The plots refer to the freshly precipitated oxide.
Uranium(IV)
2
o
3
6
5
4
683
7
6
9
10
11
12
6
?* e,
o
e_,
e_,
..,
7
;;
7
e,
_,
6
6 5 5
pM
. 4
3 3 2 2
o
o -I
o
2
3
4
6
5
pH
7
6
9
10
11
12
684
Uranium( IV)-Citrate
[Ch. 39
-I o B 7 2 3 4 6 5 16 r---'---'------1--'--....L---L---11,__-'---'------l-r-h..-J..,......,____._.,___,._._~--r t 6
14
14
12
12
~10 CI:
10
LOO BETA 0 =11 ,50 Loo•BETAnuon1z=-l ,OO LOO BETA 00:19.SO
:r::
a... ....J B CI
B
ò
o _j
6
6
4
4
a
b
2
2
e
d o -1
o
e
o 2
3
4
7
6
,o ,0 . 0001 ,0.001 ,0.01 ,0.1
M
M M M
M
8
pH -1 4 o 2 3 5 7 6 8 9 10 11 12 B+---1..---1'----'---'-----'--'-----'--'---'---'-----'-----'----'--'--~~---,-,.,-:-:~ -~~---'----'-~-t-B
7
pM
.
6
6
5
5
a
4
3
3
2
o+---,----.-.---f':'..,..-'-T-,--,---,--,----,-,--,,f----n.C,---1-r+-,---,--,----,-,--,-,----r~rT 0 -1
O
2
3
4
5
6
pH
7
8
9
10
11
12
Uranium(IV)-DCTA
685
5 6 7 e i--1---1-Lr""T-r--t-__.___,____.r.....__.......__,1s
LOO BETA 0=27 .so
14
Loo•eETAnLa"=-4 .es
\A
12
10
,- 10
a: :r::
e
a..
..J 8
a:
6
èJ
O 6
...J O :O
b
2
e
2
d 7
e
1
a
e
o
11
: 0.0001 :0 . 001 ,0 . 01 :O.I
11 11 11 11
pH 6
s
10
11
12
o -I 1-_L.J._L...1--1.._'.2Li.__J_3_L__j•t__..L_j_5_L......i..--1._L...tnr-!..L-L__J_..L,__L---L-r8 8 7
7
6
6
5
pM'
4
3
2
pH
Uranium(IV)-EDTA
686
+--'--L-...L..--L---1_
[Ch. 39
7 8 .L_....L.-----1.-L....,,.l-.,....Lor-'-,.--'---'-----'--r-'--_._----t-l6
14
14
12
- 12
~,o a:
IO
L0G BETA 0 :25 -80 L0G•BETA•Low= - 4 -80 L0G•BETA•uow1 2=- l 2 . 80
I
Q_ _J
a:
8
8
6
6
c.:,
o
_J
4
o 2
3
5
6
7
M
b
M
:O .0001 C :O . ODI d :O . DI e : O.I
2
o
O :O
M M M
8
pH 4 -I o 2 3 5 6 9 12 8 -+----'-----'--'----'---'-- ' --'---'---'---'----'---'----'--'--.....L....-~'-r--,.--,--'-------'-- - - - ' -- 8
7
7
6
6
5
-5
o 4
3
3
2
2
a -!
o
2
3
5
6
pH
7
8
9
ID
Il
12
Uranium(IV)-Sul Phate LJ(IV)) 2
4
3
687
6
5
16
o -1
L0G BETA LDG BETRo-_:3•20
oo-5 ,40
10
B
6
O :O
2
D
2
3
4
5
6
7
4
5
6
7
b
11
, 0 . 01 11
e
, 0.1
t1
d
,1
t1
pH -1 8
2
o
3
B
9
10
li
12
8
' '
7
6
5
pM'
4
4
3
io
2
o
o
-1
3
4
6
5
pH
7
8
9
10
Il
12
CHAPTER 40
Uranyl, U(VI)
Polyrrerization strongly interferes in the study of the hydrolysis of UO~~ The values log */3 1 = -5.4, *log /3 22 = -6.0 and log */3 53 = -16.3 adequately explain the behaviour of the metal in weakly acidic solution. From the experimental fact that the (3,5) species predominates above about pH 5, irrespective of the uranium concentration, it can be concluded that the next step to give UOiOHh(aq) cannot occur below pH 5.4; we tentatively propose log */3 2 = -I 1.2, which is consistent with the other values reported in the literature (log *~ = 6 and log *K82 = -5.2). The solid phase in aqueous solution at 25° is UOi0Hh-H 20. When it is in equilibrium with its saturated weakly basic solution, the solid phase becomes "incongruent", containing "uranates", which are solid solutions of various polyuranates. Tue following tentative set of constants was used for construction of the plots. log */3 1 log */32 log */3 3
= - 5.4
= - I 1.2 = -23.7
log *K50 log */3 22 log */3 53
= 6 = - 6.0 = -I 6.3
Uranyl
-1
o
6
5
3
2
689
7
9
8
10
11
12 8
."'"' ."' "'
8
e
-'
e
-'
7
--- -----
7
/ 6
I
5
......_
I
......_
6
......_
......_ 5
•
,.;
pM' '
I o
-1
o
2
I
I
I
3
2
o 3
4
6
5
pH
7
8
9
10
11
12
[Ch.40
Ur'anyl-Acetate
690 1
2
6
5
3
8
7
10
9
16
16
14
14
12
12
~IO
10
a: I a... _j a: o
8
8
6
6
4
4
LOG BETA 0 =2. 40 LO!, BETA 00 =4. 40 LO!, BETA 000:6. 30
_j
o I
M
b
M M M 11
:0.01 C :0 . 03 d :O.I e :0.3
2
2
O :O
2
pH -1
o
2
4
3
7
8
9
10
l i
12
7
7
/
.,,,....,....-p-b,.
;::
r; ( /
5
.
6
8
6
pM
5
8
.f
4
/ ::
~ -:, ,...... ,,,,_
6
V ~,,
;· i i: i I , J
5
'
4
:
3
3
?-\ f
2
2
/;/\ e
o -1
o
o
4
6
pH
7
8
9
10
11
12
Uranyl-Acetylacetone
691
2"']
uoz
10 11 s 7 a s 5 i_1--1--..1.-.J._--1-_L.--'-_,___.____._L...._J__...L_+1s
LOG BETA 0:7 ,66 LOG BETA 00 :!4,15
14
12
12 IO ,... 10
a: :r a.. .J a:
8
è)
O 6
.J
O :O :0.001 e :0.01 d : 0.1
b
2
3
M M M M
4
pH -1
o
6
5
4
3
2
9
8
7
IO
li
12
8
a 7
7
.,,,.. / - - ...____ ..........
I
//)1_---
4
6 .......... ..........
a/
5
pM'
~-$
I
6
..........
b
I
3
3
2
f/ -1
I-d
o o
2
3
o 4
6
5
pH
7
8
9
IO
11
12
692
[Ch.40
Uranyl-Fluoride o
2
3
5
4
7
6
8
9
16
16
L0G L0G L0G L0G
14
12
12
~10
IO
cr:
BETA 0:4 ,50 BETA 00 :7, 60 BETA 000 :10,20 BETA 0000 : l l , 60
:e CL ...J 8
8
cr:
e
ò
a ...J
6 d 4
e
2
2
3
5
4
6
7
B
5
6
7
a ,o b ,o ,0001
M M
e
d
,0.001 ,0.01
M M
e
,0.1
M
pH -1
o
3
2
B
9
IO
11
12
8
B
7
7
,,,-
I
6
6
i//
1/
5
. pM
5
I
4
I; /;
3
2
3
2
/I I
o -1
o o
2
3
6
5
pH
7
B
9
10
11
12
1- . . uranyl-( OH )-Ou inolinesulphonate
uofl
B
7
693
9
16
u
1'
12
12
10
,-10
a:
:i:: o....J a:_,
e
"
6
C)
L0G BETA 0 :B -52 L0G BETA 00 : t S . 68 L0G.BETA"lOH=-6. 70
B
...J
O :O b , 0.0001 e , 0 . 001 d :O.O! e : O.I
o I
2
-1
o
3
M M M M M
4
pH 6
5
4
3
2
7
9
B
IO
12
Il
B
8
7 7
/
6
,,,,..-_.,,..---_
a/ pM'
4
6
-........
-........
-........
a
I J-~ ----o,'1/
5
~ -z._
5
4
I
3
2
t
o -1
o
3
b
;-"'e J~d
e
2
d
o 6
5
pH
7
B
9
IO
Il
12
694
Uranyl-1 minodiacetate 2
3
5
6
9
8
IO
[Ch. 40 Il
16
_.L_...l..___L____J__L_.J.._J.....___J____J_.L_....L___L_--1.___JL.._-'-----'--'--+ 16
14
14
12
12
LOG BETA 0 =B -96
~,o a:
r
a.. ...J
a:
e
e!)
o
6
...J
O :O
b
M
:0.0001 M
C :0.001
M
d
M
e
:0.01 :O.I
10
Il
M
pH
-1
O
2
3
5
6
7
8
9
12
B+---'-----'--'---'----'--'----'--'--'--'---'----'--'--'----'-,--'----'-~'--'----'-----'----'--'--'-----'--+B
7
6
6
5
o+ - - - - - ~---.--l-.----r-+..,.,1----.------,L.-,--~,----.----~,----.---,--~,----,----t-O -1
o
2
6
pH
10
11
12
Uranyl-Salicylate
695
7 8 9 10 11 1s _J___js_..L-.....L---'--L---'----'-~ - ~ ~
1
LO(} BETA 0 : 12 -1 O LO(} BETA 00 :20 °80
14
1
12
10 ,.... 10
a:
B
:I:: 0--
..J 6
a:
6
CJ
O 6
...J
o 3
-1
M
O :O
2
b
: 0.001 M
e
,0.01
M
d
, 0.1
M
pH
o
3
2
9
8
7
6
5
4
Il
10
12
8
e 7
6
pM'
o/
~f I/
4
2
~(
/
---::,..... ----..// ~
/
6
-11
--::::~
-
~,
""'"""-
a b
5
e 4
/ ç_..-/
3 d 2
r---9_
I
o -1
o
2
1/
o 3
4
6
5
pH
.,
8
9
IO
l i
12
696
Uranyl-Sulphate -1
o
16
a: I a... _J a:
2
3
7
6
5
4
[Ch. 40 8 16
14
14
12
12
10
10
8
8
a_J s
6
LOG BETA 0:3, ! 0 LOG BETA 00 : 4. 20
o
d 4
4
e
O :O b : O. O! C :O . I d :I
2
2 b
a
o
2
3
o
4
5
6
7
8
4
5
6
7
8
M M M M
pH -1
o
3
2
9
10
Il
8
B
7
'' ' ..,.........-, ,ri ........
:
/ '
5
pM • 4
.I
3
2
I -I
/,
-
I 1/ . V .
6
o
12
I
I
7
3,:,
6
r I/!
5
;i
4
I
3
2
o
o
2
3
4
5
6
7
8
9
10
li
12
pH
J
Uranyl-5-Su Iphosal icyclate
uofl
5
e
7
6
697
10
9
11 16
16
14
I'
12
12
L0G BETA 0 =l 1 - 14 L0G BETA 1=3 .90 L0G BETA 00 : 19 -20
10
r 10
a:
e
:i::
O_.I 6
a: _,
6
c., O 6 _.I
2
3
-1
o
O :O
11
b e d
,0 . 0001 11 ,0.001
11
:O.O!
11
e
, 0.1
11
pH 2
3
e
7
6
5
4
9
10
li
12
e
6 7
a/ /
7
/--
.
/--~-1 ......1 ,_. .,,,_
/
6
6
/
b/
5
//
5
i/ I; //
pM' , 3
4
3
/; I I; I I Il Il J
2
o -1
e
o
2
e
o 3
4
5
6
pH
7
e
9
10
11
12
698
Uranyl-Tiron 1
2
5
3
7
6
[Ch. 40 10
9
8
16
16
14
14
12
12
~10
10
a:
L0G 8ETA 1: 6 . 40
I
Q__
8
8
Cl 6
6
4
4
2
2
_J
a:
o _J
O :O
M
b
:0,001 M
e
:0.0 1
d :o.i
o 1
2
3
M M
5
4
pH -I
o
3
2
7
6
5
4
8
8
9
10
Il
12 8
'' '
7
7
''
,,.... . . . . . ----j........._
I
6
pM
.
6
'' '
5
~-$
:
o/
/}),,-_/
5
·--,
,/1
/ i / - ....
/
~f/
4
3
/
2
/
o -1
I I/
4
3 7e
2
d
o o
2
3
4
5
6
pH
7
B
9
IO
li
12
a....
CHAPTER 41
V
Vanadium (111)
il I
y 3 + ions hydrolyse rapidly above pH 1 to fonn V(OH) 2 + and V i(OH) 24 +. V(OH)t and V i(OH)~+ have been suggested, in order to improve the agreement with experimental data, but the existence of V i(OHH+ (introduced to explain the slow kinetics in weakly acidic medium) has not really been confirmed. The behaviour in neutra! and basic media has not been very well established. Tue following data adopted from the literature agree with our own preliminary solubility measurements up to pH 8. log *{3 1 log *{3 2 log *{3 3
== =
2.70 - 6.50 -13.50
log *{3 22 log *{3 32 log *Ks0
= -3.8 = -8.0 = 7 .6
In the absence of complexing ligands, y 3 + ions exist only in strongly reducing media; they are easily oxidized by air. y 3 + ions form stronger complexes than vo 2 + ions, so vanadium(III) complexes are more stable towards oxidation than y 3 + ions.