KINETICS OF THE HOMOGENEOUS REACTION
BETWEEN PALLADIUM COMPOUNDS AND HYDRAZINE,
FORMING METAL NUCLEI
Thesis submitted for the
degree of
Doctor of Philosopy London University
by
Indra Pal Singh, M.Sc., D.Phil.
Department of Metallurgy, Imperial College of Science December, 1967. & Technology, London, S.W.7. ABSTRACT
The work discussed in this thesis comprises studies on the reduction of palladium (11) complexes by hydrazine in aqueous solutions, in order to find the causes of homogeneous nucleation in the electroless plating of palladium. This homogeneous nucleation sets in even in the absence of any third phase i.e. the article to be coated, and brings down all the palladium (11) as metallic powder, which obviously creates technical difficulties.
The work has been kinetic in nature, and the mechanistic approach has remained mainly qualitative or semi-quantitative as much more thermodynamic information and data is necessary to give a more quantitative explanation.
The experimental method consisted of measuring the time for the appearance of a cloud of metal precipitate for each concentration of the variable. The main variables which have been studied are palladium (11) concentration, hydrazine concentration and ammonia concentration. The rate dependence with respect to palladium was of a fractional order (1.76) at lower palladium ion concentration and higher orders (3) at higher palladium ion concentration. The rate with respect to hydrazine was found to be 2 .0 The rate dependence with respect to Palladium(11) and hydrazine in the system containing EDTA was found to be 1.5 and 2.5 respectively.
The effect of ammonia concentration has been found
favourable in preventing the precipitation of the metal.
The evaluation of activation energy gave a value of 17.6 K.
Cals/Mole at higher palladium ion concentration and 20.9 K.
Cals at ordinary concentrations of palladium ion in the
system containing mainly ammines. But in the system
containing EDTJ the activation energy was found to be 17.3 K.
Cals/Mole.
The spectra of the solutions with different
ranges of reactant concentration suggest that hydrazine
forms complexes with palladium by displacement of ammonia
and it is suggested that these substituted complexes are
then reduced to the metal by a free radical mechanism,
which has been discussed in detail. The spectral evidence also shows that hydrazine can displace all the four ammonia molecules of a palladous ammine in lower concentrations of ammonia. Further evidence of palladium
(11) forming complexes with hydrazine has been obtained by nixing Pd(C104)2 with N2H4 2HC104, which forms bright yellow complexes with characteristic absorption peaks. The spectral data has been useful in suggesting the type of species involved in the reduction and thus giving a better picture of the mechanism. CONTENTS Pale 1. Introduction 1
2. A short review on the theories on nucleation 8
3. Review on earlier work on oxidation of hydrazine 15
4. Experimental methods and Experimental data 22
5. Interpretation of the Experimental data 42 6. Results and Discussion 46
7. Acknowledgement 61
8. References 62
9. Appendix 65
10.Figures 67 INTRODUCTION
The work presented in this thesis was carried out
to discover the factors responsible for the decomposition of
baths in the electroless plating of palladium. The electroless plating of metals involves the reduction of complexed metal ions in solution by various reducing agents, under conditions which cause reduction at a catalytically active surface. In the case of palladium, the method of electroless plating was first developed by Rhoda and (1) Madison, who used palladous ammines and ethylene diamine tetra - acetate (ETA) complexes and reduced them with hydrazine at a suitable temperature. The optimum conditions of heterogeneous plating of palladium are given by the above authors in their paper.
The electroless plating baths used for plating palladium undergo decomposition on long standing by a type of self • nucleating process and all the metal held in solution is thrown down as metallic powder. Sometimes this may happen even during the plating process if the solution has been stored for a long period.
The decomposition of plating baths seems to involve two steps, in the first step the complex palladium ions react with the reducing agent at a very slow rate, producing palladium atoms and once a certain critical concentration of palladia= atoms is reached they agglomerate to form aggregats or clusters of atoms, until nuclei of a critical size are formed, creating a new heterogeneous phase. The second step is the participation of these nuclei in the further reduction of palladous ions by hydrazine by a catalytic process, The nuclei thus go on increasing in size by the deposition of palladium as a result of reaction at their surface and this leads to the precipitation of palladium as metallic powder.
The second step discussed in the last paragraph is a catalysed reaction and should be quite fast. Therefore, the conditions which lead to the formation of palladium nuclei in the first step by a slow homogeneous reaction can be delayed by the control of chemical concentration of reactants. Although it is unlikely to be possible to keep the baths for indefinitely long times, it is not difficult to prolong their life by controlling the various factors involved in the reduction of metal ions to metallic powder.
Though both physical and chemical factors are responsible for the decomposition of the plating baths, under normal conditions the control of chemical factors alone could produce quite effective results. This is not to say that physical factors are totally insignificant, but the physical factors are not easy to control under normal working conditions. The chemical factors on the contrary are easy to control and are sufficiently effective alone. -2 - In addition to the chemical and physical factors
responsible for the formation of palladium nuclei, there are
certain other factors, which can create a great deal of
trouble in the storing of the plating baths. These are
certain catalytically active particles introduced into the
solution from the external atmosphere which bring about a
heterogeneous decomposition of the solution before any
homogeneous reduction has taken place.
Thane external particles could be largely avoided
by the use of scrupulously clean solutions and by keeping
them in sealed vessels, which do not come in direct contact
with the atmosphere. Sometimes a material contaminating
the vessels may itself help in the decomposition of the
solution, due to the participation of the unclean surface,
which may be catalytically active. This may happen if the
baths are not cleaned properly after the decomposition of the
solution and all the metal sticking on the walls is not
dissolved off properly by the use of acids such as aqua regia.
In the present work it was found necessary to clean the flasks with fresh aqua regia as the re-used aqua regia did not dissolve all the palladium on the walls of the flasks and this -wands after lead to the rapid deoomposition of experimental solutions in subsequent runs.
Though particles from the atmosphere and other 3 .00 sources may be responsible for the rapid decomposition of
the plating baths, the main precipitation of metal in the form of powder is due to a homogendomschemical reduction and external impurities only accelerate the process if they are
present. The reproducibility of results and the effects of concentration, temperature, etc. on the time before nucleation
occurs suggest that spontaneous formation of fresh nuclei does occur.
As discussed earlier, palladium atoms are formed by a slow homogeneous chemical reaction between palladium ions and hydrazine. The reaction obviously is a redox reaction, where palladium is reduced and hydrazine is oxidized by some type of electron transfer mechanism. For the reaction to take place it is necessary that the two reactants come close together by forming an intermediate complex, which can be a stable or a short lived species.
This subj at will be discussed later in subsequent chapters.
Palladium forms fairly stable ammines and ohlora- mmines, but the palladous ammines are more labile than their platinum anologues. Therefore, it is quite safe to assume that hydrazine may replace an ammonia molecule from a molecule of palladous ammine to form a monosubstituted hydrazine complex of palladium. The further replacement of - 4 ammonia by hydrazine depends purely on the relative concentration of the two ligands and will be discussed later.
The possibility of palladium hydrazine complexes cannot be ruled out as a large number of metal hydrazine complexes are known and many metal hydrazine systems have been studied from structural and thermodynamic view points. (2) L. Sacconi and A. Sabatini have studied the I.R. Spectra of the hydrazine complexes of some bivalent metal ions. P. Abmad and S.M. Fazlur Rahman have reported some hydrazine (4) complexes of cobalt, nickel and copper. Banerjea and Singh have determined the formation constants of copper, nickel, cobalt, man;•anese and zinc complexes of hydrazine in aqueous (5) solutions. Swarzenbach and Zobrist found that four hydrazine molecules are co-ordinated to a zinc ion and six to a nickel ion in a manner comparable with ammonia. Robertus, (6) Laitinen and Bailar have found that zinc ion will co-ordinate with four hydrazine molecules with only slight differences in successive formation constants. All these studies confirm the fact that hydrazine acts as a monodentate ligand and quickly exchanges with ammonia in the palladous ammines, before any reduction of bivalent palladium ions takes place. (7) Audrieth and Ogg have pointed out that in most casts the number of hydrazine groups coordinated to a metal ion is one half of the normal co-ordination number of the -5- metal. Since no structural determinationhhave been made, it
seems quite reasonable to predict the formation of three
membered rings, but the low solubility of most of these comp-
ounds suggest polynuclear structures involving hydrazine
bridges rather than chelate structures. Very little
information is available on the hydrazine complexes of
palladium, but it may reasonably be assumed from the instances
cited earlier that palladium form hydrazine complexes in a
manner similar to ammonia. In the present work this has been
confirmed by the ultra - violet and visible spectra of
palladium hydrazine system in presence and absence of other
ligands.
The effect of hydrazine concentration, palladium
ion concentration, ammonia concentration and the presence of
EDTA on the time before spontaneous nucleation occurs has
been studied in detail at a definite temperature and constant ionic strength. While studying the effect of one variable all other variables were kept constant.
The sytem consists of a number of species of palladium (ii) complexes, reacting with hydrazine at competing rates, and the entire kinetic data is true for a limited range of concentrations of the different reactants, but beyond these limits the mechanism is likely to change.
Therefore, some of the reactions have been studied in - 6 - different ranges of reactant concentrations.
In the study of the present system it has been found safe to assume that the palladium atoms are formed by a purely homogeneous process and when the solution becomes supersaturated with the palladium atoms, the nucleation takes place.
The experimental method used to study the kinetics of formation of palladium nuclei of critical size was to measure the time between mixing the hydrazine with palladium solution and the appearance of a cloud of palladium metal powder. A SHORT REVIEW ON THE THEORIS OF NUCLEATION
According to the well accepted theories on nucleation to be discussed later, it is necessary for the solution to be supersaturated with respect to palladium before any formation of the nuclei takes place. The formation of nuclei is favoured by a decrease in free energy in trans- ferring ions from an unstable state in solution to a new phase and opposed by the increase in surface energy of the nucleus.
Nancollas and Purdie(8)in their review on the theories of nucleation and crystal growth have shown that in a super- saturated solution the atoms or molecules of solute give rise to short lived clusters formed in a step wise fashion involving single atoms or molecules. X + X X2
X2 + X X3
Xn-1 X Xn xn + x = Xn
These clusters have been assumed to be spherical in shape and their radius is defined by the Kelvin - Gibbs equation.
rn = ( 2 aviRT ) In Pn/Po - ( 1 ) Where Pn is the vapour pressure of a droplet of radius rn, containing n molecules, Po is the vapour pressure of the plain liquid surface and a is the surface tension of the - 8 - droplet and v the molal volume of the liquid. In the precipitation from condensed phases,/Pn Po is replaced by
/Mo/ which is concentration ratio of the solute in two phases and Mo is the solubility value. Xn is taken to
represent a nucleus of critical size, which only grows further, and clusters which are smaller than Xn have a
tendency to dissociate since growth requires work in extend-
ing the surface area. The only force opposing dissociation is the tendency of a supersaturated solution to get rid of
extra solute. But once a cluster of atoms has attained a critical size, the surface energy term becomes less and less
importaPt with the increase in size and this leads to further growth of nuclei and finally to the precipitation. According to Volmer(9)thers exists a state of quasi equillibrium in which the distribution of clusters of all sizes up to Xn is stationary with time. This theory is valid as long as tie assume that further growth of the nuclei is small enough not to disturb statistical distribution.
Rewriting nx = Xn
and G°n = kT In {Xn} n Where G°n is the standard free energy of formation of an n- cluster, the activities are enclosed in brackets. The partial molar free energy of a single molecule can be written as Jul 0 jel + kT In kX1 - 9 - and of a n - cluster as "In )ao + kT In vsnl
.14 0 Therefore Q G°n The free energy of n molecules in the newly formed phase is
/Is and /Is = )115.) + kT In {X0J. Where is the activity at saturation. The free energy f Xo of formation of a spherical nucleus of radius r , contains 2 a surface contribution of 47fr a . Therefore free energy of formation ,LIGn of the nucleus Xn at rest is almost equal to&en and is given by 2 Aer = n (pis - ) + 4 TT r a or Gn = - 4 TT r 3 kt In eC + 4 Ir r 2a 3 V Where oe is the supersaturation (X/x0). The size of the critical nucleus is the one which represents a maximum in free energy,i1G0 and from Kelvin - Gibbs equation can be written as
n CC ; where r is critical re = 2 av kT 1 c radius and eh G0 = 16 IT' a 3v2 / 3 ticT in 043 2
The rate at which nuclei are formed can be written as
Go/ KT - 16na 3v 2 /3 K3 t73 (inoC) J = Ac = lie Where A is the pre-exponential term. It has been confirmed by experimental observations that there is a rapid increase in the rate of nucleation as - 10 - predicted by above equation. (1 0) Christiansen and Nielsen applied a kinetic approach
in studying the precipitation of some sparingly soluble salts.
They defined the incubation period as the time required for
the formationotacluster up to the size of Xn by a steady
state process. They thought that all the preceding steps up
to the formation of Xn were in a quasiequillibrium state.
Once a cluster attained the size Xn, it has a lesser chance
to lose an ion and a greater chance to gain one. The rate of formation of clusters was defined as, k = t Co n-1
Where Co is ith root of the ionic product, if one
molecule dissociates into i ions, n and k are constants. In = 10 -11.8 the case of barium sulphate it was found t x c o and for silver chromate t x Co 5= 10 - 13.5 where t is the time of visible precipitation.
According to the theory of SmoluchowARhich has (12) been extended by La Mer , the rate of growth of crystals in a supersaturated solution is proportional to the instantaneous concentration raised to a low power. But it has been found that the rate of precipitation of some sparingly soluble salts are proportional to the concentration powers from six to nine, which is contradictory to the theory of
Smoluchowsky. The rate determining step in all such studies
- 11 - seems to be the formation of crystal germs rather than their
growth. Christiansen and Nielsen on the basis of their
experiments on kinetics of precipitation consider the power
of the concentration in the rate expression equal to the
number of single particles in a crystal germ. The
experimental evidence at the moment is not sufficient to
decide which of the two consecutive whole powers is the right (13) one. Jensen in his studies on the precipitation of calcium fluoride found a similar relationship between the incubation time and concentration. Thtsgincubation times are defined as times of appearance of visible precipitation.
But all these theories which predict an induction or incubation period are only acceptable if the supersaturation is built up by a homogeneous and slow process until critical concentration value is reached. There is measurable time interval or induction period and the formation of visible precipitation according to Becker and Dorings predicts immediate nucleation. Christiansen and Nielsen have described this delay due to a time required to attain the steady state conditions in a supersaturated solution.
Inspite of all the theories discussed earlier it remains a point of controversy whether the nucleation followed by bulk precipitation is a homogeneous or (15) heterogeneous process. Davies and Jones in their study on
-12- the precipitation of silver chloride found a critical
concentration product for silver and chloride ions and below
this value the solution showed no tendency to precipitate.
They believe that nuclei were formed only when the critical
concentration was reached and thus they support a homogeneous 16) formation of nuclei. But this idea was opposed by Turnbul2
who on the basis of his studies on the precipitation of barium
sulphate concluded that the number of nuclei produced after
homogenisation of solution was too insignificant compared to
the number produced during the mixing of the solutions
containing two ions. Some other workers like O'Rourke and
Johnson(17) found that the number of nuclei formed after
mixing of the solutions in equimolar proportions was indepen-
dent of concentration over a fairly wide range. This led
to the conclusion that nuclei were formed only by a slow rate
process. The two theories therefore, are contradictory to one another and are still in a developing stage. The experimental data on nucleation is, therefore, interpreted on the basis of
one theory or the other. There are obvious limitation in all the studies done so far on nucleation but a good deal of work is being done which will throw more light on the subject.
Many authors have studied precipitation reactions to determine the critical radius and number of atoms in each nucleus, but no such attempt has been made here as these are
- 13 - concerned with subjects of nucleation and crystal growth which is not the main field of interest in the work presented here.
The experimental work presented in this thesis deals only with the homogeneous reaction kinetics leading to the formation of metal nuclei in absence of any heterogeneous solid surface.
-14- REVIEW OF EARLIER WOW: ON OXIDATION OF HYDRAZINL
The oxidation of hydrazine has been studied by a
number of workers and there are various factors to be
considered about the reducing action of hydrazine. Brown and
ShetterlyOs)made studies on oxidising agents containing no
nitrogen upon hydrazine in acid medium in order to devise a
suitable mechanism of oxidation. They found only in a limited number of cases the formation of hydrogen azide but nitrogen and ammonia were formed in a large number of cases. In a few cases nitrogen was the only oxidation product.
Studies on the oxidation of organic derivatives of
hydrazine showed that a variety of products were obtained containing nitrogen and hydrogen which were called hydronitrogens. The parent hydronitrogens formed initially after immediate oxidation of hydrazine were so unstable that they were quickly oxidized or decomposed. The formation of these hydronitrogens is assumed to explain the formation of end products in the oxidation of hydrazine in solution.
Brown and Shetterly studied the effects of various oxidising agents on hydrazine. They added oxidising agents containing no nitrogen dropwise into a solution of hydrazine in strong sulphuric acid. They found that oxidising agents such as peroxide, potassium perchlorate and peroxidisulphate gave large amounts of hydrogen azide and ammonia. Reagents -15- like potassium permanganate, manganese dioxide and ferric ion gave little or no hydrogen azide but large amounts of ammonia. Reagents like potassium iodate, mercuric oxide, and mercuric chloride produced no hydrogen azide or ammonia but oxidised hydrazine to nitrogen. It was suggested that the oxidation of hydrazine took place involving the initial formation of a free radical
N2H2. These free radica]4 condense for the first type of compounds to give HN = N.NENH2 which decomposed to give hydrogen azide and ammonia. For compounds giving little azide and much ammonia, the intermediate was believed to be tetrazene H2N N = N.NB2 . Where as in cases where only nitrogen was formed the oxidation was assumed to proceed with out the formation of any intermediate compound. (19) Cuy, Rosenberg and Bray studied the oxidation of hydrazine by permanganate ion where considerable quantities of ammonia were found in the residual solution. They proposed that trivalent manganese was formed by a side reaction and was responsible for a lesser amount of oxidant required. On studying the oxidation of hydrazine by manganic acetate, which can be represented by the following equation: +3 rE Mn + N2B --> NH -g-N2-14.1 Mn 5 4 they propose the formation of N2H3 radical as an inter - mediate in the above reaction, which immediately undergoes -16- decomposition into nitrogen and ammonia by the mechanism
suggested below: +3 +2 11+ N2H4 + Mn N H Mn + 2 3
N2 --> NH NH + 2 N H3 3 + N 3 2 2 20) This suggestion was used by Kirk and Brow in the develop-
ment of their dihydronitrogen theory. They arranged oxidising
agents in three definite categories.
1. Those which gain one electron in being reduced were
called monoelectronators.
2. Those which gain two electrons in reduction were
dielectronators.
3. Those which are reduced by several intermediate stages
involving both one and two electron steps. On the
basis of this classification they were able to develop
the older dihydronitrogen theory used to explain the
action of various oxidising agents.
The monoelectronators which include ferric, manganic, cupric, nickelic, cobaltic and ceric ions, give nitrogen and
H ammonia on the oxidation of hydrazine. The N2 3 radical formed, condenses to produce the intermediate hydronitrogen tetrazene„ which finally decomposes into nitrogen and ammonia.
N H N H + 219 + e 2 5 .40 2 3
2 N H_ HEN. NH - NH . NH tetrazane 2 5 2 - 17 - N H N + 2NH 4 6 2 3 The dielectronators such as peroxidisulphate,
peroxide etc. produce smaller quantities of hydrogen azide
especially in strongly acidic solutions. The primary step in
the case of these oxidants was the formation of the N2H 2
radical which condensed to form tetrazene, isotetrazene and
tetrazane. Isotetrazene is believed to decompose into
hydrogen azide and ammonia.
In the case of polyelectronators like dichromate and
permanganate the reactions take place both by one electron and
two electron processes. The reaction of hydrazine with perman-
ganate takes place by two concurrent steps especially in
hydrochloric acid solutions and can be represented as:
3 D H +3 0-+ 2 NH + 2N + 3H 0 2 4 3 2 2 This equation can be represented by two separate reactions,
one being complete dielectronating and the other a monoelect-
ronating process.
N H +2 0 -40, N + 2 H2O 2 4 2 2 N2H4 + 04112 + 2 NH3 + H2O 3 In the above case if the Mnh concentration was increased before the addition of permanganate the extent of monoelectronation was increased.
Attempts have been made to prepare hydronitrogen - 18 - diimide from compounds like azodicarboxilic voter but they lead
to complete decomposition. Attempts to prepare
monophenyldiimide from phenyl hydrazine lead to the formation
of benzene and nitrogen. In azo and diazonium salts also the
nitrogen has a tendency to appear as molecular nitrogen.
Therefore, whether the diimide is a disubstituted diimide, a
diazo-compound or a diazonium salt, there is an inherent tendency in all these compounds to lose nitrogen as molecular nitrogen on decomposition.
The N disubstituted derivatives of hykszine are capable of oxidation to the tetrazenes which are derived from
hypothetical hydronitrogen N4H4. The tetrasubstituted tetrazenes undergo decomposition when treated in inert solvents to form tetrasubstituted hydrazine and nitrogen.
As diimide, tetrazene, and tetrazane are assumed to be intermediates in the oxidation of hydrazine, it is reason- able to expect nitrogen, hydrogen and ammonia as end products.
It may also be possible that imiide biradicals are formed not only from diimide but from hydrazine itself on assigning
H2N.N =1C112 structure to hydrazine. Imiide possibly reacts with N.NH to form H2N.N = NH a precurser of diazoamine 2 compound. As triazine is likely to lose nitrogen readily, therefore ammonia and nitrogen seem to be the oxidation products of triazine. -19- It seems difficult to explain the formation of
hydrazide as a product of oxidation of hydrazine. The only
hydronitrogens that give derivatives of hydrazoic acid are
the isotetrazines. Isotetrazine therefore, could be a possible
intermediate in the oxidation of hydrazine. Isotetrazine could be formed by condensation and proton migration of a diimide and a N2H2 or two N2H2 radicals. Isotetrazine would finally decompose into ammonia and hydrogen azide.
Then the complete mechanism of Browne and Kirke which involves the formation of intermediate species such as diimide, tetrazine, isotetrazine and tetrazane which finally decompose to give nitrogen, ammonia and hydrogen azide depending upon conditions and oxidants used.
The following scheme represents the above mechanism; + 1. H2N NH2-- H2N. NH + H + e
2N H -4. N H 2 3 4 6
hydrazyl tetrazane
114H6 N 2 + 2NH3
2. H2N NH2 H2N. N
or + H + 2e 2 H : : H
- 20 - (a) H:N:N:H or N2 + H2 imide or + N2++ 2HH + 2e • (b)2 H N N H -, N + N H 2 4 4 2 2 4 (c) H2N N + NH.:30.1f3N5-4 N2 + NH3
(d)2 N2H2--) HN:D.NH .DH2-) HN3 + NH3
isotetrazene
' taken mainly from "The chemistry of hydrazine" by Audrieth and Ogg.
-23.- EXPERI1ENTAL
The stock solutions of the chemicals were made by
using analar grade reagents by B.D.H. or Hopkin and Williams.
All the solutions were made in distilled water and filtered
through a 5G sintered glass funnel to remove any suspended
particles.
Palladium (11) Chloride: A known amount of pure anhydrous
palladium chloride was dissolved in water and acidified with
sufficient amount of A.R. hydrochloric acid to give a clear
solution of palladous chloride,(Pd (01) 4)-2 The pH of
this solution was adjusted between 1 and 2 to avoid any
hydrolysis.
Palladium was estimated as dimethylglyoximate and
total chloride was estimated as silver chloride after
removing the palladium by precipitation with hydrazine.
The difference between the total chloride ion
concentration and that corresponding to palladium concentration
gave the amount of free hydrochloric acid.
Ammonium Hydroxide: A stock solution of ammonium hydroxide
was made by diluting the strong ammonia solution to about 5M
concentration. This also was filtered through a 5G sintered
glass funnel to get rid of silica and other suspended
impurities. The stock solution was standardised by
dissolving in a known volume of standard acid solution and - 22 - back titrating the excess acid with a standard alkali using
Weslow's indicator (methylene blue + methyl red).
Ammonium Chloride: A stock solution of about 4M concentration was prepared by dissolving a calculated amount of analar ammonium chloride in distilled water. The solution was filtered through a 5G sintered glass funnel and standardised by estimating chloride as silver chloride.
Hydrazine: A stock solution of hydrazine about 1M concentration was prepared by diluting a concentrated solution
(20k) with distilled water. The solution was filtered as usual through a 5G sintered glass funnel and stored in an amber coloured volumetric flask. The solution was standard- ised by titrating with a standard solution of potassium iodate in the presence of 5m1 of chloroform, till the chloroform layer was colourless. The solution was stored in a refrigerator.
Ethylene Diamine Tetracetic Acid sodium Salt): A stock solution of approximately 0.2M strength was made by dissolving a known weight of the disodium salt of EDTA in distilled water. It was standardised against a standard solution of magnesium chloride in an ammoniacal buffer using eriochrome black T as indicator.
-23- Preparation of Experimental Solutions and Procedure for the
Kinetic Runs:
To e, known volume of palladium (11) chloride solution were added known volumes of ammonium chloride and ammonium hydroxide solutions, this resulted in the precipitation of silky red needlLe cf 0011(TARI (N143)41 On standing in a hot water bath at 100°C. for 15 minutes these needles dissolved to give a clear solution. After cooling to room temperature, this solution was transferred to a 50m1 flask and made nearly up to the mark and kept in a thermostatic bath at 25°C. To this solution, after it had attained the bath temperature, was added a known volume of hydrazine solution and the volume was made up exactly to the mark.
The solution was kept in the thermostatic bath in the path of a light beam which fell after passing through the solution on to a photo cell. This photo cell was connected to an electronic relay which operated an electric clock as long as the light fell on the photo cell. When the precipitate appeared and reached a certain density the light beam was interrupted thus breaking the circuit and stopping the clock. This device was accurate except in the case of very short times of precipitation, where a large error could
- 24 - be introduced due to the time lag between the first appearance
of a visible precipitate and its thickening to a certain
density. This lag was insignificant in the case of long times
of precipitation. Therefore, the recording for shorter times
of precipitation was done manually by using a stop watch. The
time of precipitation in the latter case was the time for the
first appearance of a uniform cloud of precipitate.
All the runs were repeated a number of times until
a reproducible average time was achieved. It was observed
that a few of the runs were always shorter than the average
time and this was found to be due to contamination with
catalytic impurities. A few of the runs were appreciably
longer than the reproducible time and this usually happened when the experimental solutions had been stored for a few days. In such cases it was always found that some portion of
the flask surface had become catalytically active and most of the reaction took place on this part of the surface and thus
prevented homogeneous nucleation. However, these abnormal times of precipitation accounted for less than 20% of the total number of runs.
For each individual set of runs a pH measurement was always done at room temperature using a pye Ingold glass calomel assembly. pH of all experimental solutions was adjusted by buffer action between ammonium chloride and - 25- ammonium hydroxide to about 9 - 9.5, to avoid the formation of any hydroxy species of palladous ammines.
The spectra of the various solutions were recorded by a Unicao SP-800 spectrophotometer in the visible and ultra voilet range.
The same procedure wns followed for solutions containing EDTA.
1
- 26 - TABLE 1 (Fig. 1 and 2a ) Effect of hydrazine concentration on the rate of precipitation. All the solutions contain Pd , 0.00452M; NH4C1, 0.0840M; NH40H,0.0920M with varying concentrations of hydrazine to make 50 ml. of the final solution. All the measurements were made atiL= 0.0976, pH between 9.2 - 9.3 o and at 25 - 0.1 0. Volume of 0.724i [IT H1 - log Time Log time 2 4J of hydrazine added (Moles/ [14 H (Secs) or (ml) to make 50 ml 2 4 log t of final solution litre) in the final solution 1.00 0.01448 1.839 11400 4.057 1.25 0.01810 1.742 8580 3.934 1.50 0.02172 1.664 7380 3.868 2.00 0.02896 1.538 4920 3.692 2.50 0.03620 1.441 3070 3.487 0.50 0.00724 2.140 23760 4.376 The best slope was found to be 1.13, and the order of the reaction with respect to hydrazine was 2.13, The second order rate constant was found to be 5.5 x 10-3 litre mole -1 sec-1. The different ligand/Metal ratios in the system are given below. [Chloride] / [Palladium] 18.7 [Ammonia] / [palladium] 20.4 [Hydrazine]i/ rLPalladiumfl 3.2-8 - 27 - TABLE 2 (Fig 2 ) Effect of hydrazine on the rate of precipitation. +2 Each solution contains Pd , 0.00452M, NH c1, 0.0840M, 4 NI-140R, 0.0920M with varying concentrations of hydrazine to make 50 ml. of the final solution. All the measurements were made atilt= 0.0976, between a pH range of 9.2 - 9.3 and at 25+ 0.1°0. Volume of 0.724M C N2H4 - log Time log time Hydrazine added j [17 H j (Secs) or (ml) to make 50 (Moles/ 2 4 litre) in log t ml of the final the final solution solution 0.50 0.00724 2.140 24840 4.395 1.00 0.01448 1.839 14760 4.169 1.25 0.01810 1.742 9960 3.998 1.50 0.02172 1.664 7380 3.868 2.00 0.02896 1.538 6180 3.798 2.50 0.03620 1.441 4320 3.636
The best slope was found to be 1, and the order of the reaction with respect to hydrazine was 2. The ligand / metal ratios are the same as in table 1 except [Hydrazine]Oetal] m 1.6 - 8.
The data in table 2 represents a set of long times for the same concentration of reactants, due to surface action on the walls of the flask.
-28- TABLE 3 (Fig 3 +2 E:fect of Pd ion concentration on the rate of precipitation. The composition of the final solution is given in the table. All the solutions contained 0.0200M of hydrazine in 50 ml. of the final solution. All the measurements were made at J.= 0.37 (approx.), at a pH between 8.8 - 9.0 and at 251: 0.1°C.
Volume of 0.2253M of Pe2 in PHA Cl] Volume of 4.6k - tog Time log time [Pd(C1)4] -2 added (ml) the final (m3les/litre of NH4OH added [Pd+ (secs) or to make 50 ml. of the solution in the final (ml.) to make log t final solution (moles/litre) solution 50 ml. of the final solution ....1.1•0••••••• 0.50 0.002393 0.3564 1.40 2.610 10920 4.038 0.75 0.003590 0.3525 1.45 2.445 9000 3.954 1.00 0.004786 0.3581 1.50 2.320 6960 3.843 1.50 0.007179 0.3607 1.60 2.144 4920 3.692 2.00 0.009572 0.3548 1.70 2.019 3960 3.598 2.50 0.011965 0.3574 1.80 1.922 2150 3.324 3.00 0.014360 0.3601 1.90 1.844 1327 3.123 The stock solution of Pd(C1)4\ -2 contains (.6228M of free HC1, which exists as ammonium chloride in the final solution. The best slope was found to be 0.76 and the order of the recction was 1.76. The approximate ligand/metal ion ratios in thc system are given balow. [Chloride] / [Palladium] = 24 - 146
[Ammonia] / [Pallad.ium] = 13 - 541 - 29 - TLIax; LEj.g. 3a) E?fect of Pd+2 ion concentration on the rate of precipitation. The composition of the final solution is given in the tabla. All the solutions cztpiaojfc.),ed0.02M of hydrazine in 50 ml of final solution. All the measurements sere made atil= 0.37 at a pH between 8.8 - 9.0 and at 25+ 0.1°C. +2 Volume of 0.2253m of Pd in the [ph 01] Volume of 4.6K - 3.4. Time log time [i'd(C1)4]-2 added (ml) final 4 of 14H4011 added pd -3 (Secs) or to make 50 ml. of the solution (ml.) to make log t final solution Moles/litre) 50 ml. of the final solution 0.50 0.002393 0.3564 1.40 2.610 12420 4.094 0.75 0.003590 0.3525 1.45 2.445 9300 3.969 1.00 0.004786 0.3581 1.50 2.320 8520 3.862 1.50 0.007179 0.3607 1.60 2.144 5640 3.751 2.00 0.009572 0.3548 1.70 2.019 4300 3.634 2.50 0.011965 0.3574 1.80 1.922 3405 3.532 3.00 0.014360 0.3601 1.90 1.844 1692 3.229 The stock solution of [Pd(01)0-2 contains 0.6228M of free H Cl, which existed as ammonium chloride in the final solution. he slope of the straight line pdrtion was found to be 0.70 and the order of the reaction was 1.7. The approximate metal / ligand ratios are the same as given in Table 3. 42 This Table represents a logarithmic plctof long times vs Pd Long times are obtained due to a surface action on the walls of the flash. - 30 -
) +2 Effect of Pd ion concentration on the rate of precipitation (at higher concentration of Pd+2 ion). The composition of the solutions are given below in the table. Ill the solutions contained 0.02M of hydrazine in 50 ml. of the firr*.1 sobj)tion. J11 the measurements were made atiXt= C.40 (approx), at a pH between 9.0 - 9.2 and at 25- 0.1 C. mVblume of 0.2253M of [Pd+2] [EH 01] 4 Volume of 4.6M1-i] Time log time [Pd(C1)4]-2 added (ml) (moles/litre) rnolesilitre) of ammonium [Y (secs) or to make 50 ml of the in the final in the final hydroxide added log t final solution solution solution (ml) to make 50 ml of the final solutijn 2.5o 0.01197 0.3574 2.10 1.922 2340 3.370 2.75 0.01316 0.3646 2.15 1.881 2000 3.301 3.00 0.01436 0.3601 2.20 1.8,14 1790 3.253 3.50 0.01675 0.362( 2.30 1.782 1239 3.093 4.G0 0.01914 0.3653 2.40 1.718 851 2.93o The best slope was found to be 2.2- 0.5 and the order of the reaction was 3.2 ± 0.5. A. large variation in slope was due to great fluctuation in the times of precipitation at such higher concentrations of Pd+2 ion. 3€ The approximate ligand/metal ion ratios in the system are as follows. [Chloride] / [Palladium] 17 - 28 [Ammonia] / [Palladium] 11 -- 17 - 31 - TABLE 5 (Fig 5 ) Effect of Ammonia concentration on the rate +2 All the solutions contain Pd , 0.0038M; NH C1, 4 0.1759H; hydrazine, 0.02M with different concentrations of ammonia, in 50 ml of the final solution. All the measurements were made atig = 0.18 (approx.) and at 25+ 0.1°C.
Volume of 4M of pH [NH Mil Time NE 0H added (ml.) 4 1 (secs) 4 moles/litre to make 50 ml. of in the final the final solution solution
1.00 8.84 0.0724 6600 1.50 9.12 0.1255 8484 2.00 9.38 0.1909 10092 2.50 9.56 0.2488 13572 3.00 9.66 0.2953 15156 3.50 9.72 0.3440 21390
-32- TABLE 6 (Pig 6
Evaluation of activation energy in Pd+2 hydrazine system in presence of chloride ions and ammonia. All the solutions contained 0.00377M of Pe-2; 0.1034M of NH4C1, 0.1366M of 14114014 0.04M of hydrazine and ijk 0.11 (approx.)
Temp Temp 1 x 103 Time Log time oc. T (secs) or K-1 log C
15 288 3.472 9900 3.995 20 293 3.413 5664 3.753 25 298 3.366 3432 3.536 30 303 3.300 1804 3.256 35 308 3.247 902 2.955
The best slope was found to be 4.57 ± 0.2 and the activation energy was 20.9 0.8 K Cals/mole.
-33- TABLE 7 (Fig. 7 ) +2 Evaluation of activation energy in Pd hydrazine system in the presence of ammonium chloride ions and ammonia. All the solutions contained 0.00377M of Pe-2; 0.1034M of NB 011 0.1366M of NH 011; 0.08M of hydrazine 4 4 and dll = 0.11 (approx.)
Time Log time Tempo Tempo 1 x 103 C. K T K-1 (Secs) or log t
5 278 3.597 12698 4.104 10 283 3.534 7208 3.858 15 288 3.472 4262 3.630
20 293 3.413 2110 3.324 25 298 3.356 1053 3.022
The best slope was found to be 4.46 - 0.2 and the activation energy was 20.4 + 0.9 K cals./mole.
-34- TABLE 8 (Fig 8 ) +2 Evaluation of activation energy in Pd hydrazine system containing ammonium chloride and ammonium hydroxide. +2 All the solutions contained 0.01207M of Pd ;
0.0913M of NH c1; 0.1487m of ammonia and 0.0192M of 4 hydrazine atp = 0.13 (approx.)
Temp Temp 1 x 103 Time Log time °C. °K. T -1 (Secs) or K log t
5 278 3.597 14480 4.161 10 283 3.534 8580 3.934 15 288 3.472 4927 3.693 20 293 3.413 2792 3.446 25 298 3.356 1466 3.166
The best slope was found to be 3.85 and the activation energy was 17.6 K cals.
-35- TABLE 9 ) Effect of hydrazine concentration on the rate of precipitation. All the solutions contained 0.004022M of I'd+2 0.3713M of NH4C1, 0.1587M of NH40H with different concentrations of hydrazine in 50 ml. of the final solution. All the measurements were made at/i = 0.37 (approx.), pH between 9.23 to 9.38 and at 25+ 0.1°C. Volume of IM ru H 1 log Time Log time L 2 4J of hydrazine (Moles/litre) L 2H4." (secs) or added (ml.) log t to make 50 ml. in the final of the final solution solution.
1.00 0.02 1.699 8140 3.911 1.50 0.03 1.523 5340 3.728 2.00 0.04 1.398 3981 3.600 2.50 0.05 1.301 3083 3.489 3.00 0.06 1.222 2747 3.439 4.00 0.08 1.097 2119 3.326
The best slope was found to be 0.98 and the order of reaction was 1.98, which conforms with the earlier result.
41 This work was done to examine the effect of change in constant ionic strength.
-36-
TABLE 10 (Fig. 10 )
Effect of hydrazine concentration on the rate of +2 precipitation in the system containing Pd , ammonium chloride, ammonia, IOTA and hydrazine. +2 All the solutions contain 0.004022M of Pd , 0.3533M of NH c1; 0.1587m of NH4OH, 0.005238M of EDTL with 4 different amounts of hydrazine in 50 ml. of the final solution. All the measurements were made at }L, 0.40, pH between 9.12 to 9.18 and at 25 + 0.10C. Volume of hydrazine H ] - log Time Log Time 0 2H4] (Secs) or added (ml.) to Molesl p make 50 ml. of the litre log C final solution in the final solution 0.75 0.015 1.824 14700 4.167 1.00 0.020 1.699 10050 4.021 1.50 0.030 1.523 5765 3.761 2.00 0.040 1.398 3981 3.600 2.50 0.050 1.301 2596 3.414 '3.00 0.060 1.222 2.077 3.317
The best slope was found to be 1.45 and the order
of the reaction was 2.45.' - 37 - TABLE 11 (Fig 11 )
Effect of Ammonia Concentration on rate of +2 precipitation in system containingPd , ammonium chloride, ammonia, aTA and hydrazine. +2 All the solutions contain Pd , 0.00452M; NH 01, 4 0.04M; KOTA, 0.0058M; hydrazine 0.0IM with different concentrations of ammonia in 50 ml. of the final solution. All the measurements were made at }1, 0.08 (approx) and at 25+ 0.1°C.
Volume of NH OH pH NE OH Time 4 4 , added (m1.) to Moles/litre (secs) make 50 ml. of in the the final final solution solution
1.00 9.32 0.0519 350 1.50 9.6(3 0.1001 1398 2.00 9.34 0.1507 2891 2.50 10.05 0.2026 6900 3.00 10.20 0.2490 10020
-38-
TABLE 12 (igL ) +2 Effect of Pd ion concentration on the rate of precipitation in the system containing ammonium chloride, ammonia, EDTA and hydrazine. +2 All the solutions contain 0.004022M of Pd ion, 0.3533M of NH4C1, 0.1489M of NH4013, 0.005238M of EDTA and 0.02M of hydrazine in 50 ml. of the final solution. All the measurements were made atill= 0.40, pH between 9.0, - 9.2 and at 251 0.1°C. +2 Volume of 0.01114 of Pd -q Time Log time d (01)43 added (moles/ [Pd (Secs) or (ml) to make 50 ml of litre in log t the final solution the final solution 0.15 0.000603 3.220 10170 4.007 0.25 0.001005 2.998 7604 3.881 0.35 0.001400 2.854 6480 3.812 0.50 0.002010 2.697 5422 3.734 1.00 0.004020 2.396 3981 3.600 1.50 0.006030 2.220 3031 3.482
The best slope was found to be 0.5 t 0.02 and the order of reaction was 1.5. The approximate metal / ligand ratios are given below. [pdn /N] m 0.87 - 6.7
[Pd+2 [N114019 24.7 - 247
[P(11/ [ NH4ci] 58.6 586 - 39 - TABLE 13 (Fig 13 )
Evaluation of the activation energy in the system containing Pd+2, ammonium chloride, ammonia, EDT& and hydrazine. +2 All the solutions contained 0.004022M of Pd , 0.2968M of NH4C1, 0.1487M of RH40E, 0.006984M of EDTR and 0.04M of hydrazine in 50 ml. of the final solution. All the measurements were done at a pH of 9 (approx) and .0.35 (approx.)
Temp Temp 1 x 103 Time Log time °C °K T (Secs) or K -1 log t
10 283 3.534 12300 4.090 15 288 3.472 7200 3.857 20 293 3.413 4394 3.643 25 298 3.356 2582 3.412
The best slope was found to be 3.79 and the activation energy was 17.33 K. Cala/mole.
- 40 — TABLE 14 (Fig 14 ) Data for Job's Plot
Concentration of Concentration Ligand Absorbance at Metal ion in the of Ligand in Metal 270m 280m final solution the final [ Ligand (Moles/litre) solution (Moles /litre)
0.002393 0.001875 0.44 0.64 0.70 0.002393 0.002813 0.54 0.81 0.86 0.002393 0.003750 0.61 0.80 0.86 0.002393 0.005625 0.70 0.98 1.02 0.002393 0.009375 0.80 0.98 1.02 0.002393 0.01125 0.825 0.85 0.90 0.002393 0.01340 0.848 0.68 0.76
The peak corresponds to a [ligand] /[metal ratio of 3.6.
-41-
ANALYSIS OF EXPERIMENTAL DATA
In all, the experimental data presented here, the measurable
variable has been the,time of precipitation. This is the time taken for - the formation of a minimum amount of palladium atoms by a slow
homogeneous reaction. These atoms eventually coalesce to form the nuclei, each containing a few palladium atoms which start heterogeneous reaction. Therefore the induction period for the formation of these nuclei is a function of the homogeneous reaction and depends on the concentration of all the reactants in solution. This could be expressed by the general relationship:
-dc / dt = kcn (i) ; where(dc/dt)represents
the rate of change in concentration (c) of the reactant at any instant; k stands for the rate constant and n stands for the power of the
concentration or the order of the reaction.On rewriting and integrating equation(i).becomes4ic/cn = kfdt (ii) or 611+1/ (n-1) = kt 4.A (iii); where A is the constant of integration. At t=0, c=c0 and A= col-n/ (n-1),
therefore c1n/(n-,1)=kt + col-n/ (n-1) (iv)
or (1-n)kt + c/rn (k) -n 1-n. or co kt (1+ c / kt) (vi) On taking logarithms the equation (vi) can be written as:
(1-n) log.co= log k+ log.t + log p-n/ kt +(1-n)] (vii) On making a plot of -log co ( co= initial concentration of the the reactant) vs. log t, a straight line should be obtained with slope
= (n-1), but the term in square brackets may produce a systematic
error for each value of co. However on using the approximation that
-42- c=c0, which is valid because there is very2little change in the concentration of the reactant during the homogeneous reaction it ' -becomes-= possible to calculate this error. It has been found that the error has a constant value for a second order reaction and has a negligible variation for the third order reaction, when the data are plotted on a logarithmic plot. Therefore this error affects only the value of the intercept and the slope remains virtually unchanged. These approximations are valid for a limited range of reactant concentration, and are therefore applicable to the present investigations. By another relationship, the time taken to complete a definite fraction of the reaction is given by-the following expression, n t = k co (viii) where k is the rate constant and co is the initial concentration of the reactant. The time of precipitation in these experiments is in reality the time during !'dhiah a. definite fraction: of thel.= reactant concentration undergoes a change In the case of a second order reaction the above expression can be written as: t = k1/c (ix) which shows that the time needed to complete a fraction of the reaction is inversely proportional to the reciprocal value of the initial concentration. Thus on plotting t vs.
1/c , a straight line should be obtained for a second order reaction .
-43- The slope of the straight line will give the value of the second order rate constant.
This has been confirmed in the case of the dependence of the reaction rate with respect to hydrazine; but it case of variables such as palladium the rates are fractional order and this method did not work.
The time of precipitation is inversely proportional to the rate of reaction and therefore to the rate constant.
Hence a plot of logt vs 1/T would give a straight line with a positive slope instead of a negative slope in the usual
Arrhenius plot. As the activation energy depends on the numerical value of the slope it could be evaluated in the usual manner. The activation energy was evaluated under different concentrations of palladium and hydrazine to find if any difference existed in the mechanism at either extremes.
In the study on the formation of different species of hydrazine complexes by Jobs' method(211)of continous variation, a fixed amount of metal ion was treated with increasing proportions of hydrazine and the increase in the concentration of palladium complexes was followed spectroscopically by measuring the increase in the absorbance of the solution in that particular region of the spectrum.
On plotting absorbance vs M/M +L where M stands for the palladium concentration and L stands for the hydrazine
- 44 - • concentration, the peak of the curve represented the maxima
in the ligand / metal ratio and hence the composition of the
species responsible for absorbance in that region of the spectrum.
Jobs' method could not be followed at lower
concentrations of hydrazine as it was difficult to determine the amount of palladium involved as hydrazine complex from
that present as ammine. However, the method was successfully used at the higher concentrations of hydrazine as all the ammine was converted to hydrazine complex by an exchange reaction. The spectra could successfully be used to study the composition of the solution qualitatively.
- 45 - RESULTS & DISCUSSION
The interpretation of the data presented in the previous chapters of this thesis has been a little difficult in view of the complexity of the system. The main problem has been the absence of sufficient thermodynamic data on the palladium complexes in aqueous solutions. The data available at the moment are inadequate and it is not possible to know the real composition of the solutions in terms of the species present in different ranges of reactant concentrations. The data on the stability of platinum (11) complexes is more abundant and can be used qualitatively as a rough guide in the study of palladium (11) system.
The other major problem has been the occurence of side or parallel reactions, going on simultaneously to produce palladium metal. The ultra violet and visible spectra of palladium solutions in the presence of different ligand have been very helpful in understanding the probable composition of the solutions. But the evidence from the absorption spectra cannot be taken as an absolute guide in understanding the whole mechanism of reduction.
The relative stability of different complexes of
Palladium can be inferred from data on corresponding platinum anologues. The only information available about the formation constants of palladium (11) complexes is that the - 46 - tetra chloropalladate and Pd EDTA complexes have log p 4 . (21) (22) 13.4 and log K = 18.5 respectively. In the ease of platinum (11) the value of log"; 4 is equal to 16.6(23) for 2, Pt (ClAand 1T D4 24 35.3 for (NH3)V4/ A comparison of the values of stability constants of platinum
ammines with ohloro-complexes, suggests that ammine are more
stable than the chloro-complexes. As palladium is a member
of the same family of elements to which the platinum belongs,
this anology of higher stability of ammines to chloro -complex
could be applied to palladium (11) complex with ammonia and chloride ion. One could therefore argue that palladium (11) would preferably exist as ammine rather than a chloro-complex in a system containing both ligands in more or less equal proportions. What is true for ammines when compared with chloro -complexes may not be true when compared with EDTA complex.
It is very hard to say in the absence of any data on
Palladous ammines about their relative stability to the Pd -
EDTA complex. But for the Pt group of elements the metal nitrogen bond is stronger than any other bond, the ammines should be more stable than EDTA complex. This is because in the Pd EDTA complex there are only two metal nitrogen linkages and the other two are metal oxygen linkages, where as in ammines all the four linkages are metal nitrogen only. The absorption spectra of a system containing both ammonia and - 47 - and EDTA with palladium (11) ion, show a definite existence +2 of [Pd (N113)1"gand an absorption band which could be due to Pd - EWA complex (Fig. 20).
Before discussing the kinetic data it is necessary to consider the way in which electron transfer takes place.
It is necessary for these two reactants tocome into close contact before any reduction or electron transfer occurs. There are a few complexes between hydrazine and platinum metals reported in the literaturS2511ut in the present work these have been confirmed by the UV spectra of palladium (11) in the presence of hydrazine. These absorption spectra show the existence of palladium hydrazine interaction before any reduction takes place. In figure 17 the curve (1) represents the absorption spectrum of [Pd (C1)4 in the presence of hydrachloric acid, the absorption at 223 mU being due to tetra chloropalladate ion is mentioned in the literature (26).
The curve (11) in Fig. 17 represents the absorption spectrum due to [Pd (NH3) 41+2 and the absorption at 296 mU (27) is also mentioned due to this particular species. On the +2 addition of hydrazine to a solution containing [Pd (NH3)4j a new absorption peak is abserved at 226 - 228 mU (Fig.18) whose height increases with increasing hydrazine concentration. This absorption at 226-228 mU seem to represent a complex of
Pd (11) with hydrazine, which seem to be formed immediately the hydrazine is added to the system. This indicates a rapid - 48 - exchange between hydrazine and ammonia in palladous ammine. Further confirmation that hydrazine forms complexes
with palladium (11) by the replacement of ammonia has been
obtained by Job's method.(28) If hydrazine is added in successively larger amounts at comparatively lower concen-
tration of ammonia the absorption shows an increase with an increase in the amount of hydrazine added, (Fig.15).
On making a Job's plot (Fig. 16), the ligand / metal ratio corresponding to the maxima was found to be 3.6, shows the possibility of forming a tetra substituted complex of
palladium (11) with hydrazine by successive displacement of
ammonias. The formation of Pd hydrazine complexes was proved
by mixing the solution of Pd (0104)2 with N2H4. 2 HC104, the
solution gave bright yellow colour, which turned on standing to green and finally black. The bright yellow colour
seems to represent palladium-hydrazine complex. In Figure
21 the curve (11) shows an absorption spectrum of [Pd(O1)4 2 and curve (1) shows the absorption spectrum of a solution containing Pd (0104)2 and N2114.2HC104. In figure 22 the curves (1) and (2) represent the absorption due to solutions containing pure Pd (0104)2 and Pd (0104)2 + 2N2H4.2 110104
respectively. Figure 23 shows that the absorbance of Pd (11) complexes with hydrazine in presence of sufficient concentration of ammonia show a sharp increase with different - 49 - higher concentrations of hydrazine (see fig. 18)
The absorption spectra of a system containing palladium (11) in presence of EDTA and hydrochloric acid are shown by figure 19, the absorption at 337 mU is reported in the literature to be due to the Pd - EDTA complex. In
Figure 20 the absorption of a system containing Palladium (11) in the presence of ammonia and EDTA, is shown by curve (1) the peak at 247 mU could be due to a palladium - EDTA complex.
But addition of hydrazine this peak at 247 mU shows an increase in height (curves (11) and (111) Fig. 20), which shows that the addition of hydrazine increases the absorption at this particular wave length possibly by forming a mixed complex of Pd (11) with EDTk and hydrazine which has absorption at the same wave length. There is no reference to such an absorption in the literature.
KINETICS: The studies on the reduction of palladium (11) complexes by hydrazine show that the concentrations of all reacting and non reacting substances used in the solution affect the rate of homogeneous reaction between palladium (11) and hydrazine. The concentrations of palladium (11) and hydrazine directly affect the rate of reduction but the concentration of chloride, ammonia etc. also have an indirect effect on the rate although they do not take part in the chemical reaction. The rate dependence with respect of each of these variables has been presented in the tables and - 50 - figures.
The rate of reaction shows second order
dependence on hydrazine concentration. The data are in
tables 42 MON MO (Figures 1, 2 and 2a). Table 1 shows
the normal times of precipitation at different concentrations
of hydrazine while table 2 represents a set of long times
against the same set of hydrazine concentration. These
long times represents less than 20% of the total number
of runs and are always obtained due to some reaction
taking place on the walls of the flasks which delays the
time of precipitation. However this delay in the timeof precipitation is uniform for all concentrations of
hydrazine so that a logarithmic plot of long times vs
hydrazine only affects- the intercept but not the slope.
These long times become less frequent at a higher ionic strength of the experimental solutions. While studying the effect of hydrazine on the rate of precipitation, a set of experimental runs was made at constant ionic strength by adding an extra amount of ammonium chloride (Table & Fig.9) and no difference in the value of the slope was found.
Therefore it seems that hydrazine molecules exchange with ammonia by a sort of q4ck prequilibrium to form a di-substituted hydrazine complex. This could presumably be a trans - isomer in which hydrazine reacts with palladium (11) by slow rate determining step to produce - 51 - palladium metal. This may involve the formation of some free radicals which bring about the electron transfer from these radicals to Palladium (11). The whole scheme could be represented as
N H 2 4 2H4 [Pd (NH3) 11.-]-4 Ed (N2 H4) (NH3)3)i------> fast (A) fast H311 N2113 [Pd (N2H4),(NH3)2] slow -.., d-----4 Pd + 2NH4 (B) +2112H3 ' H3N2 +2H+ NH3 intermediate 2 N2H3 ---*N4H6 --i02NH3 + N2
The rate determining step is the reaction in which disubstituted hydrazine complex (B), reacts slowly to produce palladium. The complex (B) should be a trans - isomer to be more reactive, but it is difficult to say in the absence of any evidence except that such an assumption is helpful in interpreting the data on the EDTA system. In fact very little is known about trans-directing effect of hydrazine but as a number of reducing agents show trans- affect, this could be applied to hydrazine. The rate could be expressed by following expression.
The rate = kl 1.13d (NH3)2 (N2H4)2
- 52 - = ki ld(NH3)43f N2114] 2 K1K2 E 2 oC k1 K1K2 [Pd(NH3),3 [N2111] 2
as is constant while studying the effect of N2H4 on the rate. Where k1 is the second order rate constant and l(N2H4) (NH3)3 [711d K1 = F V'd(NH3)j {N2HJ [Pd(N2H4)2 (NH3)] [q and K2 [pd(NE3 )3 (N2H4)] [N2q
Therefore the rate isc The value of second order rate constant with respect to hydrazine was found to be 5.5 x 10-3 litre -1 -1 mole See (Fig. 2'0 ) The effect of Palladium (11) ion concentration on the rate of precipitation shows a fractional order rate dependence with respect to Palladium (11). The logarithmic plot of palladium (11) ion concentration vs time shows a break at higher concentration of palladium (Fig. 3). The best slope of the upper line was found to be 0.76 and the order of reaction therefore was 1.76. This value suggests two parallel reactions with the main contribution from higher Pd concentration of the specks containing two palladium ions. ti value nearer to second order suggests - 53 - that two palladium ions are involved in the reaction, which could only happen if palladium forms a binuclear complex with hydrazine, possibly a bridged structure to be shown below. The possibility of the formation of bridged complexes with two or more palladium ions cannot be excluded particularly at higher concentrations of palladium. Lome authors have suggested the formation of these bridged or poly nuclear complexes in solution. Therefore when the palladium (11) concentration is increased without any increase in hydrazine concentration perhaps the poly nuclear complexes are also formed in addition to the binuclear structures. Therefore the overall rate at relatively lower concentrations of palladium is due to monomer and dimers reacting at the same time and giving an order near to two. But at higher concentration it becomes a mixture of dimer and other higher polymers reacting simultaneously to produce palladium metal. Figure 4 represents a logarithmic plot of a set of relatively higher concentrations of Pd+2 vs time and the order is nearly 3. This value at relatively higher concentrations is less dependable as the reproducibility of precipitation times was not good and there is greater error observed on calculating the best value of slope. On making a logarithmic plot of a set of long times versus Palladium (11) concentration (Fig. 3a), the - 54 - line seems to take the form of curve suggesting a change in the relative concentration of different species of Pd (11) complexes when we pass f.rom lower concentration range to higher concentration range. Presumably Fig. 3 also shows a similar behaviour. The slope of the straight line part was found to be 0.7 and order with reaps of to Pd+2 was 1.7. The whole scheme can be represented as follows. NH [Pd(N115),i H2H44Pd(NH3)3 (N2H4 ...21410NH3)2(112H4)p] fast fast aNa, dimerise§ /;>p fast HAN2 NH3 slow V 1,0{ N211 3,.. Pd //rN2H3 H3 P + 4H + / \ ,•-•"..#-' '`"..,, H N 3 2 N2H3 NH3 (Intermediate) 2 Pd + 452H3 + 4N}13 + 4H+ 2N4H6 ---4- 4NH3 + 4N2 rate = k2 (N2H4) (NH3) Pd (N2H4)2 Pd (N2H4) (NH3) [ 2 =k2 242 Pd (N 2H4)2 ( 3)2, [[N-H3 12 -55- 0(k2 [Pd (N2H4)2 (NH3)232 /3242 as [NH3] is kept constant 2 Therefore rate o( {-Pd.] and over all rated( kiN3 +k2[1'd] 2 Where k2 is the rate constant for bridged complex containing two Pd+2 ions and 12 Mal (NH3) Pd (112102 Pd (N2H4) ( 242' !id. (NH3)2 (N2H4)2]2 L The study of the system containing EDTA offers some interesting data when compared with the system containing only palladous ammines. As discussed earlier, the absorption spectra of a system containing palladium (11) in the presence of ammonia and EDTA show the presence of both complexes. On the addition of hydrazine the absorption due to the EDTA complex increases which indicates that hydrazine replaces the two carboxyl groups in favour a Pd N2H4 linkage, and forms a cis -disubstituted hydrazine - EDTA complex. This is a reasonable suggestion se Pd-N bonds would be more favoured than Pd-O bonds from carboxyl groups. The third hydrazine molecule then enters trans to one of the N2H4 groups already present and it is likely that it is the tri-substituted hydrazine - EDTA complex which reacts to produce palladium metal. The overall rate is therefore determined by the reactivity ofbki(NH3)2 (N2H4)211-2 +2 and 113d (N2H4)3 EDTA] and the order is - 56 - found to be 2.5 with respect to hydrazine in the system containing EDTA with ammonia. (Fig. 10). The whole scheme could be represented as follows. [Pd (EDT.)]--11-211-A-4pDTA Pd (N2H4 (1) (11) [Pa (MTh) (N2H4)4 112H4ka (EDTA) (N2H3) .2)_za7..4 (111) (1V) [1(14.2113)2 Pd (EDTA) (N2H4) Pd EDTA +211+ i-2N2H3-640N4H6-41.2NE13+132 The overall rate = k2 (N2H4)2( 5)j k3 (EDTA) (N2H4) , 2 , Therefore the overall rate [§114) .m31:21 3 N HL Where k3 is the rate constant for the third order reaction with respect to hydrazine. The rate with respect to palladium (11) in the system containing EDTIL, ammonia and hydrazine shows a fractional order dependence. The exact value of the order +2 with respect to Pd being 1.5 which shows that both monomers and dimers contribute significantly towards the overall rate. In this case no study could be made at relatively higher concentrations of palladium (11). The effect of Pd+2 concentrations is shown in Figure and Table 12. The rate was also found to be effected by ammonia concentration. Table 5 and Table 11 show the effect of NH3 on the rate presence of ammonia and ammonia with EDTA respectively (Fig. 5 and 11). The effect of ammonia could be the greater stability of complexes in presence of a higher ammonia concentration. This can be explained more clearly by the following equilibria. \ 112HA lnni, IT \ /Trvr Pd(NH3)4 2147Pd(N2H4) ____4F02n4)2krin3q (NH3 )3 I rate = kl f-Pd (N2H4)2 (NH3 )3 KI K2 [Pd (NH3),] [ N2111 2 ki ENH3 2 rate o< 1 [NH3) 2 The situation in EDTA system is made slightly more oomplex because of the presence of another equilibrium between Pd (11) and EDTA. Qualitatively speaking a higher concentration of ammonia will give better protection against nucleophilic attach of hydrazine in both the systems with or without EDTA. All that can be said from the information obtained from the above kinetic data is that a particular mechanism is suitable within limited range of reactant concentrations but it changes when the reactant concentration - 58 - is increased beyond a limit. This has been confirmed by the evaluation of the activation energies at different concentration of each reactant. In Fig. 6 and Fig. 7 the activation energies have been evaluated at two different concentrations of hydrazine and the values found were 20.4 and 20.9 IC Cals/Mole at the higher and lower concentrations respectively. This suggests that the same mechanism is operative at both these concentration of hydrazine. The activation energy when evaluated at higher concentrations of palladium (11) gave a value of 17.6 K. Cals/Mole (Fig.8) and Table 8). This is indicative that at higher concentration of palladium (11) some species are present which react more easily to produce palladium metal. It has already been suggested from the kinetic data that polymeric palladium complexes are formed at these metal concentrations and axe more reactive than the monomeric species. In the case of EDTA system the evaluation of the activation energy showed a value of 17.33 K. Cals/Mole (Fig. & Table 13) suggesting that in the 'presence of EDTA some species formed are more reactive than those present in the pure ammine system. The reactive specied could be the trisubstituted hydrazine BDTA complex as postulated earlier. The preceding discussion is thought to be the nearest approach to the mechanism of homogeneous reduction on the basis of the determined kinetic and spectral data. - 59 - The discussion has necessarily been qualitative as a great deal more kinetic and thermodynamic data on the specific rate constants and formation constants of the various complex species is necessary in order to give a more quantitative understanding of the reactions occuring in these systems. - 60 - L.CI:NOWIEDGEMENT I should like to express my deep sense of gratitude to my supervisor, Dr. k.R. 3urkin, reader in hydrometallurgy in this department, for his supervision, keen interest and helpful guidance, without which this work could never have been completed. I am also thankful to All my colleagues in general and hr. A.J. Monhemius in particular for his valuable help in the preparation of this thesis. I should also like to express my thanks to Dr. L.J. Poe of the Chemistry Department, Imperial College for his valuable discussions. My thanks are due to all the technical staff in the department for their help at different stages. I am grateful to the Ministry of Iiviation (Ministry of Technology), for providing me a grant for this project. I.P. Singh, 19th November 67. Department of metallurgy, Imperial College, London S. W. 7. - 61 - REFERENCES 1. a R.N. Rhoda, Trans. Inst. Metal Finishing 36, pt. 3,82 (1959) b. R.N. Rhoda and A.M. Madison, U.S. Patent 2, 915, 406 11959) c. h.N. Rhoda, J. lilectrochem Soc. 108, 707 (1961) 2. L. Sacconi and A. Aabatini, J. Inorg. Nucl. Chem. Z2 (11), 1389 - 93 (1963) 3. N. Ahmad and S.M. Paz fur Rahman, Z. hnorg. klieg. Chem. 330 (3-4) 210 - 16 (1964) 4. D. Banerjea and I.P. Singh, Z. hnorg. Alleg. Chem. 349, 213 (1967) 5. G. Schwargenbach and A. Zobrist, Rely. Chem. Acta. 15, 1291 (1952) 6. R.L. Robertus, H.L. Laitinen and J.C. Bailar, Jr. J. Amer. Chem. Soc. /I 3051 (1953) 7. L.P. ltudrieth and B.A. Ogg, "The Chemistry of Hydrazine" John Wiley and Sons, Inc 1951, Chapter 9, Page 181. B. G.H. Nancollas and H. Purdie Quart. Rev. (London) 18 (1), 1-20 (1964) 9. M. Volmer, "Kinetic der Phasenbildung" Edwards Bros, Ann Arber, Michigan 1945. 10. J.A. Christiansen and A.E. Nielsen, Acta. Chem. Scand, 5.1 673 (1951) 11. M. Smoluchowski, Z. Physik, Chem. 92, 129 (1918) 12. a. La Mer V.K. and R.H. Dinegar, J. Amer. Chem. Soc. 72, 4847 (1950) b. La Mer V.K. and R.H. Dinegar, J. Amer. Chem. Soc. 73, 380 (1951) -62- 13. A. Torborg Jensen, Z. Physik. Chem. k 180, 93 (1937) 14. R. Becker and W. boring, Ann. Physik, 24, 719 (1935) 15. C.W. Davies and A.L. Jones, Trans. Faraday Soc. .520 812 (1955) 16. D. Turnball, J. Chem. Phys., 221 411 (1952) 17. J.D. O'Rourke and R.A. Johnson. Analyt. Chem. 22, 1699 (1955) 18. A.W. Brown and F.F. Shetterly, J. Amer. Chem. Soc. 29, 1305 - 1312 (1907); ibid ./Q, 53 - 63 (190B); ibid, 11, 221 - 237 (1909), ibid 31, 783 - 799 (1909) 19. E.J. Cuy, M.E. Rosenberg and W.C. Bray, J. Amer. Chem. Soc. 26, 1706 - 95 (1924) 20. R.E. Kirk and A.W. Browne, J. Amer. Chem. Soc. E, 337 - 347 (1928) 21. D.H. Templeton, G.W. Watt and C.S. Garner, J. Amer. Chem. Soc. 65, 1905 (1943) 22. W.M. MacNevin and 0.H. Kriege J. Amer. Chem. Soc. J, 6149 (1955) 23. Grinberg and M.I. GU' fman, Doklady Akad. Nauk. SSR, 1038 (1960) 24. Grin'berg and M.I. GEL' fman, Doklady Akad . Nauk.SSSR.n, 137 (1961) 25. a. V.I. Goremykin Compt. rend. acad. Sci. URSS, 33, 227 (1941) b. V.I. Goremykin and K.A. Gladyshevskaya, J. Gen. Chem. (U.S.S.R) 13, 762 (1943), Ibid 14, 13 (1944) c. R.N. Savel' eva and N.G. Klyuchnikav, Zhur. Neorg. Khim, 10 2759 - 63 (1956) 26. a. R. Samuel, A.R.R. Despande, Z. Physik, 80, 395 (1933) - 63 - 26. b. A.K. Sundram and E.B. Sandell, J. Amer. Chem. Soc. al 855 (1955) c. C.K. Jorgensen, Absorption spectra and Chemical bonding in Complexes, Pergamon Press, 1962, page 287. 27. a. C.K. Jorgensen, Contract No. DA-91-508-Euc-247 with Europian Research Office, U.S. Department of the Army, Frankfurt am Main. Absorption Spectra of Complexes of Heavy Metals. Chemical and Spectro Chemical studies. ASTIA document No, 157158 Sept. 1958. b. C.K. Jorgensen, Absorption Spectra and Chemical bonding in Complexes. Pergamon Press, 1962, page 287. 28. a. P. Job, Ann Chim (10) 2, (10), 113 (1928) b. -1). Job, ibid (11) 6, 97, (1936) -64- APPETIMIX To find the best slope and intercept, and to estimate their errors in the formula y = mx + c when variable y is subject to error: In a series of results where a linear relationship is expected between two variables x and y and when a graph of these variables appears to approximate to a straight line, by assuming that x is effectively errorless, the error in y may be calculated by the following method. The error in y is dy, then the formula, y = mx + c becomes y dy = mx + c where x and y are the measured values of two variables which have been measured N times to give N number of points on the graph. It is assumed that aura the values of dy belong to the same population1that they are statistically independent and thatEdyi = 0 The best values of m and o have been calculated using the following formulae. The formulae have a mathe- matical basis in the method of least squares and can be used empirically as there is a sound reason behind them. (1) The best estimate of m, the slope ism and is given by m = N2:xi Yi - (12:xi) (1:Yi) lEx?1- - (1E:xj) 2 (11) The best estimate of c, the intercept is c and is given by c = (!SEYi - mx i ) - 65 - (111) The best estimate of Sy, the errorin dy is Sy and is given by 2- 2 Sy - (1sEy02- m NZ): N This is a fixed value irrespective of the value of y and only the relative error will vary with different values of y. (1V) The best estimate of the rror in m, is Si and is 2- given by s2-m =sy NZ.xi :x-1)2 (v) The best estimate of error in c, is Sc and is 2- 2 2 given by S c = Sy Xxi 11.Exi 2 - (x1)2 (V1) The standard deviation in y can be calculated directly once the individual results for yi corresponding to each xd have been evaluated from m and c at an individual xi 2 Sty 2N1 L (Yi - It is essential to compare this result with that from (111) In the data presented in this thesis, X = - log (where c was the concentration of the reactant in question) and y = log t (where t was the time of precipitation at each value of x) -66- 52 5Cr 46- 4.4/- 42- 40 3-8- 0 0 36- 2.3 1.1 1.2 1.4 1.6 1.8 2.0 2.2 - LOG [ N2H41 Fig.1: Effect of [N0HA ] on the rate of precipitation at 25°C (short times7.' Logarithmic plot; Slope = 1.1. 0 _I 1.4 1.6 1.8 2.0 2.2 —LOG[ N2H4] Fig.2: Effect of [N2H4] on the rate of precipitation at 25°C (long times). Logarithmic plot, slope = 1. 8 4 1 1 00 0.2 0.4 0.6 011 . 10 1.2 1.4 1.6 1.8 20 10-2[1 ] --a- Fig.2(a): a = N 2 H 4 slope = k = 5.5 x 10-3, litre mole-1 sec-1. -69- 41 40- 38- 37- 36- 35 (.9 O 34,- 32- O 31 _J 18 2'0 2 2 24 26 28 DaG[Pd-172 ] Pig 3: Effect of [Pc1+2 ] on the rate of precipitation at 25° C Logarithmic plot slope = 0.76 (i); slope = 2.7(ii). 41 3.6 - 35- 34- 33- 0 0 J 3C.1. 8 20 2.2. 2.4 2.6 2.8 - LOG [Pd4-2] Fig.3a: Effect [Pd-1-2] Of precipitation at 25°C. Logarithmic plot of long time vs [Pe-2]; slope of the straight line portion = 0.70. 34 33^ 3-2- 3.1-- 2-9- 1.7 1.8 1.9 LOG f Pd* - r +2 Fig.-: Effect of ad ] on the rate of precipitation at 25°C (at higher concentrations of Pd+2). Logarithmic plot Slope = 2.2. 24- 22 - 20- 18 - 16 - 14 - 12 - T 1 0 0 60- 40- 20- X0.0 0-1 0.2 03 0.4 0.5 I NH3) Fig.5: Effect of [NH3] on the rate of precipitation at 25°C. • -73- 40- 3.9 - 34- 37 - 34- 3.5 7 3.4 - 33 - 32 - 3.1- ... 0 -I 3.0 2.9 2-8 I 1 32 33 34 36 36 37 I 3 - X10 Pig.6: Evaluation of Activation Energy at lower concentration of hydrazine. , , Slope = 4.6. Ea = 20.92 K.cals/mole. -74- ' 42 41 •• 3:7 3-5 34 33 •,, 0 J 3.2 31 34 3.5 3-6 3.7 3.8 3 IX 10 T Pig.7: Evaluation of Activation Energy at higher concentrations of hydrazine. Slope = 4.46. Ea = 20.43 K.cals/mole. -75- 42- 41- 40- I 39 - 38- 3.7- 36- 3.5 - 34 - 3-3- .. 0 O --I 32- 3.1 30 1 1 1 • 1 32 33 34 3.5 36 3,7 -XI()1 Fig.8: Evaluation of Activation Energy at Higher Concentration of 2d+2. Slope = 3.85. Ea = 17.62 K.cals/mole. -76- 4.2 3.6 0 3.4 3 2 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 -LOG C N2H4] FIG 9-EFFECT OF EN J-141 ON THE RATE.. OF PRECIPITATION AT 25°C LOGARITHMIC PLOT- SLOPE= 0.98 4 4.1 4C 3. 88 3.7 86 3.5 34 32.1 .0 12 1.4 1.6 I8 20 2.2 -LO-G ( N 11 1 2 4 Fig.10:Effect of [N2H4] on the rate of precipitation at 25°C on the system containing EDTA. Logarithmic plot, slope = 1.45• 12 - 1 1 - 10- 90- 8,0- 60- 50,- 20- 10- OS X0.0 , 0.1 0.2 oa 0.4 ' (NH3] Fig.11: Effect of [NH3 ] on the rate of precipitation at 25°C. -79- 42 343" 3.6 34 t t t 3. t t L. 2.0 224 2. 2.6 2.81 3.0 3.2 34 3.6 _LOG[Pcr2 ] FIGI2- EFFECT OF[Pe2] ON THE RATE OF PPCIPITATION AT 25°C IN THE SYSTEM CONTAINING EDTA- LOGARITH:\as, PLOT SLOPE= 0.5 4,2 40- 38r- 37- 3.6- 3-5- 0 34,- 335 3.40 - 3 45 3.50 3.55 - MO3 Pig. 13: Evaluation of Activation Energy in the system containing EDTA. Slope . 3.8; Ea = 17.33 K.cals/mole. ' 4-2 0 without EDTA 0 with EDTA 41 common point 3.8- 37 3.5- 34- 33 3.2- 1 • 1.0 1.1 I2 13 1.4 1.5 1.6 17 1.8 1.9 20 _LOGN H 3 2 4 Fig.14: A comparative study of the effect of hydrazine concentration on the rate of precipitation on the two systems; logarithmic plot. -82- I di= MIN AM. 0.8- w 2 C 00 225 250 275 300 325 350 wave lensth in miilimtcrons - - - Fig.15: UV spectra of a solution containing 0.025n of Pd+2 ,0.08M of NH C1, (see Tabl3 14). 0.04M of NH4OH with different concentrations of N2H4 " I - 09- OR' 0.6- 05- (a) 04- 2 0 2- O .o 0 0.1 00 01 02 03 04 05 06 07 08 09 10 II 1-2 IL]/IL]-1-IM] Fig.16: Job's plot a) absorbance at 280 mU; -b) absorbance at 270 mU. M= Pd+2 ; I/M = 3.6. L =1T2H•4' wave lensthin millimicrons Fig.17: i) UV spectra of a solution containing 0.000045M of [Pd(C1)A72- with 0.4M of HC1. ii) UV 'spectra of a solution containing 0.0037M of Pd+2, 0.1gM of NH4 C1 and . 0.184M of NH4OH. 2'0 1-8 1.6 1.4 1.2 1-0 0.8 0.6 0.4 2 ?, 0.2 A 0 00 200 225 250 275 300 325 350 400 wavelength in millImletons +2 Fig.18: UV spectra of solutions containing 0.0045M of Pd 0.16M of NH401, 0.1841-1 of NH401j with different amounts of N2H4. i) with 0.011.1 of N2H4 ; ii) with 0.021A of N2H4. 2.0 i - t 1.8 - 1.6 - 00 1.4 1.2- 1.8 - 0.8 0-6 - 0.4 -- 0.2-- 0 225 250 275 300 325 350 400 450 Fig.19: (i) UV spectra of a solution containing 0.00045M of Pd+2 and 0.003M of EDTA (0.25cm cell) (ii) as (i) (in 1 cm cell). 1 ••• 0.6- . 2 0.4- * n Q2— 0.0 I 1 1 225 250 - 300 350 375 wave length in millimicrons Fig.20: UV spectra of solitiOns containing (1) 0.0038M of Pd+2, 0.164M of ITH4C1, 0.184M of NH 0H and. 0.007M - of EDTA; (ii) As (1) with 0.0214 of 11:2114; 4 (iii) As (1) with 0.0411 of N2H4. 2.0 1-6 k) 08 06 O4 - 1 02 - 00 . 1 I I I J 200 250. 300 350 450 wave length In milirnicrons Fig.21: UV spectra of solutions containing (1)0.001M of Pd(C104)2 and 0.00411 of N2H4.2110104. (2)0.0004M of [Fd(01)4]-2 with 0.16M of NH401. 2-0 18 - 16 14 - 12 - 0.8 2 02 oo20 225 n3-2-75 300 325 350 400 wave lensth in milihicron3 Fig.22: UV spectra of solutions containing (1) 0.0004M of Pd(C104 ) 2; (2) as (1) with 0.008M of N2H4.2H0104. 20 1.13- • 160- 1.4e- 1.0 - 0.6- g 04,- 1 Iv 0.2- 00. 200 250 300 350 400 wave length in millimisrons Pig.23: UV spectra of soWions containing: (1) 0.002M of Pd . 0.16M of NH Cl and 0.1611 of NH OH• (2) as (1) with 0.01M of N )HA (3) as (1) with 0.03M of NoHA ; (4) as 4'(1) with 0.05 of N • (5) as (1) with 0:08M of N2 H • (6) as (1) with .111 415r11. 11 2 H 4-' 4' 2 4.