Thesis (MSc)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: Ruthenium, as one of the platinum group metals, was investigated to
determine the aquation rate constant of [RuCl6]3- and the anation rate
constant of [RuCl5(H2O)]2-. This two reactions represent the
equilibrium reaction [RuCl6]3- + H2O ⇄ [RuCl5(H2O)]2- + Cl-. The
reactions were followed, using stopped-flow injection and UV/Visible
spectroscopy, at different temperatures. The aquation and anation
rate constants were determined with good precision and
thermodynamic values for the reactions were calculated.
The pseudo first order aquation rate constant, k65, was determined by
calculation from the regression line as k65 = 52.1 (±3.7) x10-3 s-1 at
25°C. The activation energy, Ea, is 90.1 (±1.2) kJ.mol-1 and the
enthalpy and entropy of activation is 87.7 (±1.2) kJ.mol-1 and 24.7
(±4.3) J.K-1.mol-1, respectively. The aquation rate constant was
found to be dependent on the hydrochloric acid concentration,
decreasing with increasing hydrochloric acid concentration.
From the regression line at 25°C the second order anation rate
constant, k56, was calculated as 1.62 (±0.11) x10-3 M-1s-1. The
activation energy is 88.0 (±1.4) kJ.mol-1, with the enthalpy and entropy
of activation 85.6 (±1.4) kJ.mol-1 and –11.2 (±4.7) J.K-1.mol-1,
respectively. The influence of the hydrochloric acid concentration of
the solution on the anation rate constant was not investigated.
The equilibrium constant for the reaction studied was calculated from
the rate constants for the aquation and anation reactions. The
equilibrium constant, K6, was calculated as 0.0311 M-1 at 25°C. The
equilibrium constant, when compared to literature, was found to be
dependent on the hydrochloric acid concentration. It was then used, in
conjunction with data from the literature, to construct two distribution
diagrams. Distribution diagrams for the Ru(III) aquachloro species show between 79.9% to 72.3% [RuCl6]3- present in 12M HCl. The two
distribution diagrams were very similar and it is not possible to resolve
the issue of a final distribution diagram for the aqua-chloro Ru(III)
system without further investigation into the all the other rate constants
of the Ru(III) aqua-chloro species.
The rate constants and thermodynamic values for the Ru(III) reaction
were compared to corresponding data (from literature) for Rh(III) and
Ir(III) because several comparisons between these platinum group
metals have been noted. It was found that for both the aquation and
anation rate constants, the following trend was observed: Ru(III) >
Rh(III) > Ir(III). These differences are in certain cases exploited in the
refining of these platinum group metals.
Crystals of diethylenetriamine hexachlororuthenate(III) was prepared
and characterised by x-ray crystallography and CHN analysis. The
average Cl-Ru bond length for the crystal was 2.371 Å. The crystal
structure was compared to hexaaquaaluminium
hexachlororuthenate(III) tetrahydrate and diethylenetriamine
hexachlororhodate(III). The metal-chloride bond lengths of all the
crystals were found to be similar (2.350 Å – 2.375 Å). The
diethylenetriamine crystal structures compared well. The conclusion
was that the crystals prepared were diethylenetriamine
hexachlororuthenate(III). / AFRIKAANSE OPSOMMING: Ruthenium(III), een van die platinum groep metaal-ione, is in hierdie
studie ondersoek om die akwasie tempo konstante van [RuCl6]3- en die
anasie tempo konstante van [RuCl5(H2O)]2- te bepaal. Dié twee
reaksies verteenwoordig die ewewigsreaksie [RuCl6]3- + H2O ⇄
[RuCl5(H2O)]2- + Cl-. Die verloop van die reaksies is met behulp van
UV/Sigbare spektroskopie by verskillende temperature gevolg. Die
akwasie en anasie tempo konstantes is bepaal met goeie presisie en
die termodinamiese konstantes van die reaksies is bereken.
Die pseudo-eerste orde akwasie tempo konstante, k65, is bepaal deur
middel van regressie, as 52.1 (±3.7) x10-3 s-1 by 25°C. Die aktiverings
energie, Ea, is bereken as 90.1 (±1.2) kJ.mol-1 en die entalpie en
entropie van aktivering is onderskeidelik 87.7 (±1.2) kJ.mol-1 en 24.7
(±4.3) J.K-1.mol-1. Daar is gevind dat die akwasie reaksie konstante
afhanklik was van die soutsuur konsentrasie: dit neem af soos die
soutsuur konsentrasie toeneem.
Met behulp van die regressie lyn is die anasie tempo konstante bepaal
by 25°C as 1.62 (±0.11) x10-3 M-1s-1. Die aktiveringsenergie is bepaal
as 88.0 (±1.4) kJ.mol-1 en die entalpie en entropie van aktivering,
onderskeidelik as 85.6 (±1.4) kJ.mol-1 en –11.2 (±4.7) J.K-1.mol-1. Die
invloed van die soutsuur konsentrasie op die anasie tempo konstante is
nie bepaal nie.
Die ewewigskonstante vir die reaksie wat ondersoek is, is bereken met
die tempo konstantes vir die akwasie en anasie reaksies. Die
ewewigskonstante, K6, is bereken as 0.0311 M-1 by 25°C. Toe die
ewewigskonstante vergelyk is met die literatuur waardes, is gevind dat
die ewewigskonstante afhanklik is van die soutsuur konsentrasie.
Saam met die waardes wat in die literatuur gevind is, is die
ewewigskonstante gebruik om twee distribusie diagramme te bereken. Die distribusie diagramme vir die Ru(III) spesies toon onderskeidelik
79.9% en 72.3% [RuCl6]3- in 12M HCl. Die twee distribusie diagramme
is baie eenders en dit is nie moontlik om ‘n finale distribusie diagram op
te trek totdat die uitstaande tempo konstantes tussen die akwachloro
Ru(III) spesies bepaal word nie.
Die tempo konstantes en termodinamiese waardes wat bepaal is vir die
Ru(III) reaksie is vergelyk met gelyksoortige waardes in die literatuur
van Rh(III) en Ir(III) omdat daar ooreenkomste tussen die platinum
groep metale opgemerk is. Daar is bevind dat die akwasie én anasie
reaksies die volgende patroon volg: Ru(III) > Rh(III) > Ir(III). Die
verskille word in sekere gevalle benut in die raffinering van hierdie
metale.
Kristalle van dietileentriamien heksachlororuthenaat(III) is berei en
gekarakteriseer met behulp van CHN analise en x-straal kristallografie.
Die gemiddelde Cl-Ru bindingsafstand vir die kristal was 2.371 Å. Die
kristalstruktuur is vergelyk met dié van heksaäkwaäluminium
hexachlororuthenaat(III) tetrahidraat en diëtileentriamien
heksachlororhodaat(III). Die chloried-metaal bindingsafstand vir die
kristalle was soortgelyk (2.350 Å – 2.375 Å). Die diëtileentriamien
kristalstrukture stem goed ooreen. Die gevolgtrekking was dat die
kristalle wat voorberei is wel diëtileentriamien heksachlororuthenaat(III)
was.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/16458 |
| Date | 12 1900 |
| Creators | Viljoen, Karen |
| Contributors | Koch, K.R., University of Stellenbosch. Faculty of Science. Dept. of Chemistry and Polymer Science. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | vii, 83, [51] leaves : ill. |
| Rights | University of Stellenbosch |
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