TED Ankara College IB Thesis
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INVESTIGATION OF THE EFFECT OF NATURE OF LIGAND ON THE CRYSTAL FIELD SPLITTING PARAMETER OF OCTAHEDRAL CHROMIUM(III) COMPLEXES
Full text linkTransition metal complexes are mostly coloured. These colors are known to be resulted from the energy difference between the sperated d-shells. The amount of seperation of d-shells depends on many factors, such as the size of metal ion, oxidation number of metal ion, complex geometry, nature of metal ion, and the nature of the ligand. As the nature of the ligand is is easy to change and there are lots of ligands, effect of the nature of ligands on
crystal field splitting parameter of a metal is selected as the question. As chromium(III) is common metal ion, easy to find and it forms d3 complexes, which have spectrums relatively easy to interpret; the scope of the investigation is limited to chromium(III) complexes. So, the objective of this study to investigate the effect of the nature of ligand on the Octahedral Crystal Field Splitting Parameter(Δo) of chromium(III) complexes.
A variety of chromium (III) complexes with different ligands were synthesised; and characterized with UV-visible spectrometer. Then complexes’ crystal field splitting parameters are calculated from the transition band with the longest wavelength. Also another method, involving Tanabe-Sugano diagrams, was used to calculate crystal field splitting parameters for comparison. It was found that there is no significant difference between the calculate crystal field splitting parameter values calculated from the transition band with the longest wavelength and values calculated from Tanabe-Sugano diagram.Overall, the crystal field splitting parameter values are found to be as 199442 J/mole for Cr(acac)3, 258805 J/mole for [Cr(en)3]Cl3, 203020 J/mole for [Cr(H2O)6](NO3)3, 209766 J/mole for K3[Cr(ox)3], 212761 J/mole for K3[Cr(NCS)6]. The order of the ligands in increasing order is found to be acac <H2O< C2O42- (ox)<NCS<en which matches mostly with the spectrochemical series, which shows the order as C2O42-(ox) < H2O < NCS- < en
EFFECT OF DIFFERENT ELECTRODES AND MEMBRANES ON THE ELECTROCATALYTIC ACTIVITY AND THE STABILITY OF POLYMER ELECTROLYTE MEMBRANE FUEL CELLS WITHIN AN ALKALI SOLUTION
Full text linkIn this project, the electrocatalytic activity and stability of polymer electrolyte fuel cells (PEMFC), which are prepared by using Pt (platinum), Pd (palladium) and Ag (silver) metals; Nylon and Vileda membranes, within a 2 M NaOH (sodium hydroxide) solution, are examined.
The aim of this study is to find alternatives to the Pt metal, which is mostly used in this technology, due to its high cost and limited sources. In addition, it is intended to find membranes that will substitute the Nafion membrane, which is the ideal membrane in PEM fuel cells.
For the fuel cells, which are prepared by using each electrode and membrane, 4 trials are done. In these experiments, for each combination, the potential versus time graphs are drawn to compare the precision and electrocatalytic activity of the fuel cells. Besides, logarithms of hydrogen ion concentrations versus time graphs are drawn to determine the membranes’ effect. In the conclusion of the project, the highest electrocatalytic activity is observed in the cells with Pt electrode-Vileda membrane and Pd electrode-Nylon membrane. The results with Ag metal were not satisfactory like the other metals; the cells with Ag metals have low electrocatalytic activity when compared with other membranes. When the membranes are compared for each of the electrodes, similar results are observed. The change in the concentration of hydrogen ions with time is less in the Nylon membrane than in Vileda membrane. Thus, Nylon membrane shows more stable than the Vileda about the transferring of the hydrogen ions.
To conclude, Pd is the best alternative to Pt electrode while Nylon membrane is the best alternative to Nafion membrane. In addition, it is concluded that with each electrode, a variety of membranes must be used to examine the electrocatalytic activity of the PEM fuel cells
An investigative approach into some factors effecting intact crystal growth of Copper (II) sulfate pentahydrate (CuSO4 • 5H2O) under room conditions and searching of suitable medium circumstances and alternative method favoring this type of growth.
Full text linkIn most laboratories, crystal growth of soluble salts in water is made with classical methods: obtaining a supersaturated or saturated solution at a higher temperature, slowly cooling or evaporating the solution. A chosen crystal nucleus is then used as a “seed crystal”, and the largest crystal formed is re-put into a saturated solution of itself while filtering other precipitates being formed. However, this methodical approach needs intensive and continuous care on crystal, consumes both time and solute. This study is therefore aimed to find such stable circumstances that will supply intact crystal growth of an ionic crystal under room conditions grown by this method, with an alternative method not requiring the prerequisite of periodical care.
The researches stated that one-piece crystal growth required a reversible, kinetically limited reaction pathway. Second task was to find an easily obtainable and soluble salt used commonly and could easily form intact crystals, resistant to possible random changes in the determined constants during time that may erroneously happen during experimentation in a school laboratory. It was copper (II) sulfate pentahydrate.
A series of experiments are then conducted including attempts to change the vapor pressure and phase of the solution, changing the supersaturation temperature, cooling rate, cleanliness and the evaporation rate of the system in basis of a controlled experiment. The experimentation lead itself to the conclusion that:
Combination of decreased vapor pressure in a constant room temperature; clean system in the most soluble phase let through continuous evaporation can produce intact crystals of Copper (II) sulfate with an alternative method that is requiring only initial care.
Although the experimentation was successful, I was unable to find a quantitative optimum of the mentioned variables due to the time constraint. At least, I think I prepared a basis of alternative approach on a simple growth method