Browsing by Author "Tafesse, Fikru (PhD)"

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    Bis(Trimethylenediamine) Cobait (III) Mediated Hydrolysis of Tripolyphosphate and Trimetaphosphate: Mechanistic Considerations
    (Addis Ababa Universty, 1991-07) Okadia, Charles; Tafesse, Fikru (PhD)
    The hydrolysis of tripolyphosphate ( pppi ) and trimetaphosphate (mpppi ) at 10'3 M concentration by [tn 2Co(OH)(0H2 )]^, (tn = trimethylenediamine), using Eu2 f /H+ quenching was investigated. The europium quenching was adopted since other methods interfere with phosphate analysis. The reactions were monitored by measurement of orthophosphate (pi ), pyrophosphate (ppi ), tripolyphosphate ( pppi ) and trimetaphosphate ( mpppi ) in the quenched aliquots of the reaction mixtures of the reagents. A method was developed to separate and determine the different phosphate species in the orthophos phate form using acetone- phosphomolybdate complex as the analytical reagent. The reactive species with regard to the hydrolysis were found to be a 3: 1 tn2Co( 111)ppp i and tn2Co( 111)mpppi complexes. The results showed larger amounts of hydrolytic products for the directly added systems than those of stepwise additions . The production of phosphites in the reaction solution that contain [tn2Co(OH )(0H 2)j* and tri metaphosphate was ob served . Spectrophotometric determination of the phosphite was done by first oxidising it with iodine to orthophosphate and using acetone-phospho molybdate complex as the analytical reagent . Factors affecting the formation and degradation of the reactive and unreactive species have been discussed and plausible mechanisns formulated .
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    Mechanistic Studies of the Hydrolysis of Pyrophosphate Promoted by Tetraaminecobalt(III) Ions
    (Addis Ababa Universty, 1990-06) Abebe, Zewdu; Tafesse, Fikru (PhD)
    The hydrolysis of pyrophosphate was investigated at different concentrations (2X10~3 M, 4X10~3 M and 1(f2 M) of [N4CO(OH)(OH ))2+ [N. = en2 and tn^ ten = ethylenddiamine, tn = trimathylenediamine)] 2+ + ' - using Eu /H and OH quenching techniques. The reaction was inonitored by measurement of orthophosphate (pi) in quenched aliquots of the reaction mixtures using Malachite Green phosphornolybdate complex as the analytical reagent. The reactive species with regard III to hydrolysis was found to be a 3:1 N^Co ppi complex. The results show a relatively larger amounts of degradation products for the directly added systems than for those mixed by step wise addition. Factors affecting the formation and degradation of the reactive species are discussed and plausible mechanisms are forwarded
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    Preliminary Investigations of the Electrochemical Behaviour of A Class of Conducting Polymers
    (Addis Ababa Universty, 1994-06) Telila, Gezahegn; Tafesse, Fikru (PhD)
    The electrochemical polymerization of monomers of pyrrole, thiophene, and aniline on platinum and glassy carbon electrodes was carried out with dc cyclic voltammetric technique. The oxidation peak potentials for both the monomers and the polymer films in different base electrolytes were determined by using dc cyclic voltammetry. The redox reversibility of equimolar concentrations of the (Fe (CN) 61 4-/3- couple in 0.1 M KCl on polymer coated electrodes has been compared with that on bare platinum and glassy carbon electrodes with dc cyclic voltammetry. The polymer coated electrodes have shown wider peak separations compared to the bare electrodes. Higher or lower peak currents were observed for the redox reaction of (Fe(CN)6 14-/3- systems in 0.1 M KCl depending upon the type of polymer films and the nature of base electrolytes used in the electrochemical polymerization process. The diffusion coefficients of [Fe(CN)614- and [Fe(CN)6l 3- in 0.1 M KCl were evaluated on polymer coated electrodes from rotating disk electrode experiments. The results were compared with the diffusion coefficients of these electroactive species on bare platinum and glassy carbon electrodes. These results on the bare electrodes are in good agreement with literature values. Attempts have also been made to correlate the diffusion coefficients of [Fe(CN)61 4-/3- systems on polymer coated electrodes with the type of polymer film and the nature of base electrolytes.
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    Synthesis and Study of Quinalizarin Complexes with
    (Addis Ababa Universty, 1994-06) Bizuneh, Damene; Tafesse, Fikru (PhD)
    The complexation of 1,2,5,8-tetrahydroxyanthraquinone (quinalizarin) with some trivalent lanthanide ions: Sm(III), Tb(III), Ce(III), and La(III) has been studied spectrophotometrically and potentiometrically. The methods of continuous variation and mole ratio indicate the metal to ligand ratio is 1:1. The stability of the complexes were found to be in the order Sm > Tb > Ce > La. Solid lanthanide-quinalizarin complexes were also isolated. The solid complexes are fine dark powders,insoluble in water and common organic solvents. From elemental analysis, thermal analysis and infrared spectra the complexes are characterized as chelate polymers, with a formula of [Ln(Cu H,O.)XH201 n (X = 5 when Ln = Sm, Ce and X = 6 when Ln = La, Tb). The relative thermal stability of three of the complexes were determined from differential thermal analysis, and are in the order: Sm > Ce~La.