Faculty of Science School of Chemistry 0204045a tspmkwi@hotmail.com / New possibilities in collection of polarographic and potentiometric experimental data in studies of metal–ligand systems by automated instrumental methods, and subsequent treatment of the polarographic data, whereby the degree of reversibility of the electrode processes varies, have been investigated in this work. An automated instrumental set–up was developed for applications in studies of metal–ligand solution equilibria by potentiometry and sampled Direct Current Polarography (DCP). The new set–up was designed based on virtual instrumentation principles whereby several commercially– available hardware units as well as custom–built electronic components, were interfaced to a personal computer that was equipped with appropriate hardware and control programs. The instrumental set–up was tested and validated by studying the protonation equilibria of the ligand glycine by Glass Electrode Potentiometry (GEP) as well as the complexation of the ligand glycine with Cd2+ by GEP and DCP. The new set–up provides increased versatility, accuracy and convenience in obtaining large numbers of experimental points in solution equilibria studies by DCP and GEP as opposed to the use of tedious and time–consuming manual methods. Nonlinear curve–fitting procedures, based on closed–form models that were derived here from suitable theoretical equations identified from literature, have been investigated in this work for applications in analysis of DC curves recorded on metal–ligand systems with variation in electrochemical reversibility. The applicability and limitations of the curve–fitting procedures developed have been tested in analysis of the DCP data collected on several metal–ligand systems involving Cd2+, Pb2+, Zn2+ and the ligands glycine and sarcosine, whereby the DCP studies of these systems exhibited reversible, quasi–reversible or irreversible electrochemical processes. Information on applicability and limitations of the proposed methods investigated in this work was derived by comparison of the results obtained from DCP, using the proposed methods, with either reported literature data and/or results obtained in this work by the independent analytical technique of GEP, which was deployed wherever it was found to be applicable to study the metal–ligand systems considered.

Made available in DSpace on 2014-12-17T14:36:44Z (GMT). No. of bitstreams: 1 ClaudiannyAN.pdf: 1040244 bytes, checksum: ad1fdad987ef4b04e5da0f991183dbdd (MD5) Previous issue date: 2006-06-28 / The main goal of the present study is to propose a methodological approach to the teaching of Geometry and, in particular, to the construction of the concepts of circle (circumference) and ellipse by 7th and 8th grade students. In order to aid the students in the construction of these concepts, we developed a module based on mathematical modeling, and both Urban Geometry (Taxicab Geometry) and Isoperimetric Geometry. Our analysis was based on Jean Piaget's Equilibrium Theory. Emphasizing the use of intuition based on accumulated past experiences, the students were encouraged to come up with a hypothesis, try it out, discuss it with their peers, and derive conclusions. Although the graphs of circles and ellipses assume different shapes in Urban and Isoperimetric Geometry than they do in the standard Euclidian Geometry, their definitions are identical regardless of the metric used. Thus, by comparing the graphs produced in the different metrics, the students were able to consolidate their understanding of these concepts. The intervention took place in a series of small group activities. At the end of the study, the 53 seventh grade and the 55 eighth grade students had a better understanding of the concepts of circle and ellipse / O objetivo principal deste trabalho ? propor uma abordagem metodol?gica do ensino da Geometria e, mais particularmente, de constru??o dos conceitos de circunfer?ncia e elipse por alunos de 7? e 8? s?rie. Desenvolvemos um estudo te?rico-pr?tico, baseado na modelagem matem?tica e nas Geometrias Urbana e Isoperim?trica, a fim de oportunizar aos alunos construir o seu entendimento sobre circunfer?ncia e elipse. A an?lise dessa constru??o foi realizada com base na Teoria da Equilibra??o de Jean Piaget. Foi enfatizado o uso da intui??o que estes estudantes j? tinham acumulado em situa??es cotidianas. Eles foram encorajados a levantar hip?teses, testar, discutir com os colegas e tirar suas conclus?es. No entanto, o uso das Geometrias Urbana e Isoperim?trica implica que os gr?ficos das circunfer?ncia e elipse tomem formas diferentes. A compara??o dessas formas ?s produzidas na Geometria Euclidiana foi usada para consolidar o entendimento desses conceitos, desde que s?o id?nticos, independente das m?tricas. A interven??o foi efetivada mediante o uso de uma s?rie de atividades cumpridas em pequenos grupos. Ao final do estudo percebemos que os 53 alunos da 7? e 55 da 8? s?rie, participantes do mesmo, foram capazes de obter um melhor entendimento dos conceitos de circunfer?ncia e elipse