O ajuste de funções matemáticas a dados experimentais

The least square method is analyzed. The basic aspects of the method are discussed. Emphasis is given in procedures that allow a simple memorization of the basic equations associated with the linear and non linear least square method, polinomial regression and multilinear method.

Estudo da adsorção de hidrogênio e sulfeto na superfície de paládio: aspectos experimentais (eletroquímica) e teóricos (ab initio e Teoria do Funcional da Densidade)

The adsorption of H and S2- species on Pd (100) has been studied with ab initio, density-functional calculations and electrochemical methods. A cluster of five Pd atoms with a frozen geometry described the surface. The computational calculations were performed through the GAUSSIAN94 program, and the basis functions adapted to a pseudo-potential obtained by using the Generator Coordinate Method adapted to the this program. Using the cyclic voltammetry technique through a Model 283 Potentiostat/Galvanostat E.G.&G-PAR obtained the electrochemical results. The calculated chemisorption geometry has a Pd-H distance of 1.55Å, and the potential energy surface was calculated using the Becke3P86//(GCM/DFT/SBK) methodology. The adsorption of S2- ions on Pd surface obtained both through comparison between the experimental and theoretical results, at MP2 level, suggest a S2- absorption into the metallic cluster. The produced Pd-(S2-) system was show to be very stable under the employed experimental conditions. The paper has shows the powerful aid of computational methods to interpret adsorption experimental data.

Influência de alguns parâmetros experimentais nos resultados de análises calorimétricas diferenciais - DSC

A series of experiments were performed in order to demonstrate to undergraduate students or users of the differential scanning calorimetry (DSC), that several factors can influence the qualitative and quantitative aspects of DSC results. Saccharin, an artificial sweetner, was used as a probe and its thermal behavior is also discussed on the basis of thermogravimetric (TG) and DSC curves.

Uma proposta de síntese para o ensino integrado das disciplinas experimentais de química orgânica e inorgânica nos cursos de graduação

The synthesis of the layered compound VO(PO4)(H2O)2 and its use to oxidize 2-butanol to the ketone 2-butanone, is proposed as an experiment to integrate the organic and inorganic experimental undergraduate chemistry courses, in an atempt to overcome the observed disrupture between organic and inorganic chemistry.

Dimensão fractal de ácidos húmicos em diferentes condições experimentais

The determination of fractal dimension (D) of humic particles was achieved by the turbidimetric technique where diluted suspensions of humic acids, in different experimental conditions, were analyzed by spectrophotometry UV-Vis. The slope of the lines (beta) was taken from the graphics (logtauvs loglambda) to obtain D. The results show that the values of D changed according to pH (3.0, 5.0 and 7.0), temperature (25 and 5 ºC) and shaking (magnetic and horizontal). In general, the value of D decreased with the increment of pH, increase of shaking and decrease of temperature.

Fotocatálise eletroquímica de atrazina sobre dióxido de titânio: efeito de diferentes parâmetros experimentais

The atrazine photoelectrochemical degradation has been examined in solutions containing TiO2 on immobilized films under a variety of experimental conditions. It was possible to observe that the supporting electrolyte nature affects the intensity of the photocurrent, being an indicative of the adsorption process. The disappearance of the organic molecule follows approximately a pseudo-first order kinetic. As mineralization product, NH4+ and NO3- ion have been identified. These results indicated that the formation of NH4+ ion can be associated to the effect of atrazine adsorption, due to need of potential adaptation together with a variation in the supporting electrolyte concentration.

Extração de pigmentos das sementes de Bixa orellana L.: uma alternativa para disciplinas experimentais de química orgânica

This paper describes methodologies for the extraction and characterization by TLC, UV-VIS, IR and NMR of bixin from Bixa orellana L. (urucum) seeds. Based on the results, the extraction with NaOH 5% is the fastest, uses low-cost materials, requires two to four laboratory hours and is a useful alternative for an experimental Organic Chemistry discipline.

Quimiometria II: planilhas eletrônicas para cálculos de planejamentos experimentais, um tutorial

This work describes, through examples, a simple way to carry out experimental design calculations applying an spreadsheets. The aim of this tutorial is to introduce an alternative to sophisticated commercial programs that normally are too complex in data input and output. An overview of the principal methods is also briefly presented. The spreadsheets are suitable to handle different types of computations such as screening procedures applying factorial design and the optimization procedure based on response surface methodology. Furthermore, the spreadsheets are sufficiently versatile to be adapted to specific experimental designs.

Impacto do acordo de cooperação do Conselho Nacional de Pesquisas (CNPq) com a National Academy of Sciences - (NAS)

In the beginning of the 1960's, the university education in chemistry, in Brasil, represented only a professional preparation, with no official post-graduate teaching and research, as yet. The name Federal University Rio de Janeiro, evolved, since January 30, 1959, from University of Brazil, RJ, to Federal University of Guanabara, which, on August 20, 1965, became the Federal University of Rio de Janeiro. With the Resolution nº 4, of the University direction, the first Institute of Chemistry was created, to include the Centers of Mathematical and Natural Sciences, and the Medical Sciences. The strictu sensu's system was established only in 1961.

Aplicação do ultra-som em sistemas eletroquímicos: considerações teóricas e experimentais

The aim of this review is to present and discuss the applications of ultrasound in electrochemical systems such as in sonoelectroanalysis and sonoelectrolysis for the electrochemical combustion of organic compounds. Initially, theoretical and experimental aspects are discussed, particularly those related to the enhancement of mass transport and the surface cleaning effects. Some results are included to illustrate alternative geometries for the experimental measurements and the working electrodes used in these systems. In the sequence, the available publications are presented and discussed to demonstrate that ultrasound combined with electrochemical techniques is a powerful set-up for the detection of analytes such as metals and/or organic compounds in hostile media and for the effective destruction of toxic organic substances. At the end, a table summarizes the results already published in the literature.

Extração de β-caroteno de cenouras: uma proposta para disciplinas experimentais de química

This paper reports on the development of a simple and fast procedure for β-carotene extraction from carrots and its quantification by UV/Vis spectroscopy. Carotenoids extracted from carrots may also be used as alternative reagents for TLC (thin layer chromatography) detection of natural compounds with antioxidant properties, replacing the commercial p.a. grade β-carotene. Although this reagent had around 10% b-carotene, it proved to be as efficient for TLC analysis as the commercial p.a. grade β-carotene. This practice is a useful alternative for teaching undergraduate organic chemistry laboratory classes.

Construção artesanal de um eletrodo íon seletivo a chumbo(II): uma alternativa para disciplinas experimentais

This works proposes a homemade construction of a lead(II) ISE of solid membrane (Ag2S/PbS) to determine Pb2+ ions in potentiometric titrations, using damaged combined glass electrodes. This electrode can be constructed in teaching laboratories, using it as a learning tool related to the theoretical principle of ISE. The analytical curve obtained (y = 27.056x + 337.58; R = 0.996) was linear on the range of 1 x 10-5 to 1 mol L-1 and has presented a very close behavior of the Nernstian. The homemade ISE has presented a similar selectivity to the commercial electrodes, showing to be a good alternative to the experimental activities on teaching laboratories.

O uso de aparelhos de micro-ondas domésticos em aulas experimentais de química orgânica: nitração de salicilaldeído

The use of microwave in chemistry has known benefits over conventional heating methods, e.g. reduced reaction times, chemical yield improvement and the possibility if reducing or eliminating the use of organic solvents. We describe herein a procedure for the nitration of salicylaldehyde in water using a domestic microwave oven, which can be used as an experiment in the undergraduate chemistry laboratory. The experiment involves safe and rapid preparation and identification of the position isomers by thin layer chromatography and 1H NMR, or by their melting points.

A problematização das atividades experimentais na educação superior em química: uma pesquisa com produções textuais docentes

Through the analysis of articles with proposals for experimental activities and with current pedagogical, epistemological and environmental discussion on experimentation by Chemistry professors, this paper investigates ways of highlighting relevant methodological characteristics that can be incorporated in experiments. Based on analysis of the suggestions for experiments it appears that of particular importance are: a concern for students' physical welfare and for the effects of residues; the need to confront an impoverished infrastructure that hinders experimentation; and the valorisation of clarifying student knowledge. It argues in favour of the need to set out the problems of experimentation in educators' professional development.