Adsorção e propriedades de volume de misturas binárias água álcool: um experimento didático com base em medidas de tensão superficial

An undergraduate physical chemistry experiment based on the drop counting method for surface tension measurements is proposed to demonstrate adsorption isotherms of binary aqueous solutions of ethanol, n-propanol, and n-butanol. Excess surface is obtained by the derivative of surface tension taken with respect to alcohol activity, after this activity calculation using van Laar equation. Laboratory class contents are surface tension, excess surface, percolation of hydrogen bonds, micelle, activity, and ideal solution.

Acetatos homo e heterotrinucleares de ferro: um experimento para o laboratório de química de coordenação

Homo and heterotrinuclear acetates are unique compounds having μ3-oxo bridge and many interesting properties of such compounds are derived from this structure. Some undergraduate inorganic textbooks discuss several aspects of these compounds and we present here an undergraduate experiment for the high-yield synthesis of [Fe2MO(CH3CO2)6(H 2O)3], with M = Fe3+, Co2+ and Ni2+, as well as their characterization using infrared spectroscopy and cyclic voltametry. The proposed experiment gives the opportunity to discuss several concepts of coordination chemistry that follow the characterization techniques, such as: types of acetate coordination, reversibility of electrochemical processes, quelate and trans effects and lability.

Eixo quinário: um elemento de simetria presente em moléculas e quasi-cristais - um experimento didático em cristalografia

Axis of quinary symmetry occur in molecular symmetry, as in the case of fullerenes, and in crystalline symmetry, in the quasicrystals. Minerals with pentagonal faces do not have this element of symmetry, as the pyrite (FeS2) which shows a ridge that is different from the other ones, in any face of the crystal. The purpose of this paper is to demonstrate conceptual differences between pyritohedron and regular pentagonal dodecahedron symmetries, discussing students' difficulties to identify them. Also is proposed a didactic experiment with spatial models of the above-mentioned forms and the demonstration of its symmetries in clinographic projections.

Escrita científica de alunos de graduação em química: análise de relatórios de laboratório

The purpose of this study was to analyze written arguments found within laboratory reports by undergraduate students in a practical inorganic chemistry course. The quality of students' argumentation was analyzed based on the argumentation model developed by Kelly and Takao. Students presented scientific arguments grounded in data and building toward theoretical assertions. This indicates that students have some understanding of the rhetorical power of data in their explanations. The findings of this study also support the idea that Kelly and Takao's model is effective in other disciplines and in other rhetorical tasks distinct from those originally analyzed by them in their domain of oceanography.

Artigos da revista Ciência Hoje como recurso didático no ensino de química

This paper presents the results from the selection and analysis of Ciência Hoje articles published from 2004 to 2009 with the aim to discuss some of their features which can assist teachers in chemistry teaching. Therefore, the articles were analyzed according to their content and format based on an analytical tool proposed by Kawamura and colleagues. The results indicate that this magazine offers a reasonable collection of articles related to chemistry with a variety of contents and approaches.

Experimento didático de quimiometria para análise exploratória de óleos vegetais comestíveis por espectroscopia no infravermelho médio e análise de componentes principais: um tutorial, parte I

This manuscript aims to show the basic concepts and practical application of Principal Component Analysis (PCA) as a tutorial, using Matlab or Octave computing environment for beginners, undergraduate and graduate students. As a practical example it is shown the exploratory analysis of edible vegetable oils by mid infrared spectroscopy.

A retórica da linguagem científica: das bases teóricas à elaboração de material didático para o ensino superior de Química

This work is part of a study that focused on analyzing the contributions of didactic activities related to scientific language rhetoric characteristics aimed at developing students' abilities to identify such characteristics in chemistry scientific texts and critical reading of those texts. In this study, we present the theoretical basis adopted to determine the scientific discourse characteristics and for the production of the didactic material used in those activities. Latour, Coracini and Campanario studies on persuasive rhetorical strategies present in scientific articles aided the production of such material.

Furfural - da biomassa ao laboratório de química orgânica

The goal of this manuscript is provide to students of Chemistry and related areas an alternative experiment in which they can obtain a compound and learn to observe and interpret properties and predict organic structure by obtaining furfural from biomass. Furfural is an organic compound, obtained through acid hydrolysis of pentosans, commonly used in the chemical and pharmaceutical industries. Students are guided to get furfural through extractive procedures and chemical reactions adapted to semi-micro laboratory scale. Characterization of furfural was done by chemical tests and physical properties. Identification was accomplished by a series of spectroscopic and spectrometric techniques.

Implantação e implementação das normas das Boas Práticas Laboratoriais (BPL) no laboratório de análises de resíduos da Universidade Estadual de Campinas

In the context of quality and good laboratory practices, the article recovers some historical data. From a specific Institutional situation (CPQBA/UNICAMP), is presented an experience of establishing and implementing a standard (NIT-DICLA-035) for good laboratory practice according to definitions of the Brazilian authority (INMETRO) responsible for regulating, monitoring, supervising and recognition in this area. The issue aims to focus on studies of pesticide residues in GLP parameters.

Preparação de nanopartículas de prata e ouro: um método simples para a introdução da nanociência em laboratório de ensino

A new practical experiment involving silver and gold nanoparticle syntheses was introduced in an inorganic chemistry laboratory course for undergraduate students at the Institute of Chemistry, UNICAMP. The nanoparticles were synthesized by the reduction of silver nitrate and tetrachloroauric acid with sodium borohydride and sodium citrate in an aqueous medium. Stabilities of the suspensions were tested using several different reactants including sodium chloride, polyvinylpyrrolidone, polyvinyl alcohol and cistamine. Changes in optical properties were observed by electronic spectra and also by transmission electronic microscopy, which also yielded data for estimating particle size.

Novas métricas holísticas para avaliação da verdura de reações de síntese em laboratório

New semi-quantitative metrics for simple evaluation of global greenness of chemical reactions used in teaching laboratories, namely, the Green Circle (GC) and Green Matrix (GM), were developed. These metrics globally consider all Twelve Principles of Green Chemistry. To illustrate their construction, the greenness of several syntheses performed in the laboratory under different sets of conditions was assessed. The tools were validated by comparing the results with another metric, the Green Star (GS), developed in our previous study. Results showed these new metrics were useful for the intended purpose, having the advantage of being simpler than the GS.

Uso de materiais recicláveis na determinação gravimétrica de CO2 no ar ambiente e tratamento dos resíduos de laboratório gerados

An alternative system was tested for the determination of CO2 in air using recyclable materials. The results indicate that the proposed system allows for reliable, accurate, robust and efficient collection, comparable to the standard gravimetric method. Laboratory wastes are easily treated using a filtrate that can be discharged into the sewer and solids that can be reused. The proposed system is a simple and low-cost tool that encompasses important aspects of environmental education, which should be part of the education in chemistry of undergraduate students and technicians.

Obtenção de biodiesel por transesterificação em dois estágios e sua caracterização por cromatografia gasosa: óleos e gorduras em laboratório de química orgânica

Methanolic transesterification of oils and fats was carried out in a two steps procedure, under basic and acidic catalysis. Palm, soybean, canola, corn, rice, grapeseed, sunflower, peanut, pequi and olive oils, besides tallow and lard were used as feedstock. Specific gravity, relative viscosity, thin layer chromatography and gas chromatography were used to characterize the biodiesel. Biodiesel was obtained in high yield and purity. Results were used to discuss the following key-concepts: 1 - triglycerides, composition and properties; 2 - nucleophilic acyl substitution under basic and acid conditions, 3 - thin layer chromatography, 4 - gas chromatography and its quantitative methods.

Experimento didático de quimiometria para calibração multivariada na determinação de paracetamol em comprimidos comerciais utilizando espectroscopia no infravermelho próximo: um tutorial, parte II

The aim of this manuscript was to show the basic concepts and practical application of Partial Least Squares (PLS) as a tutorial, using the Matlab computing environment for beginners, undergraduate and graduate students. As a practical example, the determination of the drug paracetamol in commercial tablets using Near-Infrared (NIR) spectroscopy and Partial Least Squares (PLS) regression was shown, an experiment that has been successfully carried out at the Chemical Institute of Campinas State University for chemistry undergraduate course students to introduce the basic concepts of multivariate calibration in a practical way.

Experimento didático de quimiometria para planejamento de experimentos: avaliação das condições experimentais na determinação espectrofotométrica de ferro II com o-fenantrolina. Um tutorial, parte III

The objective of this manuscript is to describe a practical experiment that can be employed for teaching concepts related to design of experiments using Matlab or Octave computing environment to beginners, undergraduate and graduate students. The classical experiment for determination of Fe (II) using o-phenanthroline was selected because it is easy to understand, and all the required materials are readily available in most analytical laboratories. The approach used in this tutorial is divided in two steps: first, the students are introduced to the concept of multivariate effects, how to calculate and interpret them, and the construction and evaluation of a linear model to describe the experimental domain by using a 2³ factorial design. Second, an extension of the factorial design by adding axial points is described, thereby, providing a central composite design. The quadratic model is then introduced and used to build the response surface.