SBQ-25 anos: Físico;Química

The authors present a concise but critical review on the development of physical chemistry in Brazil, as seen by two experimental scientists with more then 25 years of experience in the Brazilian academics.

Avaliação dos métodos de extração sequencial de Tessier, Keller e Miller na determinação de ferro nativo em três tipos de solos: orgânico, brunizem e latossolo

Sequential extraction is not totally effective to dissolve distinct forms of trace elements. The extractive solution, for example, can dissolve less of the target fraction and more than another not wished fraction. The goal of this work is to compare the extraction of native iron with three sequential extraction methods of the heavy metals, using three soils with different physical chemistry characteristics: a histosol, an oxisol, and a mollisol. The results obtained in this work demonstrate that a smaller relation soil/extractor results in a larger extraction in almost all phases. The use of many stages of the sequential extraction, with the purpose of more association of the metal with different components of the soil, can result, among other things, in modification of the substratum by the action of the reagents used, besides reducing the selectivity of the more specific extractors. Readsorption and redistribution of the heavy metals could have happened with larger intensity in the fraction where hidroxilamine was used with higher temperature. Sequential extraction of iron, without enrichment of soil samples, in the respective fractions in each method, it was important to better understand the behavior of the reagents considered specific to each form of the metal in soil.

Adaptação no método do peso da gota para determinação da tensão superficial: um método simplificado para a quantificação da CMC de surfactantes no ensino da química

The discussion based on surfactant cleaning action is commonly used in chemistry classrooms for the comprehension of theoretical concepts related to surface tension and micelle formation. The experimental quantification of surface tension of aqueous solutions of surfactants provides the practical instruments for this discussion. The present paper describes a simplification on the common apparatus employed for the drop-weight method, making the determination of surface tension accessible to any chemistry lab. The surface tension of various liquids and the critical micelle concentration, CMC, of three commercial surfactants were measured with this modified method, and proved to be consistent with literature values.

O ensino de química quântica e o computador na perspectiva de projetos

This paper aims to discuss and reflect about the use of computers in the teaching of Quantum Chemistry. A course on Computational Quantum Chemistry concentrating on Medicinal Chemistry projects was developed for undergraduate and graduate students. The results showed that students got more motivated and involved when there is an articulation between theory and practice. This work presents an alternative way to teach Theoretical Chemistry using projects.

Preparação de compostos lamelares: síntese do hidrogenofosfato de zircônio cristalino e sua intercalação com aminas. Um experimento para estudantes de graduação

The present paper describes the synthesis of crystalline zirconium hydrogen phosphate by direct precipitation and its intercalation with pyridine and n-butylamine. The simple experiment was tested in the undergraduate inorganic chemistry laboratory course for chemistry students at IQ-UNICAMP using inexpensive reagents. The materials were characterized by powder X-ray diffraction and infrared analyses in order to obtain detailed information of the solid structure changes as a result of the intercalation process. Pyridine and n-butylamine are focused in this work as clear and elucidative examples leading to acid-base interactive processes that result in the well-formed infinite sequence of inorganic lamellar structures.

Façamos Químicos: a "certidão de nascimento" dos cursos de química de nível superior no Brasil

This work presents a brief retrospective of José de Freitas Machado's prominent role in the creation, development and consolidation of Chemistry undergraduate courses in Brazil. Freitas Machado defended in many occasions the importance of chemical studies for the economic development of this country. We analyze, here, his important paper "Façamos Químicos" [Let's Make Chemists] (1917), seminal for the implantation of Industrial Chemistry undergraduate courses in Brazil.

Otto Redlich: chemist and gentleman from the "old school"

The name of Otto Redlich is generally remembered as co-author of one of most used equations of state for the calculation of volumetric and thermodynamic properties of pure substances and their mixtures. Nevertheless, he made also important contributions in different areas of chemistry and chemical engineering. Pursuits of race and religious order forced him and his family to leave his native Austria and emigrate to the United States. His professional career included both academic and industrial research achievements.

Joseph Neng Shun Kwong: a famous and obscure scientist

Many students and professionals in chemistry and chemical engineering related the name Kwong with one of the most remarkable equations of state with two parameters. In the same way, very few people know who Kowng was. This article shows some of the unknown personal and professional facts of Joseph Neng Shun Kwong, a person who devoted almost four decades of his life to the industrial research in the adhesives industry.

Avaliação da estabilidade oxidativa de biodiesel de óleo de girassol com antioxidantes

Biodiesel can contain unsaturated fatty acids, which are susceptible to oxidation, being able to change into polymerized compounds. In this work biodiesel was characterized according to physical-chemistry parameters and the antioxidant activity of butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT) and tert-butylhydroquinone (TBHQ) added to biofuel was analyzed. Biodiesel was submitted to accelerate oxidation in the Schaal oven test, and peroxide value was analyzed.The absorptivity values at 232 nm and 270 nm and oxidative stability in Rancimat®were determined. It was observed that TBHQ presented superior antioxidant activity than BHT and BHA.

Avaliação de uma proposta contextualizada sobre o ensino de polarimetria nos cursos de farmácia e engenharia de alimentos, na Universidade Federal do Ceará

This work deals with an evaluation of an experimental application about polarimetry for pharmacy and food engineering courses. Foods obtained from the undergraduate students were used for demonstrating multidisciplinary concepts and these concepts were associated to the teaching of polarimetry. According to the results, the benefits of the contextualization are beyond the class and the undergraduating students became interested in control of quality of foods. From these results, it can be concluded that the experimental emphasis given is valid and creates motivation and interest for learning physico-chemistry, in comparison with the traditional methodology applied to teach polarimetry.

Determinação potenciométrica da concentração micelar crítica de surfactantes: uma nova aplicação metodológica no ensino de Química

The participation of the students in the planning, execution and discussion of experimental results is important for the valuation of the role of them in the construction of the chemical knowledge implicited in the approach between education and research. This work relates either the construction of selective membrane electrodes for surfactants and its application in the potenciometric determination of the critical micellar concentration of the sodium dodecyl sulfate (SDS) and dodecyltrimethylammonium bromide (DTAB) surfactants. In adition it´s possible to discuss the potenciometric results in matching with the data valued for the tensiometric and condutimetric traditionally used in the physical-chemistry lessons.

Eletrodo de hidrogênio: o que há nos livros didáticos além de E¸ = 0?

The results of an exercise on electrochemistry for General Chemistry students are presented. The difficulty encountered by students in predicting the shift in the potential of the hydrogen electrode under non-standard conditions prompted a search in textbooks on how the subject is developed. Besides several instances of inconsistencies in defining the standard state, such as including the temperature in the definition, a number of incorrect depictions of the hydrogen electrode were discovered. Of the 28 General Chemistry books, 16 Physical Chemistry books and 24 Internet pages, 30, 20 and 46%, respectively, showed devices that would not work in practice.

The pre-history of cryoscopy: what was done before raoult?

Cryoscopy is considered one of the foundations of the modern theory of solutions and of physical chemistry. This paper shows in order the first regularities pointed out by several scientists on the subject, in the first chapter of its birth as a scientific discipline. The study is focused on the identification of the different steps that helped, first qualitatively and then quantitatively, to adjust the different classes of possible solutions, including those that formed hydrates, to a basic formulation that the French scientist François-Marie Raoult would later generalize in the law that bears his name.

Implantação das diretrizes curriculares nacionais para formação de professores de química em uma instituição federal de ensino superior: desafios e perspectivas

The Curricular Proposals for Chemistry Teaching Courses aim at producing a reflexive-researcher teacher, who will be able to deal with cross-disciplinary subjects. The challenge faced by the majority of the federal universities, in implementing these guidelines, is to attain these objectives inside their departmental structure. We present here the formulation of the Chemistry Teaching Course Pedagogic Project from Federal University of Pelotas concerning on the CNE/CP 1/2002 and 2/2002 Resolutions. We discuss the impact of these Proposals, the difficulties faced and the new perspectives of organization inside of these institutions, which resulted in new spaces with cross-disciplinary and cross-departmental orientation.

Síntese de fotoprotetores e sua imobilização em poli(metacrilato de metilo): um projeto integrado de química orgânica, química de polímeros e fotoquímica

Dibenzalacetone and other aldol condensation products are known sunscreens commonly used in cosmetics. This type of compounds can easily be prepared in an Organic Chemistry Lab by reaction of aldehydes with ketones in basic medium. These compounds can be incorporated in poly(methyl methacrylate) and used as UV light absorbers, for example in sunglasses. This project has the advantage of using inexpensive reagents which are readily available in Chemistry Laboratories. This experiment can also be a base starting point for discussions of organic, polymer and photochemistry topics.