Avaliação das condições de precipitação do azul da Prússia sobre pó de grafite visando o desenvolvimento de eletrodos de pasta de carbono para a quantificação de nitrito

An amperometric FIA method for nitrite quantification based on nitrite electroreduction and employing a carbon paste electrode (CPE) chemically modified with iron hexacyanoferrate (HCF) as an amperometric detector was developed. The influence of experimental conditions on the preparation of the electrode materials was evaluated and the materials obtained in each study were used for the development of modified electrodes. The electrochemical sensors were prepared by a fast, simple, and inexpensive procedure, and the long-term performance of the electrodes were quite satisfactory as the stability was maintained over one year. HCF was an effective redox mediator for nitrite electroreduction in acidic media, allowing nitrite detection at +0.2 V vs. Ag/AgClsat, which is a potential free of possible interfering species that are normally present in food and water samples. The electrochemical cell used in the FIA system was similar to a batch injection analysis cell, enabling recirculation of the carrier solution. This is an attractive feature because it allows the use of a high flow rate (6 mL min-1) leading to high sensitivity and analysis speed, while keeping reagent consumption low. The proposed method had a detection limit of 9 μmol L-1 and was successfully employed for nitrite quantification in spiked water and sausage samples. The obtained results were in good agreement with those provided by the spectrophotometric official method. At a 95 % confidence level it was not observed statistical differences neither in nitrite content nor in the precision provided by both methods. The experimental conditions for the synthesis of HCF were optimized and the best electrode material was prepared by mixing FeCl3, K4[Fe(CN)6] and carbon powder subjected to an acid and thermal treatment (400 ºC), followed by ultrasonic agitation at 4 °C. This material was used to construct an electrode with improved analytical performance to reduce nitrite, which presented greater stability compared to HCF film electrodeposited on the EPC, showing that the preparation procedure of the electrode material is an effective strategy for the development of HCF modified electrodes.

O tema água no ensino de ciências:uma proposta didático pedagógica elaborada com base nos três momentos pedagógicos

Science and technology are increasingly present in society’s everyday living, interfering with the appearance and social relationships, which requires from the population: knowledge, skills and actions to intervene consciously and responsibly in the new socio-cultural setting. The science education might become a great ally in the task of literacy and / or enable students to live consciously and critically in a world even more influenced by scientific and technological aspects. The aim of the dissertation is to develop a didactic-pedagogic proposal for science classes of the 6th year of elementary school, based on the "Generator Theme: Water and its treatment", involving the dynamics of the Three Pedagogic Moments. Such proposal consists of a Course which embraces seven teaching modules containing topics related to Generator Theme. The modules were designed and developed with four student groups of 6th year in twelve hours / class per group, with a total of approximately 120 students. The interpretation of the developed content, resulting from the thematic modules with students, led to the creation of five analysis categories. Considering the results, it is possible to conclude it is necessary, for successful teaching practices in the school environment, that the teachers embrace the aim of teaching in a meaningful way, drawing up activities that really recognize and include the student as an active subject of the educational and learning process. The use of activities that lead students to recognize themselves as main process actors, developing practices based on previous knowledge and on their specific learning, results in a situation which they will recognize the science in their lives, learn to be reflective and aware of their attitudes about the world where they live.

Avaliação de sustentabilidade ambiental do sistema de abastecimento de água e esgotamento sanitário de Uberaba - MG

This paper analyses the sustainability under the environmental (ecological) perspective of Water Supply and Sanitary Sewers Systems from Uberaba city, MG. It was accomplished in this analysis, An Environmental Sustainability Assessment of those systems, by the means of specific sustainability indicators proposed for Uberaba, but which may be used for other simi-lar cities. To the characterization of the systems, visitations were made to the main units as well as a documental was elaborated. The definition of the level or stage of the sustainability by the indicators was made based on a literature review, on interviews with the technicians and managers of the systems and based on the characterization and observation of the system reality, being attributed to them the following classification: Non Sustainable, Low Sustaina-bility, Medium Sustainability and High Sustainability. It was verified that the indicators that have lower compatibility to the process of sustainability to the studied systems are those rela-ted to the water physical losses, to the water per capita consumption, to the electricity con-sumption and to the sludge from the water treatment plants disposal untreated into a water body, for the Water Supply System. And those ones related to the attendance with sewage treatment, to the electricity consumption and to the usage of the treated sewage, for the Sani-tary Sewers, all of them classified as Non Sustainable.

O tema água no ensino de ciências: uma proposta didático pedagógica elaborada com base nos três momentos pedagógicos

Science and technology are increasingly present in society’s everyday living, interfering with the appearance and social relationships, which requires from the population: knowledge, skills and actions to intervene consciously and responsibly in the new socio-cultural setting. The science education might become a great ally in the task of literacy and / or enable students to live consciously and critically in a world even more influenced by scientific and technological aspects. The aim of the dissertation is to develop a didactic-pedagogic proposal for science classes of the 6th year of elementary school, based on the "Generator Theme: Water and its treatment", involving the dynamics of the Three Pedagogic Moments. Such proposal consists of a Course which embraces seven teaching modules containing topics related to Generator Theme. The modules were designed and developed with four student groups of 6th year in twelve hours / class per group, with a total of approximately 120 students. The interpretation of the developed content, resulting from the thematic modules with students, led to the creation of five analysis categories. Considering the results, it is possible to conclude it is necessary, for successful teaching practices in the school environment, that the teachers embrace the aim of teaching in a meaningful way, drawing up activities that really recognize and include the student as an active subject of the educational and learning process. The use of activities that lead students to recognize themselves as main process actors, developing practices based on previous knowledge and on their specific learning, results in a situation which they will recognize the science in their lives, learn to be reflective and aware of their attitudes about the world where they live.