O papel da experimentação para professores de ciências

A importância da experimentação, para despertar o interesse do aluno ou ajudá-lo a desenvolver suas ideias, deve ser de conhecimento do professor. Mas será que estes sabem o real papel desta atividade? Qual a concepção apresentada pelos professores sobre este tema? Este trabalho expõe um estudo sobre a concepção de experimentação dos professores participantes de um Programa de Formação Continuada, buscando uma relação entre as concepções e sua formação. Por meio de questionários e registros, observou-se que as concepções dos professores em relação à experimentação baseiam-se em: comprovação, demonstração e prática da teoria. Nota-se ainda que muitos professores atuam fora de sua área de formação, sendo necessários cursos de formação para que professores possam garantir aos alunos atividades experimentais que possam envolvê-los em problematizações e discussões

O papel da experimentação para professores de ciências

A importância da experimentação, para despertar o interesse do aluno ou ajudá-lo a desenvolver suas ideias, deve ser de conhecimento do professor. Mas será que estes sabem o real papel desta atividade? Qual a concepção apresentada pelos professores sobre este tema? Este trabalho expõe um estudo sobre a concepção de experimentação dos professores participantes de um Programa de Formação Continuada, buscando uma relação entre as concepções e sua formação. Por meio de questionários e registros, observou-se que as concepções dos professores em relação à experimentação baseiam-se em: comprovação, demonstração e prática da teoria. Nota-se ainda que muitos professores atuam fora de sua área de formação, sendo necessários cursos de formação para que professores possam garantir aos alunos atividades experimentais que possam envolvê-los em problematizações e discussões

O papel da experimentação para professores de ciências

A importância da experimentação, para despertar o interesse do aluno ou ajudá-lo a desenvolver suas ideias, deve ser de conhecimento do professor. Mas será que estes sabem o real papel desta atividade? Qual a concepção apresentada pelos professores sobre este tema? Este trabalho expõe um estudo sobre a concepção de experimentação dos professores participantes de um Programa de Formação Continuada, buscando uma relação entre as concepções e sua formação. Por meio de questionários e registros, observou-se que as concepções dos professores em relação à experimentação baseiam-se em: comprovação, demonstração e prática da teoria. Nota-se ainda que muitos professores atuam fora de sua área de formação, sendo necessários cursos de formação para que professores possam garantir aos alunos atividades experimentais que possam envolvê-los em problematizações e discussões

Layered double hydroxides for remediation of industrial wastewater containing manganese and fluoride.

This work describes an environmentally-friendly procedure for the removal of manganese and fluoride from industrial wastewaters (IW) using layered double hydroxides (LDHs) and calcined layered double oxides (LDOs). Ternary Mg-Mn-Al LDHs (LDH-IW) were produced from IW containing a high concentration of manganese, which decreased from (99.420 ? 3.110) mg L 1 to (0.003 ? 0.001) mg L 1 after the synthesis procedure. Synthetic Mg-Al LDH was also produced for comparison purposes. Both materials were calcined and the resulting oxides (LDO and LDO-IW) were used for the removal of fluoride present in the same IW. The materials were characterized by X-ray diffraction, electron energy-loss spectroscopy, thermal analysis, Raman spectroscopy, and electron microscopy. The kinetics and adsorption isotherms for fluoride removal from aqueous solutions were studied in batch mode. For both LDO and LDO-IW, the adsorption of fluoride followed pseudo-second order reaction kinetics. Langmuir-type adsorption was observed for LDO, while adsorption by LDO-IW was according to the Freundlich model. The results showed that the oxides were able to remove 94% of the fluoride present in the IW at an initial concentration of 162 mg L 1. The procedure reduced the concentrations of the pollutants (manganese and fluoride) to levels that complied with Brazilian effluent standards

How does the use of surfactants in polymer-salt based aqueous twophase systems affect the annatto dye (Bixa orellana L.) partitioning?

In this work, the partitioning of natural annatto pigments in aqueous two-phase systems formed by poly(ethylene) glycol polymers (1500 or 4000 or 6000?g?mol?1) or triblock copolymer L35 (2000 g?mol?1) + sodium citrate + water was studied in the presence of cetyltrimethylammonium bromide. The hypothesis investigated was that the use of surfactants as additives in traditional two-phase aqueous systems could improve the solubility of the annatto extract in the phases of these systems through a mechanism of mixed micelle formation. This would make it possible to implement the use of these systems in the annatto dye extraction process. For this, several experiments were conducted. The annatto extract partition coefficient was determined as a function of pH, surfactant concentration, molar mass and hydrophobicity of the polymer, tie-line length, and the nature of the electrolyte. These results showed the potential of surfactant as a modulation agent for dyes transfer between the aqueous two-phase systems phases. The effect of surfactant was attributed to its interaction with norbixin from annatto, which was studied by means of surface tension and spectrophotometric measurements. The driving force governing annatto extract partitioning was dependent on the system composition and the temperature. Lower partition constants values for annatto extract obtained in the presence of surfactant demonstrated the potential of the aqueous two-phase systems for the extraction or purification of annatto

Synthesis of new phytogrowth-inhibitory substituted Aryl-p-Benzoquinones

Reaction of [(2-alkyloxy)methyl]-1,4-dimethoxybenzene 10 (alkyl=butyl, hexyl, decyl, tridecyl, tetradecyl, hexadecyl, and octadecyl) with ceric ammonium nitrate in order to produce p-benzoquinones (=cyclohexa-2,5-diene-1,4-diones) afforded 5-[(alkyloxy)methyl]-2-(4-formyl-2,5-dimethoxyphenyl)benzo-1,4-quinones 12a-12g in yields that varied from 46 to 97%, accompanied by 2-[(alkyloxy)methyl]benzo-1,4-quinones 11a-11g in only small quantities (< or =5%). These quinones resemble the natural phytotoxic compound sorgoleone, found in Sorghum bicolor. This reaction exemplifies a general procedure for the synthesis of novel aryl-substituted p-benzoquinones. The selective effects of compounds 12a-12g, at the concentration of 5.5 ppm, on the growth of Cucumis sativus, Sorghum bicolor, Euphorbia heterophylla, and Ipomoea grandifolia were evaluated. All compounds caused some inhibition upon the aerial parts and root growth of the tested plants. The most active compound, 2-(4-formyl-2,5-dimethoxyphenyl)-5-[(tridecyloxy)methyl]-benzo-1,4-quinone (12d), caused between 3 and 18%, and 12 and 29% inhibition on the roots and aerial parts development of Cucumis sativus and Sorghum bicolor, respectively, and between 77 and 85%, and 34 and 52% inhibition on the roots and aerial parts growth of Euphorbia heterophylla and Ipomoea grandifolia, respectively

Influence of the ionic strength on the physicochemical properties of methotrexate-loaded chitosan polyelectrolyte complexes

Polyelectrolyte complexes (PECs) as drug delivery systems are widely explored since they are easily obtained by coacervation and biopolymers can be associated. However, particle distribution is a challenging critical parameter that has been infrequently focused. This work evaluated the effect of NaCl concentration on the physicochemical properties of PECs based on chitosan and hypromellose loaded with methotrexate. The particle size, zeta potential and polydispersity index (PdI) were determined by DLS, besides of drug entrapment efficiency (EE) and&nbsp;in vitro&nbsp;drug release profile determination. Particle size decreased while NaCl concentration rised, achieving a narrower size distribution of (345±79 nm) and PdI (0.285±0.067) with 200 mmol/L NaCl. The higher the NaCl concentration, the lower the zeta potential at acid pH. The EE was kept similar ((28.2±4.5) %) from 0 to 300 mmol/L NaCl, while 400 mmol/L NaCl impaired the drug entrapment. The addition of (200 and 300) mmol/L NaCl did not affect the drug release profile, but it was faster with (100 or 400) mmol/L. In conclusion, the addition of 200 mmol/L NaCl reduced particle size and PdI with no changes in the EE and drug release. Therefore, the ionic strength plays an important role on PECs development

Thermodynamic investigation of the aqueous two-phase systems formed by PEG 400 + water + either sodium carbonate or potassium carbonate at different temperatures : experimental and correlational approaches.

Systems composed of poly(ethylene)glycol (PEG 400) + water + either potassium carbonate or sodium carbonate were studied at 283.15, 298.15, and 313.15 K. The effects of temperature and the electrolyte on phase segregation were evaluated. The phase segregation process was endothermic and entropically driven. The efficacy of the cations in inducing phase formation with PEG 400 followed the order K2CO3 < Na2CO3. The binodal curves were successfully described using the empirical equation suggested by Merchuk and modified to include the effect of temperature. Tie-line compositions were correlated using the Othmer?Tobias, Bancroft, and Hand equations. The experimental tie-line data for PEG 400 + K2CO3 + water and PEG 400 + Na2CO3 + water were also correlated using the nonrandom two liquid model. The use of this thermodynamic model resulted in reliable data for the system while reducing the number of experiments needed. All of the correlations indicated satisfactory fits between the calculated and experimental data