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O discente, ao estudar o conteudo geometria molecular, muitas das vezes nao consegue visualizar estas estruturas no espaco tridimensional dificultando assim o seu entendimento no processo de aprendizagem. Visando diminuir essa lacuna,esse artigo apresenta a construcao e emprego de modelos molecularesdo tipo bola e ima como uma ferramenta para facilitar a visualizacao, por parte do aluno, bem como desenvolver a sua habilidade de utilizar modelos para visualizacao de moleculas.Na construcao dos modelos, os alunospassaram a ser agentes ativosdo processo de aprendizagem do conhecimento, construiram representacoes, assim como, reconheceram que foi uma boa estrategia didatica para tornar a aula mais dinâmica.

In the present work is described a new on-line solid-phase extraction system using a novel ion imprinted polymer as adsorbent for the preconcentration and determination of mercury(II) in natural water samples by Cold Vapor Atomic Fluorescence Spectrometry (CV AFS). The ion imprinted polymer was prepared by the improved bulk polymerization technique, occurring in only 3 h, based on mercury(II)-dithizone chelate, using methacrylic acid as monomer, ethylene glycol dimethacrylate as cross-linking reagent, 2,2′‑azobisisobutyronitrile as radical initiator, and dimethyl sulfoxide and acetonitrile as porogen solvents. The obtained polymer was characterized by Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Thermogravimetry (TG), Derivative Thermogravimetry (DTG) and X-ray Diffraction (XRD). The on-line system was mounted by the easy coupling the mini-column packed with the Hg2+-IIP sorbent to the cold vapor system of the spectrometer. The optimum experimental conditions for the on-line preconcentration system were established employing multivariate methodology (two-level full factorial design and Doehlert matrix). Under the optimized conditions, limits of detection and quantification of 0.02 and 0.06 μg L−1, and preconcentration factor of 29 were obtained for the determination of mercury using the developed on-line system, considering a sample volume of 50 mL. Precision expressed as a relative standard deviation (RSD%) was of 5.2% (n = 7) for a standard solution with mercury(II) concentration of 0.5 μg L−1. Then, the on-line system was applied for the selective preconcentration and determination of mercury (II) in four natural water samples, and addition/recovery tests were performed to evaluate the accuracy of the method. All analyzed samples presented Hg2+ concentrations below the limit of quantification of the proposed method and the recovery values found were in range from 90 to 105%.

Leaves of Lippia alba (Mill.) N.E. Brown are used for the preparation of tea infusions that are employed in folk medicine. In this paper, the mineral composition of Lippia alba (Mill.) leaves, collected from different Brazilian cities, was evaluated. The samples were digested using nitric acid and hydrogen peroxide on a hot plate and were analyzed using inductively coupled plasma optical emission spectrometry (ICP OES). SRM 1515 apple leaves from NIST were used for checking accuracy. The results demonstrated that calcium, magnesium and phosphorus have average contents of 1,950, 2,856 and 2,335 mg 100 g -1 , respectively, and concentration ranges of 767-3,887, 314-8,591 and 247-9,214 mg 100 g -1 , respectively. The microelements barium, zinc, copper, iron, manganese and nickel have average contents of 2.16, 2.95, 0.94, 11.2, 4.25 and 0.09 mg 100 g -1 , respectively, and concentration ranges of 0.66-7.1, 1.35-6.3, 0.33-1.7, 0.98-34, 0.82-7.4 and 0.03-0.15 mg 100 g −1 , respectively. The data were also evaluated using principal component analysis (PCA).

Multicomponent reactions in water are an important method in organic synthesis. One of the benefits of Green Chemistry is atom economy and safe solvent. Based on this some secondary and tertiary amine have been prepared in an aqueous medium in good yields. Wei and co-workers have obtained some propargylamines by coupling aldehydes, alkynes and amines in water in good yields. Aromatic amines are important building blocks for a broad range of biologically active compounds, and intermediate to dyes and pigments. In previous work, our group synthesized homoallylic amines from coupling reaction between secondary amines, methanal and halides in high yields. Herein we report the synthesis of aromatic amines in water with iminum from aniline and methanal.