Uncovering Students' Understanding; Evidence For The Teaching of Acid-Base Properties of Salt Solution

<p>Este estudio tuvo como objetivo descubrir la comprensión científica y no científica de los estudiantes sobre el tema de las propiedades ácido-base de la solución salina. Este estudio descriptivo involucró a 300 estudiantes de tres escuelas secundarias públicas en Malang, Java Oriental, Indonesia. El instrumento de cuatro niveles en el tema desarrollado y considerado válido de nuestro trabajo anterior se utilizó para la recopilación de datos. Se encuentra que la comprensión científica de algunos conceptos por parte de los estudiantes es sólida. Sin embargo, también se descubrieron algunos conocimientos no científicos. También se discute la implicación para la enseñanza del tema.</p>

Evaluation of the reactivity, selectivity and lifetime of hydrotalcite-based catalysts using isopropanol as probe molecule

Hydrotalcite catalysts derived from NiAl and NiAlMg mixed oxides were successfully prepared by coprecipitation at a constant pH of 11. Physicochemical methods were investigated to determine their structural and textural properties. Using isopropanol as a probe molecule, the acid–base properties of the catalysts were investigated, and the evaluation of reactivity, selectivity and lifetime was established.

Influence of Substrate Concentration on Kinetic Parameters of Ethanol Dehydration in MFI and CHA Zeolites and Relation of These Kinetic Parameters to Acid–Base Properties

The catalytic activity of zeolites is often related to their acid–base properties. In this work, the relationship between the value of apparent activation energy of ethanol dehydration, measured in a fixed bed reactor and by means of a temperature-programmed surface reaction (TPSR) depending on the amount of ethanol in the zeolite lattice and the value of activation energy of H/D exchange as a measure of acid–base properties of MFI and CHA zeolites, was studied. Tests in a fixed bed reactor were unable to provide reliable reaction kinetics data due to internal diffusion limitations and rapid catalyst deactivation. Only the TPSR method was able to provide activation energy values comparable to the activation energy values obtained from the H/D exchange rate measurements. In addition, for CHA zeolite, it has been shown that the values of ethanol dehydration activation energies depend on the amount of ethanol in the CHA framework, and this effect can be attributed to the substrate clustering effects supporting the deprotonation of zeolite Brønsted centers.

CYTOTOXIC PROPERTIES OF NANOSTRUCTURES BASED ON ALUMINUM OXIDE AND HYDROXIDE PHASES IN RELATION TO TUMOR CELLS

Background. Currently, the use of nanoparticles and nanostructures as components of tumor therapy is the subject of numerous scientific articles. To change the parameters of cell microenvironment in presence of nanoparticles and nanostructures is a promising approach to reducing the tumor cell viability. Aluminum hydroxides and oxides have a number of advantages over other particles due to their porous surface, low toxicity, and thermal stability.The purpose of the study was to investigate the influence of the acid-base properties of aluminum hydroxide structures with different phase composition on the tumor cell viability (Hela, mda, pymt, a549, B16F10).Material and methods. Aln/al nanoparticles were used as a precursor for obtaining structures with various phase compositions. The anoparticles were produced by electric explosion of an aluminum wire in a nitrogen atmosphere. Such nanoparticles interact with water at 60 °Ϲ, resulting in formation of porous nanostructures. They are agglomerates of nanosheets with a planar size of up to 200 nm and a thickness of 5 nm. The phase composition of the structures was varied by the calcination temperature. A change in the phase composition of nanostructures led to a change in the acid-base properties of their surface. To estimate the number of acidic and basic centers on the surface of nanostructures, the adsorption of Hammett indicators was used. The amount of adsorbed dyes was determined spectrophotometrically.Results. It was found that the differences in the acid-base characteristics of the surface of the nanostructures led to a change in their antitumor activity. Γ-al2o3 had 6.5 times more basic centers than acidic ones, which determined its ability to exhibit more pronounced antacid properties, i.e. Longer to neutralize protons secreted by tumor cells. This sample had the highest antitumor activity against all tested cell lines.Conclusion. The antitumor activity of synthesized structures was found to be related not only to an increase in the ph of the cell microenvironment, but also to the ability to maintain the alkalinity of the microenvironment for a longer time due to the adsorption of protons released by tumor cells.