Candelaria Tejada

Aprovechamiento de Cáscaras de Yuca y Ñame para el Tratamiento de Aguas Residuales Contaminadas con Pb(II)

espanolSe modificaron quimicamente cascaras de yuca y name con acido citrico y se evaluo su comportamiento para la adsorcion de Pb(II). Los experimentos de adsorcion se llevaron a cabo usando un tamano de particula en el rango de 0.5 a 1mm y un pH de 6. La determinacion del metal remanente en solucion fue medida mediante espectroscopia de absorcion atomica. Se obtuvo una capacidad de adsorcion de 52.34 y 98.36mg/g para las cascaras de yuca y name respectivamente. Ademas, se encontro que el modelo de Elovich y la isoterma de Langmuir y Freundlich ajustan adecuadamente los datos experimentales de adsorcion. Se establece tambien que el enlace se da principalmente por fuerzas fisicas, formandose solo una monocapa. Se concluye que los materiales en estudio modificados quimicamente con acido citrico pueden ser usados para el tratamiento de aguas residuales, especificamente en la remocion de metales pesados como el plomo (II). EnglishCassava and yam peels were chemically modified with citric acid and its performance for the adsorption of Pb(II) was evaluated. The adsorption tests were carried out using particle size between 0.5 and 1mm, and pH=6. The determination of the remaining metal in solution was measured by atomic absorption spectroscopy. These adsorption capacities were of 52.34 and 98.36 mg/g for cassava and yam peels, respectively. In addition, it was found that Elovich’s model and Langmuirs and Freundlich’s isotherms adequately fit the adsorption experimental data. It is also established that the bond occurs mainly due to physical forces, forming a single monolayer. It is concluded that the materials under study, which were chemically modified with citric acid, can be used for wastewater treatment, specifically for the removing of heavy metals such as lead (II).

Teoría de la Formación por Etapas de las Acciones Mentales (TFEAM) en la Enseñanza y Aprendizaje del Concepto de Valencia Química

The objective of this project was to apply Theory of Stepwise Forming of Mental Actions in the teachinglearning process of the concept of chemical valence, evaluating its effect in the appropriation of the concept. Time was considered as an indicator of the valence concept’s internalization and this was related to the quantity of successes that each student achieved. This was done in a test of nine exercises, organized in five categories with the aim of classifying the results in both the own language as well as in the mental stage. The analysis was carried out by the application of the Pearson’s lineal correlation coefficient. This showed that more students were over the 15 minutes in the mental stage; while in the stage of own language the majority of the students spent more than 25 minutes.

Didáctica para la Enseñanza del Concepto de Valencia Química

The present study was aimed to propose an educational tool for teaching the concept of chemical valence. For this, an initial diagnosis among a sample of teachers on how they teach and evaluate the concept of valence chemistry was performed, and the concept features taken into account in their teaching. Likewise questions were asked about the pedagogical and methodological strategies used in the classroom, which encourage student learning concept. From these results some of the features that enabled the construction ho of the concept of valence emerged. This was complemented with exercises done by the students who perform the four intellectual operations: super-organized, sub-organized, organized and exclusive. All features identified and selected for this specific case, were organized to propose a conceptual graphical representation (mentefacto) as a tool to teach the concept of valence.

Influencia de los Textos de Química en la Enseñanza y Aprendizaje del Concepto de Valencia

The aim of this study was to identify the influence of chemistry textbooks in the process of teaching/learning of concepts, particularly chemical valence. For this, the form in which the concept is discussed was analyzed in several chemistry textbooks. Also, the influence of the texts was evaluated by applying a survey to a group of 40 students. It was observed that the concept of valence in the texts considered in his study the concept of valence is presented introduces students in incomplete and static form, which allows to explain and comprehend some simple molecules only. The concept of primary valence is not included in most of the books, except those of Chang and Collage and of Petrucci. They are the only ones that include the contributions by Alfred Werner regarding primary and secondary valence. It is concluded that this may be causing the incomplete form in which student understand the concept of valence.