Abstract:

In order to encourage high school students to be interested in Chemistry, the Faculty of Chemistry (Universidad Nacional Autónoma de México, UNAM) has been working closely with several schools during the last years. One of the core activities in this approach of teaching Chemistry is to find a chemical solution to a real problem.

A group of 4 to 6 students are supervised by a Science teacher of their school, with the coordination of a Research Professor at the University. They work 4 h. a week at a research laboratory during 4 months, in order to perform all the experiments and find a solution to the initial problem.
The problem presented by the students was "Find a practical an economical way of preserving wood". In order to solve this problem a bibliographic search was conducted, with the surveillance of the Professor at the University, and they found that mineralization of wood was a practical approach to solve the problem.

The project was focussed on the flammability properties of wood and increase its preservation. The proposed process allows a stronger resistance towards fire and wood durability, and therefore, in the products and furniture made with it, obtaining a building material of higher quality. This is an alternative solution to the problem of short life and high flammability of this material, primarily designed for the construction of furniture and interior decorations.

The process consists in soaking the wood with a solution of sodium meta-silicate and other chemical substances, such as calcium chloride at 200°C and vacuum. Crystallization of these minerals between the wood´s voids provides the properties of a higher resistance towards fire exposure and it´s preservation.

Ten diverse types of wood were used, with distinct porosity and density characteristics. It is important that the students understand the way of performing scientific research and thus several independent variables were analyzed in the study, different substances on which the wood was subjected, and their concentrations. The response or dependent variable was the wood´s flammability in various time intervals and the type of wood. The experimental process of the project was conducted at the Division of Postgraduate Studies of the Faculty of Chemistry of UNAM.

The use of constructive learning is highly motivatating and the students tend to go very deep in the acquisition of knowledge in order to solve the problem. Having a real model motivate the students to understand all the variables involved in the solution.

Acknowledgments
This work was partially supported by a grant from Dirección General de Asuntos del Personal Académico (DGAPA) Universidad Nacional Autónoma de México PE205313 and IOCD (International Organization for Chemical Science in Development).

Keywords:

Teaching Chemistry, competence, motivation.