F. Cañada1, R. Álvarez1, M.J. Arévalo1, M.V. Gil1, J. Cubero1, L. Ortega2

1University of Extremadura (SPAIN)
2Colegio Público Los Glacis (SPAIN)
This work aims to ascertain the previous ideas of students in the third cycle of Primary Education (PE) on material systems and on the differences between pure substances and mixtures. Substance is regarded as one of the most important concepts in chemistry, since according to Sosa (1999) it allows to know and to identify the scope of this field of study. Material systems are introduced firstly in PE through the Environmental Knowledge subject and they are studied more in-depth in the secondary education.
Constructivist teaching-learning model, which is promoted by the actual education system, takes special interest in knowing students' previous ideas. These ideas lead to conceptual mistakes and they are an obstacle in learning scientifically correct concepts.
In our study a sample of thirty nine students from third cycle of Primary Education was chosen. A questionnaire consisting of five open, closed or drawing items was used as instrument.
The results obtained showed that students have a restricted conception of mixtures that is specially focused on what they perceive and it excludes products that are naturally mixed. Nevertheless, the students possess academic knowledge respect to the distinction between homogeneous and heterogeneous mixtures. Moreover, at this level, students have not assimilated the composition of matter yet.
On the other hand, the presence of previous ideas in the students has been detected. They do not difference between a pure substance and a mixture, especially if the mixture is a natural product like cow milk. In addition, students are not able to distinguish between the concepts of “matter” and "no matter" and they identify the fire and the light as material substances.
Therefore from this study we highlight that the concepts of pure substance and mixture are difficult to assimilate by the students. It would be desirable to change students’ previous ideas into scientific conceptions. Indeed, this change must be addressed in Primary Education because these ideas persist and are shaped as mental structures that impede the science learning.

Sosa, P. (1999). De palabras, de conceptos y de orden. Educación Química, 10(1), 57-60.

This work has been supported by Project ACCVII-21 (2011) from University of Extremadura.