Abstract:

In recent years, and in the field of chemistry teaching, many articles, dealing with the problem of learning difficulties of students in the concept of mole, can be found in science education literature and therefore all other concepts related to it such as Avogadro constant, atomic, molecular and molar masses, and so on. From the standpoint of educational research, the problem could be define within the field of interrelationships between dimensions and categories of Chemistry proposed by Jensen (1): Molar, molecular and electrical. At the same time is very important to take into account the three domains of representation in Chemistry proposed by Johnstone (2): molar, molecular and electric; De Jong and Van Driel (3) called macroscopic, microscopic and symbolic. In Spain Furió (4), (5), has addressed the problem from a historical-epistemological point of view. Other authors such as Gabel (6) emphasize the fact of differences between experts (teachers) and novices (students) when inadvertently moved between different domains and categories. Finally, Pozo (7) points out that the main core of the difficulty is that the magnitude of Avogadro's number is far beyond what the student can conceive or imagine.

Taking into account this last consideration, in the present work, considering the mole as the fundamental unit of the magnitude "amount of substance", we are developed a series of comparative analogies with other key units familiar to students of Teachers Education (length, mass and time). In this way they can relate Avogadro’s number, which is quite closer to a quadrillion (1024) of elementary entities, with more known quantities which become surprising for the students when dealing with these orders of magnitude. The fundamental difficulty seems to be that the students think mechanically when they operate exponential values without being aware of the real dimension of the quantities they handle. We have found that with the analogies and similarities we suggest, students get a much better comprehension of these magnitudes and are much better able to resolve issues and problems related to the concepts of mole and Avogadro’s number in different contexts.



References:
[1] Jensen, W.B. (1998). Logic, History, and the Chemistry Textbook I, does Chemistry have a Logical Structure? Journal of Chemical Education, 75,7, 817-828
[2] Johnstone, A.H. (1993). The developmento of chemistry teaching: A changing respone to changing demand. Journal of Chemical Education. 1993, vol. 70, no9, pp. 701-705.
[3] De Jon, O. & van Driel, J. “Prospective teachers’ concerns about teaching chemistry topics at a macro-micro-symbolic interface” Paper presented at a 1999 NARST annual meeting. Boston. USA.
[4] Furió, C. ; Azcona, R. y Guisasola, J. (1999). Dificultades conceptuales y epistemológicas del profesorado en la enseñanza de los conceptos de sustancia y de mol. Enseñanza de las Ciencias, 17 (3). p. 359-376.
[5] Furió, C y otros (2002). Revisión de investigaciones sobre la Enseñanza-Aprendizaje de los conceptos cantidad de sustancia y mol. Enseñanza de las Ciencias 20 (2), p. 229-242.
[6] Gabel D. J.(1993), Use of the particle nature of matter in developing conceptual understanding, J. Chem. Educ., 70 [3], 193-194.
[7] Pozo Municio, JJ. (1998). Aprender y Enseñar ciencia. Ed. Morata. pp. 185.