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and analogies An Analogy to Illustrate Miscibility of Liquids Barry K. Thornton
Scnool of Appl eo Chem stry C~nmUnverslv of Technotoav Perth. Western Australia Analogies are useful teaching strategies that allow students temporarily to fit new pieces of information or concepts into existing frameworks and pathways. These temporary connections may then be used by the student to further extend the concrete framework. Thev have been used successfully to illustrate concepts a s diverse a s electron configurations (1)and enthalpy (2).The topic of miscibility/solubility of covalent liquids often is introduced or concluded with the statement "like dissolves like", vet the concepts involved are difficult to grasp and certaihy not easv to visualize. These concepts include a n a~preciation of &e energy that is required to overcome the ioiven&solvent interactions, the solute-solute interactions and finally, the energy produced in the solven&solute interaction. One analogy that I have used successfully both a t the high school level and for beginning students a t the university level involves the use of either inter-school or inter-faculty rivalry to demonstrate these concepts. The students a r e asked to imagine t h a t two students from another schoolifacultv will he visiting the class for the dav. Your own studen& represent the Lolvent and the two "&tors" the solute. Bv choosine vour "visitors" carefullv all of the interactions "involved-in the dissolution can "be demonstrated clearly. Basically, there are three steps involved in the dissolving process and each one has a n analogy.
156
Journal of Chemical Education
Middle Georgia College
Cochran. GA31014
A hole must be made in the body of the class to accommodate the "visitors".You should explain that this takes energy be-
cause the class has a camaraderie or spirit binding them to each other. (This is an endoenergetic process.) 'The "visitors" must be separated from each other. This also requires energy because they too have a camaraderie. (This also is an endoenergeticprocess.) The "visitors" have to be assimilated into the class, i.e., made to feel welcome. (This is an emenergeticprocess.) By careful choice of the "visitors" i t is possible to develop situations where the "welcome" felt is strong. (as in the case of a school with which there is little rival&)or, where there is little or no "welcome" felt (as i n the case of a school/faculty with which there is traditional rivalry). Thus, dissolving or otheryise can be seen as being the result of these three energetic processes. If the "welcome" xiven by the class (and felt bv the "visitors") is large when compared with the other two processes the "visit&? will "dissolve". On the other hand, if the "welcome" is less than enthusiastic the "dissolution" will not take place. Some of the combinations I have used include chemistry students attempting to dissolve engineering students and vice-versa. I n these cases the welcoming energy is never enough to lead to dissolution. Chemistry students will, however, invariably "dissolve" Nursing or Pharmacy students. Most high schools have traditional sporting rivals and the choice of the nondissolving "visitors" should not be difficult. The dissolving visitors may be from a brother or sister school. Literature Cited 1. Rieek, D. F J Chrm.Edue. 1980,67,378. 2. Bonneau,M.C. J. C&m Educ. 1987,62,486
