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'The Density of Solids Dale Burgess Eastern Wyoming College, 3200 West C Street, Torrington, WY 82240 An experiment to determine the density of a solid usually do not fit easily into a graduated cylinder or are too heavy to is a simnle one in which the student carefullv slides a cvlinder be weiehed on the trinle beam balances, so the students must ~- ~~- . of metal into a graduated cylinder partially filled with water think Gp ways to weigh the objects using the trip balance and in order to determine volume bvdisnlacement and weiabs the to determine the volume with a reasonable degree of accu- metal cylinder. The student calculkes the density fGm the racy. formulaD = MIV and answers a few pertinent questions. There is generally a short period of student confusion and In my experiment, however, I have a large collection of as- aimlessness, but then the students start getting ideas and the sorted objects. This collection includes rebar, concrete, boards, experiment becomes both challenging and fun for most of rocks, gears, hose, pipes, corks, styrofoam, rubber stoppers, them. In my last class a couple of the students found a box that and odd vieces of metal. contained vermiculite that had been used as packing, and they ~ach silldent is given onts of the ohjects and is told that he used the vrrmic~~lite as a d~splaccment mrdium a i d the box can "st, anvthine in the lab in his determination ofthe ohiect's as a rontniner ro determine the vulume o i a large hoard. density, b& that the size of the measuring device musthave Following the experiment I discuss: (1) the comparison of an accuracy commensurate with the size of the object being the measured densities with the real densities, (2) the com- measured. The volume of the object must be obtained both parison of the results of the two methods, (3) the possible er- by displacement and hy using a ruler to get its dimensions. rors introduced by the measuring devices, (4) relative error The students have the normal chemistry lab equipment and in the experimental data, and (5) other methods of density some large pans to be used for large object displacement. determination. The discussion of relative error leads nicely There is also a trip balance with no weights. The objects either into a discussion of significant figures. 242 Journal of Chemical Education
