Chemistry for Everyone edited by
Overhead Projector Demonstrations
Doris K. Kolb Bradley University Peoria, IL 61625
Illustrating the Properties of Magic Sand Robert H. Goldsmith Department of Chemistry, St. Mary’s College of Maryland, St. Mary’s City, MD 20686;
[email protected] Magic sand was originally a novelty item sold for amusement purposes. Magic sand is regular sand treated with a hydrophobic liquid like silicone spray (1). It can be purchased from Flinn Chemical Company or prepared from directions provided in the book Teaching Chemistry with TOYS (2). The properties of magic sand lend themselves to some interesting demonstrations on the overhead projector that should illustrate the differences between hydrophilic materials, such as regular sand, and hydrophobic magic sand. All that is needed for this demonstration is an overhead projector and two petri dishes with lids. Place at least 1.5 g of regular sand in one dish and the same amount of magic sand in an adjacent dish on the projector. Gently move the two dishes from side to side, keeping them in contact with the projector. The students should observe how both sands readily move about back and forth. Now add enough water to each dish to cover the sand, and again move the two dishes back-and-forth on the projector. It is noted that the magic sand either moves as little clumps floating on the water like a film or adheres in a single clump and resists any movement, while regular sand moves slowly, appearing as individual sand particles. The magic sand particles illustrate a lack of interaction with the water molecules.
An interesting variation involves the use of sand shapes. Simple sand shapes, such as letters L or O, can be made by taking a larger amount of each sand and manipulating the dry sands into the pattern in their respective dry dishes. Very carefully add water to the sands so that the shapes are maintained and completely covered with water. Again gently move the dishes side to side and observe the behavior. The magic sand retains the shape while the regular sand moves about and the pattern or shape is quickly lost. Finally, if you use a small pipet to remove all the water that you can from the two dishes, the magic sand is recovered in a nearly completely dry condition and the regular sand in a wetted condition. This is observed as the back-and-forth motion now reveals the rapid individual-particle motion of nearly all of the magic sand and the stuck-together condition of regular sand, illustrating the water-attracting behavior of the regular sand. Literature Cited 1. Vitz, E. J. Chem. Educ. 1990, 67, 512–515. 2. Sarquis, J. L.; Sarquis, M.; Williams, J. P. Teaching Chemistry with Toys: Activities for Grades K–9; Terrific Science Press: Middletown, OH, 1995; pp 183–187.
JChemEd.chem.wisc.edu • Vol. 77 No. 1 January 2000 • Journal of Chemical Education
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