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Disappearing Foam Cup Activity

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Styrofoam Cups Vanish Into Thin Air Activity (continued) + ward ' s science 5100 West Henrietta Road • PO Box 92912 • Rochester, New York 14692-9012 • p: 800 962-2660 • wardsci.com Find materials for this activity at wardsci.com. Discover more free activities at wardsworld.wardsci.com Procedure: 1. Fill bowl or pie plate with ½ cup of acetone. 2. Set the styrofoam cup in the dish of acetone. 3. Observe the cup sinking slowly into the acetone (you may have to apply some pressure to the top of the cup with the chopstick or spoon to get it started.) 4. Observe the remains of the dissolved cup after the acetone evaporates. Expected Results: Results may vary based on materials used, setup, procedure, and other factors, however, here is an example on what to expect: • When combined, the Styrofoam seems to disappear inside the acetone. The acetone is a solvent that easily breaks down the polystyrene, releasing the little air pockets trapped inside and leaving minimal residue at the end. In other words, the polystyrene dissolves, as the Styrofoam molecules become interspersed in the acetone. • Without these little air pockets, the cup is just a clump of gooey polystyrene on the bottom of the dish! You can pour off the excess acetone and let the clump of polystyrene dry into hard plastic. Follow Up: • You can see a less-dramatic version of the same effect by dissolving other polystyrene items in acetone. Common polystyrene products include disposable razors, plastic yogurt containers, plastic mailers, and CD jewel cases. • Allow students the opportunity to observe dissolving vs. melting. Use substances other than water and ice melting. Place various substances (butter, wax, chocolate, etc.) in an egg poacher. Gently warm the poacher and note when each substance melts. Ask students to predict which substance will melt first. Later, place the poacher in ice water to cool and again ask students to predict and observe the order in which the substances solidify. Teaching Notes: Weigh the acetone and Styrofoam material before and after to observe if all of it is still there after the cup collapses. Questions and observations for students: Many students at this level see melting and dissolving as indistinguishable. Although the dissolving process requires two materials, students tend to focus only on the solid, so they regard this process as similar to 'melting.' 1. How does this activity demonstrate the difference between dissolving and melting? 2. Compare and contrast the intermolecular forces in the gooey material with the original Styrofoam object. What is similar about the two materials? What is different about the two materials? 3. Describe the interactions between the acetone molecules and the Styrofoam molecules. What do you think happened when you put the cup into the acetone? How does this demonstrate the concepts of intermolecular forces and bonding? 4. Does Styrofoam dissolve in water? 5. Why would a compound or molecule be soluble in one solvent yet insoluble in another? 6. Why is Styrofoam a good insulator? Disposal/Clean-up: – Follow all the manufacturer's clean up instructions listed on the container of acetone. Discard leftover foam into the trash.

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