Popcorn Is A Gas

Katz, Linda Orr Academy

Objectives: Students will understand why popcorn pops. Students will be exposed to questioning how Chemistry/science is integrated into everyday affairs. Students will learn to take concept and apply to other phenomenon. Students will understand how pressure, volume, and temperature are related. Apparatus needed: Popcorn popper (any type) popcorn sharp knife to cut popcorn petri dishes or paper muffin cups balance hot plate 250 ml Erlenmeyer flasks Recommended Strategy: Preplanning: Cut kernels of corn - some longitudinally, some transversely (cutting just the bottom tips off will be fine. Make sure you save all the pieces.) About ten (10) of each will do the trick. Have popcorn popping/popped as students enter the room! Intro: If you allow students to eat in your lab class, pass out a handful to each student. Elicit comments from students about popcorn. It's tasty, fun to eat, reminds them of movies, etc. Then ask: What causes popcorn to pop?? Pass out unpopped kernels for them to compare with popped kernels. Have them make observations comparing the two. Remind them they are looking for clues as to how one gets from the unpopped to the popped stage. Have a student make a list on the board of observations/suggestions what causes the popcorn to pop. Write down all of students ideas. Have students review list and decide which they think is a plausible cause for the pop. If need be, coax them to think about what is inside the kernel. Once they have started to think about the internal kernel, ask what should be tested for and how. One thing students will probably recommend doing is massing the kernels before and after popping the corn. Have students predict which will mass more and why. Then get a few students to volunteer to mass the kernels before and after. (The popped corn will mass significantly less due to a loss of water.) Test the differently cut kernels to see which pop. Do each 'type' of kernel in different flasks on a hot plate. You will find the only ones that do not pop are the longitudinally cut kernels. From this discussion you will be able to discuss: There is water inside the kernel, which when heated increases the movement of the molecules. As the molecules move, they increase the pressure on the sides of the kernels, so that the volume must increase - therefore the popping!! References: CHEM MATTERS,October, 1984.

Strongin, Herb. Science on a Shoestring. Addison Wesley: Menlo
Park, California, 1985.
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