Chemical Education Today edited by Erica K. Jacobsen JCE Secondary School Editor
Classroom Activity Connections
Soda Can Density and Unexpected Results by Erica K. Jacobsen, Donald R. Paulson, and Michael J. Sanger
photo: D. R. Paulson
Reading through the latest JCE Classroom Activity may lead to thoughts of “Yes, I’ve used that before. But… [you can fill in the blank].” Maybe it would be “But I did this part differently.” “But I had this problem when we did it in this environment.” “But I wish they’d mentioned this other part the students could try.” JCE reader Donald Paulson was very familiar with the idea behind the soda can density Classroom Activity Michael Sanger presented in the November 2006 issue. But (here’s Paulson’s fillin-the-blank) he had a very interesting experience performing the sink/float test in a mountain town in California. Paulson’s description sparked an additional discussion of extensions to the Activity, by both the original author Sanger, and editor-in-chief John Moore. Thoughts from all three educators appear below.
A sugared soda normally has a density greater than water and sinks while a diet soda floats. However, the sugared soda shown at left floats due to the air bubble retained in the depression at the bottom of the can.
Featured Activity ◭ Extension to JCE Classroom Activity: #84. Whatever Floats (or Sinks) Your Can by Michael J. Sanger, J. Chem. Educ. 2006, 83, 1632A–1632B.
Turn Your Ideas into Dollars! JCE invites you to become part of the Classroom Activity discussion! Please share your thoughts about connections you’ve made between previously published Classroom Activities and your own experiences inside and outside the classroom. Submit items to the JCE editorial office (see http://www.jce.divched. org/Contributors/Authors/index.html for general submission guidelines). Be sure to indicate that your submission is intended for the Connections feature. If you’d like feedback on an idea before you submit or have any questions, contact Erica Jacobsen at
[email protected]. The feature is still in its beginning stages, so we need your submissions! If you are a high school educator and your item is published in Connections, the Secondary School Chemistry Office offers a $25 gift certificate to your choice of Office Depot or Educational Innovations to buy needed classroom supplies or just something fun. Erica K. Jacobsen is Editor, Secondary School Chemistry, JCE;
[email protected].
Floating Cans, Sinking Cans Reader Report, Activity #84 I was happy to see the floating/sinking soda cans demonstration get the wider coverage provided by J. Chem. Educ. in the November 2006 issue. I have been using that activity for more than 20 years in my work with precollege teachers and students. About ten years ago I was working on the concepts of sinking and floating with some 4th grade students in a mountain town in Southern California. When I placed two Coke cans (one sugared and one diet) in the local tap water, both cans floated even after I had removed the air bubble on the bottom of the cans. This same regular Coke can had sunk in Los Angeles tap water the day before and sank again the following day. The teacher later told me that the water in that town was the hardest she had ever experienced. Apparently the dissolved minerals in the tap water had raised the density of the water so that even the regular Coke floated. John Moore pointed out to me the need to test cans before using them with students because in the same water you will sometimes find some cans of sugared soft drink that will 18
float and some that will sink. His plausible explanation is that different kinds of sugar may be used in different batches of soft drinks. Soft-drink makers will use whatever sugar provides the appropriate sweetness at the lowest cost, which could lead to some cans containing high-fructose corn syrup and others containing different sugars. I often have teachers in workshops add salt to water to get a fresh egg to float. Since most teachers have seen this demo I also have them use sugar. Many of them predict that salt will work but not sugar so this makes a great learning tool. In addition, I have used the air bubble on the bottom of the can as a teaching tool. If you carefully lower the regular soda can into the water while retaining that bubble the regular soda can will also float. Donald R. Paulson Department of Chemistry and Biochemistry California State University Los Angeles, CA 90032
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Journal of Chemical Education • Vol. 85 No. 1 January 2008 • www.JCE.DivCHED.org • © Division of Chemical Education
Chemical Education Today
Author Response, JCE Classroom Activity #84 I am glad that my JCE Classroom Activity is proving to be useful for the readers of this Journal, and it is leading to more discussions on this very interesting demonstration. Just as Paulson has, I have recently noticed that some regular soda cans (especially Coke and Sprite) tend to float sometimes instead of sinking. In fact, I have found that different cans from the same 12-pack (presumably canned at the same time using the same source of sugar) can behave differently, so I always check the cans’ buoyancies before letting students use them. I have not noticed this difference in behavior from the diet soda cans, which implies that the densities of the regular soda cans are much closer to the density of water than the diet soda cans. When I use this experiment in my chemistry or physical science classrooms, I also have the students add initially either salt or sugar and then rubbing alcohol to the sample of water in which the cans are immersed. The students find that when salt or sugar is dissolved in the water, all of the soda cans float because the density of the
surrounding water sample has increased, so it is not surprising that these cans would float in mineral-rich tap water. These students also discover that when they add enough rubbing alcohol to the water, all of the soda cans sink because of the decreased density of the surrounding water sample. Michael J. Sanger Chemistry Department Middle Tennessee State University Murfreesboro, TN 37132
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http://www.jce.divched.org/Journal/Issues/2008/Jan/abs18.html Abstract and keywords Full text (PDF) with links to cited URLs and JCE articles
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