Demonstration pubs.acs.org/jchemeduc
CO2 Dry Cleaning: A Benign Solvent Demonstration Accessible to K−8 Audiences Reuben Hudson,*,† Henry M. Ackerman,† Lindsay K. Gallo,† Addison S. Gwinner,† Anna Krauss,† John D. Sears,† Alexandra Bishop,†,‡ Kristin N. Esdale,†,‡ and Jeffrey L. Katz*,† †
Department of Chemisty, Colby College, 5750 Mayflower Hill Drive, Waterville, Maine 04901, United States Beyond Benign, Wilmington, Massachusetts 01887, United States
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S Supporting Information *
ABSTRACT: A quick demonstration is described to showcase the use of CO2 as an alternative, benign dry cleaning solvent. The demonstration includes visible evidence of CO2 as a solid, a liquid, and a gas, making it ideal as part of a broader lesson on states of matter. The demonstration relies on a technique for generating liquid CO2 in a centrifuge tube, which has been used for extractions in undergraduate teaching laboratories for over a decade. This report represents a unique attempt to transfer this method to the K−8 curriculum.
KEYWORDS: Elementary/Middle School Science, Demonstrations, Analogies/Transfer, Green Chemistry
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INTRODUCTION The emergence of undergraduate green chemistry courses1−7 over the last 25 years continues to drive the development of sustainability-themed materials for a college level audience; example reports include laboratory exercises, activities, and demonstrations.8−15 Some green chemistry concepts, such as the use of renewable feedstocks or generation of benign/ degradable products,16,17 transfer well to the learning goals of K−8 outreach audiences.14,18,19 Even more advanced topics, such as the use of recyclable catalysts20−22 or benign solvents23−25 for reactions or extractions, can, with a bit more effort, also be put into context for K−8 outreach audiences.15 The hands-on use of liquid CO2 as a benign solvent has become a mainstay in undergraduate green chemistry education. Hutchison’s 2004 report showcased a method to generate liquid CO2 from dry ice in centrifuge tubes for the extraction of limonene from orange peels.26 The technique’s popularity spurred follow-ups27 for the extraction of eugenol from cloves,28 caffeine from tea leaves,29 and anethole from fennel seed,30 but no reports to our knowledge address the adaptation of this popular and simple scheme for a K−8 audience. Indeed, teaching the isolation of natural products requires a discussion about the polar/nonpolar characteristics of the desired compounds and the solvents we use to extract them, which does not fit into the K−8 curriculum, nor do the advanced spectroscopic techniques typically used to verify the presence of these compounds. This activity, catered toward a K−8 audience, uses the same technique to instead demonstrate a concept the students are more familiar with: dry cleaning. © XXXX American Chemical Society and Division of Chemical Education, Inc.
Verification of a successful experiment relies not on the appearance of a thin film or a drop of an unidentified material at the bottom of a tube, but instead on the disappearance of a stain from a piece of cloth.
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DEMONSTRATION DETAILS Depending on the age and number of students, as well as the availability of safety glasses, this exercise can be animated as a hands-on activity for everyone, or simply as a demonstration. Combining this with other dry ice31 or liquid nitrogen32−34 demonstrations provides for a fun lesson on solids, liquids, and gases. This demonstration requires centrifuge tubes with caps, dry ice, wire, cloth, oils (eugenol, limonene, oil of oregano, etc.), and a warm water bath. Following established procedures,26−30 fashion a wire basket to settle at the bottom of the centrifuge tube with a handle extending to the top of tube for easy removal (details are provided in the Supporting Information). With the oil of your choice, stain a small piece of cloth (not much larger than the diameter of the centrifuge tube). Secure this cloth in the wire basket, and lay the basket into the centrifuge tube. Fill the tube with crushed dry ice, cap it, and immerse in the warm water bath. As the pressure builds inside the centrifuge tube, the solid dry ice will turn to liquid. Some will escape as gaseous bubbles out of the top of the tube, so students will be able to visualize CO2 as a solid, liquid, and Received: June 2, 2016 Revised: November 8, 2016
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DOI: 10.1021/acs.jchemed.6b00412 J. Chem. Educ. XXXX, XXX, XXX−XXX
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Figure 1. Procedure for CO2 dry cleaning. A wire basket, stained cloth and dry ice are placed into a centrifuge tube. The tube is capped and immersed in a warm water bath. Under pressure, the dry ice melts, serving as the solvent to remove the stain from the cloth. The CO2 slowly escapes through the cap’s lid, and once the tube stops bubbling, the wire basket is used to pull the now clean(er) cloth from the centrifuge tube.
gas. After a few minutes, all of the CO2 will have bubbled out. At this point, you can uncap the tube, and refill with dry ice for a second “washing” or remove the cloth to show that it is cleaner than before (Figure 1).
standing that the liquid inside the tube was CO2 (not water), and that this was an example of dry cleaning. Most of the students could provide evidence to support the existence of solid, liquid, and gas in the tube.
HAZARDS Eugenol (clove oil), limonene (orange oil), and oil of oregano are typically considered safe, and can be purchased from a health food store. Dry ice is extremely cold, and should not be handled with uncovered hands. The most significant hazard for this experiment is the high pressure of the centrifuge tubes. Hutchison26 reported that 15 mL Corning tubes (catalog #430052) work best, and even with these, about 4% of caps failed (popped off) under high pressure. Therefore, safety glasses are required for the animator and anyone else in close proximity. Additionally, the container for the warm water bath should not be glass, in case the immersed tube fails (potentially shattering the glass). A clear plastic cylinder works best. For large groups, a document projector can effectively capture the action, allowing students to stay a safer distance away in the rare event of a burst centrifuge tube.
SUMMARY The demonstration outlined here represents a unique adaptation of an established liquid CO2-generating technique for dry cleaning in a K−8 outreach or classroom setting. The demonstration fits into a broader “states of matter” lesson and can even open a dialogue on sustainability, since CO2 can be used in this context as an alternative for more hazardous dry cleaning solvents.
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available on the ACS Publications website at DOI: 10.1021/acs.jchemed.6b00412. Instructor notes (PDF, DOCX) Student observations (PDF, DOCX)
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DISCUSSION As part of a broader activity on states of matter with other liquid nitrogen and dry ice demonstrations, this modeling of CO2 dry cleaning provides students with a real life application and allows a brief discussion of sustainability. The technique to generate liquid CO2 in a centrifuge tube is typically used for extractions in undergraduate laboratories, but a meaningful discussion of extractions would require content outside of the typical K−8 curriculum. This dry cleaning relies on the same concepts as similar activities, but focuses the students’ attention on simpler topics (states of matter) in an exercise centered around an application they can relate to. Over the course of several demonstrations for 20+ students of mixed grade level (K−8), most students had heard of dry cleaning, and several could articulate that it did not involve water. After watching the demonstration, the students walked away with the under-
AUTHOR INFORMATION
Corresponding Authors
*E-mail:
[email protected]. *E-mail:
[email protected]. ORCID
Reuben Hudson: 0000-0001-9612-681X Jeffrey L. Katz: 0000-0001-6975-5880 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The authors thank Beyond Benign for supporting students as Green Chemistry Fellows, as well as Colby College and the National Science Foundation (SMA-1415189) for financial support. B
DOI: 10.1021/acs.jchemed.6b00412 J. Chem. Educ. XXXX, XXX, XXX−XXX
Journal of Chemical Education
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