Communication Cite This: J. Chem. Educ. XXXX, XXX, XXX−XXX
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Simple Glowmatography: Chromatographic Separation of GlowStick Dyes Using Chalk Thomas S. Kuntzleman,* Kasey R. Bunker, and Ashlee A. Bartlett Department of Chemistry, Spring Arbor University, 106 East Main Street, Spring Arbor, Michigan 49283, United States
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S Supporting Information *
ABSTRACT: An experiment is described that uses easily obtained materials (glow sticks, chalk, and acetone or alcohol) to separate the dyes contained in glow sticks that actively emit chemiluminescent light. The experiment is very easy to carry out, making it amenable for students to perform in laboratory or outreach settings. The separation occurs fast enough that the experiment can be conducted as an in-class demonstration.
KEYWORDS: General Public, High School/Introductory Chemistry, First-Year Undergraduate/General, Demonstrations, Laboratory Instruction, Public Understanding/Outreach, Hands-On Learning/Manipulatives, Chromatography, Consumer Chemistry, Dyes/Pigments
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INTRODUCTION
Chromatographic experiments with an aesthetic quality have spawned several publications that explore fun and artistic aspects of chromatography.1−8 For example, chromatography has been used to create faux flowers,1,2 to explore what dyes are in candy,1,3,4 and to decorate T-shirts.1,2,5 These colorful experiments tend to be popular at outreach events and science camps9 as well as in middle-school, high-school, and introductory-level chemistry courses.10 It is especially attractive to incorporate inexpensive, familiar, and easily obtainable supplies into experimental protocols intended for these settings. Modifying standard chemistry experiments to include household materials makes such experiments accessible to a larger audience of students and teachers. We previously reported on the chromatographic separation of the contents of glow sticks on a silica-gel column in a process whimsically termed glowmatography.8 Motivated by the factors outlined above, this previously reported glowmatograpic experiment has been adapted to instead use readily obtainable materials. In this updated procedure, chalk is used as the stationary phase and either 91% isopropyl alcohol or acetone is used as the mobile phase.
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Figure 1. Chemical structures of 9,10-bis(phenylethynyl)anthracene (BPA, top) and rhodamine 6g (R6G, bottom). Note that possible hydrogen-bonding and ion−ion interactions between R6G and carbonate ions (in red) are displayed.
bis(2,4,6-trichlorophenyl)oxalate (C14H4Cl6O4) by hydrogen peroxide:8,11 C14 H4Cl 6O4 + H 2O2 → 2C6H3Cl3O + 2CO2 + energy
BACKGROUND
The light emitted from glow sticks originates from the conversion of chemical energy into light. Generally speaking, the chemical reaction that powers glow sticks involves the oxidation of a substituted phenyl oxalate ester such as © XXXX American Chemical Society and Division of Chemical Education, Inc.
Received: April 2, 2018 Revised: December 17, 2018
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DOI: 10.1021/acs.jchemed.8b00237 J. Chem. Educ. XXXX, XXX, XXX−XXX
Journal of Chemical Education
Communication
Fluorescent dyes contained within a glow stick gain energy from this chemical reaction and convert that energy into light, which is emitted by the glow stick.8 By including different dyes or mixtures of dyes within glow sticks, different-color glow sticks are produced.8 For example, 9,10-bis(phenylethynyl)anthracene (BPA) and rhodamine 6g (R6G) are used for green and red-orange light, respectively (Figure 1).8 It is of note that BPA is a hydrocarbon and therefore highly nonpolar, whereas R6G contains highly electronegative N and O atoms and is charged throughout a wide pH range.12 In the experiment described here, chromatography is used to separate fluorescent dyes contained in various glow sticks. Chalk, which is composed of either calcium carbonate or calcium sulfate,13 is used as the stationary phase. Isopropyl alcohol or acetone is used as the mobile phase. Although acetone and isopropyl alcohol have permanent dipole moments, they have much weaker interactions with polar dyes than the ionic compounds within the chalk. Thus, dyes such as R6G, which can participate in ion−ion, ion−dipole, or hydrogen-bonding forces with the carbonate ions in chalk,14 tend to remain fixed on the stationary phase. In contrast, the nonpolar BPA tends to travel with the solvent. Thus, this activity is well-suited to introduce students to concepts involving intermolecular forces, in addition to allowing students to explore the chemistry of glow sticks.
using chalk as a stationary phase to separate dyes in markers.15,16 A glow stick is activated and cut open with a pair of sharp scissors or PVC pipe cutters. A dropper is used to transfer the glowing fluid onto the chalk such that the fluid encircles the chalk about 1 cm from its bottom (Figure 2, left). The glow-stick mixture should be liberally applied; small drops are added until each drop does not immediately soak into the chalk. The chalk is then placed into a beaker into which solvent (91% isopropyl alcohol, acetone, or other suitable solvent) has been added. The chalk should rest in the beaker of solvent such that the top layer of solvent is about 0.5 cm below the glowing line on the chalk (Figure 2, right). The assembly should be viewed in a very dark room.
PROCEDURE The protocol outlined here is a slight modification of previously described experiments that have been reported
RESULTS Best results for this experiment tend to be achieved using hot pink or orange glow sticks, the latter of which contain a combination of red-orange and green fluorescent dyes.8 Immediately after preparing a stick of chalk with glowing fluid, as described in the Procedure, no separation was observed when viewed in the dark (Figure 3). Within 60 s, an upper band emitting green light was observed to separate from a lower band of red-orange light. The green-emitting dye continued to separate over the course of 5 min, traveling upward with the isopropyl alcohol mobile phase (Figure 3). On the other hand, the red-orange-emitting dye remained relatively fixed on the chalk stationary phase. Assuming the green-emitting dye is BPA and the red-orange-emitting dye is R6G, it is straightforward for students to rationalize the observed separation with the structures of these dyes (Figure 1), the ionic composition of chalk, and the relatively nonpolar mobile phase. That is, R6G would be expected to remain fixed on the stationary phase because of the strong ion−dipole,
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HAZARDS Goggles and gloves should be worn at all times during this experiment. Acetone and 91% isopropyl alcohol are flammable; keep them away from all sources of ignition. The ingredients in glow sticks are claimed to be nontoxic by the manufacturer. In rare cases, irritation of the skin or eyes at the site of contact may be experienced upon exposure to the contents of glow sticks.17 Leftover fluid from glow sticks that have been cut open should be transferred to a container designated for halogenated organic waste.
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Figure 2. Preparation of chalk for glowmatography experiment. Left is a piece of chalk with a band of activated orange-glow-stick fluid applied. Right is the prepared piece of chalk balanced upright in a 100 mL beaker with about 15 mL of 91% isopropyl alcohol added.
Figure 3. Separation of activated orange-glow-stick mixture on chalk stationary phase with 91% isopropyl alcohol mobile phase. B
DOI: 10.1021/acs.jchemed.8b00237 J. Chem. Educ. XXXX, XXX, XXX−XXX
Journal of Chemical Education
Communication
variables that can be manipulated in this experiment (glowstick brand and color; chalk brand, color, and porosity; and composition of the mobile phase), it is well-suited for students to explore in various small research projects. This experiment has been used in this regard on many occasions.
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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.8b00237. Notes on the use of various brands of chalk, notes on the use of various brands of glow sticks, other tips, emission spectra of glow sticks of various colors, pre- and postquizzes for students in a general-science course, and student laboratory sheet used in an introductory chemistry course and a general-science course (PDF, DOCX)
Figure 4. Separation of activated glow-stick mixtures (left to right: red, orange, yellow, green, blue, and purple) on chalk stationary phases with 91% isopropyl alcohol mobile phase.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Thomas S. Kuntzleman: 0000-0002-2691-288X Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS We wish to thank the many students at Spring Arbor University who tried out many rounds of this student activity, specifically Megan Connors, Nicole Redman, Carly Bender, Jordan Guikema, Tessa Diaz, Ryan Laier, and Ashley Parker.
Figure 5. Separation of activated glow-stick mixtures (left to right: red, orange, yellow, green, blue, and purple) on white Cra-Z-Art brand sidewalk chalks with acetone mobile phase.
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hydrogen-bonding, and ion−ion interactions with the carbonate ions in the chalk. On the other hand, nonpolar BPA would be expected to travel with the mobile phase, because it would be much less attracted to the stationary phase than R6G. It is possible to achieve separation of dyes contained within glow sticks of other colors (Figure 4), and varied effects can be observed using different brands of chalk or different mobile phases (Figure 5). Because these separations occur so quickly, this experiment is amenable to being performed as an in-class demonstration. When doing so, it is advisable to use the larger sidewalk chalk (Figure 5) for greater visibility. Details regarding these additional separations, along with a sample student laboratory sheet, may be found in the Supporting Information.
REFERENCES
(1) Colorful Separations. In Fun with Chemistry: A Guidebook of K12 Activities; Sarquis, M., Saarquis, J., Eds.; Institute for Chemical Education: Madison, WI, 1993; Vol. 2, pp 1−35. (2) Becker, R.; Ihde, J.; Cox, K.; Sarquis, J. L. Making Radial Chromatography Creative Chromatography: For Fun Flowers on Fabrics. J. Chem. Educ. 1992, 69, 979−980. (3) Kandel, M. Chromatography of M&M Candies. J. Chem. Educ. 1992, 69, 988−989. (4) Birdwhistell, K. R.; Spence, T. G. A New Glow on the Chromatography of M&M Candies. J. Chem. Educ. 2002, 79, 847. (5) Buccigross, J. M. T-Shirt Chromatography: A Chromatogram You Can Wear. J. Chem. Educ. 1992, 69, 977−978. (6) Editorial staff. The Write Stuff: Using Paper Chromatography to Separate an Ink Mixture. J. Chem. Educ. 2000, 77, 176A−176B. (7) Kimbrough, D. R. Supermarket Column Chromatography of Plant Pigments. J. Chem. Educ. 1992, 69, 987−988. (8) Kuntzleman, T. S.; Comfort, A. E.; Baldwin, B. W. Glowmatography. J. Chem. Educ. 2009, 86, 64−67. (9) Sheridan, P. M.; Szczepankiewicz, S. H.; Mekelburg, C. R.; Schwabel, K. M. Canisius College Summer Science Camp: Combining Science and Education Experts To Increase Middle School Students’ Interest in Science. J. Chem. Educ. 2011, 88, 876− 880. (10) Yaniv, D.; Heled, H.; Ariel, M. Chemistry is Fun: A Laboratory Program Designed for Inquisitive High School Students. J. Chem. Educ. 1982, 59, 869−870. (11) Kuntzleman, T. S.; Rohrer, K.; Schultz, E. The Chemistry of Lightsticks: Demonstrations to Illustrate Chemical Processes. J. Chem. Educ. 2012, 89, 910−916.
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CONCLUSIONS The activity described herein demonstrates a way to use simple and easily obtainable household materials to separate the dyes contained in glow-stick mixtures. The process can be quickly accomplished on glow-stick mixtures that are actively emitting light via chemiluminescence, allowing for the experiment to be performed as an in-class demonstration. This colorful, illuminating experiment has provided a motivating way to introduce principles of intermolecular forces and chromatographic separations to students in introductory and generalchemistry classes, in science courses for nonmajors, at science camps, and during outreach events. Because of the many C
DOI: 10.1021/acs.jchemed.8b00237 J. Chem. Educ. XXXX, XXX, XXX−XXX
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(12) Milanova, D.; Chambers, R. D.; Bahga, S. S.; Santiago, J. G. Electrophoretic Mobility Measurements of Flurescent Dyes Using On-Chip Capillary Electrophoresis. Electrophoresis 2011, 32, 3286− 3294. (13) Garribba, E.; Micera, G.; Panzanelli, A.; Strinna-Erre, L.; Stara, G. Distinguishing Calcium Carbonate from Calcium Sulfate W Dihydrate by Instrumental Methods: A Set of Laboratory Experiments for Analytical Chemistry and Spectroscopy. J. Chem. Educ. 2001, 78, 1090−1092. (14) The structure of R6G contains N−H bonds. These N−H bonds can act as hydrogen-bond donors to oxygen atoms (which act as hydrogen-bond acceptors) on the carbonate ions in the chalk, forming a hydrogen bond. (15) Wollrab, A. Chromatography on Chalk. J. Chem. Educ. 1975, 52, 809−810. (16) Summerlin, L. R.; Borgford, C. L.; Ealy, J. B. Chalk Chromatography. In Chemical Demonstrations: A Sourcebook for Teachers; American Chemical Society: Washington, DC, 1987; Vol. 2, pp 259−260. (17) Hoffman, R. J.; Nelson, L. S.; Hoffman, R. S. Pediatric and Young Adult Exposure to Chemiluminescent Glow Sticks. Arch. Pediatr. Adolesc. Med. 2002, 156, 901−904.
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DOI: 10.1021/acs.jchemed.8b00237 J. Chem. Educ. XXXX, XXX, XXX−XXX
