Colorful and Creative Chemistry: Making Simple Sustainable Paints

Activity pubs.acs.org/jchemeduc

Colorful and Creative Chemistry: Making Simple Sustainable Paints with Natural Pigments and Binders Jillian L. Blatti* Department of Chemistry, Pasadena City College, 1570 East Colorado Boulevard, Pasadena, California 91106, United States S Supporting Information *

ABSTRACT: This activity presents a simple method for producing sustainable, nontoxic, and environmentally friendly paints from materials purchased at a local grocery store and offers suggestions for experiments to test the properties of the student-made paints. This activity has been used to engage elementary, middle, and high school students in scientific outreach efforts aimed at teaching chemical concepts in a creative way, inspiring the next generation of scientists and educators to use the tools of chemistry toward the development of a sustainable future. In addition to highlighting the important concepts of sustainability and green chemistry throughout the science curriculum, this activity inspires creative thought and uses observational exercises that are essential to the scientific method. Extracting pigments from natural sources teaches students important laboratory techniques while emphasizing chemical concepts, such as polarity and “like dissolves like”. Students begin to see chemistry everywhere and realize that chemistry can be applied to make useful products in a sustainable way. Also discussed is a cutting edge, collaborative experiment for paint analysis through remote access to a scanning electron microscope, which gives students in any classroom hands-on experience with advanced analytical equipment via the Internet. In a wide range of educational settings, students have used their synthesized paints to craft beautiful artwork depicting what chemistry and sustainability now means to them. KEYWORDS: General Public, High School/Introductory Chemistry, First-Year Undergraduate/General, Public Understanding/Outreach, Hands-On Learning/Manipulatives, Inquiry-Based/Discovery Learning, Dyes/Pigments, Green Chemistry, Student-Centered Learning, Organic Chemistry

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INTRODUCTION

In its most basic state, paint consists of something that has color and something that is “sticky” so that it can adhere to a surface. In nature, there are plentiful resources that can be used as natural paint materials. For example, many fruits and vegetables contain pigments that selectively absorb and reflect wavelengths of light in the visible range of the electromagnetic spectrum resulting in beautiful colors. This offers a natural color resource for paints, a “green” alternative to inorganic metal-based pigments.9,10 To make red, blue, and green paint, pigments were extracted from raspberries, blackberries, and spinach (or algae), respectively. Methods were developed to extract the pigment molecules from their biomass source using solvents obtained by buying readily available commercial materials, as the idea was to purchase everything from the local grocery store. A range of solvents disguised as commercial products were tested. Rubbing alcohol (isopropanol) was found to be the best universal solvent for pigment extractions, as it readily dissolves the pigments, evaporates quickly, and is widely available. The goal was to be able to perform the extractions, combine pigment extracts with binder, and paint an art piece in one class period of 50 min, and the activity was optimized

As sustainability is a requisite component for a greener world, it is important that educators incorporate this idea into modern science curricula.1−3 The theme of sustainability should permeate chemical education, as chemistry is a powerful tool that can be used to solve current global issues, including those that impact the environment and society. As such, a major objective in developing this Sustainable Paints activity was to emphasize the concept of sustainability and the 12 Principles of Green Chemistry.4 The goal was for students to learn chemistry in a fun and engaging manner as they experienced the scientific method. The scientific process is dynamic and interactive, and it can begin with an observation about something that affects society.5 In paints, many colors are derived from inorganic pigments containing copper, iron, lead, and other heavy metals, which pose a risk to the environment.6 Recently in this Journal, an outreach activity was described in which the copper-based pigment malachite was synthesized and made into tempurabased paint in a middle school outreach activity.7,8 Although this activity is very practical and illustrates important concepts in inorganic pigment synthesis, the problem of paint toxicity remains. This article describes an engaging chemistry activity that uses nontoxic, environmentally friendly, grocery-storebought materials to make artists’ paints in a classroom setting. © 2016 American Chemical Society and Division of Chemical Education, Inc.

Received: August 4, 2016 Revised: November 5, 2016 Published: December 14, 2016 211

DOI: 10.1021/acs.jchemed.6b00591 J. Chem. Educ. 2017, 94, 211−215

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Activity

Figure 1. Raspberry paint-making process. (A) 15 raspberries and 7.5 mL isopropanol are added to a sturdy mixing bowl and mixed thoroughly using a garlic press. (B) A small portion of the raspberry purée is added to the coffee filter. (C) The coffee filter/purée is placed into the garlic press without folding (coffee filter is wrapped around the purée loosely). (D) The garlic press is carefully squeezed to filter the colored liquid through the coffee filter into the loaf pan yielding the pigment extract dissolved in alcohol. (E) Raspberry pigment extract dissolved in isopropyl alcohol. (F) A hand-held fan is used to evaporate the alcohol solvent. (G) Egg yolk binder is added to the dry pigment extract. (H) The binder and pigment are mixed thoroughly to yield red paint.

the resources at hand to conduct those experiments (see Suggestions for Paint Property Testing section). It is also important that students learn to take rigorous observations in a notebook and connect their results to the broader world of science and find meaning. This activity serves as a platform for students to experience the scientific method early in their education. The Sustainable Paints activity has been implemented in a range of educational settings, including elementary, middle, and high school classrooms through outreach (ages 9−18), in general chemistry undergraduate courses, in undergraduate research,12 and in informal settings, such as Chemistry Day with the Girl Scouts and Boy Scouts (ages 7−9) and in the Pasadena community’s Girls Science Day (ages 11−14). What follows is a description of protocols to make sustainable paints from natural resources, ideas for paint property tests using makeshift apparatuses amenable to the classroom, and possible chemistry topics for discussion through a student worksheet used in outreach. See the Supporting Information (SI) for further details.

accordingly. The slow step of this activity is the alcohol evaporation to isolate the pigment extract. To be efficient in the classroom, a minimal amount of alcohol was used: a ratio of 7.5 mL isopropanol to 15 raspberries (or 15 blackberries or 15 spinach leaves) accomplishes this goal. The only device not obtained from the grocery store was a hand-held fan (3 speed fan, purchased online) used to evaporate the alcohol solvent in the classroom, a clever, inexpensive alternative to a rotary evaporator. Creativity was employed in the design of apparatuses to conduct the experiments in a classroom setting. Notably, a garlic press and coffee filter were used to separate the colorful pigment extract from the crushed biomass (Figure 1). Although there are many natural resources that have the property of “stickiness”, egg yolk was chosen as an ideal binder to make egg tempera paints. Although there are many other natural binders that can be used, egg yolk was the fastest drying, strongest binding substance tested, which explains its widespread historical use in paints.11 Once the pigment has been extracted and dried, egg yolk is added and mixed thoroughly to make paint. It can be diluted to yield different consistencies and colors, but dilution is not necessary. Figure 1 outlines the paintmaking process in which colorful biomass is combined with alcohol solvent and crushed thoroughly using a garlic press (extraction), filtered through the coffee filter and garlic press to separate the biomass residue from the pigment extract (filtration), and the alcohol solvent is evaporated, affording the dried pigment extract that is mixed with binder to make paint. The beauty of this activity is that it can be easily modified to reach a broad range of students at various levels. If desired, this activity can be scaled to make more paints, or by encouraging students to brainstorm other natural pigments and binders, new interesting paints can be made. There are many creative experiments to test paint properties using either makeshift devices or more advanced equipment, such as an electron microscope. Paint property tests are intentionally left openended so that students can design their own experiments and experience the creativity inherent in the scientific method and experimental design. It is so important for young scientists to practice designing their own experiments, which includes using

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THE ACTIVITY The Sustainable Paints activity can be performed in two parts or more, depending on how many paint property experiments are carried out. In the first session of 50 min, students make the artist’s paint (extract the pigment, evaporate the solvent, and combine with the binder) and paint a chemistry-themed art piece. In the following session(s), paint properties are observed, analyzed, and assessed.

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MATERIALS All materials for paint preparation, including apparatuses to extract and evaporate, were purchased at a local grocery store in Pasadena, CA, with the exception of the safety glasses and hand-held fan, which were purchased online. Materials for each paint included a sturdy, nonbreakable glass mixing bowl, 1 egg, 1 garlic press, 1 aluminum loaf pan (8 in. × 3 7/8 in. × 12 15/32 in.), 1 coffee filter, a 15 mL graduated cylinder (or 1 tablespoon measuring spoon), 7.5 mL (∼1/2 tablespoon) of rubbing alcohol, 6 oz. of natural pigment source (blackberries, raspberries, or spinach), 1 small hand-held fan 212

DOI: 10.1021/acs.jchemed.6b00591 J. Chem. Educ. 2017, 94, 211−215

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Activity

SUGGESTIONS FOR PAINT PROPERTY TESTING To mimic the industrial paint fabrication process, experiments to analyze the properties of the newly made paints were carried out. There are many properties that one can test, such as light fastness, drying time, durability, viscosity, and solubility. Paint properties such as texture and cracking/peeling can be observed using an optical microscope or a scanning electron microscope to relate the microscopic properties to the macroscopic properties. Students can also paint on various surfaces (i.e., paper or wood) and test the aforementioned properties in a comparative study. Paints must be durable and stable to light. Furthermore, they should be homogeneous, without cracks, and not prone to peeling. Drying time and light stability of paints are simple observational experiments. Students can study paints hourly/ daily/weekly and record what they see in their notebook. As an example of a creative, inexpensive, student-designed experiment, the paint’s durability was qualitatively assessed using a “tape test”. (See the Supporting Information, Figure S1.) Once the paint dried on a surface, tape was applied to a section of the paint for 5 s and peeled off to see how well the paint adhered to the surface of the material it was painted on.

(three-speed fan), 2 small paper cups for mixing (or beakers), ice cream sticks (wooden) for stirring, a container for the final paint (i.e., small paper cups or weighboats), paper and a paint brush, and safety glasses (see the Supporting Information for additional details).

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TIMING, SUGGESTIONS, AND EXPERIMENTAL NOTES Each color paint takes approximately 45 min to make. A group of 2−4 students can work on a particular color paint, and if time is limited, students can share paints at the end of the activity when creating their art. The slow step is the evaporation of the alcohol solvent, during which time the instructor can point out that the bottom of the pan is cold and describe what is occurring during the evaporation of isopropanol at the molecular level (see the Supporting Information for chemistry topics relevant to this activity). Students are encouraged to paint a chemistry-themed painting and then present each art− chemistry piece to the class, describing in detail their chemical idea and how it relates to green chemistry. A ratio of 15 raspberries:1/2 egg yolk binder is ideal for paint, and it should be noted that the addition of egg yolk changes the color of the pigment. Egg yolk should be poured slowly into pigment with vigorous mixing. Students can alter the yolk:pigment ratio to modify the paint’s texture, drying time, color, and other properties. Students can experiment with dilutions of the egg yolk or the final paint (pigment combined with yolk binder) with water; they can even combine pigments to make hybrid colors. Students can mix the pigment extracts, egg yolk binder, and water in whatever ratio they hypothesize will give desired paint properties. As a modification to the activity, students can bring their own ideas for natural pigments and binders to make paints. Paint properties can then be observed and analyzed. Students are encouraged to be creative in their experiments and record observations in their notebooks.

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PAINT PROPERTY TESTING RESULTS: MICROSCOPY/OBSERVATIONS Microscopy was used to analyze the student-made paints. Remote access13 to an optical microscope allowed students to assess the homogeneity of the paint mixture (Figure 2A). To

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PROTOCOL TO MAKE PAINT The protocol to prepare red paint from raspberries is described below; see the Supporting Information for protocols to make blue paint from blackberries, and green paint from spinach leaves. Raspberries (15) and 7.5 mL (∼1/2 tablespoon) of rubbing alcohol are added to a sturdy, nonbreakable glass bowl and crushed thoroughly using a garlic press (Figure 1A). One can observe the isopropanol solvent extract the red pigment from the raspberry biomass as the liquid becomes a reddish color. To separate the colored liquid extract from the crushed biomass, the raspberry purée is added in small amounts to the coffee filter paper (Figure 1B), and the colored liquid is filtered into the loaf pan by slowly squeezing the garlic press (Figure 1C,D). This is the filtered extract of solvent and pigment (Figure 1E). The alcohol solvent is evaporated using the hand-held fan (Figure 1F); once all of the liquid evaporates, only the pigment extract remains at the bottom of the loaf pan. After about 15 min, the pigment extract should be dry. Using a beaker (or over a sink), egg yolk is isolated and placed in a separate container. One-half of the egg yolk is then slowly added to the loaf pan that contains the dried pigment and mixed thoroughly with an ice cream (wooden) stick to make the paint (Figure 1G,H).

Figure 2. Paint property testing via microscopy. (A) Optical image of raspberry paint; scale bar = 2 mm. (B) Scanning electron micrograph of raspberry paint showing a “microcrack” (128 μm); scale bar = 200 μm.

observe the microscopic nature of the student-made paints, a scanning electron microscope was also remotely accessed from the classroom via the Internet.13 Although obvious “microcracks” appeared when paint was analyzed via SEM (Figure 2B), cracks smaller than 150 μm are not readily observed through the optical microscope (Figure 2A). Analysis of paints by remotely accessing an SEM gives students hands-on experience with advanced instrumentation from their classroom and provides an opportunity for scientific observation and recording of data and results in students’ notebooks. Drying time and light stability of paints are observational experiments that should also be recorded in the students’ notebooks (Figure 3). 213

DOI: 10.1021/acs.jchemed.6b00591 J. Chem. Educ. 2017, 94, 211−215

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Figure 3. Paint property observations: light fastness. (A) Photograph taken at the time it was painted. (Reprinted from ref 12 with permission.) (B) Photograph taken one year after painting, showing fading; certain pigments fade more when exposed to light than others.

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PAINT PROPERTY TESTING RESULTS: LIGHT FASTNESS As an example of a student’s application of this activity to every day commercial materials, β-carotene pills were used as a source of pigment and combined with egg yolk to make orange paint. This was painted on canvas, and light fastness was observed over a one-year period (Figure 3). Another student brought in coffee grinds, ground them with a mortar and pestle, and mixed them with egg yolk to make brown paint. Compared to other pigments, paint made using β-carotene (orange) faded more when exposed to light as observed on the student’s painting on canvas (Figure 3B).

DISCUSSION This chemistry activity is a fun, engaging, creative exercise for students that can be used to teach key chemical principles such as polarity, phase changes, states of matter, intermolecular forces, pigments and colors, and natural product extraction. It introduces important laboratory practices, such as extraction, evaporation, filtration, and dilution, while emphasizing the overarching principles of sustainability, green chemistry, and the scientific method. Although a number of activities in this Journal use pigments and paint to teach chemistry, this activity is uniquely focused on sustainable, natural resources and creativity. Rather than use traditional chemistry glassware, makeshift devices are employed to do the extractions, filtrations, and evaporations in a classroom setting: A nonbreakable glass bowl and garlic press serve as a mortar and pestle as well as a filtration apparatus, and a hand-held fan is used to evaporate the solvent rather than an expensive rotary evaporator. In contrast, remote access to an SEM provides students hand-on experience with advanced analytical equipment, which also inspires and engages them. This Sustainable Paints activity is at the art−science interface, and as such, it evokes students’ natural curiosity and encourages their development as creative scientists. This is incredibly important in science education,18 as creativity and critical thinking will be necessary to solve the distinctive challenges of our time. As Albert Einstein said:19 I am enough of an artist to draw freely upon my imagination. Imagination is more important than knowledge. For knowledge is limited, whereas imagination embraces the entire world, stimulating progress, giving birth to evolution. Imagination is essential to science and its applications, and it should be inspired in any effective chemistry curriculum.18 This hands-on Sustainable Paints activity awakens a student’s awareness of nature and embraces the active learning pedagogy that has been shown to be very effective in science instruction.20,21 With the freedom to explore the chemistry of paint, students arrive at conclusions in their own way, fostering true understanding of chemical principles. A diverse and broad range of students have been taught using this activity, all with different ideas and versions of experiments to test paint properties, and they have always commented on how much fun it was doing chemistry. Enthusiasm is key to persistence in science, and as our nation strives to produce more STEM majors,22 it is necessary for science educators to inspire students, realize aptitude for scientific discovery, and bring out

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MODIFICATIONS TO THE ACTIVITY Students will become curious and more observant of the world around them due to these creative activities and start to see color everywhere in nature. As a result, they may want to bring in other sources of natural color, for example, mulberries from their backyard, and desire to extract the pigment molecules from them. Or, students might identify different natural binders by observing “sticky” things in nature, such as various cooking oils, saps, resins, and so on. This is an opportunity to encourage creativity and problem solving and to inspire student-driven research! Perhaps as a class you can generate a matrix of various binders and pigments, mix and dilute them in different ratios, and create your own unique paint palette. Then, students can design their own experiments to test the properties of their newly made paints, record all observations and results in their notebooks, and present their findings to the class. This activity can be used alongside many other related activities in this Journal to demonstrate chemical concepts through paints, pigments, and color.8,9,14−17 To emphasize the broader impact, students can compare and contrast the natural paints to commercial paints and use this as a platform to discuss the 12 Principles of Green Chemistry.

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HAZARDS

Paints should not be consumed. Evaporation of alcohol solvent should be done in a well-ventilated area. None of the alcohol vapor is meant to be inhaled. If a student has an allergy to eggs, linseed oil or gum arabic can be used an alternative binder. Safety glasses should be worn at all times during this activity to demonstrate proper personal protective equipment to students. 214

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(7) Gaquere-Parker, A. C.; Doles, N. A.; Parker, C. D. Chemistry and Art in a Bag: An Easy-To-Implement Outreach Activity. J. Chem. Educ. 2016, 93, 152−153. (8) Solomon, S. D.; Rutkowsky, S. A.; Mahon, M. L.; Halpern, E. M. Synthesis of Copper Pigments, Malachite and Verdigris: Making Tempura Paint. J. Chem. Educ. 2011, 88, 1694−1697. (9) Orna, M. V. Chemistry, Color, and Art. J. Chem. Educ. 2001, 78, 1305−1311. (10) Brunning, A. Compound Interest. http://www.compoundchem. com/2014/03/21/inorganic-pigment-compounds-the-chemistry-ofpaint/ (accessed Oct 2016). (11) Mayer, R. The Artist’s Handbook of Materials and Techniques, 5th ed.; Viking: New York, 1991. (12) Blatti, J. L.; Cuccinello, A. F.; Juarez, B.; Liang, W.; Lu, J.; Massine, N.; Portillo, J.; Pourmand, E.; Ramirez, A.; Sanchez, V.; Sepulveda-Torres, C. The City of RosesPasadena City College and the Chemistry Research Laboratories. J. Sust. Educ. 2016, 11; http:// www.jsedimensions.org/wordpress/content/pasadena-the-city-ofroses-pasadena-city-college-and-the-chemistry-research-laboratories_ 2016_03/ (accessed Oct 2016). (13) Remote access to a scanning electron microscope (SEM) and other advanced analytical equipment for paint analysis can be facilitated through the Nanotechnology Applications and Career Knowledge (NACK) Network at Penn State University and the Remotely Accessible Instruments for Nanotechnology (RAIN) program. For assistance with this, see: http://www.nano4me.org/ remoteaccess (accessed Oct 2016). (14) Gettys, N. S. Pigments of Your Imagination: Making Artist’s Paints. J. Chem. Educ. 2001, 78 (10), 1320A−1320B. (15) Lech, J.; Dounin, V. Artistic Anthocyanins and Acid−Base Chemistry. J. Chem. Educ. 2011, 88, 1684−1686. (16) Cousins, K. R.; Pierson, K. M. A Simplified Method for the Microscale Extraction of Pigments from Spinach. J. Chem. Educ. 1998, 75 (10), 1268. (17) Johnston, A.; Scaggs, J.; Mallory, C.; Haskett, A.; Warner, D.; Brown, E.; Hammond, K.; McCormick, M. M.; McDougal, O. M. A Green Approach To Separate Spinach Pigments by Column Chromatography. J. Chem. Educ. 2013, 90 (6), 796−798. (18) Gurnon, D.; Voss-Andreae, J.; Stanley, J. Integrating Art and Science in Undergraduate Education. PLoS Biol. 2013, 11 (2), e1001491. (19) Einstein, A. Einstein on Cosmic Religion and Other Opinions and Aphorisms; Dover Publications: Mineola, NY, 2009; p 97 (unabridged republication of Cosmic Religion and Other Opinions and Aphorisms, originally published in 1931 by Covici-Friede, Inc., New York). (20) Handelsman, J.; Ebert-May, D.; Beichner, R.; Bruns, P.; Chang, A.; DeHaan, R.; Gentile, J.; Lauffer, S. Scientific Teaching. Science 2004, 304 (5670), 521−522. (21) Freeman, S.; Eddy, S. L.; McDonough, M.; Smith, M. K.; Okoroafor, N.; Jordt, H.; Wenderoth, M. P. Active Learning Increases Student Performance in Science, Engineering, and Mathematics. Proc. Natl. Acad. Sci. U. S. A. 2014, 111 (23), 8410−8415. (22) PCAST STEM Undergraduate Working Group. Engage to Excel: Producing One Million Additional College Graduates with Degrees in Science, Technology, Engineering, and Mathematics; Gates, S. J., Jr., Handelsman, J., Lepage, G. P., Mirkin, C., Eds.; Office of the President: Washington, DC, 2012. (23) Dweck, C. Mindset: A New Psychology of Success; Ballantine Books: New York, 2006.

passion for science through hands-on, engaging activities. By encouraging students to design their own experiments while providing an open space to “fail” and realize that it is part of the process, we are instilling a resilient and positive mindset,23 which will promote student success as they persist through rigorous science courses. Inspiring creativity in our future scientists will ensure that they imagine clever solutions to global challenges as they dream of a sustainable future fueled by chemistry.

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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.6b00591. Student worksheet used in outreach and additional experimental details, protocols, and results (PDF, DOCX)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Jillian L. Blatti: 0000-0002-6136-222X Notes

The author declares no competing financial interest.

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ACKNOWLEDGMENTS The Chemistry Department at Pasadena City College and the Dean of Natural Sciences, Dave Douglass, are acknowledged for support. All of the students involved in the development and implementation of this activity are recognized for their hard work, dedication, and enthusiasm, especially PCC students Anthony Cuccinello, Jennifer Portillo, Betsy Juarez, Ken Lu, and William Liang. Vince Aguirre, Jr., Lorenzo Ramirez, Vanessa Sanchez, and Carina Sepulveda-Torres were incredibly helpful in remote access experiments. Students who participated in the outreach activities from local elementary, middle, and high schoolsin particular, the APEX Academy (Hollywood, California) and biology instructor Ralph Gomez and his AP biology class are highly appreciated for their participation in sustainable paints outreach and remote access experiments. Research reported in this article was supported by the United States Department of Education under award number: P031C110056-13.

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REFERENCES

(1) McMichael, A. J.; Butler, C. D.; Folke, C. New Visions for Addressing Sustainability. Science 2003, 302, 1919−1920. (2) Graedel, T. E.; Klee, R. Getting Serious About Sustainability. Environ. Sci. Technol. 2002, 36, 523−529. (3) Kirchhoff, M. M. Education for a Sustainable Future. J. Chem. Educ. 2010, 87, 121. (4) Anastas, P. T.; Warner, J. C. Green Chemistry: Theory and Practice; Oxford University Press: New York, 1998; p 30. https://www.acs.org/ content/acs/en/greenchemistry.html (accessed Oct 2016). (5) Understanding Science. http://undsci.berkeley.edu/ (accessed Oct 2016). (6) Tchounwou, P. B.; Yedjou, C. G.; Patlolla, A. K.; Sutton, D. J. Heavy Metals Toxicity and the Environment. EXS 2012, 101, 133− 164. 215

DOI: 10.1021/acs.jchemed.6b00591 J. Chem. Educ. 2017, 94, 211−215