Chemistry for Everyone edited by
Chemistry for Kids
John T. Moore Stephen F. Austin State University Nacogdoches, TX 75962
Visual Experiments Illustrating Four Basic Concepts in Chemistry
David Tolar R. C Fisher School Athens, TX 75751
François Saint-Antonin Commissariat à l’Energie Atomique, DRT-DTEM/SMP/LESA, 17 rue des Martyrs, 38054 Grenoble Cedex 9, France;
[email protected] Two to three times a year, a group of teenagers (aged 14–16 years) spends a few days at the laboratories of Commissariat à l’Energie Atomique to find out what scientific research is and what work in science entails. Hoping to engage the interest of these students, I take this opportunity to show them several visual experiments that illustrate some basic concepts in chemistry, including these principles: •
The chemical process of dissolution forms one new, homogenous phase from the mixture of two phases. Water is a solvent.
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Chemical mixing can generate movement.
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Contact between disparate chemical species or compounds induces transformation or reaction.
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Chemical reactions either create heat (release energy as exothermic reactions) or require heat to initiate or maintain chemical reactions (draw energy as endothermic reactions).
What is the best way to describe or illustrate these concepts to students who may not have any idea of what atoms, chemical species, and other terms commonly used in chemistry are? The main idea is to begin with the vocabulary used in ordinary life and then to shift slightly towards terms more dedicated to chemistry. For instance, the term transformation is associated more with an observation, while the term reaction refers more to a mechanism or an interpretation in chemistry rather than an observation.
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Ceramic or porcelain spoon
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Book with images of volcanoes, craters, lava, fumes, sulfur deposits, and other volcanic phenomena (See Selected Bibliography for suggestions.)
The different chemical products can be presented in reference to everyday experience: copper sulfate solutions are used agriculturally for disease control (in France this use is called the Bordeaux mixture as it is commonly sprayed in vineyards to prevent some vine leaves’ diseases), iron-based solutions are found in some volcanic landforms, and hydrogen peroxide is typically used to disinfect superficial skin injuries. Conducting the Experiments These visual experiments consist in connecting liquid puddles of different colors placed on a flat horizontal piece of glass. The phenomena that occur will then be observed and described. What kind of scenario or story can be used for introducing the different experiments? This can be done with a description of what may have been the situation prevailing in Earth’s early, prebiotic history and in the ongoing process of crust formation. The prebiotic life period corresponds to
Materials and Equipment List Only a small amount of equipment is necessary to illustrate these concepts with the help of colors (see Figure 1). •
Blue color: copper(II) sulfate (CuSO4) powder (Crystalline copper sulfate can be used, although dissolution time is longer. Mixing copper sulfate crystals in water while heating reduces the dissolution time.)
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Brown color: iron(III) chloride (FeCl3) in solution (about 27.5–29% FeCl3)
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Transparent or colorless: deionized water or a hydrogen peroxide (H2O2) solution (30% mole/mole)
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Flat glass surface (about 200 cm2 and a few millimeters thick: perhaps a glass tray or the reverse side of a large crystallizing dish)
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Thermometer
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Four plastic drop dispensers (few mL)
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Four glass beakers or Erlenmeyer glass flasks (about 200–300 mL)
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Figure 1. Materials needed for the experiments. From left to right; iron chloride (FeCl3) solution, 4 plastic drop dispensers, deionized water, copper sulfate (CuSO4) solution, and a porcelain spoon. Near the thermometer, one glass beaker contains CuSO4 powder. The other beaker contains CuSO4 crystals, which can be ground up before dissolution or dissolved in hot water. CuSO4 dissolved in water, obtained after the dissolution experiment, is also shown. On the right, the bottom of a large crystallizing dish was used as a flat surface.
Journal of Chemical Education • Vol. 80 No. 3 March 2003 • JChemEd.chem.wisc.edu
Chemistry for Everyone
the chemical phenomena taking place before the advent of living species. Most scientists think that Earth’s landscapes during this time looked similar to volcanic areas encountered today. It can be supposed that water (or more generally, liquids) and fumes may have contained different chemical species. Present-day examples include these phenomena: •
Lakes exist in volcanic craters with colors such as dark blue, clear green, and brown. For instance, the Kelimutu volcano in Indonesia has craters containing liquids of varying colors and chemical composition: a crater containing green liquid is rich in sulfuric acid and ferrous ions, whereas a crater with brown liquid does not contain any acid. When ferrous ions from the green crater flow into the second crater they are oxidized: the green liquid is then changed into a dark red-brown liquid (1).
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Yellow powder from volcanic exhaust fumes is deposited in the surrounding environment. In one example four metric tons of sulphur are deposited each day within the crater of the volcano Kawah Idjen in Indonesia (1).
in science and that simple experiments can lead to the observation of interesting phenomena.
Dissolution Pour about 30 g CuSO4 powder (blue powder) into a glass beaker or flask containing about 150 mL deionized water (colorless liquid). Mix them together with a ceramic spoon until the powder is completely dissolved. A blue liquid (Figure 1) is obtained by dissolution. Keep this liquid for the subsequent experiments. (This dissolving experiment can also be performed by heating the water—notice that heat accelerates the process. Copper sulfate crystals can also be used but they need to be ground up before dissolution. They can be dissolved directly in hot water, but the operation takes longer than with CuSO4 powder.)
During crust formation on Earth, liquids or fumes of chemical species (with varying properties, including color) mixed, either by flow or flooding, with the help of rain or wind, or other climatic and erosion phenomena. It can be easily imagined that small ponds or puddles of different constituents commingled, for example by rain. The following experiments are based on such a situation so as to illustrate some basic concepts in chemistry. Small puddles of different liquid compositions are connected with a few drops of liquid falling like rain between the puddles. This experimental procedure can be described as close to the kind of situations that may have lead to the formation of simple molecules during prebiotic Earth history. Mainly, I use this scenario to lend a sense of reality to the experimental procedure. Moreover, the students get the idea that complex instrumentation is not always necessary
Transport or Movement First, using a drop dispenser, deposit a large puddle of CuSO4 in solution (blue liquid) from the above dissolution experiment on the flat glass. Next, place a large puddle of deionized water (colorless liquid) on the glass, 0.5 cm apart from the blue puddle (Figure 2a). Then, deposit a drop of colorless liquid between the two puddles, so as to link them. Immediately the blue liquid diffuses into the colorless liquid (Figure 2b). The linked puddles are then both blue, but the blue color is lighter as dilution has occurred. Thus, the transportation of the dissolved blue powder (the movement of the blue liquid) has occurred spontaneously without any external help. The same kind of experiment can be obtained with the brown liquid (FeCl3 in solution) and the colorless liquid. Some interesting features can be observed during this experiment with the brown liquid. During the natural mixing, depending on the relative size and geometry of the two initial puddles before being connected, vortexes, spirals, or small whirlpool structures are generated that may last for several minutes. It can then be explained that natural mixing or transportation can generate movement.
Figure 2a. Two large separated puddles of colorless liquid (deionized water) and blue liquid (CuSO4 in solution).
Figure 2b. Diffusion of the blue liquid once connection has been made.
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Transport and Transformation (or Movement and Reaction) Materials needed: FeCl3 in solution (brown liquid), CuSO4 in solution (blue liquid) from the dissolution experiment, two drop dispensers, and a flat glass positioned horizontally. Deposit a large puddle of FeCl3 in solution (brown liquid) and a large puddle of CuSO4 in solution (blue liquid) from the dissolution experiment on the flat glass, 0.5 cm apart (Figure 3, top). Add a drop of one of the two liquids so as to connect the two puddles together. Immediately, the two liquids move towards each other and begin to mix, thus inducing a change of color to green at the contact front (Figure 3, bottom). Hence, it can be stressed that transport can induce transformation. Depending on the concentration, puddle geometry, and relative volumes of the puddles of brown liquid and blue liquid, interesting features can be observed. The contact front can be like a line, but various other contact fronts such as channels, spheres, polygons, and other geometrical structures can be generated, which internally delimit the liquid. Mirroring this geometry, the analogy could be made here that in general, living species can be described as ‘envelope structures containing something’. Reaction and Heat After making sure that both liquids are at room temperature or about 20 ⬚C, deposit a large drop of FeCl3 in solution (brown liquid) on the flat glass. Place the thermometer within this large puddle. Place a small puddle of hydrogen peroxide solution (colorless liquid) about 0.5 cm apart from the other puddle. Add a drop of the colorless liquid: when the connection of the two puddles is made, the colorless liquid rushes into the brown liquid. There is first a color change to dark brown, then small bubbles appear, followed by large bubbles. Direct addition of some colorless liquid drops within the brown liquid induces a large heat production that can be observed with the thermometer: the temperature can rise to 50 ⬚C (Figure 4). Thus, a reaction can induce heat.
Figure 3. (top) Two large separated puddles of brown liquid (FeCl3 in solution) and blue liquid (CuSO4 in solution). (bottom) Formation of the green contact front once connection has been made.
Hazards Read the safety instructions on the bottle containing hydrogen peroxide. Perform several experiments before the demonstration using hydrogen peroxide in order to have an idea of the volumes needed: when sufficient quantities of hydrogen peroxide and FeCl3 are mixed together they can result in large temperature increases due to the great amount of heat generated. Since the reaction produces some noxious vapor, conduct the experiments in a well-ventilated room. Acknowledgments The author is indebted to the French poet Arthur Rimbaud (1854–1891) who wrote a poem about colors; Thibault Fascina, Sébastien Mounier, and Audrey MaretMercier (the young students who first saw these visual experiments and helped me to clarify my talk); Gérard Bourgeois for the organization of the students’ day in the laboratory; the Grenoble team of CEA/Direction de la Communication for the organization and management of the students 290
Figure 4. Reaction between the brown liquid (FeCl3 in solution) and the other colorless liquid (hydrogen peroxide solution). The thermometer shows about 45 ⬚C.
Journal of Chemical Education • Vol. 80 No. 3 March 2003 • JChemEd.chem.wisc.edu
Chemistry for Everyone
visit; François Chorrier, author of Expérience de Chimie Amusante; James Tabony for the careful reading of the initial manuscript. Selected Bibliography Volcanoes and Volcanic Phenomena
1. Kraft, K.; Kraft, M. Volcans, Le réveil de la Terre; Les Quatre Eléments: Hachette, Italie, 1990. 2. Fischer, R. V.; Heiken, G.; Morris, A. K. Volcanoes; Princeton University Press: Princeton, NJ, USA, 1998. 3. Sigurdsson, H.; Houghton, B.; McNutt, S. R.; Rymer, H.; Stix, J. Encyclopedia of Volcanoes; Academic Press: San Diego, CA, USA, 2000. 4. Bardintzeff, J.-M.; McBirney, A. R. Volcanology; Jones & Bartlett Publication: Boston, MA, USA, 2000. 5. Simon, S. Volcanoes; Morrow Junior Books: New York, USA, 1988. (ages 4–8 years) 6. Adams, S.; Jakeway, R.; Donohoe, B. The Best Book of Volcanoes; Kingfisher Books: New York, USA, 2001. (ages 4–8 years) Colors
9. Berthier, S. Les Couleurs des Papillons ou l’Impérative Beauté; Springer Verlag: Paris, 2000. 10. La Couleur; Dossier Hors Série, Pour la Science; No. 7627, Avril 2000. Chemical Concepts
11. Corwin, C. H. Introductory Chemistry: Concepts and Connections, 2nd ed.; Prentice-Hall: Upper Saddle River, NJ, 1998. 12. Moore, J. W.; Stanitski, C. L.; Wood, J. L.; Kotz, J. C.; Joesten, M. D. The Chemical World, Concepts and Applications; Saunders College Publishing: Fort Worth, TX, USA, 1998. 13. Atkins, P. Concepts in Physical Chemistry; W. H. Freeman: New York, NY, 1995. 14. Hansen, L. D.; Garner, J. D.; Wilson, B. J.; Cluff, C. L.; Nordmeyer, F. R. J. Chem. Educ. 1996, 73, 840–842. The Chemistry of Life
15. Kaim, W.; Schwerderski, B. Bioinorganic Chemistry: Inorganic Elements in the Chemistry of Life. An Introduction and Guide; John Wiley & Sons: New York, USA, 1994. Teaching Chemistry to Nonscientists
7. Zollinger, H. Color: A Multidisciplinary Approach; Verlag Helvetica Chimica Acta: Zurich, Switzerland, 1999. 8. Tilley, R. J. D. Colour and Optical Properties of Materials: An Exploration of the Relationship Between Light, the Optical Properties of Materials and Colour; John Wiley & Sons: Chichester, UK, 2000.
16. Schultz, E. J. Chem. Educ. 2000, 77, 1001–1006. Chemical Demonstrations Based on Human Senses Other Than Vision
17. Gettys, N. S.; Jacobsen, E. K. J. Chem. Educ. 2000, 77, 1104A–1104B.
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