Mickey Sarquis1* and Lynn Hogue2
Terrific Science, USA
1 Professor Emerita Department of Chemistry & Biochemistry and
Director Emerita Center for Chemistry Education, Miami University, Ohio, USA
Present address: 1514 Lupine Rd, Healdsburg, CA 95448 USA,
2 Retired Associate Director, Center for Chemistry Education, Miami University, Ohio, USA
One of the most important aspects of teaching any science is to convey the methodology of scientific investigation in such a way that students develop the skills that are fundamental to scientific inquiry and the scientific way of processing information. As students develop their own testable questions about the system being studied, design experiments, collect data, formulate claims that can be substantiated by the evidence, develop multimodal models to represent this understanding, and subsequently share these with others by engaging in open discussion, debate, and scientific argumentation, students become immersed in the scientific endeavor. In the process, students learn to reflect on this discourse and come to challenge their preexisting beliefs and refine their original claims as new evidence becomes available. Examples of these strategies are shared in this paper.
Key Words: Claims and evidence; Chemical education
As chemistry educators who have been touched by Professor Fortunato Sevilla III, we share his drive to inspire, motivate, and share our mutual enthusiasm for chemistry with our students, colleagues, and the general public. We aspire to capture the attention of others by providing positive energy, exuberance, and even certain “magnetic” qualities that are embodied in the charisma of chemistry.
My dear young friends, If I were to present myself before you with an offer to teach you some new game—if I were to tell you an improved plan of throwing a ball, of flying a kite, or of playing leapfrog, oh, with what attention you would listen to me!
Well, I am going to teach you many new games. I intend to instruct you in a science full of interest, wonder and beauty; a science that will afford you amusement in your youth, and riches in your more mature years. In short, I am going to teach you the science of chemistry.
– Professor John Scoffern, 1849, Chemistry no Mystery
A wide variety of actively engaging experiences empowers students to gradually formulate their own understandings about abstract, complex chemical systems. As teachers, we need to make sure we are not dissociating fun, hands-on play from minds-on challenges. We need to broaden our teaching repository by interweaving diverse instructional methods to target different learning styles and engage different parts of the brain. We also need to support our students’ learning by helping them identify misconceptions, by asking higher-level questions, and by providing a safe environment that encourages students to think critically and take risks.
Developing Understanding with Claims and Evidence
One of the most important aspects of teaching any science is to convey the methodology of scientific investigation in such a way that students develop the skills that are fundamental to scientific inquiry and the scientific way of processing information.
While process skills such as observing, sorting, and classifying are important life skills that transcend the discipline of science, science is more than this set of skills; it is a way of looking at, learning about, and interacting with the world. Scientists ask questions, investigate systems, develop methods, and collect data. Next, scientists use information gathered through these actions to formulate claims that can be substantiated by their findings and subsequently shared with the larger community, allowing for open discussion, debate, and scientific argumentation. Scientists must be willing to reflect on this discourse and refine their original claims as new evidence becomes available. The open nature of scientific discourse provides an important safeguard in scientific endeavors.
Students need numerous opportunities to build these skills and experience this process in total. Through experience, the scientific method becomes more than a list they memorize from a textbook, but rather a working system that is an integral part of their lives. Teachers can maximize student learning by selecting meaningful experiences that grab student’s attention, challenge their preexisting beliefs, and encourage the development of testable questions. Careful observation plays a key role in the process as a catalyst for raising questions and as a means to gather evidence. Students will need to think about what they are observing, discuss their observations with peers, ask questions about what they are seeing, and reflect upon their observations.
Let’s consider three different commonly available toys: light sticks (available in a wide array of sizes, colors, and styles available from toy, novelty, and fishing/hunting suppliers), light-sensitive paper (sold commercially under the brands Nature Print® and Sunprint®), and UV-sensitive beads (often described as color-changing beads, are sold by many science and craft suppliers) and see how can students can be engaged in the claim and evidence learning approach to the scientific method as they discover the basic chemistry of these common toys. We would typically recommend that you have the whole class focus on just one of these systems at a time, working in small groups. In this way, students discover a great deal about each system through their own work and by hearing other groups’ observations, questions, and results. Later, by repeating the entire process for the other systems, students gain critical practice applying the methodology of scientific investigation to a series of different questions.
To begin students are asked to explore the assigned system and record their observations. In some cases the materials include instructions for use. If so, students should begin by following those instructions. (This step is especially important for the light-sensitive paper, because without initial instructions, discovering the properties of the paper would be quite difficult.) After the students have explored the system, allow time for discussion. Compiling a list of observations as well as comments and questions is often helpful.
Once students have explored a material, have them work in small groups to decide what else they would like to know about their system. Suggest they think about questions that start with “What would happen if…” Once each group of students has identified and listed some possible questions, have them choose one specific question to explore and design an experiment that could answer this question. Depending on your students’ experience, you may want to structure their work by asking them to answer questions such as the following:
- What is your testable question?
- Is there something you observed about your system that led you to ask this question?
- What materials will you need for your experiment?
- What data will you need to gather in order to provide evidence to answer your question?
- What tools and methods will you use to collect this data?
While we strongly recommend that students develop and investigate their own testable questions, teacher may need to seed the discussion with possible questions particularly when students are new to the methodology. Some examples of testable question might include the following:
- light sticks—How does temperature affect the activated light sticks? Does wrapping a light stick in insulating materials before activating it affect its glow? Do different sizes, colors, or shapes of light sticks last for the same amount of time or emit the same amount of light?
- light-sensitive paper—What effect does a translucent object’s color have when exposing light-sensitive paper? What about objects with different opacities?
- What is the effect of exposing the paper using different types of light sources such as UV, fluorescent light, or light-emitting diodes (LEDs)? What about different colors of light? When exposing the paper to direct sunlight, does the time of day matter? What about the duration of exposure?
- UV-sensitive beads—What happens if UV-sensitive beads are covered with sunscreen of various sun protection factor (SPF) values? What if the beads are covered with fabrics of different opacities? How about sunglasses with various UV ratings? Does clear plastic or glass give a different result than a sunglass lens? What is the effect of exposing the beads using different types of light sources such as UV, fluorescent light, or LEDs? What about different colors of light? How do different colors of LEDs affect different colors of beads?
- Does changing the temperature of the beads affect how long it takes them to change back to white?
Teachers are encouraged to review and approve the proposed experiments before students proceed or set limits in advance based on availability of materials, time constraints, or other classroom management issues. Emphasize that the goal is to collect data that will provide evidence that allows the testable question to be answered. Note that data, along with the interpretation of that data, provide the evidence. As students are working, you may hear comments such as “This isn’t working,” or “My results are wrong.” Evidence is what it is, and the results may be unexpected. Sometimes, no noticeable change occurs in an experiment, and this is valuable information. Depending on the questions being explored, digital photos or movie clips may be a useful form of data for students to collect.
When the experiments are complete, ask students to share their claims and the evidence for their claims and defend them with the rest of the class. Much like the practice in the scientific community, the class is encouraged to openly discuss, debate, and engage in argumentation about the presented evidence. Students must then reflect on this discourse and refine their original claims.
Allowing students to ask and strive to answer their own questions gives them a much bigger stake in the outcomes of their investigations, which in turn leads to improved conceptual understanding.
Because this experience is so important to students’ growth as scientists, we hope you can work such sharing into your schedule. As an alternative to verbal presentations, students can be asked to write a position statement presenting their claim and their evidence for it. These papers could be peer-evaluated for clarity, strength of argument, and other evidence the peer-evaluator might be aware of. Other options include students participating in poster sessions; writing informative letters to their families, younger students, or the school board; or developing PowerPoints or YouTube-style videos. By providing these experiences you will help your students become stronger communicators, an important skill in all careers.
The Chemistry of Our Examples
Light sticks consist of a sealed plastic tube that contains two solutions. One solution is in a thin glass vial within the plastic tube. The light stick is activated by bending the plastic tube, breaking the glass vial so the two solutions can mix. When mixed, the two solutions react, producing light.
The glass vial contains hydrogen peroxide (H2O2), and the solution in the plastic tube contains a fluorescent dye and a phenyl oxalate ester. The ester and H2O2 react first, producing an intermediate compound that transfers energy to the dye molecules. This energy transfer results in ground-state electrons being “kicked up” to a higher energy state called the excited state. The visible glow results as an excited-state dye molecule loses energy as visible light and returning back to the ground state.
In general, the speed of a chemical reaction increases as the temperature increases. (The speed of a reaction is also proportional to reactant concentration.) Typically, two reactants must collide with sufficient energy to overcome the activation energy barrier.
At a higher temperature, a larger fraction of the reacting molecules have sufficient energy to exceed the activation energy and thus react upon collision. Therefore, at a higher temperature, the glow is brighter because the number of molecules reacting is greater. Likewise, at a lower temperature, the lower intensity of the glow indicates the reaction speed is slower. Since each light stick contains a fixed amount of material, the lower the temperature, the longer the light stick will glow but with less intensity. If an activated light stick is stored in a freezer, the rate of reaction becomes so slow that there is very little, if any, perceptible glow. However, when removed from the freezer and warmed, the light stick will give off light, even after being stored for several months.
Light-sensitive paper forms images due to a photographic process called blueprint or cyanotype. Cyanotypes are made by mixing aqueous solutions of potassium ferricyanide and ferric ammonium citrate (green type). This mixture is then coated onto paper, textiles, or any other natural material and dried in the dark. Exposure to UV light (natural sunlight is the traditional light source, but UV lamps can also be used) causes the iron(III) (ferric) ions to reduce to iron(II) (ferrous) ions with citrate ion as the electron donor. The iron(II) ions then react with the ferricyanide ions to form insoluble Prussian blue, which is essentially ferric ferrocyanide [also called iron(III) hexacyanoferrate(II)]. After the above reaction sequence is completed, the print is washed in water to remove the soluble unexposed salts. Upon drying, the final image darkens as a result of slow oxidation in air.
The cyanotype process has remained virtually unchanged since its invention by Sir John Herschel (1792–1871) in 1842. Herschel was an astronomer, and he used cyanotype as a way of copying his intricate notes. He placed his notes over a sheet of blueprint paper and placed the paper in sunlight. Given a long enough exposure time, sunlight exposed the blueprint paper through the white areas of the page, thus creating a “photocopy.” Anna Atkins (1799–1871), a botanist, became the first person to photographically illustrate a book using cyanotypes. Atkins’ book, British Algae: Cyanotype Impressions, uses 424 cyanotypes. The blueprints used in engineering and architecture were originally cyanotypes.
UV-sensitive beads contain pigments that change color when exposed to UV light from the sun or other sources. When removed from UV exposure, they will turn back to their original white or colorless form. The lower-energy pigment molecules consist of two flat planes at right angles to each other. UV light energy causes the two planes to twist into one plane, which is the colored and higher energy form of the pigment. The higher-energy form loses energy in the form of heat, rather than light, to convert back into the lower-energy form.
Exposing UV beads that have been coated with different sun-protection products affects how quickly and deeply the beads change shade. Beads covered with no sun protection product or a low SPF product quickly change to a deep shade. Those covered with a high SPF product remain white or nearly white.
Placing different types of fabric over the UV beads shows that fabrics offer various degrees of UV protection. The density of the weave plays a more important role than the color or type of fabric. Several lines of UV-blocking clothing are commercially available, and UV-blocking laundry additives such as SunGuard™ can be used to treat clothing.
Most plastic sunglass lenses are treated with a coating or contain an additive to block UV light. Sunglasses with a higher UV rating block more UV than those with a lower rating or no specific rating, typically causing differences in how quickly and deeply beads change color. Glass absorbs all high-energy UV light and much low-energy UV light.
The shade created by a building or tree is less protective than clothing and sunglasses. Even in the shade, UV light reflected from the surroundings can reach the beads. If an object is illuminated by sunlight, either directly or indirectly, it is also receiving at least some UV radiation. Going deeper into natural shade will reduce but not eliminate UV exposure. People on beaches and boats often get a suntan or burn even if they are in the shade because of UV reflection off the sand and water.
The temperature of the UV beads also contributes to the intensity of the observed colors. On a hot summer day with high UV levels, the high UV level causes the beads to become colored. The hot day, however, causes the colored beads to thermally convert to white at a faster rate. On a cold winter day with high UV levels, the UV light causes the beads to become colored as expected; however, less thermal energy is available to the colored beads so they are slower to convert to the colorless form. The result is more intensely colored beads on a cold sunny day than on a hot sunny day. The UV conversion to colored and the thermal conversion to colorless are examples of a forward and reverse reaction in equilibrium.
Sarquis, M.; Hogue, L.; Hershberger, S.; Sarquis, J.; Williams, J. Chemistry with Charisma (volume 1); Terrific Science Press: Middletown, OH 2009
Sarquis, M.; Hogue, L.; Hershberger, S.; Sarquis, J.; Williams, J. Volume 2 Chemistry with Charisma; Terrific Science Press: Middletown, OH 2010