Article pubs.acs.org/jchemeduc
Students Doing Chemistry: A Hand-On Experience for K−12 Jodye I. Selco,*,† Mary Bruno,‡ and Sue Chan‡ †
Cal Poly Pomona, Pomona, California 91768, United States Rialto Unified School District, Rialto, California 92736, United States
‡
S Supporting Information *
ABSTRACT: A hands-on, minds-on inquiry chemistry experiment was developed for use in K−12 schools that enables students to combine the chemicals of their choice and observe the results. The chemistry involved is water based and builds upon acid−base, double displacement, and iodometric detection of starch reactions. Chemicals readily available in the supermarket are mixed in zippered bags thus reducing the risks, cost, and lead time for preparation. In this experiment, students experience a variety of indicators of chemical change including changes in texture, temperature, color, and the evolution of a gas. The “mix and match” design of the experiment provides students with a wealth of data that is used to facilitate students’ abilities to develop a testable question as well as plan and conduct their own experiment. This experimentation is fun and engaging while building students’ science content and process skills. KEYWORDS: Elementary/Middle School Science, High School/Introductory Chemistry, Curriculum, Hands-On Learning/Manipulatives, Inquiry-Based/Discovery Learning, Acids/Bases, Descriptive Chemistry, Reactions, Student-Centered Learning
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question to determining the answer, which makes the experience more meaningful to them. Designing an inquirybased9 chemistry experiment that is safe enough for elementary school classrooms10 (where many of the rooms do not have sinks) and accomplishing these objectives was a challenge. Building upon the excellent GEMS experiments “Chemical Reactions” and “Of Cabbages and Chemistry” by Jacqueline Barber at the Lawrence Hall of Science at UC Berkeley11 and the American Chemical Society experiments “Lose the Indicator Blues” and “Heat Up to Some Cool Reactions”,12 a “mix and match” experiment was designed that uses chemicals available from grocery, drug, and home improvement stores. This “experiment” is actually an exploration of what happens when different chemicals are mixed together. All of the experiments use plastic zipper bags13 as reaction vessels to lower cost and reduce risk.
any curricular changes have occurred in schools in response to the national1 and state education standards. California requires that a minimum of 20−25% of instructional time in science be done via “hands-on” activities.2 Although a specific amount of time spent “doing” science is not specified in the National Science Educational Standards,1 California’s requirement is consistent with these recommendations. Previous articles in this Journal detailed hands-on experiments for elementary students3,4 that were relatively narrow experiments designed to answer a single question. A hands-on experience for elementary students is presented here that is inquiry based and broader in scope. The experiment enables students to discover the indicators of chemical change, ask testable questions, and design an investigation to answer their own questions. Although this experience was designed to satisfy the California science standards,5 without modification it is applicable to the standards of many other states including Texas6 and New York.7 Chemistry instruction begins in earnest in California at the 5th grade where the physical science curriculum consists entirely of early chemistry concepts, and the “investigation and experimentation” process skills are fairly sophisticated.5 To meet this challenge, an experience was designed where students, even at the elementary school level, experience chemistry as chemists do. One of the biggest challenges was to get students to generate their own testable questions in science;8 this was partly because of a lack of hands-on experience in the sciences. In this protocol, the students design their own experiments, and then they do those investigations. In this way, students “own” the entire process from asking the © 2011 American Chemical Society and Division of Chemical Education, Inc.
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EXPERIMENTAL OVERVIEW The materials used in this experiment consist of six powders labeled A−F and six liquids labeled 1−6;14 using a single symbol to represent each chemical facilitates data recording. Ingredients used in this experiment are presented in Table 1 and the experimental setup is shown in Figure 1. One teaspoon each of two different powders is placed into a sandwich sized zipper bag and the powders recorded. Approximately 15 mL of a liquid is poured into a small plastic condiment cup, and the identity of the liquid is recorded. The cup with the liquid is placed into the zipper bag without mixing it with the powders. Published: December 13, 2011 206
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Table 1. Ingredients Used in This Experiment Powders Epsom salts Baking soda Calcium chloride anhydride Powdered lemonade Washing soda (sodium carbonate) Cornstarch
Table 2. Samples of Student Data for This Experiment
Liquids
Liquid
Vinegar and red cabbage juice Water and red cabbage juice Lemon juice and red cabbage juice Baking soda solution and red cabbage juice Washing soda solution and red cabbage juice Diluted tincture of iodine
1 2 5 3
Powders A A A B
+ + + +
B B C C
Observation Got Got Got Got
hot, turned green hot, turned green, fizzed, bag exploded hot, turned pink, got squishy cold, turned purple, smelled like lemons
Addition of tincture of iodine (which contains the I3−ion) reacts with starch to yield a blue-black color. Temperature changes also occur. Not only do the chemical reactions have associated enthalpy changes, the solvation of anhydrous calcium chloride is exothermic, and the solvation of magnesium sulfate heptahydrate is endothermic. When calcium chloride anhydride and cornstarch are combined with any of the liquids, the contents become hot enough to “cook” the starch, which results in the formation of a gel. These changes are easily noticeable upon mixing. Over 100 teachers in elementary and middle schools have used this experiment. They report that the students are excited about observing the chemical changes and are especially entranced by reactions that result in a texture change or the evolution of a gas. Having students randomly combine chemicals to observe what happens enables them to become chemists and ensures their ownership of the experiment. When asked to develop a testable question, students have difficulty because they do not understand what these might be. To ensure that the student-generated questions are appropriate (in this case, defined as a question about a single variable that has a yes or no answer), each group states their question and receives feedback from the instructor about their question. This feedback might be “that requires too many additional experiments to answer” or “that question does not have a yes or no answer”. Samples of acceptable questions are presented in Table 3. To assist students with low skills in English or the
The air is squeezed out of the bag, and the bag is zipped shut. The materials are then mixed together; observations are made with all senses, except taste, and are recorded. (Details about the materials and procedures are available in the Supporting Information.) Samples of student data for this experiment are shown in Table 2. Each small group of students (2−6) performs 10 different tests with randomly chosen sets of chemicals and records their data. This takes the group about 10−15 min. After performing 10 tests, the data from each group is shared with the entire class (e.g., by using white boards, museum walk, or iGoogle survey) to generate a large amount of class data quickly. Depending upon how quickly students work, the sharing of data may need to occur the next day. Students are asked to examine the data with the goal of generating a testable question. To limit the amount of time spent and materials used, the studentdeveloped testable question is restricted to an investigation in a single variable (e.g., using powders A and B, but using each available liquid). An alternative way to present the limitation is to have the students come up with “a testable question that has a yes or no answer and that can be answered with 5 additional tests or less”. Student groups are usually able to generate an appropriate testable question within 5 min. Students then decide which tests need to be done to answer their questions, and then do those tests. This last portion of the experiment is the quickest; it takes less than 5 min.
Table 3. Examples of acceptable testable questions
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When A and B are used with any available liquid, does it always turn green? When C and 4 are used with any other powder, does it always get hot? When F and 6 are used with any other powder, does it always get gooey? When A and D are used with any available liquid, does it always form a hard rock?
HAZARDS Most of the ingredients will cause irritation to eyes, but are not harmful as they are common foodstuff. RESULTS AND DISCUSSION The materials were chosen so that the chemical reactions involve acid−base chemistry, evolution of a gas, precipitation reactions, texture change reactions, temperature changes, and the iodine detection of starch. The bases are carbonates that react with acid to produce CO2 gas. The red cabbage juice added to the solutions is a universal indicator and results in easily observable color changes upon pH change. Reaction of magnesium sulfate heptahydrate or calcium chloride anhydrate and a carbonate (either a liquid or powder) results in magnesium or calcium carbonate, which are insoluble and “clump up” into a single solid piece within the zipper bag.
language of the discipline, students could complete the sentence frame, “If I use _______ and _______ will it always _______ (an observed change)?” However, even before students are formally asked to generate testable questions for the experiment, they are already informally asking testable questions such as, “Does A always make it cold?” or “When F is used, does it always get hot?” After one group or the teacher states a question that holds two of the chemicals constant, the rest of the student groups easily generate an acceptable testable question. The instructor checks to ensure each student group are asking a different question.
Figure 1. Setup of this experiment for a classroom with (left) the powders labeled A−F and (right) solutions labeled 1−6. 207
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Students then determine a set of tests to answer their question (see Table 4 for an example) and then do those tests.
giving the impression that chemistry can be done only under carefully prescribed conditions that allow us to describe the reactions we observe. Of course, this is not true!
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Table 4. Experiments To Answer the Testable Question, “When A and B Are Used, Does It Always Turn Green?” Liquid 1 2 3 4 5 6
Powders A A A A A A
+ + + + + +
B B B B B B
REFLECTION IN THE DISTRICT EXAM A newly developed district-wide 5th grade examination on the chemistry unit was first administered in 2009−2010. Approximately 27% (454) of the 1664 5th grade students in the district did the experiment detailed here during 2009−2010. The six exam questions pertaining to this topic are presented in Figure 2. There are two numbers presented in parentheses; the bolded, first number indicates the responses of the 454 students that participated in this experiment and the second number indicates the responses of the other 1210 students in the district. The correct answer is labeled with an asterisk. A preliminary analysis indicates that of 4 of the 6 questions addressed by this experiment (questions 1, 2, 5, and 6 in Figure 2) at least 52% of the students throughout the district that did this experiment were able to correctly answer the questions. For two of the questions (questions 3 and 4 in Figure 2), it is unclear why so many students answered these questions incorrectly. Although the most popular answer to question 4 in Figure 2 is the correct one, the correct answer is “all of the above” which is more difficult for students to correctly identify. A comparison of the students’ responses to the questions on the benchmark exam questions (Figure 2) is shown in Table 5. Students who had performed this experiment tended to answer the questions correctly more often than those who had not, with the exception of question 4. The correct answer to question 4 is “all of the above”, which proved as difficult for both sets of students. The large number of students choosing answer A to question 3 probably indicates a misconception: many students (and probably their teachers) think that dissolving something in water is a chemical process.
Observations Got hot, turned greena Got hot, turned green, fizzed, bag explodeda
a
Note that some of these tests have already been done and were used to generate a question.
Elementary school students easily determine which experiments need to be done to answer their question. Even weeks later, students remember their question, what experiments they performed, and the answer to their question. After performing this experiment, everyone wants to know which chemicals were used. Many students report doing additional “experiments” at home as the materials are readily available to them. This experiment has been used with students in both elementary and middle school; the experiment satisfies educational standards for multiple grades. The conversation with different ages of students needs to focus upon different aspects of chemistry mandated by the standards. Elementary school students in California are required to be able to tell whether a change in matter is the result of a physical or chemical change, so the conversation focuses upon the indicators of chemical change. Students readily volunteer the list of changes observed during this experiment: changes in temperature, texture, color, the evolution of a gas, and the formation of a new solid. The spiral curricular model in California revisits these ideas in greater depth in middle and high school. The older students also need to know about the observable properties of acids, bases, and salts. The inclusion of a universal indicator provides information about the pH of the beginning solution as well as final pH of the mixture. Middle and high school students in California also need to know about the conservation of matter and that chemical processes have energy changes associated with them. The use of a balance can prove that mass is conserved, even when the reaction is carried out in a zippered bag and a gas is formed. Students can easily prove to themselves that gases have mass by releasing the collected gas and reweighing the bag. Additionally, temperature changes are easily noticeable and measurable. At the high school level, more quantitative analyses are required, but can still be done within this experimental design. The tincture of iodine/starch reaction is included in this exploration even though it is not part of the chemistry instruction because elementary students learn how to detect starches while studying life science or biology to verify the presence of starch formed during photosynthesis. One advantage of this experiment is that there are many different things that happen and can be observed. Virtually every combination results in some sort of observable change. This was a surprise! Upon reflection, it is probably because this experiment does not really “conform” to the way chemistry is often taught. The reactions inscribed in texts document the deconvolution of the work of many generations of chemists,
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CONCLUSIONS There are many advantages to using “supermarket” chemicals: they are readily available, they are usually less expensive than purchasing the same materials from science supply stores, they tend to be less dangerous than most science supply stores’ chemicals (which is a distinct advantage at the elementary school level), and they are less intimidating for many of the teachers to use. Because fairly large quantities (teaspoon) are used, there are no real “contamination” issues; if no running water is available, the condiment cups can be rinsed in a pail of water between experiments without greatly affecting the results. The products, condiment cups, and zipper bags can be safely disposed of in a trash can. Lastly, the ongoing use of this experiment is sustainable by K−12 schools as the materials are both readily available and inexpensive. Students enjoy this experiment. Its design is accessible even to young learners. When participating in this experience, they become excited about chemistry and want to do more. The students are allowed to be “real” scientists in that they actually “do” chemistry and become chemists. This results in students taking ownership in the investigation as evidenced by their recall of details weeks later. Students report feeling important when asked to come up with a “real” scientific question; all of which is based upon the work they have already done. After a testable question has been modeled, the students are always able to generate a question of their own. Students even as young as nine years of age can consistently generate the 208
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Figure 2. Questions on school district benchmark exam for 5th grade pertaining to chemical changes; the correct answer is marked with an asterisk. The first percentage indicates the responses of the 464 students that participated in this experiment, and the second indicates the responses of the other 1210 students in the district.
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Table 5. Comparison of the Answers from Students Who Did the Experiment versus Those Who Did Not Ab (%) Question 1 2 3 4 5 6
a
B (%)
C (%)
D (%)
Did Exp
Did Not Do Exp
Did Exp
Did Not Do Exp
Did Exp
Did Not Do Exp
Did Exp
Did Not Do Exp
62.3* 5.5 36.3 20.0 52.0* 31.5
51.9* 12.6 32.1 22.8 43.2* 27.0
19.4 12.8 11.0 28.2 13.2 8.1
23.0 13.6 16.7 24.4 16.0 15.9
12.6 61.7* 26.2 20.3 13.4 51.8*
15.0 50.4* 27.8 21.9 21.1 45.3*
4.8 19.4 25.8* 30.8* 20.7 7.9
10.3 29.0 23.2* 30.9* 19.7 11.7
a
Of the 1664 students in the school district, 464 students that participated in this experiment and 1210 students did not. bCorrect responses are marked with an asterisk.
“experimental design” to answer their question without help from adults. Being able to develop their own questions provided students with a memorable scientific experience that stays with them beyond the end of the school day. Hands-on, minds-on inquiry experiences such as this are invaluable in generating interest in students in the content they are expected to learn in school and, more importantly, in becoming scientists when they get older.
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information to answer a question abut the results of an experiment; select appropriate tools and make quantitative observations; record data using appropriate graphic representations and make inferences based on those data; draw conclusions from scientific evidence and indicate whether further information is needed to support a specific conclusion; and write a report of an investigation that includes conducting tests, collecting data or examining evidence and drawing conclusions. (6) Texas Science Standards: http://ritter.tea.state.tx.us/rules/tac/ chapter112/index.html (accessed Nov 2011). (7) New York Science Standards: http://schools.nyc.gov/ Academics/Science/EducatorResources/ NYC+Scope+and+Sequence+for+Science.htm (accessed Nov 2011). (8) Middlecamp, C. H.; Nickel, A.-M. L. J. Chem. Educ. 2005, 82 (8), 1181−1186. (9) Bruck, L. B.; Towns, M. H. J. Chem. Educ. 2009, 86 (7), 820− 822. (10) Science Safety Handbook for California Public Schools, California Department of Education: Sacramento, CA, 1999; available at http:// www.cde.ca.gov/pd/ca/sc/documents/scisafebk.pdf (accessed Nov 2011). (11) Barber, J. “GEMS Great Explorations in Math and Science”, Lawrence Hall of Science, UC Berkeley available at http://www. lhsgems.org/gemsguidestopic.html#Chemistry (accessed Nov 2011). (12) Kessler, J. H. J. Chem. Educ. 2004, 81 (10), p 1398−1399 and experiments posted at http://www.inquiryinaction.org (accessed Nov 2011). (13) Criswell, B. J. Chem. Educ. 2006, 83, 1167−1169. Robinson, M; Barrow, G. M. J. Chem. Educ. 1992, 69 (12), 1026−1027. (14) This setup has also been used in the ACS U.S. National Chemistry Olympiad lab exams; http://portal.acs.org/portal/acs/ corg/content?_nfpb=true&_pageLabel=PP_ SUPERARTICLE&node_id=1017&use_sec=false&sec_url_var= region1&__uuid (accessed Nov 2011).
ASSOCIATED CONTENT
S Supporting Information *
Detailed information about the preparation of materials, student directions, and some of the chemical changes observed. This material is available via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected].
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ACKNOWLEDGMENTS This experiment was originally developed for a professional development workshop for Rialto Unified School District 5th grade teachers supported by a California Mathematics and Science Partnership (CaMSP) grant sponsored by the California Department of Education. We thank the Rialto Unified School District administrators for their support of the teachers, the teachers and students for helping us refine the original experiment, and Ed D’Souza for having the wisdom to make us a teaching team.
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REFERENCES
(1) National Science Education Standards; National Academy Press: Washington, DC, 1995; available at http://www.nap.edu/openbook. php?record_id=4962 (accessed Nov 2011). (2) Curriculum Development and Supplemental Materials Commission; Science Framework for California Public Schools; California Department of Education: Sacramento, CA, 2003, p 11. Available at http://www.cde.ca.gov/ci/cr/cf/documents/scienceframework.pdf (accessed Nov 2011). (3) Borer, L. L. J. Chem. Educ. 1977, 54, 703. (4) George, A. J. Chem. Educ. 1983, 60 (2), 129−130. (5) California standards, Science Content Standards for California Public Schools; California Department of Education: Sacramento, CA, 2003. Available at http://www.cde.ca.gov/be/st/ss/documents/ sciencestnd.pdf (accessed Nov 2011). The California process skills at the 5th grade include requirements that students develop a testable question; plan and conduct a simple investigation based on a studentdeveloped question and write instructions others can follow to carry out the procedure; identify the dependent and controlled variable in an investigation; identify a single independent variable in a scientific investigation and explain how this variable can be used to collect 210
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