JCE Classroom Activities are edited by Erica K. Jacobsen
Instructor Information
JCE Classroom Activity: #99
Clip Clues: Discovering Chemical Formulas
Carmen Fies1 and Diana Mason2* 1Interdisciplinary Learning and Teaching, The University of Texas at San Antonio, San Antonio, TX 78249 2Department of Chemistry, University of North Texas, Denton, TX 76203 *
[email protected] In this Activity, students use their deductive reasoning skills as they identify formulas of unknown elements and compounds modeled by paperclips. Each color of paperclip represents a different element, with linkages between different paperclips in appropriate ratios representing 20 unknowns. The Activity supports formation of a basic understanding of elements and compounds, including allotropes, oxidation states, and diatomic elements. This Activity supports curriculum units dealing with physical and chemical properties of matter, nomenclature, and how various metal–nonmetal compounds form. Prior knowledge of ionic and covalent compounds, diatomic elements, and nomenclature rules are necessary for students to complete this culminating discovery activity. A prior publication in this Journal (1) also uses paperclips and could be used as an introduction to this Activity. The Activity is an alternative to using molecular model kits. “More Things to Try” suggests using the paperclips for balancing equations.
Preparing paperclip models for students.
About the Activity The Activity is low cost, reusable, and a suitable complement to a lecture or stand-alone laboratory. Each group (2–3 students) is given three bags (e.g., small plastic zip-seal bags) of paperclips linked to represent elements and compounds. A carton of 750 variously colored small and large paper clips (2) was used to make seven sets of the bags described below. The color scheme was based on the size of the paperclips available, with large clips for metals and small clips for nonmetals. Students are given clues along with the bags. Using this information, students can identify formulas for the unknown elements and compounds. Naming can be more cumbersome if FeO42− is not known as the ferrate ion, an example of iron(VI). Color images of the linked paperclips in each bag are part of the online supplement to this Activity. Students could use color printouts to make sure their bags contain the correct clips and linkages, or even as a paper-only lab if clips are not available. Table 1. Paperclip Assignment for the Selected Elements with Number and Size Used per Set Yellow (5 large)
Red (7 large)
Black (7 large)
Green (9 small)
Blue (8 small)
Purple (20 small)
sodium
potassium
iron
chlorine
hydrogen
oxygen
perforated
Bag A: blue–purple–purple–blue (H2O2); blue–purple–blue (H2O); blue–blue (H2); purple–purple (O2); purple– purple–purple (O3). Bag B: single black (Fe); black–purple (FeO); 2 blacks–3 purples (Fe2O3); black–3 greens (FeCl3); black–2 greens (FeCl2); 2 reds–black–4 purples (K2FeO4). Bag C: red–purple–red (K2O); yellow–purple–yellow (Na2O); red–purple–blue (KOH); yellow–purple–blue (NaOH); yellow–green (NaCl); red–green (KCl); single yellow (Na); single red (K); green–green (Cl2).
Answers to Questions 1. Answers may vary, but most students will identify Bag A since it contains the two common allotropes of oxygen: diatomic oxygen and ozone. Others might answer Bag B since it contains the most complex compound, potassium ferrate. 2. Six colors of paperclips represent six different elements. There are 14 compounds. 3. Three diatomic elements are present: hydrogen, oxygen, and chlorine. 4. Six. Bag A: none. Bag B: iron(II) oxide and iron(III) oxide. Bag C: sodium chloride, potassium chloride, sodium oxide, and potassium oxide. (Note: students may need to refer to an electronegativity chart to answer questions 4 and 5.) 5. Four. Bag A: water and hydrogen peroxide. Bag B: iron(II) chloride and iron(III) chloride. Bag C: none. 6. K2FeO4. 7. Allotropes of oxygen gas. Allotropes are elements in the same physical state with different structures. 8. Atomic sizes don’t change when ions form, ionic/covalent bonding and single/double bonds are not distinguishable, and geometric shapes aren’t displayed.
This Classroom Activity may be reproduced for use in the subscriber’s classroom.
fold here and tear out
Integrating the Activity into Your Curriculum
References, Additional Related Activities, and Demonstrations 1. Blake, Bob; Hogue, Lynn; Sarquis, Jerry L. Classifying Matter: A Physical Model Using Paper Clips. J. Chem. Educ. 2006, 83, 1317–1318. 2. Paper clip value pack, assorted sizes, assorted colors, pack of 750, item #668-920. http://officedepot.com (accessed Sep 2008). Supporting JCE Online Material at http://www.jce.divched.org/Journal/Issues/2008/Dec/abs1648A.html
© Division of Chemical Education • www.JCE.DivCHED.org • Vol. 85 No. 12 December 2008 • Journal of Chemical Education
1648A
JCE Classroom Activity: #99
Student Activity
Clip Clues: Discovering Chemical Formulas Scientists often use data and observations along with their own reasoning skills to outline a new concept. For example, John Dalton deduced from laws of chemical composition that matter was made of atoms. Dmitri Mendeleev used formulas of known compounds and his periodic table to predict formulas of compounds of elements that had not yet been discovered. In this Activity, you will follow in the footsteps of these and other scientists by using your reasoning skills to identify unknowns. You will be given three bags, each containing a set of colored paperclips that are linked together in specific ways. Each paperclip color represents an element. Each combination of paperclips linked together represents a chemical formula. Your task is to determine which element corresponds with each paperclip color and to determine the chemical formula of each element and each compound modeled by the clips. To solve the puzzle you need to look at all three bags. Top: 2R–BL–4P; P–BL
Top to bottom: 3P 2B; 2P
Bottom: 3P–2BL; BL–2G; 3G–BL; BL.
B–P–B Bag A combinations and colors. P = purple; B = blue.
B–2P–B
Bag B combinations and colors. R = red; BL = black; P = purple; G = green.
Top to bottom: 2G Y; R Y–G R–G R–P–R B–P–Y B–P–R Bag C combinations and col- Y–P–Y ors. G = green; Y = yellow; R = red; P = purple; B = blue.
Try This You will need: three bags of pre-linked paperclips matching the graphics above (obtain from your instructor). Clues In Bag C, one group of paperclips represents the formula of a compound that you can use to season food and another group represents a compound that can serve as a substitute for the first compound. Potassium ferrate is in one of the bags. It is a purple paramagnetic compound that is a powerful oxidant. Paperclips representing metals are larger than those representing nonmetals. __1. Obtain three bags of pre-linked paperclips from your instructor. As you look at the paperclip formulas, do not change the links. Keep the paperclips from one bag separate from those in the other bags. If things get mixed up, the photographs above show which paperclips go with which bag. Work with a group of students as assigned by your instructor. __2. Using the clues above and the particular ways the paperclips are linked together, deduce the formulas of the different elements and compounds as represented by the different colored paperclips. __3. Create a table to record the name and symbol of the element that corresponds with each paperclip color. __4. Discuss with the other members of your group why you think each color corresponds with the element you have chosen for that color.
More Things To Try Use the paperclips to represent a balanced chemical equation for the reaction of the purple element with the black element. You might like to take other unknowns and use the clips to practice balancing equations in a similar way.
Questions 1. 2. 3. 4. 5. 6. 7. 8.
Which bag helped you the most as you figured out which element corresponded with which color? Why? How many elements are represented? How many compounds? How many elements are represented as diatomic molecules? Name those elements. How many binary formulas correspond with ionic compounds? Name those compounds. How many binary formulas correspond with covalent compounds? Name those compounds. What is the formula for potassium ferrate? Which formulas represent allotropes? Define the term “allotrope”. In this Activity, paperclips represent elements and combinations of paperclips represent chemical formulas for elements and compounds. What are some limitations of this model for chemical elements and compounds?
Information from the World Wide Web (accessed Oct 2008) Allotropy. http://www.chemie.de/lexikon/e/Allotropy/ Potassium ferrate. http://www.chemie.de/lexikon/e/Potassium_ferrate/ This compound is important as a “green oxidant” since its byproducts are considered innocuous. Find information on other “green” oxidants or solvents and their uses. This Classroom Activity may be reproduced for use in the subscriber’s classroom.
1648B
Journal of Chemical Education • Vol. 85 No. 12 December 2008 • www.JCE.DivCHED.org • © Division of Chemical Education
