Gak Polymers Grade Level: 8th
This is a micro lesson designed to last one 30‐minute class period (with an additional 15 minutes for English to Chinese translation and questions from the audience). Science/Mathematics Concepts and Conceptual Understanding: o Monomers are molecules able to bond in long chains o Polymers are made up of many monomers linked together Misconceptions students may have: o Students may have trouble grasping that monomers and polymers are both chains of molecules, but represent different levels of complexity. They may also have trouble grasping that the cross‐
linkers themselves are molecules. Science and Mathematics Process/Inquiry Skills: “Gak” (or silly putty) is an example of a polymer made from hydrocarbons joined together by weak intermolecular bonds. Elmer’s glue is the source of hydrocarbons, and sodium borate links monomers together to form the polymer. Students will create “gak” while experimenting with what ratio of Elmer’s glue to sodium borate will produce the greatest “bounce” (height rebounded after dropping from a consistent height). List of Materials: 55% Elmer’s glue solution in water 4% borax solution (sodium borate) Cups Ziplock bags Optional food coloring Safety Precautions: Students should wear goggles and potentially lab aprons, as borax is a bleaching agent and could burn the eyes. Instructional Objectives ‐ Students will be able to: o Create gak using their own ratio of Elmer’s glue to borax solution o Collect data on how high the gak bounces o Make conclusions from class data as to what ratio of elmer’s glue to borax produces the best bounce o
Understand that borax is responsible for cross‐linking molecules in Elmer’s glue together to form polymers Engage Phase: Begin by showing students images or physical examples of structures made out of polymers (plastics, plants, DNA). Explain that all matter is composed of atoms, and that two or more atoms can make up a molecule. Long chains of molecules (or monomers) can be cross‐linked together to form polymers. Questions for students: o What are all of these structures (images or physical examples) composed of? o What is all matter in the world composed of? o When atoms bond together, what do they form? o How are atoms bonded to form molecules? How are molecules bonded to other molecules? Acetate groups in Elmer’s glue cross‐linking with B‐OH groups in borax molecules to form polymers. Explore Phase: Student groups of 4 will be given the attached procedure (below) and access to the materials listed above. Students will record the amount of Elmer’s glue and borax solution they use in their gak, as well as the height the ball of gak bounces when dropped from 50 centimeters. Explain Phase: Students record their “recipe” for gak and height bounced by their gak ball on the blackboard. Instructors will ask students to identify which groups gak was the most successful bouncer. Elaborate Phase: The attached worksheet will allow students to think about polymerization in two different ways, making the connection between the chemical structure on the page and the experiment they just completed. Evaluate Phase: (include rubric) Students will explain on their worksheet why they believe that the correct ratio between Elmer’s glue and borax actually matters, which will allow us to evaluate whether they understand how the two solutions are interacting (polymerizing) to form “gak”. Gak Polymer Procedure 1) Wear goggles and lab aprons. 2) Decide how much Elmer’s glue to use in your “gak” (no more than 50 mL). Measure and pour this amount into your cup. 3) Decide how much of the Borax solution to add to each cup (no more than 30 mL). Measure and pour this amount into your cup. 4) Immediately stir the solutions together using the wooden stick. 5) After a couple of minutes of mixing, the silly putty can be removed from the cup and kneaded with your hands. Knead until the desired consistency is reached. 6) Using a ruler to measure, drop the ball from a height of 50 centimeters. To what height does it rebound? Student Worksheet Elmer’s Glue Molecule Borax Molecule Describe what is happening in the above image. How does this relate to the experiment you conducted today?