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Polymer Pie

Grades: 11-12, Chemistry
Author: Jessica Cleaver
Source: This material is based upon work supported by the National Science Foundation under Grant No. EEC-1161732.


Abstract

Students should investigate which starches will create the "best" pie. They will first brainstorm what qualities they would like to have in a custard-type pie, they investigate the properties of different commercially available starches like corn and potato in order to develop a recipe for making a "pie filling" sample that exhibits the desired properties. Students can then further investigate how the human body digests the different components of the starch (amylose and amylopectin)


Objectives

What should students know as a result of this lesson?

  • Students should be able to understand and describe the properties of a gel as it relates to states of matter (liquid vs. solid), the concept of a viscoelastic liquids and solids, demonstrate how gels exhibit the Tyndall effect, relate the use of gels to their everyday life

What should the students be able to do as a result of this lesson?

  • Students should be able to relate this lesson to various aspects of their everyday life, they should be able to describe the properties of a mixture and apply this to other mixtures, and use the Scientific Method to solve other problems

Materials

  • Starches (potato, corn, rice etc. available at health food stores)
  • water
  • sugar
  • heat source like a Bunsen burner or hot plate
  • semicircular lenses and hand-held lasers to demonstrate the Tyndall effect
  • refrigerator to store samples
  • Luegel's Reagent for a starch test to test the amylose content
  • Internet access

Procedures

Engagement/Assessment

Pre-assess students understanding of gels by providing samples of several everyday gel products and asking the students to categorize them according to their state of matter. Provide them the opportunity to use some of the same testing methods on a known gel sample such as gelatin and describe the results. Brainstorm the desired properties of a gel for a pie filling and devise a method for preparation and testing. Teacher should provide a "recipe" for pie filling and the students should do the calculations to scale down the recipe and convert to SI units. The teacher should divide the students into groups so that each group can test different types of starch.

Exploration/Assessment

After the teacher approves of the plan, students will carry out an experiment to create gels of the desired consistency.

Explanation/Assessment

Students should explain how the different polymers in the starch (amylopectin-branched polymer and amylose-little branching/linear polymer) affect the final gelation properties of the pie filling. They should create a report showing the properties and results of their experiment including the stability of the gel and how the Tyndall effect is demonstrated. In order to test the starch in the gel, Luegel's reagent can be used along with a colorimeter (if available.) If practical, they could also make a pie using their recipe and fill out a questionnaire (student designed) that evaluates the effectiveness of the recipe.

Elaboration/Assessment

Students should design a way to test for other desired properties such as shelf life. Students interested in health can investigate how different components of starch (amylose and amylopectin) affect the body differently and formulate a pie filling that is healthier for diabetics or people with food allergies.


Prerequisites

A basic understanding of states of matter, dimensional analysis.


Best Teaching Practices

  • Questioning
  • Hands-on/minds-on learning
  • Authentic problem-based learning
  • Real-life situations and problem solving

Alignment with Standards

NGSS Standards:

  • HS-PS2-6 Communicate scientific and technical information about why the molecular-level structure is important in the functioning of designed materials.
  • HS-PS1-2 Construct and revise an explanation for the outcome of a simple chemical reaction based on the outermost electron states of atoms, trends in the periodic table,and knowledge of the patterns of chemical properties.
  • HS-LS1-6 Construct and revise an explanation based on evidence for how carbon, hydrogen, and oxygen from sugar molecules may combine with other elements to form amino acids and/or other large carbon-based molecules.

Common Core Standards:

  • RST.9-10.3 Follow precisely a complex multi-step procedure when carrying out experiments, taking measurements, or performing technical tasks, attending to special cases or exceptions defined in the text.
  • WHST.9-10.2 Write informative/explanatory texts, including narration of historical events, scientific procedures/experiments, or technical processes.

National Standards:

  • Quantifying matter: using metric measuring system, dimensional analysis, significant figures
  • Intermolecular chemical bonding: intermolecular forces that exist between the starches, water, and iodine. There should also be some discussion of how the degree of branching in the starches affects the gel temperature

Ohio Standards:

  • Quantifying matter: using metric measuring system, dimensional analysis, significant figures
  • Intermolecular chemical bonding: intermolecular forces that exist between the starches, water, and iodine. There should also be some discussion of how the degree of branching in the starches affects the gel temperature

Content Knowledge

  • Internet will be used to research many of the structures
  • Vernier colorimeters could be used to rate the "blueness" as an extension if needed
  • Students should gain experience designing and conducting an experiment using the scientific method
  • They should be able to see how differences in structures on a very small scale can affect the macroscale properties of a material

Safety

  • Goggles
  • General safety precautions using hot plates and burners
  • Care with transfer of the starches as they are fine powders and can make the floor very slippery

Applications

Dietary planning and nutrition

Food service

"green" plastics industry


Assessment

Varies with the class environment and level of student: could simply be completing the worksheet, completing a formal lab report according to normal class requirements, or doing the extension projects.


Other Considerations

Grouping Suggestions: Since students will be designing a method for testing properties that are related to health or food service, dividing students into groups of similar interest or future plans makes sense. Make sure that at least one student in each group is strong in math skills.

Pacing/Suggested Time: Most of the gels take about 15 minutes to form but they will need to cool to room temperature to test the proper properties. Altogether, the lab and the research should take approximately 3 40-minute class periods. If the extension of research option is taken, 1-2 weeks additional time to do the projects would be appropriate.


Printable PDF Worksheets

Polymer Pie Worksheet

Polymer Pie Teacher Guide