Teacher Notes
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Teacher Notes![]() Recycling Plastics by DensityStudent Laboratory KitMaterials Included In Kit
Corn oil, 500 mL†
Ethyl alcohol 250 mL†‡ Glycerin, 500 mL† Sodium chloride solution, 10%, 500 mL† HDPE #2: Plastic sheet, 3" x 3"* LDPE #4: Round bottles, 4-oz, 2* PETE #1: Soda bottle, 1-L* PP #5: Medicine cups, 4 PS #6: Disposable Petri dishes, 2* PVC #3: Black plastic disks, 2* Weighing dishes, 6 *“Unkown” plastic samples †Liquids for density determination ‡See Prelab Preparation. Additional Materials Required
Water, distilled or deionized, 1 L†
Beakers or cups, 150-mL, 5 (may be shared) Forceps Metric ruler* Paper towels Rinse beaker, 400-mL Scalpel or file (see Lab Hints) Scissors, heavy-duty* Wash bottle *See Prelab Preparation. †Liquid for density determination Prelab PreparationUnknown Plastic Samples, A–F: Assign each type of plastic a random letter code A–F, and record the code in a notebook or file for this experiment. Use heavy-duty scissors and a metric ruler to cut the plastic samples supplied with the kit into 1-cm squares. (Remember to keep each type of plastic separate.) Label six large weighing dishes A–F and place the cut up plastic squares into their respective weighing dishes. Safety PrecautionsEthyl alcohol contains a denaturant and is toxic by ingestion. It is a flammable liquid and a dangerous fire risk—keep away from heat, flames and other sources of ignition. Do not use a Bunsen burner in the lab when working with flammable solvents. Please observe all normal laboratory safety guidelines. Wear goggles or safety glasses whenever working with chemicals, heat or glassware in the laboratory. Please review current Safety Data Sheets for additional safety, handling and disposal information. Remind students to wash their hands thoroughly with soap and water before leaving the lab. DisposalPlease consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. Corn oil, glycerin and the sodium chloride solution may be saved for future use. The ethyl alcohol solution may be disposed of by rinsing down the drain with plenty of excess water according to Flinn Suggested Disposal Method #26b. (Evaporation of ethyl alcohol during the course of the experiment will change the density of the solution and may alter the results of the experiment.) Lab Hints
Teacher Tips
Correlation to Next Generation Science Standards (NGSS)†Science & Engineering PracticesDeveloping and using modelsDisciplinary Core IdeasMS-PS1.A: Structure and Properties of MatterHS-PS1.A: Structure and Properties of Matter Crosscutting ConceptsScale, proportion, and quantityStructure and function Performance ExpectationsMS-PS1-1. Develop models to describe the atomic composition of simple molecules and extended structures. Answers to Prelab QuestionsThe following flow chart describes the order in which the density tests will be done. All plastics will be placed in water. If a plastic floats in water, it will be tested next in ethyl alcohol solution. If it sinks in water, it will be tested next in sodium chloride solution. The “path” for each plastic will be different, based on whether it floats or sinks in a given liquid.
Sample Data{12554_Data_Table_2}
Answers to Questions
ReferencesThis activity was adapted from Flinn ChemTopic™ Labs, Vol. 21, Polymers; Cesa, I., Editor; Flinn Scientific Inc.: Batavia IL (2006). Recommended Products
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Student Pages
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Student Pages![]() Recycling Plastics by DensityIntroductionThe United States produces almost 100 billion pounds of plastics every year. In 2005, only about 4% of this amount was recycled—considerably less than the recycling rate for either paper (45%) or glass (23%). Recycling plastics is a special challenge because of the number of different plastics in everyday use. Let’s investigate the composition and properties of plastics and their recycling codes. Concepts
BackgroundMost plastics are obtained from byproducts of petroleum refining and natural gas processing, such as ethylene (CH2=CH2), propylene (CH3CH=CH2), and styrene (C6H5CH=CH2). Manufacturing plastics consumes nonrenewable resources and requires large investments of energy. Disposing of plastics is also an environmental concern, because most plastics are non-biodegradable. It has been estimated that it would take more than five years for a discarded plastic milk jug to decompose when exposed to environmental conditions. {12554_Background_Table_1_Recycling Codes for Plastics}
*This range is for rigid PVC, which normally contains fillers. Plasticizers are added to make flexible PVC, which has a lower density. Experiment OverviewThe purpose of this experiment is to identify unknown plastics based on their densities. The density range for each plastic will be determined by testing whether it floats or sinks in a series of liquids having different densities. All of the plastics will be tested first in water (d = 1.0 g/mL). A plastic that floats in water will then be tested in 35% ethyl alcohol (d = 0.94 g/mL), and in corn oil (d = 0.91 g/mL), if necessary, until the plastic sinks. A plastic that sinks in water will be tested in 10% sodium chloride solution (d = 1.07 g/mL) and in glycerin (d = 1.25 g/ml), if necessary, until the plastic floats. See the flow chart in the Prelab Assignment. Materials
Corn oil, 90 mL*
Ethyl alcohol in water, 35% w/w, 90 mL* Glycerin, 90 mL* Sodium chloride solution, 10%, 90 mL* Water, distilled or deionized (DI), 90 mL* Beakers or cups, 150-mL, 5 Forceps Metric ruler Paper towels Scissors, heavy-duty “Unknown” plastic samples, cut into uniform 1-cm square pieces, labeled A–F (e.g., plastic containers, bottles, bags, toys, cards) Wash bottle *Liquids for density determination (one set may be shared) Prelab QuestionsThe flow chart in Figure 1 describes the order in which the density tests will be done. All plastics will be placed in water. If a plastic floats in water, it will be tested next in ethyl alcohol solution. If it sinks in water, it will be tested next in sodium chloride solution. The “path” for each plastic will be different, based on whether it floats or sinks in a given liquid. {12554_PreLab_Figure_1_Flow chart for the identification of plastics based on density}
Safety PrecautionsEthyl alcohol solution contains a denaturant and is toxic by ingestion. Please observe all normal laboratory safety guidelines. Wear goggles or safety glasses whenever working with chemicals, heat or glassware in the laboratory. Wash hands thoroughly with soap and water before leaving the lab. Procedure
Student Worksheet PDF |