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Auburn University Science in Motion

Auburn University Science in Motion. “Microdensity of Plastics”. Introduction:. Density is used to identify substances. Density is found by measuring mass by volume. Density =. Density can be determined by comparison. A low density object will float on top of high density liquid.

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Auburn University Science in Motion

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  1. Auburn University Science in Motion

  2. “Microdensity of Plastics”

  3. Introduction: • Density is used to identify substances. • Density is found by measuring mass by volume. • Density =

  4. Density can be determined by comparison. • A low density object will float on top of high density liquid. • A high density object will sink to the bottom of a low density liquid. • If the density of the object is equal to the density of the liquid, the object will be suspended; neither sinking nor floating. • The density of the object can be determined indirectly by measuring the density of liquid.

  5. Purpose: • Determine the density of a small piece of plastic and used the density to identify the type of plastic.

  6. Equipment/Materials: • 4 inch test tube • Known plastic • Unknown plastic • Micropipet • Micropipet tips • Parafilm • Dropper bottle of saturated KI • Dropper bottle of methanol • Dropper bottle of distilled water • Weigh boats • Analytical balance

  7. Safety: • Always wear goggles in the chemistry lab • Never eat or drink in the chemistry lab. • Avoid any contact with chemicals. • Wash hands after conducting lab.

  8. Procedure • Obtain dropper bottle of methanol, potassium iodide, and distilled water. • Fill the test tube one-third full of distilled water. • Obtain a small piece of a known plastic. • Record its recycling code on the data table.

  9. Carefully place the plastic in the water, trying not to create air bubbles on the surface of the plastic. • If bubbles form, gently tap the side of the test tube with your finger to knock the air bubbles off the surface. • If the plastic floats, add a few drops of methanol. • If the plastic sinks, add a few drops of KI solution.

  10. Cover the test tube with Parafilm, and hold it in place with your finger. • Carefully (to avoid forming bubbles) invert it several times until the liquid is thoroughly mixed so that it is homogeneous. • Keep the open end of the test tube covered with the Parafilm to prevent evaporation of the methanol.

  11. Repeat these steps until the plastic is suspended in the solution. • Once the plastic is suspended in the solution, the plastic's density is equal to the density of the solution.

  12. To find the density of the solution: • Place a weigh boat on the balance and tare (rezero) the balance.

  13. Put a clean tip on the micropipette and remove 1.000 mL of the solution from the test tube; dispense the liquid into the weigh boat.

  14. Quickly record the mass of the solution on the data table. Known Plastic:

  15. Repeat the procedure for a piece of plastic with an unknown density. Record the data for the unknown plastic on the data table. Unknown plastic:

  16. Rinse the used micropipette tips, test tubes and weigh boats with water. Return all unused samples and solutions to the appropriate reagent bag.

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