Question

You will need: seven kinds of plastic containers with different recycle codes, scissors, two cups or beakers, two stirring rods or wooden craft sticks, room temperature water, 70% isopropyl alcohol, graduated cylinder, acetone, 2 plastic pipets, hot plate with a 400 mL beaker of boiling water (student groups may share the boiling water), tongs, and forceps.

Cut a small, flat piece (1.5 cm ´ 1.5 cm) from each container (seven total) and start a data table to record the color and shape of each piece as well as the permanent marker letter label (A–G) your instructor previously marked on each container. If two containers are the same color, cut different shapes (triangle, rectangle, circle, etc.) to help with piece identification. Now you are ready to follow the flowchart. Record your observations in the data table as you go along.

Tap Water Test: Place all seven pieces of plastic in a beaker or cup of room temperature tap water. Stir vigorously with a stirring rod or wooden craft stick to dislodge any bubbles from the plastic pieces. Bubbles tend to adhere to plastics. How would this change the apparent density? Observe and record which pieces sink and which float.

70% Alcohol Test: Remove the pieces that float from the water. Add them to a beaker or cup containing about 20 mL of 70% isopropyl alcohol. Stir. Do the pieces sink or float in the 70% alcohol? How does the density of alcohol compare to water?

Using a plastic pipet, add a squirt of tap water to the beaker containing alcohol. Stir. Do any of the pieces begin to float? When adding water to 70% alcohol, how does the density of the solution change? Keep adding squirts of water and stir until one piece floats. According to the flowchart, what is the identity of this plastic? Remove the piece and record your results.

Add more squirts of water until a second piece floats. Remove the piece and record the identity of the second plastic. You can now identify the third piece since it is still sinking.

Boiling Water Test: Place the four pieces that sank in tap water in the beaker of boiling water for a minimum of 30 s. Using tongs, remove them one at a time and test their flexibility, noting their size and color. Record your results. Which plastics can you now identify using the flowchart?

Acetone Test: Place the final two plastic samples in a small amount of acetone for one minute. Record your results.

Check with your instructor to see whether you correctly identified the seven plastics. You are now ready for an unknown. If your unknown floats in the tap water test, you will need to use the known pieces for PP, HDPE, and LDPE along with your unknown to help you with the identification in the 70% alcohol test.

Table 1. Selected Physical Properties of Common Plastics
Number	Plastic Type and Composition	Density, g/mL	Glass Transition Temperature, °C	Melting Temperature, °C
1	PET or PETE: poly(ethylene terephthalate)	1.38–1.39	60–85	250–265
2	HDPE: high-density polyethylene	0.95–0.97	~ –125	~138
3	PVC or V-poly(vinyl chloride)	1.16–1.35	81–98	200–300
4	LDPE: low-density polyethylene	0.92–0.94	–128 to –30	~138
5	PP: polypropylene (isotactic when all methyl groups are on the same side of the chain)	0.90–0.91	–8	174–177
6	PS: polystyrene	1.05–1.07	80–100	240
7	PLA: polylactic acid (d and l conformations cause numbers to differ)	1.25–1.26	50–80	173–178

Fill out the following table:

Letter Label	Sample’s Color	Sample’s Shape	Floats in Water? (Yes/No)	Sinkers— Boiling Water Results (Note color/shape changes.)	Sinkers— Acetone Test Results (Note texture changes.)	Floaters— Alcohol Test Results (Note number of squirts.)	Plastic Type
A
B
C
D
E
F
G