Students are probably aware that oil and water form separate layers when mixed together, but they may not have thought of this fact in terms of density. They will conduct a simple experiment demonstrating the variable densities of corn syrup, water, glycerin, and vegetable oil. Students will then transfer this concept to an examination of cleanup methods used in the Exxon Valdez oil spill. They will conclude by writing paragraphs hypothesizing what would happen during an oil spill if oil and water were the same density and therefore mixed together easily.

Geography, physical science

Standard 14: "How human actions modify the physical environment"

Two to three hours

• Computer with Internet access
• Blank Xpeditions outline maps of Alaska
• The following ingredients for each pair or group of students working on the experiment (or just for you if you're going to demonstrate the experiment)
  • 1/3 cup (80 milliliters) light corn syrup
  • 1/3 cup (80 milliliters) glycerin (available in drugstores)
  • 1/3 cup (80 milliliters) water
  • 1/3 cup (80 milliliters) vegetable oil
  • 4 small glasses
  • 1 tall, clear glass or jar
  • Food coloring
  • Funnel

Students will

• do the Layered Liquids experiment;
• discuss density and examples they've seen of liquids having different densities;
• examine a map of the Exxon Valdez oil spill;
• hypothesize how an oil spill might be cleaned up;
• view pictures and read about cleanup methods used in the Exxon Valdez oil spill, and answer questions about what they learn; and
• write paragraphs about what it would be like to cleanup after an oil spill if water and oil were the same density.

Have students do the Layered Liquids experiment. If you don't have enough materials, or if you want to save time, do this experiment yourself as a demonstration for the class.

Discuss why the experiment works. Students should understand that the least dense liquid is the one that stays on top. Ask students what would have happened if they had poured the liquids into the jar in a different order.

Discuss the density difference between oil and water. Which liquid is more dense? As students have seen in this experiment, water is more dense than oil.

Ask students if they have seen examples of liquid density differences in the "real world." Perhaps they have noticed oil or other liquids in water puddles on the ground, or maybe they've strained to get the tasty garlicky part of the salad dressing out of the bottle before the oil.

Ask students to think about the relationship between the experiment they have conducted and an oil spill. What do they think happens to the oil that has spilled out of a ship and into the ocean?

Have students use the Prince William Sound: Paradise Lost? Web site to learn about the infamous Exxon Valdez oil spill.

On the home page, students will see a picture of a bird covered with oil. Explain that this is what can happen when an oil tanker spills its oil into the ocean.

Ask students to link from the home page to "Introduction" and then "Overview," and have them look at the map. Explain that this map shows the place where the oil was first discharged into the water and the direction and distance it spread over the course of fifty-six days. They can compare this map to a map of Alaska to see where the spill occurred.

Ask students to hypothesize how an oil spill might be cleaned up. Do they think the fact that oil doesn't dissolve into water would make the cleanup easier or harder than if it completely dissolved into the water? Read students this quote from the Overview page with the map: "Much of the oil was converted by wind-driven mixing of the oil and sea water into an emulsion known as mousse that will not burn and which is very difficult to remove from the surface of the sea or from shoreline." How do they think this "mousse" would affect the cleanup process?

Have students link to "The Cleanup" and then "Methods." Ask them to link to each of the "On the Water" methods to see pictures and read about these four ways of cleaning up the oil spill.

[Note: As a time-saving option, you can have students look at these Web pages in groups and assign each group one cleanup method. Groups can then share their findings with the rest of the class.]

As students look at the pictures and read about each cleanup method, ask them to answer these questions about each one (a good way to do this would be for them to create a chart showing the questions down the left column and the cleanup methods across the top row).

• What does this cleanup method involve? What is done?
• What are the benefits of this cleanup method?
• What are the drawbacks of this cleanup method?

Discuss students' findings as a class. Which cleanup method or methods do they think are the most effective? Which are the easiest? Which take the best advantage of the basic physical properties they have learned about in the experiment?

Ask students to hypothesize what would happen during an oil spill if oil and water were the same density. How might the spill be cleaned up? How might it affect the ocean differently from the way it does now? Have them write paragraphs comparing and contrasting this hypothetical cleanup to the cleanup methods that are used in "real life."

• Have students explore the concept of density further at the Science Museum of Minnesota site. Under "That makes me think," ask students to ponder the second question ("Is a bottle of diet soda more or less dense than regular soda - how could you find out?") and, optionally, to conduct an experiment to test a hypothesis related to this question.
  
  
• Ask students to do this density experiment at home and report on the results (they could do it in class, but you'd have to bring in a lot of eggs—expensive and potentially messy!)

NOAA: Images From the Exxon Valdez Spill
National Geographic Kids: Try This! Layered Liquids
ThinkQuest: Prince William Sound—Paradise Lost?
ThinkQuest: The Sciences ExplorerDensity Experiment
Thinking Fountain: Density