Oil and Floating Objects
By John Cowens

Adding color accentuates the different densities in this multilayered experiment.

When two liquids are mixed, they will form either a mixture or two separate layers. If solids are placed on liquids, they will either float or sink. Therefore, it's important to know that density is a measure of how much space or volume a certain amount of mass takes up. An object that floats in a liquid has a lower density than that of the liquid.

Hold up a box of pennies and a box of feathers, each weighing two pounds (about 1 kilogram). Ask students, "Which weighs more?" Many students will assume the bigger box weighs more. A two-pound box of pennies takes up less space than a two-pound box of feathers. Feathers have a low density; pennies have a high density.

Making layers with liquids
Here are several experiments that demonstrate properties of density. Some chemicals mix easily with water; they're called solutions and look the same throughout. Others don't mix with water and may clump together to avoid water. In this case, distinct areas or layers usually are seen.

1. In this experiment, three distinct layers should be visible.

   Materials:
   

   • one tall, clear glass or jar
     
   • a measuring cup
     
   • water
     
   • cooking oil
     
   • honey or syrup
     
   • food coloring
     
   • a spoon

   Procedure:
   

   1. Pour two ounces (60mL) of honey or syrup into a tall, clear glass.

   2. Rinse the measuring cup thoroughly with water to remove any syrup residue.

   3. Measure two ounces (60mL) of water, add two drops of food coloring and stir with a spoon.

   4. Gently and slowly pour the water down the side of the glass. The colored water should form a layer on top of the syrup.

   5. Again, rinse the measuring cup thoroughly with water.

   6. Pour about two ounces (60mL) of cooking oil down the side of the glass. Does the oil mix with the water, sink through the water or float on top of the water?

   What Happened?
   When you finish adding the liquids in the glass, you should have three different-colored layers in the glass due to three different densities. A liquid with a high density is heavier than the same volume of a liquid with a low density. The low-density liquid will float on top of the high-density liquid. Which liquid had the lightest density? Which had the heaviest?

2. In this experiment, several distinct layers are created.

   Materials:
   

   • light corn syrup
     
   • water
     
   • vegetable oil
     
   • glycerin (available in drugstores)
     
   • four small glasses
     
   • one tall, clear glass or jar
     
   • food coloring
     
   • a plastic medium-size funnel

   Procedure:
   

   1. Pour 1/3 cup (80 mL) each of corn syrup, glycerin, water and vegetable oil into four separate cups.

   2. Add a few drops of blue food coloring to the corn syrup and red food coloring to the water. Do not color the vegetable oil or glycerin.

   3. Pour the blue syrup into the glass or jar. Try not to let it dribble down the sides.

   4. Use the funnel to pour the glycerin down the inside of the glass. Pour carefully to avoid disturbing the bottom layer. Wash the funnel.

   5. Repeat step four, first adding the red water, then the oil, washing the funnel well between steps. The liquids will stay in separate layers if you are careful not to shake the glass.

   What Happened?
   Each liquid has its own density. The liquids were assembled in order from highest to lowest density. The oil stays on top because it is least dense.

3. Drop a few objects in a tall glass of various liquids and find out which layer "captures" them.

   Materials:
   

   • one tall glass or jar
     
   • a measuring cup
     
   • syrup
     
   • water
     
   • cooking oil
     
   • a coin or a metal washer
     
   • a grape
     
   • a few grains of rice
     
   • a cork

   Procedure:
   

   1. Pour about two ounces (60mL) of syrup into a tall glass.

   2. Rinse the measuring cup with water until no more syrup remains.

   3. Slowly pour about two ounces (60mL) of water down the side of the glass. The water should stay on top of the syrup.

   4. Next, pour about two ounces (60mL) of cooking oil down the side of the glass. It should float on top of the water. You should have three layers in the glass.

   5. Gently drop the coin or metal washer down the side into the glass. What happens to the coin?

   6. Repeat the above step with the grape, grains of rice and cork. Where do they end up?

   What Happened?
   In this experiment, you formed three separate layers because the three liquids have different densities. A liquid with a lighter density will float on top of a liquid with a heavier density. Objects will sink in liquids until they reach a liquid that has a density greater than itself. Another way to think of this is that lighter objects will sit on top of heavier objects. Which object has the highest density? Which object has the lowest density?

4. Discover how to float an egg in water.

   Materials:
   

   • one glass or wide-mouth jar
     
   • one egg
     
   • salt
     
   • warm water
     
   • a spoon

   Procedure:
   

   1. Pour four ounces (240mL) of warm water into the glass.

   2. Carefully place the egg in the glass. What happens to the egg?

   3. Remove the egg from the glass.

   4. Add about 10 spoonfuls of salt to the water. Stir until it all dissolves.

   5. Carefully add the egg to the glass. What happens to the egg now?

   6. If the egg still sinks, add a little more salt until it floats. How many spoonfuls of salt does it take to make the egg float in four ounces of water? Eight ounces? 12? 16?

   What Happened?
   Objects will sink in a liquid if the liquid has a lower density than the object. If the liquid is denser than the object, the object will float. Adding salt to the water created a higher density than the egg, which pushed the egg to the top of the solution.

5. Egg whites can be used to help oil mix with water.

   Materials:
   

   • one clear glass
     
   • cooking oil
     
   • one egg
     
   • a small bowl
     
   • water
     
   • a spoon

   Procedure:
   

   1. Carefully separate the egg and put the white in the bowl.

   2. Fill the glass half-full of water.

   3. Add one or two spoonfuls of oil to the water; watch what happens to the oil.

   4. Pour some of the egg white into the glass and stir. What has happened to the oil now?

   What Happened?
   Oil does not mix well with water since there is a major difference in density between the two liquids. A chemical in the egg white keeps the drops of oil from forming large cohesive clumps, which makes it easier for water to surround the small droplets of oil.

   Did you know?
   When we eat foods that have fats or oils in them, the fat in our blood behaves like the oil in the water and clumps together. Sometimes these clumps of fat get caught in blood vessels and make it difficult for the blood to move through the vessels. The chemical found in egg white is also in some other foods, like eggplant. Can you think of a reason to include such foods in your diet when you eat foods containing fats or oils?

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   John Cowens teaches sixth grade at Fleming Middle School in Grants Pass, OR.

   May, 2005, Vol.35, No.8