Oil and water don't mix

Oil and petroleum products are toxic to people, wildlife, and plants. One quart of motor oil can pollute 250,000 gallons of water, and one gallon of gasoline can pollute 750,000 gallons of water! Used motor oil is the largest single source of oil pollution in lakes, streams, and rivers.

Oil and water experiment

Materials needed

• 2 clear containers with lids (plastic bottles or glass jars work)

• 2 cups of water

• One-half cup of oil (olive, cooking or vegetable oils will all work)

• Liquid dishwashing soap

• Clock or timer

• Permanent marker

• Measuring cup

• Measuring spoon

• Food coloring (optional)

Preparation

• Remove any labels from your containers.

• Use your marker to label the containers: Label the first “Oil+Water” and the second “Oil+Water+Soap.” Write the labels as close to the tops of the containers as possible.

• Pour one cup of water into each container.

Procedure

• 1. Carefully measure and pour one-quarter cup of oil into the container labeled Oil+Water. Allow the container to sit on a countertop or flat surface while you observe the water and oil. Does the oil sink to the bottom of the bottle, sit on top of the water, or mix with the water?

  2. Repeat this step, adding one-quarter cup oil to the container labeled Oil+Water+Soap. Does the oil sink to the bottom, sit on top of the water, or mix with the water?

  3. Carefully add three tablespoons of dish soap to the container labeled Oil+Water+Soap. Try not to shake the container as you add the dish soap.

  4. Make sure the lids are screwed on tightly to each container.

  5. Holding a container in each hand, vigorously shake the containers for 20 seconds.

Observe the contents of each container. Hold them up to a light one at time so you can clearly see what is happening inside the container. Did anything change when you shook the containers? Do the mixtures look the same in both? If not, what is different between them? How would you explain the differences that you observe?

• 6. Set the containers down on a flat surface with plenty of light.

  7. Note the time on your clock or set a timer for 10 minutes.

After 10 minutes have passed look at the contents of the containers and note the changes. What does the oil and water look like in each container? Has the oil mixed with the water? Did the oil sink to the bottom or rise to the top?

It is easy to observe how oil and water do not mix, no matter how much they are stirred. This is because oil is made of carbon and hydrogen atoms that form non polar chemical bonds. Water is made of oxygen and hydrogen atoms that form polar chemical bonds. It’s pretty advanced chemistry! The important part is that oil and water are made of different kinds of chemical bonds that prevent them from mixing.

It’s also easy to observe how oil floats on top of water. Oil is less dense than water, meaning that it will always end up on top, no matter which liquid is added first.

Used motor oil should never be poured on the ground, down the drain or into the storm sewer. Oil cannot be disposed in the trash, but oil filters can be disposed in a trash cart if a hole has been punched in the bottom and all of the oil has been drained out. Motor oil and filters are accepted at Household Hazardous Waste collection events. Used motor oil is also accepted at many tire and lube centers.