Understanding How Oil Reacts on Water: A Simple Experiment

Posted Fri, 06/12/2020 - 13:48

Originally published on Oct. 21, 2016.  

An oil sheen.
Rainbow sheen, such as the one shown here from a different incident in the Gulf of Mexico, has been spotted near the leaking natural gas well off the Louisiana coast. (NOAA)

Have you ever seen a rainwater puddle on a street and wondered why it seemed to have a rainbow floating on top? That rainbow effect is caused when oil on the street floats to the top of the puddle.

Understanding how oil and water react together is an essential part of the science of cleaning up oil spills. One of the goals of NOAA’s Office of Response and Restoration (OR&R) is to share our scientific expertise and experience. Fostering scientific understanding of oil spills helps everyone prevent and prepare for marine pollution.

Here is a simple experiment for elementary-aged children that can be done with common household items to understand how oil reacts in water.

How Does Oil Act in Water?

Try this slick and simple experiment for elementary school students in class or at home to see how oil behaves with water.

  1. A person pouring a substance into a glass bowl filled with a clear liquid and black spots in it.
    You can also add a little cocoa powder to make the oil look brown.
    Get a large, clear glass bowl and some vegetable oil.

    If you'd like, you can mix a little cocoa powder into the vegetable oil to make it show up better and look more like crude oil.

  2. Fill the bowl with water to an inch or two below the rim.

    Place it on a table, and have everyone crowd around it.

  3. Pour a little oil on the water.
  4. Now, watch what happens.

    The oil, even a little drop, will spread out over the water surface and break up into many little blobs. This will happen very quickly.

All oils are not the same. Different oils, whether diesel for a truck or heating oil for a house or oil for an engine, all spread out at different rates.

A bowl of liquid with a dark substance floating in it.
Here, the oil has spread out and broken up into blobs on the water surface.

Also, note that the oil floats. This seems a simple observation, but it is very important. Since you have a glass bowl, you can see two layers, or phases: oil and water, which do not mix. You have probably seen this before in some bottles of salad dressing. In the bottle of dressing, just like in the bowl, the oil stays on the top and the water stays on the bottom.

When oil is spilled onto the ocean, because it stays on the top of the water in this same way, it can be pushed by the wind in whatever direction the wind is going. Wind, along with currents and tides, are the three main factors that affect the transportation of oil during an oil spill. We look at all three of these to predict where the oil might go and what it might encounter in its path.

OR&R has more experiments and activities for elementary school students and life-long learners on our education page.