You may have noticed shiny oil floating on a water puddle after it rains. In this experiment, we will play with oil and water, two things that do not naturally mix, to learn how to treat oil spills and care for the ocean.
Materials:
Two plastic containers
Vegetable oil
Dish soap
Spoon
Paper towel
Cotton cloth or cotton balls
Time Estimated:
10 minutes
Directions:
Fill the plastic bowl with about ¾ full of water, then add about two spoons of vegetable oil to simulate a body of ocean water polluted by an oil spill.
It’s time to try out our different methods to clean up the mess! Throughout this experiment, you can observe and compare the three methods we will test.
First, carefully use a clean spoon to scoop oil off of the water’s surface, and collect the oil in another container. Notice how long it would take to remove all the oil!
Then, refill the water with two spoons of oil. Let’s try our second method by using cotton balls and paper towels to absorb oil.
Again, refill the water and add another two spoons of oil. This time, pour dish soap into the oily water. Use your spoon to stir and mix it up to see what happens!
Think Like a Scientist!
Compared to salt, which dissolves in water, what property of oil makes it able to be recovered from water?
Which method did you observe to be the most efficient and why?
How Does It Work?
It is possible to scoop out or absorb oil from water because the two do not mix together, as water molecules are polar while oil is nonpolar. A polar molecule has a positive charge on one end and a negative charge on the other. One water molecule's positive end is attracted to another's negative end to form strong hydrogen bonds. In contrast, oil molecules are nonpolar, meaning their charge is evenly distributed and therefore not attracted to the water molecules. As a matter of fact, oil molecules are hydrophobic, or “water fearing,” in that they will actually get repelled by water molecules. This is why when you add oil to water, they will not mix together.
In addition, because oil molecules are more loosely packed, they can take up more space with fewer molecules, so the oil has a lower density and less weight for the same volume compared to water. Buoyant force is an upward force on objects in a fluid and equals the weight of the fluid displaced. For instance, when you add two spoons of oil to a full cup of water, the oil will displace two spoons of water. Since the oil weighs less than the water, the buoyant force of the displaced oil is less than water so it will float on top. The hydrophobicity and lower density of oil are two properties that allow it to now mix with water and make it possible for us to use a spoon, or a skimmer, to easily remove it from the surface of the water.
The cotton balls and paper towels we used in our second method are sorbents or insoluble materials that can also recover oil. Cotton balls absorb oil by picking up and retaining liquid, including oil and water, that will distribute throughout its molecular structure and cause the cotton to swell. An ideal sorbent would be both oil-attracting and hydrophobic so that it can only remove oil without taking out too much water.
Lastly, dish soap represents a dispersant chemical that can break down oil into smaller droplets to mix with water. The chemical contains molecules that have water-compatible ends to bind with water and other oil-compatible ends to bind with oil. This way, oil is chemically able to bind with water with the mediation of this chemical. So, when we add soap to the oily water and stir it up, we will see the oil broken down and mixed with water.
Further Exploration:
The three methods we tested are common ways to treat oil spills in the ocean. An oil spill is an accidental leakage of oil that can harm many marine lives, as it can block sunlight and reduce oxygen levels in the ocean. Each of these methods has its own advantages and shortcomings. For instance, skimmers can effectively recover oil but would take a substantial amount of time and labor. The recovered oil can be used for its original purpose, like as fuel, because it can be easily separated from the water. We observed this in method one of our experiments; the collected oil did not mix with the water when we scooped it out.
In contrast, sorbents are a more efficient method of removing oil, but the recovered oil can only be burnt for heat and cannot be used for its original purpose. This is because it is now mixed up with water on the sorbent, just like how we saw that we could not separate oil from the cotton balls. Finally, while dispersant is also commonly talked about as a method to clean up oil spills, it is less frequently used because it does not remove oil but instead lets it mix up with water. It can only dilute the pollution but not actually solve it.
Looking for more fun at-home STEM activities for your young scientist? Check out our workbook full of exciting science experiments and empowering activities!
Learn more and purchase today!
