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Title: Density: Do oil and water mix?
Principle(s) Investigated:
- (Review) What is mass? How much matter (anything you can physically touch) an object contains.
- (Review) What is volume? How much space a substance occupies or contains.
- What is density? A physical characteristic of a substance. It is defined as the measure of mass per unit volume of a particular substance (d=m/v).
Standards: Density and Buoyancy
8. All objects experience a buoyant force when immersed in a fluid. As a basis for understanding this concept:
a. Students know density is mass per unit volume.
b. Students know how to calculate the density of substances (regular and irregular solids and liquids) from measurements of mass and volume.
c. Students know the buoyant force on an object in a fluid is an upward force equal to the weight of the fluid the object has displaced.
d. Students know how to predict whether an object will float or sink.
Materials:
- ½ cup of vegetable oil
- ½ cup of water
- Food coloring
- Clear plastic cup
Procedure:
- Each group of students receives the list of materials stated above. Students will be instructed to complete the Density Worksheet while they are conducting the experiment.
- Students will be instructed to pour the water into the plastic cup, followed by the oil. Each group will observe and discuss as a group what is taking place. They will draw, label and write their observations on the Density Worksheet.
- Once the students note their observation (the two substances separate), they will add several drops of food coloring into the cup. They will again record their observations in an illustration and written format (the food coloring falls from the oil to the water).
- After the group experiment is completed, there will be a whole class discussion on the concept behind the experiment (i.e. what is density, what solutions do when they are more or less dense than others, and other examples of density). Students will also volunteer answers from their worksheets.
- Finally, the instructor will direct students’ attention to a clear plastic glass with water and oil. One student will be asked to stick one finger in the glass and what remains on his/her finger as it was pulled out (i.e. water, oil, or both). When the student indicates oil, the teacher will go into a short discussion on the oil spill of 2010 and the harmful aftermath to the environment (real world application).
Student prior knowledge:
Characteristics of matter
- Matter has mass
- Matter takes up space (volume)
- Matter is measureable (we can measure its volume and mass)
Explanation:
- This experiment would be used as a visual representation of the mass, volume and density (d=m/v) of three different solutions (water, oil and food coloring). Here, students will be able to see how substances interact when they are more and/or less dense than others. They will see that less dense substances will float, while denser substances will sink. The denser solutions have molecules that are packed closer together.
- Students will also have the opportunity to see how density is an active phenomenon in their daily lives (i.e. swimming) and how the non-mixing capabilities of oil and water can be represented in historical events (oil spill of 2010). This will enable students to make real-world connections and hopefully identify future examples of density in their everyday experiences.
- Furthermore, this demonstration is formatted so that students can work together and develop their problem solving skills. The Density Worksheet that students complete in groups acts as a visual representation (Step 1) of density even after the class demonstration is taken away.
- Finally, this demonstration accommodates students with a variety of different learning styles. For example, visual learners will be able to directly see the materials and how they interact with one another. They will also illustrate/label a related image. Auditory learners will have the opportunity to hear instructions given by the teacher and listen to ideas and/or solutions from their peers in the group setting. Kinesthetic learners will be able to manipulate the materials involved in order to grasp the concept of density.
Questions & Answers:
1. What do you think will happen when oil is added to water in the plastic cup? (prediction)
a. This will allow students the opportunity to make a prediction before beginning the group experiment. Once the two substances are added to the plastic cup, two layers will ultimately form. Water will form a layer at the bottom of the cup while the oil will settle above the water.
2. What makes the oil less dense than water?
a. This will allow the instructor to assess whether students understand the concept of density. The molecules present in water are closer together, while the molecules in oil are farther apart. More dense substances (i.e. water) tend to sink and less dense substances (i.e. oil) float. These substances do not mix.
3. How can this phenomenon (density) negatively affect the environment?
a. Remembering the oil spill of 2010, the oil remained on the surface of the water. It took over the habitat of the marine animals. The oil floating on the water caused harm to many different animals such as, sea birds, otters, and killer whales. These animals would eat the oil that was stuck to their prey or get covered in it. Since the oil is poisoned the animals in direct contact with it would have most likely died.
Applications to Everyday Life:
- Students would be able to relate this phenomenon to the oil spill of 2010. Since oil is less dense than the water, a thick layer of it formed on top of the Atlantic Ocean (Gulf of Mexico). This caused many animals to die as they lost their habitat to the oil (Environment Science connection).
-Students can related the concept of density to swimming in a pool. Even though we seem big and heavy, our bodies are less dense than the water in our pools. This causes us to float instead of sink.
-Students would also be able to link density to an event in history: The California Gold Rush. Miners would use pans of various sizes and fill them with a small amount of material found in the water of a river. The pan was then submerged in water and if there was any gold it would sink to the bottom. Gold is denser than water (History connection).
Photographs:
Please refer to the following photos for this experiment in the demonstration web album:
- IMG_9869.JPG
- IMG_9861.JPG
- IMG_9862.JPG
- IMG_9868.JPG
Videos:
http://www.youtube.com/watch?v=sLhjZg4lwZI
http://www.youtube.com/watch?v=rznxL9VRBnk
http://www.csulb.edu/~lhenriqu/300demo.htm#vicente
en.wikipedia.org/wiki/California_Gold_Rush
en.wikipedia.org/wiki/Mass
en.wikipedia.org/wiki/Volume
en.wikipedia.org/wiki/Density
http://library.thinkquest.org/CR0215471/oil_spills.htm
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