Floating Foods and Underwater Eruptions: An Exploration of Density

Tony Hartmann, Oak Crest Elementary, Belle Plaine, MN
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Summary

Students will explore the concept of density by investigating how various solids and liquids interact. Through hands-on activities and a teacher demonstration, the students will develop a greater understanding of density by using their observational skills, recording data, and making inferences.

Learning Goals

Students will:
Understand that density is a property of matter.
Explain the difference between density and weight.
Record observations while experimenting with various household liquids and foods.
Hypothesize that liquids and solids will interact in certain ways.
Design their own experiment to expand on their knowledge of density.

Vocab Words:
Density: Mass/Volume - How much "stuff is in and object and how tightly packed that "stuff" is
Mass: A measure of the quantity of matter. It is always constant, not the same as weight .
Volume: Amount of space an object occupies

Context for Use

This activity is intended for middle school students but could easily be adapted to fit younger and older students as well. This lesson involving a short teacher demo and two group activities could be done in one 60-90 minute lesson or broken into two 30-45 minute class periods. The follow-up homework activity is inquiry based and is designed to give students the opportunity to explore density even further and give them the opportunity to present their findings to the class.

Subject: Chemistry:General Chemistry:Properties of Matter
Resource Type: Activities:Classroom Activity, Lab Activity
Grade Level: Intermediate (3-5), Middle (6-8)

Description and Teaching Materials

Introduction: Ask the students what would happen if you place an orange in a bucket of water. Demonstrate. The orange will float because there are numerous air pockets inside the peel causing the orange to float. Now ask the students what will happen if you remove the peel from the orange and place the orange back into the water. Most will say it will float. Demonstrate. The peeled orange will sink because once you removed the peel you removed the air pockets that allowed the orange to float. I would use this experiment to explain the difference between density and weight. The whole orange was heavier before it was peeled, yet it floated, and the peeled orange was lighter in weight, yet it sunk.

Materials:
Liquids: Water, vegetable oil, salt water solution, rubbing alcohol (teacher demo)
Containers: 400-600 ml beakers (glass mug size), 25-50 ml beakers (shot glass size),
Foods: Cheerios, M&M's, fried tater tots, grapes, kernels of corn, ice cubes
Other Items: aluminum foil, food coloring (red, blue, and green), mixing spoons, paper towels, salt

Activity 1. "Floating Foods"
Students will investigate whether certain foods sink or float in various liquids. Break the students into group of 4-5 and have them complete the floating foods activity sheet. Each group will need a beaker of freshwater, a beaker of salt water, and a beaker of vegetable oil. They will also need approximately 5 of each of the food items on the materials list above. Have all the materials placed on the table in the front of class and assign a student from each group to gather all the needed materials. Students will make predictions prior to placing each food item in the fresh water, salt water, and vegetable oil. The students will record their predictions and actual results on the floating foods activity sheet. The teacher will end this investigation by demonstrating what happens when you place each food item in a beaker of rubbing alcohol. Have the students predict what happen before placing the food items into the rubbing alcohol. Ask them to write down the results on the floating foods activity sheet. Have the students explain what happened and why certain foods sink or float in the various liquids by answering the floating foods questions and discussing their findings amongst their group.

Activity 2. "Underwater Eruptions"
Students will investigate how certain liquids of varying densities interact with each other. The students will submerge fresh water, salt water, and vegetable oil into a beaker of fresh water and observe what happens. First the students should use food coloring to dye each liquid a different color. Color fresh water blue, salt water red, leave the vegetable oil alone because it already has a gold color that can be seen in the water. Students will fill a 25 ml beaker with one of the liquids and cover the beaker tightly with aluminum foil. Students will carefully place the 25 ml beaker into a 400 ml beaker of clear, fresh water that is 2/3 full. Have one student from the group take a pencil and gently poke the pencil through the aluminum foil. Students should carefully observe what happens and take notes on the "Underwater Eruptions" activity sheet. Did the colored liquid remain in the 25 mil beaker? Did it rise? Did it rise fast or slowly. Did it form a separate layer or mix in with the water? Students should discuss these questions with each other and determine what liquids have the least and greatest density and what liquids had similar densities. Students will repeat the process until each of the liquids have been submerged into the beaker of fresh water. The teacher will go from table to table having the students explain why certain liquids remained in the submerged beaker while other liquids rose to the top. When the students have finished, the teacher will demonstrate what happens when you submerge rubbing alcohol into a beaker of fresh water. Teacher should color the rubbing alcohol with some green food coloring so it can be seen rising up in the fresh water.

Activity 3: Design your own density experiment
Student will be assigned a homework assignment to design an experiment that further investigates the concept of density. The students will create a chart for record keeping and write down their observations. Students will try their experiments out at home and share their results with the class. Encourage the students to come up with their own idea, but remind them that the Internet is a great resource if they need help coming up with ideas. You may want to brainstorm ideas with the class. Discuss the ideas of layering liquids, or investigating whether or not water temperature, or salinity have an effect on the density of liquids. They could even explore density using different food items or other non-food items. I would give the students about a week or so to do this homework assignment, and maybe spend 1-2 periods to share results with each other in class. Some students may want to demonstrate their experiments to the class if there is time. Remind the students they need to get permission from their parents before they start their investigations.

Teaching Notes and Tips

Plastic beakers are recommended when working with younger children. Goggles are also recommend because they are working with glass beakers that may break or salt water could splash in their eyes.

Remind the students not to eat the foods used in the experiments.

Assessment

The students will be assessed through their participation in classroom and small group discussions. They will be required to turn in their answers to the two activity sheets. The students will also be assessed on their final density experiment designs.

Standards

Grade 6.I.B.1 - Scientific inquiry
Grade 6 II, A, 5. - The student will distinguish between volume, mass and density.

References and Resources

Kids Science Experiments Website http://www.kids-science-experiments.com/ (link down)

Elmhurst College: Science Demonstrations Website http://chemistry.elmhurst.edu/demos/