Summary

In this lab, students explore the concept of density. They will examine the density of a plastic sandwich bag compared to water. Students will create their own experiment and investigate factors that affect floating and sinking.

Grade Level

Middle or elementary school

NGSS Alignment

This lab will help prepare your students to meet the performance expectations in the following standards:

• 3-5-ETS1-3: Plan and carry out fair tests to which the variables are controlled and failure points are considered to identify aspects of a model or prototype that can be improved.
• Scientific and Engineering Practices:
  • Planning and Carrying Out Investigations
  • Constructing Explanations and Designing Solutions

Objectives

By the end of this lab, students should be able to

• describe the factors that affect density.
• explain density by particle proximity.
• successfully design and carry out their own scientific investigation.

Chemistry Topics

• Density
• Observations

Time:

Teacher Preparation: 30 minutes

Lesson: 60 minutes

Materials

• Water tanks (5 gallons) or small aquariums
• Stop watches
• Plastic sandwich bags
• Coke and Diet Coke or golf ball and ping pong ball to show floating and sinking
• Optional: Additional classroom materials or student materials from home may be used in Part 2 of the lab investigation.

Safety

• Always wear safety goggles when handling chemicals in the lab.
• Students should wash their hands thoroughly before leaving the lab.
• When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.

Teacher Notes:

• I would do this lesson after students learn about density. The ACS Inquiry in Action Book has a good lesson that could be helpful to do beforehand, Density and Sinking and Floating.
• According to Mother Nature Network, sea turtles around the world are eating plastic at an unprecedented pace. This study reveals that some species are “downing twice as much as they did 25 years ago. This indigestible, potentially fatal diet is especially popular among young turtles in the open ocean, deepening concerns about the ancient animals' long-term outlook.”
• Other notable points from the research, “Plastic bags can bear a striking resemblance to jellyfish underwater, and scientists have long known they have a tendency to confuse hungry sea turtles. But the problem has exploded lately amid a historic surge in plastic pollution, which is forming giant oceanic "garbage patches" that are expected to continue growing for centuries. The new study is the first global analysis of the issue since 1985, covering more than a quarter century of research on green and leatherback sea turtles, both of which are endangered.”
• Classroom Procedure:
  • Students should use the student handout to answer questions and record results.
  • Part 1: Using the Coke and Diet Coke ask the students what they think will happen when the unopened cans are placed in the container of water. Will one float and one sink? Will both sink? Do the demo by putting the cans in the tanks of water.  Why is there a difference between the two?
  • Students will watch this density animation.  It is helpful to explain mass/volume and the common units for density g/ml.
  • After the pre-lab has been completed by the students, have a class discussion: Create two columns on the classroom board. In the first column write the density ideas from the students. In the second column write down what they think affects density (pre-lab question #3 a& b).
  • Now students will investigate “Flinking”. Flinking (make sure that students know this is not a proper scientific term, but a hybrid between the words “float” and “sinking”) is an object that doesn’t float or sink. Students will place their sandwich bag (opened) in the water and make sure to get any air out of the bag. When the bag is in the middle of the tank they will time how long it “flinks”. Make sure students are careful to not make a current with their hand.
  • Optional: Record the averages from each group on a classroom data table. Find the class average flinking time.
  • Part 2: Students should brainstorm how they can change the “flinking” time of the bag in the water. Record the ideas on the board. Students will choose an idea from the board or come up with a new idea to test (Depending on available time, teachers may want to have students test multiple ideas).
  • Students should complete part 2 of the lab handout while conducting their experiment.

• Additional Extensions/Assessments
  • Have students bring in other cans of pop (soda) or other drinks to see if they float or sink. Create a chart with the can’s weight and volume and see if they can come up with an answer before they try to float or sink them.  Write an investigation (lab report) with data table and graph.
  • Listen to questions the students may have about “Flinking” and create an activity to only change 1 variable to make comparisons. Have the students write an investigation (lab report) as an assessment. The investigation will include a data table and graph.
  • Create a “Density Tower”.
  • Ask the students how can we save the sea turtles? Listen to and discuss their solutions.
  • Show the PhET simulation “Balloons and Buoyancy”.