BioEd Online

Teacher Background

About 78% of the volume of dry air is nitrogen gas (N₂). Oxygen (O₂), the component of air required by our bodies, comprises less than one fourth of dry air. Argon, a nonreactive gas, makes up slightly less than 1% of dry air. Carbon dioxide (CO₂), a gas released from our bodies when we exhale, is present in even smaller quantities (less than one part per 1,000). Very minute amounts of many other naturally-occurring gases (such as neon, helium, methane, and ammonia), as well as gases resulting from pollution, are present in air. Water vapor, when present, can occupy up to 5% of the total volume of air. When we breathe, nitrogen, oxygen, and all the other components of air enter and exit our lungs.

Objectives and Standards

Concepts

• Gases occupy space.

• Air is a mixture of different gases.

• Oxygen, a gas needed by the human body, is not the principal component of air.

Science, Health, and Math Skills

• Measuring

• Observing

Materials and Setup

Teacher Materials (see Setup)

• 30 cups of popped popcorn (see Setup for alternatives)

• 3 clear resealable plastic bags, 1-gal size (12 in. x 15 in.)

• clear plastic bag, 15-gal size (or a bag from the cleaners)

• dry soft drink mix: 2 pkgs of yellow, 1 pkg each of green and red

• transparency of "Let’s Measure" student sheet

Materials per Group of Students

• clear resealable plastic bag, 1-gal size (12 in. x 15 in.)

• measuring cup, 8-oz size

• copy of "Let’s Measure" student sheet

Setup

1. Pop and tint three small batches of popcorn before you begin this activity.

2. First, pop the corn. To tint it, measure 6 cups of popcorn into a sealable plastic bag. Add a tablespoon of yellow soft drink mix and 1–3 teaspoonfuls of water. Seal the bag and shake to distribute the color.

3. Repeat the tinting process with the red, and again with the green mix—but use only 1 cup of white popcorn with each of these colors. Ultimately, you should have 6 cups of yellow popcorn in the first bag, 1 cup of red popcorn in the second bag, and 1 cup of green popcorn in the third bag. Let the popcorn dry by spreading it on a paper towel or leaving the bags open.

4. When dry, put each color of popcorn in separate containers. You also will need about 22 cups of white popped corn.

5. As an alternative, you may use purchased popcorn. Select different flavors to represent three colors. You also can use different-colored styrofoam packing peanuts or small balls of crumpled paper in different colors.

6. If you would like to create a larger model of air, multiply the materials by two or more.

Procedure and Extensions

1. Divide the students into six small groups. (If your students are very young, you may prefer to conduct the activity as a discovery lesson with the entire class.)

2. Have the Materials Manager from each group collect a measuring cup and a sealable plastic bag. Give three groups approximately 7 cups of white popcorn each. Give 1 bag of colored popcorn to each of the remaining three groups.

3. Project the "Let’s Measure" student sheet while you explain that each group with white popcorn will measure 5 cups of popcorn into its bag; the group with yellow popcorn will measure 4 cups; the group with red popcorn will measure 1/4 cup; and the group with green popcorn will place only one kernel in its bag.

4. When the students have finished measuring, ask one student from each group to empty the popcorn from the group’s bag into the large, clear plastic bag (which you will hold in a central location).

5. Shake the large plastic bag. Ask, What do you think I’m doing? Lead the students to understand that the popcorn is being mixed. Ask, Are the colors of popcorn arranged in a special way in the bag? Students should note that the colors are mixed randomly.

6. Have the students identify which color of popcorn is represented by the most kernels in the bag, by the second-most kernels, and so on, until you mention the single kernel of green popcorn. Follow by asking students to name other kinds of mixtures (e.g., fruit salad, crayons of different colors in a container).

7. Explain that air also is a mixture, made up of different kinds of gases. The different colors of popcorn in the large bag are present in the same proportions as the different gases in air. (Some students will already know that oxygen and carbon dioxide are involved in breathing. If the class is not familiar with this information, point out that the gas we take out of air when we breathe in is known as oxygen, and the gas we release when we breathe out is carbon dioxide.) Ask students to guess which color of popcorn represents oxygen molecules (yellow) and carbon dioxide molecules (green) in air.

8. Finally, point out that air is mostly nitrogen, represented by the white popcorn. The red popcorn corresponds to argon, gases present in air but not absorbed by the body during breathing.

Extension

Make your own colored and flavored popcorn using the “Fiesta Popcorn” recipe (see PDF).

Handouts and Downloads