BioEd Online

Teacher Background

Gases are one of the three basic states of matter (the other two are liquids and solids). Unlike liquids or solids, gases will expand indefinitely if they are not in a container. Even though we cannot see or smell many gases, it is possible to observe them in other ways. For example, it is relatively easy to detect the pressure exerted by a gas on the walls of a balloon or an inflatable tire.

The air we breathe is a mixture of several gases. One of these, carbon dioxide, is produced as a waste product by most living cells. Carbon dioxide also can be produced by a number of other means, including the mixing of a weak acid (vinegar) with sodium bicarbonate (baking soda).

Objectives and Standards

Concepts

• Gases take up space.

• Carbon dioxide is a gas.

Science, Health, and Math Skills

• Observing

• Drawing conclusions

Materials and Setup

Teacher Materials (see Setup)

• 2 balloons

• 1 tsp of baking soda

• 1/4 cup of vinegar

• note card or creased sheet of paper

• soft drink bottle, 2-liter size

Setup

1. Place a clear soft drink bottle, a balloon, baking soda, and a container of vinegar in the area you usually use for demonstrations.

2. Conduct this activity as a discovery lesson with the entire class.

Procedure and Extensions

1. In front of your students, inflate a large balloon. Ask them if there is anything inside the balloon. Stimulate a discussion about the contents of the balloon, leading them to the conclusion that the balloon contains air.

2. Tell students, Air consists of gases we cannot see or smell. However, we can tell gases are present in the balloon because they place pressure on the sides of the balloon and make it expand. Let the students feel the sides of the balloon.

3. Ask the students to observe as you place a few tablespoons of vinegar into the soft drink bottle. Next, using a note card that you have creased down the center, slide about one teaspoonful of baking soda inside the second balloon. Fasten the balloon over the mouth of the bottle, without letting the baking soda fall into the bottle.

4. Gently lift the balloon upward and let the baking soda fall into the vinegar at the bottom of the bottle. As carbon dioxide is produced inside the bottle, the balloon gradually will inflate. Challenge students to think about what might be causing the balloon to expand. Lead them to understand that mixing the two compounds produced a gas, known as carbon dioxide, which also is released from our bodies when we breathe out.

Extensions

• Small groups of students may enjoy mixing the compounds themselves to produce carbon dioxide. When conducted by students, this activity will take about 30 minutes to complete. Materials needed to conduct a class activity with six student groups are 6 soft drink bottles, 12 balloons, 1½ cups of vinegar, 6 teaspoons of baking soda, and 6 note cards.

• To demonstrate how living organisms release carbon dioxide when they use food for energy to grow and reproduce, place one tablespoon of dry yeast, one teaspoon of sugar, and 1/4 cup of warm water in a soft drink bottle. Mix by gently swirling the bottle. Attach a balloon to the top of the bottle, and set the bottle aside for about 30 minutes. The balloon will begin to swell as the yeast cells become active, use the sugar for food, and release carbon dioxide.

• Have the students make the cylinder flyer described in the storybook Mr. Slaptail’s Secret. (Directions for creating the flyer are given at the end of the book.) Talk about what might be holding the flyers up as they soar through the air.

Handouts and Downloads