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ACTIVITY
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By Erica K. Jacobsen
Technical Review Seth Brown, University of Notre Dame David Voss, Medina High School, Barker, NY
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Do You See What I See?
Y
ou may have heard the saying, “The optimist sees the glass half full. The pessimist sees the glass half empty.” An addition seen on the Internet: “The chemist sees the glass as completely full, half in the liquid state and half in the vapor state.” If something cannot be seen by the human eye, we tend to forget about it. Air is in the glass and all around us, but we do not really think about it. We breathe it in, the body takes what it needs, we breathe it out. We do not see air, but it is a critical part of our environment. In the activity below, you will investigate the effect of something you cannot see on something you can. This activity was adapted from “Lose the Blues with Materials CO2!”—an activity produced by the American • Red cabbage leaves Chemical Society as found in “Science • Zip-seal plastic bag Activities for the Classroom” at: • ¾ cup (180 mL) of water http://bit.ly/co2losetheblues • Piece of white paper • 3 clear, colorless cups Safety recommendations • Baking soda • Wear eye protection. • Vinegar • Never eat or drink while conducting • Tablespoon, teaspoon an experiment, and be careful to • Plastic bottle with wide mouth (about 500 mL) keep all of the materials used away • 2 straws from your mouth, nose, and eyes. 1. Tear two red cabbage leaves into small pieces. Place in a zip-seal plastic bag. 2. Add ¾ cup (180 mL) of water to the bag. Squeeze out as much air as possible and seal the bag. 3. Continue to squish the leaves in the bag until the water turns a blue to purplish-blue color. Open the bag and pour the water into a cup. This liquid serves as an indicator solution to show changes in pH. 4. Place two clear, colorless cups on a piece of white paper. 5. Measure 2 tablespoons of the indicator solution into each of the two cups. 6. Measure 3 teaspoons of baking soda into a plastic bottle with a wide mouth. Add 1 tablespoon of vinegar. Hold your hand over the mouth of the bottle and swirl to mix.
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What was the gas you added? What effect did it have on the indicator? Red cabbage juice turns pinkish-red as it becomes more acidic and bluish-green as it becomes more basic. Try this, too! Use a straw to blow bubbles through a small amount of blue to purplish-blue indicator. What happens?
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7. Tilt the bottle over one cup to pour any gaseous contents into the cup, but DO NOT pour any liquid out. 8. After 1–2 minutes of pouring, use a straw to stir the contents of both cups. What happens to the color of the indicator solution in the cup to which you added the gas?
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Teacher’s Guide William Bleam, Editor Donald McKinney, Editor Ronald Tempest, Editor Barbara Sitzman, Editor Regis Goode, Editor Susan Cooper, Content Reading Consultant David Olney, Puzzle Contributor
