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Fuel for Living Things

Author(s): Nancy P. Moreno, PhD, Barbara Z. Tharp, MS, and Judith Dresden, MS.

Sessions 1 and 2: Cabbage Juice Indicator

In this activity, students will learn that most organisms release carbon dioxide when they use food. Students will make predictions and qualitative observations, and draw conclusions based on their investigation. They will discover that yeast consumes sugar and produces carbon dioxide as a by-product. In session 1, students will observe that cabbage juice (the indicator liquid) will turn pink in the presence of carbon dioxide, which acts as an acid.   

Have the Materials Managers collect the materials for their groups. Students should place the sliced red cabbage in the plastic bags, along with 1/2 to 1 cup of warm water, and seal the bags tightly. Direct students to take turns gently rubbing the cabbage inside the bags until the water becomes dark purple (usually about 10–15 minutes). This is the indicator solution.

Explain that the indicator liquid will be used to test for the presence of carbon dioxide, which becomes a weak acid in water. If necessary, identify some common examples of acidic items, such as lemon juice and vinegar. 

Pour some indicator liquid into a clear cup. Ask students, What color is the liquid? What do you think will happen if I put something acidic into this water? 

Add a few drops of vinegar to the solution, until it turns pink (this indicates an acid). You also may show how the indicator reacts to baking soda (the solution will turn pale blue or green indicating a base). Explain to students that they will use the indicator to test for the presence of carbon dioxide, a gas that is given off when living things use food for energy. This gas when dissolved in water turns it more acidic.

Funded by the following grant(s)

National Institute of Environmental Health Sciences, NIH

National Institute of Environmental Health Sciences, NIH

My Health My World: National Dissemination
Grant Number: 5R25ES009259
The Environment as a Context for Opportunities in Schools
Grant Number: 5R25ES010698, R25ES06932

Houston Endowment Inc.

Foundations for the Future: Capitalizing on Technology to Promote Equity, Access and Quality in Elementary Science Education