Unit 36 Laboratory Activity: Acids, Bases, and the release of gas

Goal: Make an acid-base indicator and use it to measure the acidity of common substances.

Equipment and Materials:

• A chunk of red cabbage (¼ to ½ head)
• Grater
• Pot and water to cover grated cabbage
• Glass canning jar with lid (should be able to handle boiling water).
• Strainer
• White vinegar
• Baking soda
• Dishwashing detergent

Procedure

1. Grate the cabbage into the water.
2. Boil the mix until the water turns dark purple (20-30 minutes).
3. Pour the mix through the strainer into the glass jar. You now have an acid-base indicator containing a pigment, anthocyanin. You can make litmus paper by soaking strips of coffee filter in the liquid and letting them dry.
4. Add some drops of cabbage solution to the white vinegar. What happens to the color?
5. Add some drops of cabbage solution to a solution of baking soda and water. What happens to the color?
6. Add some drops of cabbage solution to a solution of dishwashing detergent and water. What happens to the color?
7. Try some other solutions made from common foods or household compounds such as soaps or cleaning fluids.

Report

• If you change the procedure, describe the materials you used and the steps that you actually followed.
• Make a table of your test results. List the substances you test and record the color for each one. Can you make a range of colors? What substances test out for similar colors?

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