Color-changing Cabbage Chemistry

Prep Work

1. Children should wear goggles or other protective eyewear and adults should supervise and use caution when handling bleach because it can irritate eyes and skin.

Instructions

1. Grate a small red cabbage. Put the grated cabbage into a large bowl or pot.
   
   
   
2. Boil a pot of water. Use caution when handling the boiling water. Pour the boiling water into the bowl with the cabbage pulp until the water just covers the cabbage.
3. Leave the cabbage mixture steeping, stirring occasionally, until the liquid is room temperature. This may take at least half an hour. The liquid should be reddish purple in color.
   
   
   
4. Place a strainer over another large bowl or pot and pour the cabbage mixture through the strainer to remove the cabbage pulp. Press down on the pulp in the strainer, such as by using a large spoon, to squeeze more liquid out of the pulp.
   
   
   
5. In the bowl, you should now have a clear liquid that will either be purple or blue in color. (It should look darker after the pulp is removed.) This will be your indicator solution.
   
   
   
6. Fill a small white paper cup, drinking glass, or small white dish with 1 tablespoon (tbsp.) of your cabbage indicator solution. What is the color of your indicator solution?
7. Add drops of lemon or lime juice to the indicator solution until you see the solution change in color. Gently swirl the solution and make sure the color stays the same.

   What color did the solution become?

8. The color of the solution will change depending upon how acidic or basic it is. This is based on the pH of the solution. pH is a numerical measure of how acidic or basic something is. A solution with a pH between 5 and 7 is neutral, 8 or higher is a base, and 4 or lower is an acid. The solution will be the following colors based on its pH: Red indicates pH 2; Purple indicates pH 4; Violet indicates pH 6; Blue indicates pH 8; Blue-green indicates pH 10; Greenish-yellow indicates pH 12. In summary, acidic solutions should be red or purple in color, neutral solutions should be violet, and basic solutions should be blue, blue-green, or greenish-yellow in color.
9. Based on its color, what is the pH of the lemon or lime juice solution?
10. In another small white paper cup, add 1 tbsp. of your original cabbage indicator solution. Add drops of vinegar until you see the solution change color.

    What color did the vinegar solution become? What is the pH of the solution? Is it an acid or a base?

11. In a third small white paper cup, add 1 tbsp. of your original cabbage indicator solution. Handling it with caution, add drops of the bleach cleaning product until you see the solution change color.

    What color did the bleach solution become, and what does this indicate about its pH? Is it an acid or a base?

12. If you want to test the pH of other foods, again add 1 tbsp. of your original cabbage indicator solution to a small white paper cup and add drops of the food until you see the solution change color. If the food is not in liquid form, crush it or dissolve it in a small amount of water before adding it to the indicator solution. What color did the solution become, and what does this indicate about its pH, and whether it is an acid or a base?

Cleanup