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Make a Splash! - Cabbage Juice pH indicator What do I need? 1 head red cabbage
Water
White coffee filters, cut into strips
Liquids to test
Sauce pan
Stovetop and an adult
Knife and an adult
Bottle with a wide mouth, such as a clean juice bottle.
Strainer
Waxed paper
What do I do?
**Knives are very sharp and the stove is very hot. Please let your adult help**
Have the adult chop the cabbage into small (~1 inch) pieces. Place the pieces in the saucepan, and add just enough water to cover. Turn the stove to medium and bring the water to a boil. Allow the cabbage to boil; for 15 minutes, then turn off the heat and remove the pot from the stove. After allowing the cabbage solution to cool, strain out the cabbage, collecting the juice in the bottle. Discard the cabbage pieces.
In a shallow bowl, pour a small amount of the juice. Drop in the coffee filter strips one at a time. Let the strip soak completely, then remove it. Place it on the waxed paper to dry. Repeat until all of the strips are used.
You can now test your strips by dipping them into various liquids. Try water, vinegar, baking soda and water, soapy water, clear soda, and other things you can think of. Note what happens to the color of your strip.
Why did that happen?
Your strips changed color! You can also add some of your cabbage juice to the different liquids to see the same color change. Always remember not to eat your experiments.
Cabbage juice contains chemicals called anthocyanins, pigments that react in a different way to acids and bases. You made a pH indicator – something that can tell you whether a substance is an acid or a base!
What does that mean?
The pH scale: is used to rank acids and bases with the numbers 0-14. The numbers 1-6 are assigned to acids, with 0 being the strongest acid. The numbers 8-14 are assigned to bases, with 14 being the strongest base. The number 7 represents something that is neutral – neither an acid or a base. For cabbage juice, strong acids turn red, weak acids turn pink, neutral turns purple, weak bases blue, and strong bases green or yellow.
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