Make Your Own pH Indicator Using Red Cabbage

Who here likes red cabbage? It is widely celebrated as a cancer-preventing super-food. Some people love to cook it up in some variety of stir fry. Personally, I like to eat it raw in a salad with nuts, seeds, and dried cranberries with a drizzle of oil and vinegar over the top. Whether or not you like to eat red cabbage, I just know you are going to love doing science with it.

It turns out that red cabbage contains a chemical called anthocyanin that changes color depending on the acidity of its environment. In an acidic environment it is reddish-pink, in a neutral environment it is purple, and in a basic (or alkaline) environment it turns bluish-green and even yellow. This is a great way to introduce the concept of acids and bases to a child since they can see the color change before their very eyes.

This experiment can be found in 50 Science Things to Make & Do. In the coming days and weeks I am so excited to show you several spin-off experiments and activities that you can do using the same materials!

Let's get started, shall we?

Total Time: 40 minutes to prepare the indicator, two hours to let it freeze; 10 minutes to carry out the rest of the experiment

Difficulty: This one definitely requires the aid of an adult to prepare the indicator, unless you trust your child with a sharp knife and a hot saucepan full of boiling cabbage (I don't, personally). It's pretty easy, though, as far as actual skill goes.

Materials You Need:
One half of a head of red cabbage
Ice cube tray
Tall clear cups
Vinegar
Baking Soda
Water
Optional: More acidic/basic household items such as lemon juice, washing soda, cream of tartar, or antacids

Directions:
To make the indicator solution:

1. Chop up your red cabbage into small pieces. Place 2-3 cups in a saucepan and cover with water.
2. Bring the solution to a boil and then turn off the heat. Let it sit for about 30 minutes to cool down.
3. Pour the cabbage water through a strainer into a jar or large measuring cup. The dark purple liquid in the jar is your indicator.
4. Pour your red cabbage indicator liquid into the compartments of an ice cube tray. Freeze for a couple of hours to make ice cubes.

pH Experiment:

1. Fill one cup with water (this is neutral, or your control), one with vinegar (this is acidic), and one with a teaspoon of baking soda mixed with water (this is basic).
2. Drop a couple of indicator ice cubes into each cup. Notice how the colors change in each one. Draw a picture of what you see.
3. Repeat with other acidic or basic household items in other cups. Try to guess what color the solution will be before dropping an ice cube in!

Print These Instructions
 
I was shocked at how fast the colors changed and how delightfully brilliant and beautiful the colors were! My three-year-old daughter was excited because the solutions turned into her three favorite colors: pink, purple, and blue.

This is a fantastic way to introduce children to acid/base chemistry. And, who knows, maybe they'll even get excited to eat some red cabbage, too!

 

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