Make Your Own pH Indicator Using Red Cabbage

 Who here likes red cabbage? Anyone? Anyone? For those of you who may not like to eat it, I’ve found a great new way to use it in a science experiment! Anything for the kiddos, right?

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. We use this book all the time up in here.

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. Make soup with the leftover cabbage pieces.
  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. (Don’t eat these. They taste like cabbage water.)

pH Experiment:

  1. Fill one cup with water, one with vinegar, and one with a teaspoon of baking soda mixed with water.
  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.

Print These Instructions
 
Now, I’ll be honest. My son wasn’t all that impressed with this experiment. He may just be too young to grasp the idea of what acids and bases are. The idea that we could make our very own pH indicator was kind of ho-hum for him, even though I thought it was pretty cool. I was shocked at how fast the colors changed and how delightfully brilliant and beautiful the colors were. This experiment worked perfectly, but I think it will be more impressive for a child closer to 8 or 9 years old than it was for my four-year-old. Let me know how it works and how your kiddo enjoyed it!

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