Acids and Bases: Using Red Cabbage Juice

Some science experiments really wow. This is one of them.

My oldest son tested a variety of different substances to determine if they were acids, bases, or neutral. He did this using an indicator that we made from red cabbage.

Here's how we did it.

Make the Indicator

Peel about five leaves off a head of red cabbage and put in a blender with nine cups of water. Set on high until the cabbage is finely ground and the water is purple. Note: This makes A LOT of indicator so if you're not planning to go crazy testing many substances, reduce the mixture down to 3 leaves and 6 cups of water.

Beware; it smells. B-A-D

Using a fine mesh sieve, strain the blended cabbage over a pitcher. Voila! Your red cabbage indicator is ready!

Testing substances

Fill small disposable plastic tumblers half full of the indicator. Add a teaspoon or two of every substance to each cup. If the substance is an acid, it will turn the liquid from purple to pink or red. If the substance is a base, the red liquid will turn blue, green, or yellow.

I made an worksheet with a scale to help my son. I printed an extra of the color scale and laminated it so he could even hold it next to the tested liquids. Click on the picture below to download a free PDF on Google Drive.

Remember not to pour any substance in one of the cups. This will help you compare those substances which may not appear to turn the water.

The acids-bases scale shows the corresponding pH. Substances that are acids have a ph of less than 7; substances that are bases have a pH of more than 7.

Possible test substances include:

vinegar

salt

baking soda

lemon/lime juice

rubbing alcohol

handsoap

bleach*

milk

egg whites

*Exercise caution when using bleach. It's a powerful chemical! Grown ups should pour this.

Our favorite test substances were vinegar, lime juice, baking soda, and bleach.

To explain acids and bases, why not watch a YouTube video?!

This great activity came from Steve Spangler Science.