Red Cabbage Juice

A Natural pH Indicator

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Useful in Units: Acids & Bases

Background and Uses

The juice that can be made from Red Cabbage is a natural pH indicator.  Although it will make your house (or prep room) a little stinky, I find the rewards well worth the smell.  It is a universal indicator and changes to many different colors – see below.  

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I use the indicator to have the students test the pH of many household products. These include many cleaners, ammonia, Liquid Plumber, bleach, lemon juice, milk, orange juice, and anything else I can find in the house.  In general, foods often test in the acidic range and cleaners test in the basic range.

One point you could make to the kids is that red cabbage is sometimes more red and sometimes more purple at the grocery store.  This is due to the pH of the soil in which the cabbage was grown.

Alterations to try and pitfalls to avoid for this demo:  

1. Make sure that Ammonia and Bleach based products are not mixed.  The reaction between these compounds is a chlorine-based gas that is poisonous.
2. I put my cabbage juice in a big jug that has a spout on the bottom.  This makes it easy for students to get a little of the juice out of a big container.
3. Milk may not indicate too well.  

Safety Considerations: (This list is NOT all inclusive – see all disposal laws and use your professional judgement)

• Make sure that Ammonia and Bleach based products are not mixed.  The reaction between these compounds is a chlorine-based gas that is poisonous.

Concepts the Demo Illustrates:

Indicators, Acids, Bases, pH

Where I found this demonstration:

I first learned about this demonstration as a MAT student at Union College from another student – most likely my chemistry partner Lisa Saccochia.  

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Procedure (Red Cabbage Juice pH Indicator)

Making Cabbage Juice

1. Chop up a head of red cabbage.
2. Put cabbage in a large pot and fill with water.
3. Heat mixture on stove to a boil and allow it to simmer for a half hour or so.
4. Allow the mixture to cool.
5. Strain cabbage out of mixture – collect dark purple cabbage juice.
6. Put cabbage juice in container.  It can be diluted greatly so add as much water as you like to make the volume of juice you desire.  

Household Products to try

• cleaners
• ammonia
• drain cleaner
• bleach
• lemon juice
• milk
• orange juice
• dishwasher detergent
• colorless soda