How do you make a pH indicator from red cabbage?

Chop a red cabbage into small pieces, boil them in water for 10-15 minutes until the water turns deep purple, then strain the liquid. This purple liquid is your pH indicator, which changes color when mixed with acids or bases.

What colors does red cabbage pH indicator turn in acids and bases?

The indicator turns red or pink in strong acids, purple in neutral solutions, and blue, green, or yellow in bases. The exact color depends on the pH level of the substance tested.

Can you use red cabbage pH indicator to test household items?

Yes, you can test common household items like lemon juice, vinegar, baking soda, and soap by adding a few drops of the indicator. The color change reveals whether the item is acidic, neutral, or basic.

How long does a homemade red cabbage pH indicator last?

The indicator can be stored in a sealed container in the refrigerator for up to a week. For longer storage, freeze it in ice cube trays and thaw cubes as needed.

Is red cabbage pH indicator safe for kids to use?

Yes, it is a safe and non-toxic science experiment for children, as red cabbage is edible. However, supervise young kids when boiling the cabbage and avoid testing strong acids or bases.

How to Make a Red Cabbage pH Indicator: Easy Guide

If you have a head of red cabbage in your kitchen, you already own a simple chemistry lab. The pigment that gives red cabbage its color, a type of anthocyanin, changes structure depending on the acidity or alkalinity of whatever it touches. This makes it a natural pH indicator. To make a red cabbage pH indicator, you chop the cabbage, boil or steep it in water to extract the purple pigment, and then strain out the solids. The resulting purple liquid will turn bright pink or red in acids and green or yellow in bases. You can use it to test household liquids like lemon juice, baking soda solution, or tap water.

What You Need for the Experiment

The ingredient list is short, and you probably have everything except the cabbage itself.

1/2 a head of red cabbage (purple-leaved Brassica oleracea)
A pot or heatproof bowl
Water (distilled water gives the most reliable color, but tap water works)
A strainer or coffee filter
A knife and cutting board
Small clear cups or jars for testing

For the testing phase, gather a few common household liquids. Good candidates include lemon juice, white vinegar, baking soda dissolved in water, liquid antacid, club soda, and plain tap water. Avoid testing strong acids or bases, bleach, or drain cleaners — the indicator is for gentle household items only.

How to Extract the Indicator

There are two easy ways to get the purple dye out of the cabbage. Both work well.

Hot Water Method

Chop the red cabbage into small pieces — roughly 2–3 cm squares. Put the pieces in a pot and add enough water to cover them. Bring the water to a boil, then reduce the heat and let it simmer for about 10 minutes. The water will turn a deep purple. Turn off the heat and let it cool.

Pour the liquid through a strainer into a bowl or jar. Discard the cabbage pieces (they are safe to eat but will be very bland). The dark purple liquid is your indicator. You can store it in the refrigerator for a few days in a sealed jar.

Cold Water Method

If you want to avoid heat, put the chopped cabbage in a blender with enough water to cover it. Blend for 30 seconds until the water is deeply colored. Pour the mixture through a strainer lined with a coffee filter or a clean cloth. This method produces a slightly cloudier liquid, but it works just as well for testing.

Testing the Indicator

Now you can see the color change in action. Pour a small amount of the purple indicator into each of your clear cups — about 2–3 cm deep is enough. Add a spoonful or a small splash of your test liquid to each cup and stir gently.

The color shifts are predictable:

Strong acid (pH 2–3): The liquid turns bright pink or red. Lemon juice and vinegar will do this.
Weak acid (pH 4–6): The liquid turns pinkish-purple or magenta. Club soda or orange juice will show this.
Neutral (pH 7): The liquid stays purple. Tap water or distilled water will not change the color much.
Weak base (pH 8–10): The liquid turns blue. Baking soda solution is a good example.
Stronger base (pH 11–12): The liquid turns green or yellow. Liquid antacid or washing soda will produce this.

A quick example: if you add a teaspoon of lemon juice to the purple indicator, it will turn bright pink. If you then add a pinch of baking soda to that same cup, the color will shift back toward purple and then blue as the acid neutralizes.

Why the Color Changes

The pigment in red cabbage is an anthocyanin, a type of flavonoid that is sensitive to pH Wikipedia — Red cabbage. In acidic conditions, the molecule holds extra hydrogen ions, which shifts its structure and makes it reflect red light. In neutral conditions, it is purple. In alkaline conditions, it loses hydrogen ions and reflects blue or green light.

The same pigment is why red cabbage leaves themselves can look different depending on the soil they grow in. Acidic soil produces redder leaves, while alkaline soil produces bluer or greenish leaves. When you cook red cabbage, adding vinegar or lemon juice keeps it red; without acid, the cabbage turns blue.

Safety and Cleanup

This experiment is safe for children with adult supervision. The indicator is not toxic, but it will stain clothes and countertops. Wear an apron or old clothes, and wipe up spills quickly with soap and water. Do not taste the test liquids unless you know they are food-safe. Discard the used indicator and test liquids down the sink with plenty of running water.

If you want to keep a record, take photos of the cups lined up from most acidic to most basic. You can also dip strips of white coffee filter paper into the indicator, let them dry, and then dip them into test liquids to make your own pH test strips.

Key Takeaways

Red cabbage contains a natural pigment (anthocyanin) that changes color based on pH.
To make the indicator, chop red cabbage and boil or blend it with water, then strain out the solids.
The purple indicator turns pink or red in acids, stays purple in neutral solutions, and turns blue, green, or yellow in bases.
Common household liquids like lemon juice, vinegar, baking soda solution, and tap water work well for testing.
The experiment is safe for kids with adult supervision, but the liquid can stain fabrics and surfaces.

How to Make a Red Cabbage pH Indicator: Easy Science Experiment