The Lab | Red Cabbage Juice: A Natural pH Indicator
From making fertilizer and plastic to keeping your body healthy, acids and bases are
important to a variety of areas of your life. If you are curious about what substances
around your house are acids and bases, you can make an indicator from a red cabbage.
An indicator changes color depending on whether it comes in contact with an acid or
base. The juice from a red cabbage can indicate the following:
EVERY step.
Here are some suggestions:
Pour a small amount (less than half-way up the container) of your collected substances each in their own small, colorless cup (medicine cups work well or see-through bathroom cups). Add about an equal amount of red cabbage juice to each substance. Observe what color it becomes and determine whether it is acidic, basic, or neutral using the chart above.
that produces OH- (hydroxide ions) in water. Acids and bases are commonly found in everyday life.
The pH of a solution tells us whether it is an acid or a base. If the pH of a liquid is less than seven, then it is an acid. If the pH of a liquid is greater than seven, then it is a base. If the pH equals seven, the liquid is neutral.
Indicators are another way of determining whether a substance is an acid or base by looking at color changes. Red cabbage juice contains pigments (something that causes color) called anthocyanins that make it purple. Anthocyanins can be found in the petals of flowers and even the leaves of trees (that is why some tree leaves become red in the fall). Anthocyanins change color depending on the amount of H+ and OH- present, therefore telling us whether the substance is an acid or base.
important to a variety of areas of your life. If you are curious about what substances
around your house are acids and bases, you can make an indicator from a red cabbage.
An indicator changes color depending on whether it comes in contact with an acid or
base. The juice from a red cabbage can indicate the following:
Color Change |
What It Means |
| Red/Pink | Really acidic |
| Pinkish Purple | Slightly acidic |
| Dark Purple |
Neutral (neither acidic or basic, like water) |
| Blue | Slightly basic |
| Green/Yellow | Really basic |
Procedure
Here is the procedure for making red cabbage juice. Please have an adult help you withEVERY step.
- Chop up a head of red cabbage and put it in a bowl that can withstand heat (if you
have too much cabbage to fit in one bowl, you can just repeat the following steps
several times or not use the entire head). -
Pour boiling water over the cabbage.
- After 10 minutes, pour the mixture through a strainer into another container. I
usually pour it into a large, glass measuring cup in the sink. The spout of the
measuring cup then allows me to pour it into an empty 1 gallon milk jug to use for
storage. - Throw away the used cabbage.
- If you do not use the entire amount of cabbage juice and you would like to save it
for later, put it in a sealed container in the refrigerator. If you would like to keep it
for even longer, you can pour the liquid into ice cube trays and freeze it.
Here are some suggestions:
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The Science Behind the Effect
An acid is a chemical that produces H+ (hydrogen ions) in water. A base is a chemicalthat produces OH- (hydroxide ions) in water. Acids and bases are commonly found in everyday life.
The pH of a solution tells us whether it is an acid or a base. If the pH of a liquid is less than seven, then it is an acid. If the pH of a liquid is greater than seven, then it is a base. If the pH equals seven, the liquid is neutral.
Indicators are another way of determining whether a substance is an acid or base by looking at color changes. Red cabbage juice contains pigments (something that causes color) called anthocyanins that make it purple. Anthocyanins can be found in the petals of flowers and even the leaves of trees (that is why some tree leaves become red in the fall). Anthocyanins change color depending on the amount of H+ and OH- present, therefore telling us whether the substance is an acid or base.

















