The question: Can a vegetable tell us whether something is an acid or a base?
Make a prediction
What color do you think lemon juice will turn the cabbage juice? What about baking soda? Write your guess on the worksheet before you start. Scientists call this a hypothesis.
What you need
1/4 head red cabbage, chopped
Hot water (adult)
A strainer and a pitcher
6 clear cups
Test liquids: lemon juice, vinegar, plain water, milk, baking soda mixed in water, a little dish soap in water
Spoons
Steps
An adult pours about 3 cups hot water over the chopped cabbage. Let it steep 15 minutes until the water is deep purple.
Strain out the cabbage. The purple liquid is your indicator.
Pour about 1/4 cup indicator into each cup.
Add 1 tbsp of a different test liquid to each cup and stir.
Record the color you see. Line the cups up from pink to green!
🔬 Make "magic potion" art: paint with cabbage juice on paper, then dab on lemon juice and baking-soda water to make pink and green designs.
⚠️ Safety: Hot water is for adults only. The juice can stain clothes and counters.
What's happening? The science
Red cabbage gets its color from natural pigments called anthocyanins. They change color depending on how acidic or basic a liquid is, which scientists measure on the pH scale (0 to 14).
Acids (low pH) like lemon juice and vinegar turn the juice pink or red. Neutral liquids like water keep it purple. Bases (high pH) like baking soda turn it blue or green, and very strong bases can turn it yellow.
Think further
Is your favorite drink an acid or a base? Test it!
What happens if you add vinegar to the green baking-soda cup?
