1 Use red cabbage juice to find out if a liquid is an acid. Red cabbage juice contains chemicals that cause the juice to change color when it is mixed with some certain other chemicals. The cabbage juice will turn different shades of red when mixed with acids, and different shades of blue when mixed with bases.
2 First you need to prepare your cabbage juice:
3 Grate some red cabbage into a medium-sized bowl.
4 Cover the cabbage with cold water and let it sit for 45 minutes.
5 Strain the juice into a plastic container.
6 Pour an equal amount of cabbage juice into each plastic cup.
7 Add 1 teaspoon of baking soda to all but one of your cups. The baking soda (which is a base) will turn your cabbage juice blue. Now you can test different liquids to see how much of each it might take to turn the cabbage juice back to its original color. If the juice looks like it is turning back, the liquid you added is probably an acid. The cup without the baking soda is your control. This is the color that you want to get all of your mixtures to match.
8 Get permission to test different liquids. Add your first liquid, one teaspoon at a time, to your first cup. How much do you need to get your original color? Test the rest of your items in the same way.
9 It will take different amounts of different acids to turn the juice back to its original color. If the juice stays blue, the liquid is probably not an acid.
head of red cabbage
clear plastic cups
various liquids to test like lemon juice, vinegar, cola