Making Litmus Paper
Litmus Paper
A pH indicator is a chemical that changes color in the presence of an acid or a base. An acid is a substance that has lost an electron. A substance that is capable of neutralizing an acid is called a base or alkali. You may have noticed, when you buy a "red" cabbage at the store, it's actually purple. In the course of preparing the cabbage, if you submerge it in tap water, it appears blue. When you add it to your coleslaw, it takes on a red color. This is because the cabbage contains a pigment that functions as a natural pH indicator. Tap water is slightly basic, causing it to turn blue. The vinegar in coleslaw is a dilute form of acetic acid, which makes the cabbage turn red. If the juice is extracted from the cabbage and allowed to dry on filter paper it makes a neutral litmus paper and can be used to test for acidic or basic conditions.
Do It
To make your own litmus paper, cut or shred some red cabbage leaves into small pieces. Place the cabbage leaves in a bowl and pour enough boiling water over them to cover the leaves. Set aside for 30 minutes. Pour the mixture through a coffee filter to remove the cabbage leaves, collecting the juice in a clean, lidded jar. Allow solution to stand at room temperature until cool. Cut some small strips of blotting paper. Dip them into the cabbage solution, then lay them on a plate to dry. Once the strips are completely dry they are ready to use.
To test your litmus paper, take three strips and dip them into one of the following: lemon juice, Gatorade, or ammonia-based window cleaner. The lemon juice is an acid and should turn it bright pink. The Gatorade is neutral and shouldn't change the color at all. And the ammonia is a base, which should turn your paper green.
How it Works
By pouring the boiling water over the shredded cabbage, you extracted a type of pigment known as an anthocyanin. The color of anthocyanin molecules changes depending on the pH of their surrounding environment, which made them very useful in the creation of litmus paper. This particular litmus will not tell you the exact pH of a substance, only if it is an acid or a base.
Tags: cabbage leaves, litmus paper, acid base, boiling water, boiling water over