There is something very exciting about the idea of a making a magic potion. In particular if the potion can change its colors from deep-purple to bright-pink or to vivid-blue. Today we made pH indicator (magic potion) from purple cabbage and water. This is a very simple exercise and a great opportunity to learn about pH, a measure of acidity or alkalinity of a solution. It is interesting to know that acidic foods, like lemon or vinegar, taste sour, and alkaline foods like baking soda taste bitter.
To make the pH indicator the girls tore red cabbage leaves into small pieces. The cabbage leaves were carefully placed in a food processor, boiling water was added, and the leaves were blended for a few seconds. That's it. The cabbage solution can be used as is, or it can be strained to remove the cabbage pieces from the solution using a strainer or a cheesecloth. Keep in mind that the solution is boiling hot and needs to cool off before handling it (I made additional cabbage solution in advance so it would have time to cool off).
Now the fun begins. We added the pH indicator solution to small cups containing lemon juice, vinegar, baking soda, water, or liquid soap and watched as the deep-purple color of the cabbage changed to pink in the acidic solutions (Vinegar and lemon), vivid-blue in the alkaline solution (baking soda) and purple in neutral solution (water and soap).
Another fun thing to do with the cabbage potion, is to reveal a secret message written with invisible ink. The girls wrote a secret message using vinegar as an invisible ink.
After the invisible ink dried, we painted the paper with the cabbage potion , and revealed the secret message. The cabbage interacts with the vinegar on the page and turns blue. The blue color becomes more prominent once the page is fully dried.