Writing a secret message is always a fun way to communicate. There are a number of different ways in which this can be done, but this one I’ve not seen before and it is fairly quick to do with some household chemicals.
Materials:
- Baking Soda
- Rubbing Alcohol (Isopropyl Alcohol)
- Turmeric
- Q-tip
- Paint Brush or Cotton Ball
- Plastic Table Cloth or Garbage Bag
- Cookie Tray
- Sheet of White Paper
- Spoon
- Glass or Disposable Cups
- Tablespoon, Teaspoon, and ½ Cup
- Measuring Instruments
- Mini Marshmallows
Caution:
The spice turmeric can stain fingers and surfaces. You may want to wear disposable gloves if you’re using a cotton ball to paint on the turmeric.
Experiment:
Mix 1 tablespoon of baking soda with ½ cup of warm water in a cup and stir with a spoon. The more dissolved the baking soda the better the experiment will work. Dip the Q-tip into the solution and write your message on the paper. Make sure that the Q-tip is fully wet so it may need to be added to the solution for each letter. The hard part of this experiment is to see what you’ve written so do the best you can. Set the paper aside to dry.
Now make your turmeric solution by mixing 1 teaspoon of turmeric with ½ cup of rubbing alcohol in a cup and stir with a spoon. Once your paper is dry put it in the cookie tray and with a paint brush or cotton ball (don’t stain your fingers), wipe the surface of the paper with the turmeric solution. Allow this to dry and view your secret message in red.
What’s happening?
Curcumin is the active ingredient in turmeric. This compound is an acid and is yellow in color. The baking soda (active ingredient is sodium bicarbonate) is a base. When the acidic curcumin reacts with the base, it turns red and therefore we call turmeric an acid-base indicator since the color will tell us if curcumin is reacting with an acid or a base. The change from yellow to red occurs at approximately a pH of 8 which is just a little more basic than a neutral pH of 7.
Extension:
Can you find other substances around the house that will change the turmeric from yellow to red (window cleaner, oven cleaner, etc.)? Another common acid-base indicator is red cabbage juice. This substance will undergo many color changes and will be more specific with regard to the pH and the color of the solution. You can check the pH of other common household ingredients using red cabbage juice.
References:
https://childrens-museum.org/blog/2020/04/science-magic-invisible-ink
To view past “ChemShorts for Kids” activities, go to:
https://chicagoacs.org/ChemShorts.
