Can you write your friend a secret note, one that no one but the two of you can read? Chemistry can help! In this chapter, you learned that some compounds and solutions are colored, while others are clear. In this activity, you and an adult family member will make two different solutions. One is an invisible ink, and the other makes the ink visible!
- small saucepan
- toothpick, cotton swab, small sponge, or paintbrush
Make sure you have an adult family member help you. Start by adding 1 teaspoon iodine to about 10 teaspoons water. Set the mixture aside. Next, mix 2 tablespoons cornstarch with 4 teaspoons water in a small pan. Heat the cornstarch mixture in the pan on the stove, stirring until the mixture is smooth. (It is okay to boil the mixture, but be careful not to burn it!) Remove the mixture from the heat. This is your “ink.” Dip a toothpick, small paintbrush, or cotton swab into it and use it to write your message on paper. Let the paper air-dry. Does the paper look blank? Brush a cotton swab, small sponge, or paintbrush dipped in the iodine solution over the paper. The secret message should appear!
Why do you think you needed to use such exact measurements for each of the compounds used in the solution? Which of the ingredients used in this experiment was a pure element? Which were compounds? Why do you think the mixture of compounds needed to be heated in order for the experiment to work?