Making colored soap bubbles can actually be a more complex project that it sounds like. The project itself is easy but the hypothesis and conclusions can make for an impressive project. Adding food coloring to soap bubbles will not give you bright colors but this project will. Not only that but you can make your colors disappear and explain pH levels in the process.
Bubble solution, store bought or homemade
White dish cloth or towel
Sodium hydroxide is a strong base, alkaline, substance. Be careful when using it and if any gets on your hands wash them immediately. Safety glasses are recommended to keep air borne bubbles out of your eyes.
You may need to use a small amount of alcohol to dissolve your indicators, the thymolphthalein and phenolphthalein. You can use a ready made indicator solution to simplify this step. Just add your sodium hydroxide to the indicator solution instead of diluting it with water.
You will need to add one and one half to two teaspoons of the blue thymolphthalein or the red phenolphthalein to one liter, or about four cups, of bubble solution. Add your sodium hydroxide until your indicator solution changes from colorless to brightly colored. This will require about one half of a teaspoon of sodium hydroxide. Adding a bit more of the sodium hydroxide will make your bubbles hold their color longer but adding too much can make them harder to have “magically disappear”. This can be solved by using club soda.
When your bubbles land on your dish cloth or towel you should have a red or blue stain. Gently rub the stain, which exposes the solution to air, and the color should disappear. If you have used to much sodium hydroxide you can rub a bit of club soda into the stain and have the color disappear.
This experiment works due to the fact that your pH indicators, the blue thymolphthalein and the red phenolphthalein will change at a pH level of about 10. There are other pH indicators you can use and some that will change color at a higher base level. Thymol Blue will be red in an acid and yellow in a base. Phenol red will change from yellow in an acid to red in a base. Use an indicator chart if you wish to add more color changing bubbles to your experiment.
Remember that you are working with a substance that can be harmful if it comes into contact with your skin or eyes. Do not use this as a bubble bath solution and avoid contact with your mouth when you blow the bubbles. Have fun experimenting with the colors and be prepared to explain why the colors change at different pH levels.