Science Buddies: "Ask an Expert"

My son in 6th grade is going to be starting a science project on the effect of pH on soap bubbles (how long they last). We are trying to figure out what to add to the soap bubbles (vinegar, baking soda, distilled water, etc...) and in what amount, in order to do this experiment. Any suggestions? It is due in one month.

Hello jkgutter and welcome!

First, you will want to get some pH test strips if you want to know the exact pH of the different solutions. (If you are just testing acids versus bases, then you will be fine without).

Some common bases are soap, baking soda and bleach. Because bubble formulas already have soap in them, they are already basic. You will need to add something that is a stronger base than the soap in order to get a higher pH.

Common acids include lemon juice and vinegar.

As far as amounts, it really just depends on the target pH you want to achieve. Because you are starting with a soapy, basic substance, you may need to add more of the acid than you do the base to get it to a pH below 7.

Also, just a note. Diluting an acid or a base won't change its pH, so adding water (a neutral pH 7 substance) won't change something's pH.

Best wishes!

Hello jkgutter,
This sounds like a fun experiment. Following up on Zoomhex's comment, your local pool supply store will probably have the pH test strips as well as the chemical to increase / decrease the pH in the bubble solution. If you would like a more precise measurement than the test strip, pH meters are also available online at retailer like Amazon for as little as $10 - 20. The other advantages of using the pH meter is that you can measure the pH as you are changing the solution.

Best of luck with the experiment!

Hello jkgutter,

You've had some nice responses here. I do, however, want to clarify a point. This isn't essential to your project, but for the sake of accuracy, please note that adding water to a solution of an acid or base *does* change the pH of the solution. pH is defined by the concentration of H+ ions in the solution. Adding more water changes that concentration and therefore changes pH.