Observations and results
Did the bath bomb made using more cornstarch (following the second recipe) take longer to dissolve than the one made with less cornstarch (following the first recipe)? Did the one made with less cornstarch fizz more?
When a bath bomb comes in contact with water, the baking soda and citric acid react to make carbon dioxide bubbles. This is an acid–base reaction, where baking soda (also called sodium bicarbonate) is a weak base and citric acid is a weak acid. The cornstarch acts as a "filler" to control the reaction between the baking soda and citric acid. In this activity the second recipe used more cornstarch, and less baking soda and citric acid, compared with the first recipe. Consequently, you should have seen that a bath bomb made using the first recipe produced more vigorous bubbles and impressive fizzing, and dissolved much faster, compared with a bath bomb made using the second recipe. (The size of the bath bombs also affects how long it takes them to dissolve, because larger bath bombs will typically take longer than smaller ones to dissolve. But because the bombs from the different recipes should have been similar in size, this factor should not have greatly affected the comparison.)
If you have extra bath bombs and want to save them for later, put them in a sealable plastic bag. Once you've settled on your favorite recipe, you can also make them and give them out as gifts!
More to explore
What's New, CO2? Get to Know a Chemical Reaction (pdf), from the American Chemical Society
Try This: A Chilling Recipe, from the Commonwealth Scientific and Industrial Research Organization
Fun, Science Activities for You and Your Family, from Science Buddies
Shimmy, Shimmy Soda Pop: Develop Your Own Soda Pop Recipe, from Science Buddies
This activity brought to you in partnership with Science Buddies