May 2017:

What is a bath bomb and why does it fizz when it goes into water? A bath bomb is a solid, powdery substance which can take many shapes. Here is one pictured below.

As it's submerged in water, it bubbles. This is the result of the release of CO2 also known as carbon dioxide. This is the gas you breathe out. The release of this gas occurs because of an acid-base reaction. Although we tend to think of acids as scary, many foods we eat are acidic, such as lemons or tomatoes. The acid and base found in a bath bomb are weak and will not hurt your skin. Here is the balanced equation:

3 NaHCO₃ + C₆H₈O₇  ->  CO₂ + 3 H₂O + Na₃C₆H₅O₇

Sodium bicarbonate (NaHCO₃), also known as baking soda, reacts with citric acid (C₆H₈O₇). In the foods you eat, citric acid is often used as a preservative or as a flavoring agent. Baking soda would be considered the base in this reaction. You can guess that the citric acid is, of course, the acidic component. The products (what forms at the end of the reaction) are carbon dioxide, water, and sodium citrate. Sodium citrate (Na₃C₆H₅O₇ ) is also commonly found in the foods you eat.

You might be wondering, how can these ingredients be together in a bath bomb and not react until water comes into the picture? Chemicals are often most stable as a solid. Therefore, water allows the acid and base to react with each other.

Bath bombs are cheap and easy to make. All of the ingredients are safe to handle which makes it fun for people of all ages! Here is an ingredient list and procedure on how to make them:

Materials:

• 1 cup of baking soda (sodium bicarbonate)
• 1 cup of citric acid
• 1/2 cup of coconut oil
• 1/4 cup corn starch
• 1/4 cup of Epsom salts (magnesium sulfate)
• A few drops of the desired color or dye
• A few drops of desired fragrance

Experiment:

• Mix the dry ingredients in the bowl
• Melt the oil if necessary and add fragrance and dye to the oil.
• Mix everything together and use 2” spherical molds or make your own mold
• Be sure to pack the ingredients tightly to yield approximately 10 bath bombs
• Let sit for 24 hours

Oil is necessary to help bind the ingredients together. This also helps moisturize your skin. If you have allergies to coconut oil, it can be substituted using ingredients such as almond oil, sunflower oil, or shea butter. The cornstarch and Epsom salts prevent excess moisture from activating the acid-base reaction.

If proper soap dye is used, there should not be any bath stains. Food coloring can work as well. Essential oils or spritz of fragrances can help scent the bath bombs. As a note, citric acid can often be found at local grocery stores in the spice aisle. Also, to form the bath bombs, soap molds can be purchased at arts and crafts stores.

If you happen to use a bath bomb, don't forget to still use soap in your bath since this is not a soap-containing product! Due to the product being a solid, it will last a long time if kept in a dry area. Bath bombs are exciting to make and use, and you can even make them as a gift for someone. Experiment with different quantities of ingredients and see how it affects the bomb. Have fun and play around as a formulating chemist! J

Amanda Rountree, North Central College

To view all past “ChemShorts for Kids”, go to: http://chicagoacs.org/articles.php?article_category=1