Bath Bomb Chemistry
How do fizzy bath bombs work? The coolest part of a bath bomb is watching it fizz as soon as it’s dropped into water. What causes that blast of effervescent, fizzy bubbles? Amazingly, it’s chemistry that is responsible for this phenomenon and there is a chemical reaction taking place. There are not many chemical reactions that occur while using a beauty product. Bath bombs are an exception and they are a fun way to learn about chemical reactions.
In a chemical reaction, reactants are the starting materials that yield the products, or new chemical substances. Below is the chemical equation for a bath bomb reaction. All of the reactants are on the left hand side of the chemical equation and the products are on the right hand side.You’ll notice that each side is chemically different but made up of the same elements: C (Carbon), H (Hydrogen), O (Oxygen) and Na (Sodium).
Citric Acid and Sodium Bicarbonate are the starting materials in this reaction. Citric Acid is naturally present in citrus fruits and Sodium Bicarbonate is commonly known as Baking Soda. When Citric Acid and Sodium Bicarbonate are combined they do not react until they come into contact with water. This is how they can coexist in the same formulation without fizzing and bubbling in the package. When water is introduced, it acts as a catalyst to promote the acid-base reaction and form the products, or new chemical compounds. The products in this reaction are Sodium Citrate, Water, and Carbon Dioxide which are a salt, liquid and a gas. Carbon Dioxide gas is responsible for all the bubbles that you see when your bath bomb comes in contact with water.
There’s a reason that there is more than Citric Acid and Sodium Bicarbonate in a bath bomb formulation. Cosmetic formulations are not chemical reactions but there is chemistry involved in their creation. Each ingredient is a molecule that interacts with each other and has a function in the formulation.
Corn starch, colorants, fragrance and water are also necessary to make a fizzy bath bomb. Corn Starch is added as a binder which helps all of the ingredients blend together into a uniform shape. Oil, color and fragrance are added for aesthetics which is the way that a product looks, smells and feels. They are also the liquids that are necessary to hold all of the powders together. Making a bath bomb is similar to making a sand castle at the beach where wet sand is needed to form and hold the shape of the castle. For a bath bomb, oils are typically used to avoid starting the chemical reaction prematurely.
The amount of each ingredient is also important. Varying the ratios of each ingredient can affect the bath bomb’s appearance or the amount of bubbles formed. For example, if you add too much water, the reaction will occur in your bath bomb and it will rise like a cake. As a result, you will not have as many bubbles when it’s added to your bath. If you add more oil or leave the water spritz out, you will have a denser product that will bubble more when it comes in contact with water. If you leave Citric Acid or Sodium Bicarbonate out, you will not form the acid-base reaction which forms the fizzy bubbles. Changing the amounts of each ingredient would make a fun experiment. Give it a try!
Check out this fun Sweet Tart Fizzy Bath Bomb formulation to learn how to create your own bath bomb and see the chemical reaction in action. Happy Formulating!