Bath Bombs

Fizzy bath bombs, the scented balls you place in your bath, are an example of a chemical reaction between an acid and a carbonate.
Below is a simple recipe for making your own bath bombs.

Equipment	Procedure
mixing bowl jar waxed paper 2 tablespoons citric acid 1/4 cup sodium bicarbonate 1/4 teaspoon fragrant oil (eg lavender oil) 3 tablespoons vegetable oil (eg olive oil)	1. Mix sodium bicarbonate and citric acid together in the mixing bowl. 2. Mix fragrant oil and vegetable oil together in the jar. 3. Slowly add contents of jar to mixing bowl while stirring. 4. Form small balls of mixture and place on waxed paper. 5. Allow balls to dry for 1 or 2 days before storing. 6. Add a ball to your bath water and enjoy!

When you drop your bath bomb into water, the process of dissolving the bath bomb allows the sodium bicarbonate and citric acid to react to produce soluble sodium citrate, water and carbon dioxide gas. The bubbles of carbon dioxide given off during the reaction is why the bath bomb fizzes in the water.

The vegetable oil is not soluble in water, so as the sodium bicarbonate and citric acid react, vegetable oil is released into the water forming a thin layer on your skin which can help "moisturize" it. At the same time, the fragrant oil, which is also insoluble in water, is released, so you can smell the scent.

Further Reading
Definitions and Properties of Acids and Bases
Reaction Calculations: Mass and Moles
Limiting Reagents and Reactants in Excess

Suggested Study Questions

1. Sodium bicarbonate is also known as sodium hydrogen carbonate, baking soda, bread soda and cooking soda. Write the chemical formula for sodium bicarbonate.
2. Write a word equation for the reaction between citric acid and sodium bicarbonate.
3. A balanced chemical equation for the reaction between citric acid and sodium bicarbonate is :
   C₅H₇O₅COOH + NaHCO₃ → C₅H₇O₅COO^-Na⁺ + H₂O + CO₂
   Name each of the following compounds:
   • NaHCO₃
   • C₅H₇O₅COOH
   • C₅H₇O₅COO^-Na⁺
   • CO₂
   • H₂O
   
   
4. Write a chemical equation to show citric acid acting as a Bronsted-Lowry acid.
5. Sodium bicarbonate is amphiprotic.Write a chemical equation to show sodium bicarbonate
   • accepting a proton
   • donating a proton.
6. In the reaction between citric acid and sodium bicarbonate, is sodium bicarbonate acting as an acid or a base? Explain your answer. 
7. For the bicarbonate ion, give the formula for its
   • conjugate base
   • conjugate acid 
8. The density of citric acid is about 1.5 g/mL. If a tablespoon has a volume of 15 mL, what mass of citric acid was used in preparing the bath bomb? 
9. Sodium bicarbonate has a density of about 2.2 g/mL and there are 16 tablespoons in 1 cup. What mass of sodium bicarbonate was used to make the bath bomb?
10. For the reaction between citric acid and sodium bicarbonate given the quantities used in the procedure provided above, which reactant is
    • the limiting reagent
    • the reactant in excess
11. Calculate the mass of carbon dioxide you would expect to be released during the reaction between citric acid and sodium bicarbonate as described in the above procedure. 
12. Assuming a temperature of 25^oC and a pressure of 100 kPa, what volume of carbon dioxide gas would be released using the data above? 
13. If the amount of sodium bicarbonate used to make the bath bombs as described above were doubled, what effect would that have on the amount of carbon dioxide produced when the bombs were placed in water?
14. Write an aim for the experiment described above.