Kids, “bath bubblers” or “bath bombs” are fancy bath bars that can be found at bath & body stores. But even better, they are easy to make with materials found in the home. A chemical reaction occurs when a bath bubbler comes in contact with water which involves citric acid (H3C6H5O7, a weak acid) and baking soda (NaHCO3 , a weak base).
Please note: All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.
You will need baking soda, cornstarch (C6H10O5), citric acid, Epsom salts (MgSO4-7H2O), sweet almond oil, witch hazel, a fragrance oil, food coloring, molds (three small plastic Easter eggs, small muffin tins or ice cube trays), aluminum foil, plastic wrap, and rubber gloves. Measure these dry ingredients into a large bowl: 1/2 cup baking soda, 1/4 cup cornstarch, 1/4 cup citric acid, and 2-1/2 Tbsp Epsom salts. Grind the lumps out with a large plastic spoon and mix well. Measure and combine these liquid ingredients into a small cup: 4 tsp almond oil, 3/8 tsp witch hazel, 1/8 tsp of fragrance oil, and 1 drop of food coloring. Seal plastic wrap over the cup. While holding the wrap in place over the top of the cup, swirl the ingredients to mix them well.
The next step is for an adult partner. While stirring constantly with gloved hands, have them slowly add the liquid mixture to the dry mixture in the bowl. (If too much liquid hits the dry ingredients a reaction will start, so go slowly; using witch hazel instead of water helps). Mix in all of the liquid. The mixture should be crumbly (like damp sand). Now you can pack the damp mixture into molds. Press firmly. Work quickly so that it does not dry out completely. (When using egg molds, pack each side and then add some loose mixture to one half and firmly push the halves together. Do not twist, and the halves do not need to fit together perfectly). Let the molds rest undisturbed for 48 hours. Unmold the bubblers onto aluminum foil, tapping gently against the tabletop. Without twisting, unmold one side at a time.
Try two bubblers by placing one in a container of hot water and another in cold water. Record your observations about the fizzing. Can you guess what gas is causing the bubbles in this reaction? Store the rest of the bubblers for yourself in a sealed container (most plastic wraps will let humidity in).
Why is water needed to start the reaction? Water dissolves the solids and enables the ions to move, collide, and produce a reaction in solution. The reaction is citric acid with baking soda to produce carbon dioxide. Carbon dioxide fizzes and the bubbler releases the fragrant oils into the bath water as it whirls and spins. How does the water temperature affect the action? Bath bubblers will spin and fizz in water. The rate of bubbling increases with an increase in water temperature. Why could humidity lead to problems? If high enough, humidity can provide enough moisture to dissolve the solids and start the bubbler reaction.
Notes: Sweet almond oil and citric acid can be found in natural food stores; fragrance oils are in craft stores that sell soapmaking supplies. Soap molds from craft stores can be used for fancier shapes. Do not substitute ascorbic acid for citric acid because it yellows and freckles the bar.
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Kathleen Carrado Gregar, PhD, Argonne National Labs
[email protected]
March 2005
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References: Journal of Chemical Education, 2003, 80(12), 1416A by Mary E. Harris and Barbara Walker;
Brenda Sharpe at http://www.ncf.carleton.ca/~aj471/BathBombs.html
