Fizzy Bath Bomb Reaction

Some bath products fizz and make bubbles when added to water. Ever wonder why? Try this experiment to find out. (Adult supervision recommended.)
Materials:

• 1 cup baking soda
• 1/2 cup citric acid in powder form
• 1/2 cup cornstarch
• 1/3 cup Epsom salts
• 2-1/2 tablespoons olive or almond oil
• 3/4 tablespoons water
• 1/2 teaspoon fragrance oils
• 1/4 teaspoon borax
• Plastic mixing bowl
• Gloves
• Jar with lid
• Molds or ice cube trays

What To Do:

1. Put the gloves on and combine the baking soda, citric acid, corn starch, and Epsom salts together in a bowl. (Citric acid can be found in craft stores like Hobby Lobby in the candle and soap making section. It can also be found in health food stores that sell spices in bulk quantities.) Mix well and set aside.
2. Combine the oils, water, and borax in a jar. Cover it with the lid and shake vigorously to mix the ingredients well.
3. Slowly add the liquid mixture to the dry mixture, but stir continuously and quickly. Do not add too much liquid at one time or else it will start fizzing. The mixture will be very dry and crumbly.
4. Pack the mixture into molds or ice cube trays and let rest for two days.
5. After two days, remove the mixture from the molds. Take one of the finished bath bombs and drop it in water. What happens?

What's Happening?
A bath bomb is really showing how acids and bases react when they are mixed together. In this experiment, the baking soda is the base and the citric acid is, well, the acid. But the reaction of this acid-base combination can be controlled by the other ingredients in the bath bomb.
The cornstarch and Epsom salts both act as liquid absorbers to help keep the baking soda and citric acid from reacting with each other when liquids are added. They are also helpful if you live in a place with high humidity. The borax acts as both a preservative and an emulsifier - it stabilizes the acid and the base and keeps them from reacting with each other before entering the water.
Water is needed for the reaction to occur because is dissolves the solids and allows the ions in the acid and the base to move and collide with each other, causing a reaction to occur. This reaction forms carbon dioxide, which comes up to the surface of the water in the form of bubbles. And, of course, the oils and the fragrances are useful as a liquid to help form the bath bombs as well as cause the skin to be smooth and scented.
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