Baking soda (sodium bicarbonate) plays an important role in the formulation of bath bombs. When combined with an acidic ingredient, it undergoes a chemical reaction that releases carbon dioxide gas. This is what causes the bath bomb to fizz and bubble when it comes into contact with water.

The chemical reaction involved is:

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NaHCO3 (sodium bicarbonate) + HCl (acid) -> CO2 (carbon dioxide) + NaCl (sodium chloride) + H2O (water)

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The carbon dioxide gas bubbles create a fizzy, effervescent effect that can be visually appealing and relaxing. It also helps to disperse the other ingredients in the bath bomb throughout the water, creating a more enjoyable bathing experience.

In addition to its role in creating the fizz, baking soda can also help to soften the water and soothe irritated skin. It can also be beneficial for people with dry skin, as it can help to restore the skin's pH balance.

Overall, baking soda is a key ingredient in bath bombs due to its ability to create the characteristic fizz and provide additional benefits for the skin and water quality.