The Chemistry of Bath Bombs

Introduction

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  • While the name may be slightly alarming, a bath bomb is anything but scary.  Basically, it is a hand-sized sphere that dissolves in warm water.  Why would this be useful?  The item is used for luxury during a bath, and contains essential oils that can be soothing, relaxing, or energizing.  It may also contain food coloring, which dyes the water, and other compounds that are good for skin, such as coconut oil or epsom salts.

  • I chose this topic because I love bath bombs.  I use them all the time and make them as gifts for my friends and family.  I think that the more relaxation in someone’s life, the better.

  • To go along with why I picked this topic, bath bombs affect my life by helping me relax and enjoy luxury in the comfort of my own home.


Composition of ...

  • A bath bomb has nine ingredients, the main two being Sodium Bicarbonate (NaHCO3) and citric acid (C6 H8O7).  Cornstarch (C27H48O20) and epsom salts (MgSO4 + 7H2O) are the other two dry ingredients.  Two essential oils are used in the bath bomb I made, and they are Frankincense and Lavender.  Frankincense is composed of 56% Leukotriene B4 (C20H32O4), 30-36% Gum Arabic (C26H34N2O13), and 4-7% Terpene Obilene (C10H16).  Lavender is composed of Pinene (C10H16), Limonene (C10H16), Camphor (C10H16O), and Acetate (C2H3O2-).  Coconut oil is added to nourish skin, and it contains water (H2O), Vitamin E (C29H50O2), and various fatty acids.  Finally, indigotine (C16H8N2Na2O8S2) is added for the blue color.


Main Chemicals, Compounds, Components

Sodium bicarbonate (NaHCO3), also known as baking soda or sodium hydrogen carbonate, is one of the two main parts of bath bombs.  It is a slightly alkaline, white powder with a pH of 8.3 and no odor.  Because this ionic compound is a weak base, it does not completely ionize in water.  Baking soda forms sodium and bicarbonate ions upon separation, which buffers excess hydrogen ions and leads to a higher blood pH.  The melting point is 108.8 C°, the boiling point is 851.1 C°, and the density is 2.1 g/cm­³.

 

Citric acid (C6 H8O7) is colorless and odorless with an acidic taste due to its pH of 3.24.  It is found in citrus fruits and is a key factor in metabolism.  Citric acid maintains stability among ingredients, so it is used as a preservative.  Pharmaceutical preparations often use citric acid because of this molecules antioxidant properties.  It chelates calcium in the blood, which treats heavy metal poisoning.  The melting point is 152.7 C°, the boiling/decomposing point is 310 C°, and the density is 1.665 g/cm­³.


Chemistry's Role

How are Bath bombs made?

  • Baking soda

    • Baking soda is derived from soda ash. Soda ash is obtained by passing carbon dioxide and ammonia through a solution of concentrated NaCl (AKA table salt), or it is mined in an ore called trona.  

  • Citric Acid

    • Cultures are fed sucrose or glucose to produce citric acid. The source of these products is usually molasses, or other cheap sugars. The mold is filtered out to isolate the citric acid and then precipitated with calcium hydroxide to produce citrate salt. This is then treated with sulfuric acid, as in the extraction from citrus fruit juice.

  • The cornstarch and water mixture has a high viscosity, which helps to hold the citric acid and baking soda together.  Cornstarch is made of long starch molecules.  When forced together, they trap the water between the strands of starch.  As the bath bomb dries in the mold, the water evaporates, leaving a solid structure.  Then, when the bath bomb is set into a larger mass of water [full bath tub], the ratio of cornstarch to water is too uneven to form a semi-solid again.


Background Research

 One wonderful aspect of bath bombs is that they are chemistry that can be prepared right from the kitchen.  However, combining the ingredients can be a little tricky.  The wet ingredients will initiate the reaction between the baking soda and citric acid, so it is important to blend the coconut oil mix quickly with the dry mix.  Once all of the ingredients are mixed thoroughly, the mixture is pressed into molds to dry.  When dried, the bath bomb is complete, and will react with the warm bath water.


Upon touching the water, the citric acid + baking soda yields Sodium Citrate (Na3C6H5O7) + Water (H2O) + Carbon Dioxide (CO2).  Effervescence occurs as the CO2 is produced, resulting in fizzing and foaming.  The food coloring (indigotine = C16H8N2Na2O8S2) dissipates and dyes the bath water faintly.  The epsom salts are dissolved by the water, and the essential oils disperse as well, leaving the water mildly fragrant and lightly tinted whatever color was used.   



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About the Author
Beccah Chambers is a junior at Billings Senior High School.  She enjoys all types of art, traveling, and random fun facts.  She has three siblings, and spends a lot of time thinking of new and crazy ideas.










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