The Chemistry of Bath Bombs

 Dec 26,2022

What is a Bath Bomb?

Bath bombs, also known as bath fizzers, are dry ingredients that are designed to effervesce once in contact with warm water. Once it hits the water, it releases Essential Oils, scents, colors, and bubbles to elevate your bath experience. Bath bombs can help condition the skin and soothe sore muscles. Additionally, they may help detox and relax the body and mind.

Traditional bath bombs are made up of a few simple ingredients that, when submerged in water, make a fantastic chemical reaction! Here is a list of the essential ingredients used in making most bath bombs:

Sodium bicarbonate (also known as baking soda or bicarb)
Citric acid
Magnesium sulfate (commonly known as Epsom salts or bath salts)
Cornstarch or Arrowroot Powder
Coconut Oil
Various Essential oils (optional)

The Purpose of Baking Soda and Citric Acid in Bath Bombs

Baking soda, also known by its chemical name, sodium bicarbonate (NaHCO3) or bicarb for short, is classified as a base. Citric acid (C6H8O7) is classified as an acid. In their dry, powder forms, these two substances do not react. However, put the two in water and POW – a neutralization reaction occurs!

When the baking soda reacts with the citric acid in water, three products are formed: sodium citrate (Na3C6H5O7) which is classified as a salt, carbon dioxide gas (CO2) which is responsible for the famous bath bomb “fizzing”, and water.

Here’s what the chemical reaction looks like:

C₅H₇O₅CO₂H _(aq.) + NaHCO_{3 (aq.)} → C₅H₇O₅CO₂⁻Na⁺_(aq.) + H₂O_(l) + CO_{2 (g)}

Baking soda + citric acid + water → sodium citrate + water + carbon dioxide

The Purpose of Epsom Salts, Cornstarch, and Oil in Bath Bombs

Epsom Salts- Contains magnesium that is absorbed through skin to soothe sore muscles when dissolved in water.

Cornstarch- Acts as a stabilizer to slow the fizzing reaction between baking soda and citric acid. Controls dissolution rate.

Coconut Oil- Added for several reasons:

Moisturizes and hydrates skin
Binds ingredients together as a solidifying agent
Easily accessible and affordable
Provides a longer shelf life

How to make a bath bomb at home

What You'll Need

1 cup baking soda
1/2 cup of citric acid
1/2 cup cornstarch
1/2 cup of Epsom salt (optional)
2 tsp. essential oil of your choice (we love eucalyptus, rose and lavender)
2 tbsp. emollient oil, such as coconut oil, jojoba oil or sweet almond oil
A few drops of liquid food coloring
A mold (we love round metal molds and molds in fun shapes)
Decorative accents, such as orange peels or rose petals
Whisk
Two mixing bowls

Steps

Pour the baking soda, citric acid, cornstarch and Epsom salt (if using) into a bowl. Whisk the ingredients until fully combined.
Pour the essential oil, emollient oil and food coloring into the other bowl. Mix the ingredients together until the food coloring is fully incorporated.
Slowly pour the oil mixture (from step 2) into the dry ingredients (from step 1). When the oil is all in, keep whisking and add drops of water in between.
If you decide to add decorative accents, like rose petals or orange peels, to your bath bombs, drop them into the bottom of the mold. Then, tightly mash your mixture into the molds.
Leave your bath bombs in the molds for two to four hours before removal. Now you're ready to admire your new creations as they fizz away in your tub!

Tips

If using a bath bomb mold, fill each half of the mold until it’s overflowing, packing in slightly. Press halves together firmly and let mold sit 1 min. Gently tap mold and gently pull mold apart. Let dry 24 hours.
Instead of using an ice cube tray or a mold, try sprinkling the mixture directly into a warm bath. Save any remaining mixture in a resealable container.