How does a Bath Bomb Work – The part that makes them fizz is the same as an Alka Seltzer or soluble aspirin tablet: sodium bicarbonate and citric acid. These chemicals are inert when they are dry powders, but in water they dissolve and the citric acid reacts with the sodium bicarbonate to form sodium citrate and carbon dioxide.
The sodium citrate stays in solution and you don’t really notice it, but the carbon dioxide bubbles out as a gas that helps the bath bomb break up. This lets the detergents, perfumes and oils that make up the rest of the bath bomb mix with the bathwater.
How does a Bath Bomb Work – Bath bombs are awesome balls of fizzy goodness, with some interesting science behind them! They were invented in 1989 by Mo Constantine, one of Lush’s founders. Bath bombs contain the chemical sodium bicarbonate, also known as baking soda, as their key ingredient
Bath bombs are awesome balls of fizzy goodness, with some interesting science behind them! They were invented in 1989 by Mo Constantine, one of Lush’s founders. Bath bombs contain the chemical sodium bicarbonate, also known as baking soda, as their key ingredient.
Some of you might remember that baking soda isn’t good for your skin because it’s a base, with a high pH. High pH (alkaline or basic) products disturb the skin’s acid mantle, which protects your living tissue from the environment, particularly bacteria, like acne-causing Propionibacterium acnes.
But don’t fret! The second key ingredient in a bath bomb is a solid acid, such as citric acid or tartaric acid (cream of tartar). This lowers the pH by reacting with the baking soda when water is added to the mixture. Unless the maker of the bath bombs has really messed up their proportions, the final pH should be reasonably neutral. Until the water dissolves the acid and baking soda and allows them to mix at a microscopic level, nothing happens.
Aside from neutralisation, the acid + base reaction with sodium carbonate also produces tiny bubbles of carbon dioxide gas, which is what causes the fizzing:
How does a Bath Bomb Work – The Chemical Reaction
Citric acid + sodium bicarbonate → sodium citrate + water + carbon dioxide
C6H8O7(s) + 2NaHCO3(s) → Na2C6H6O7(aq) + 2H2O(l) + 2CO2(g)
How does a Bath Bomb Work – This is almost the same reaction as the one commonly used in volcano science projects to create foaming “lava” (they usually use vinegar as the acid). Of course, in bath bombs, there’s also fragrance and colours and glitter – the fizzing helps the bath bomb disperse faster, and combined with heat from the hot water, spreads the scent faster and makes the whole bathroom smell amazing.
Bath bombs can slowly absorb water from the air, using up the acid and sodium carbonate and releasing carbon dioxide prematurely – this is why bath bombs get less fizzy as they get old! Make sure you keep your bath bombs in a dry place until you’re ready to use them.
How does a Bath Bomb Work – When the weather outside is frightful, soaking in a hot bath can sound especially appealing. And adding a bath bomb to the water can elevate the experience. But what exactly is in these scented spheres, and what makes them so fizzy?
Bath bombs are usually made from three key ingredients: baking soda, citric acid and cornstarch, said Frankie Wood-Black, an instructor in chemistry at Northern Oklahoma College and an experienced bath-bomb maker. Often, bath bombs also include dyes and perfumes, and sometimes they have epsom salt.
How does a Bath Bomb Work – The fizziness of bath bombs comes from the chemical reactions that happen when the baking soda and citric acid come into contact with water, Wood-Black told Live Science. Baking soda, or sodium bicarbonate, has the chemical formula NaHCO3. In water, baking soda quickly dissolves, and the positively charged sodium (Na+) breaks apart from negatively charged bicarbonate (HCO3-).
Meanwhile, the citric acid also dissolves, with a single hydrogen ion (H+) separating from the rest of the molecule, Wood-Black said. Then, that positively charged hydrogen from the citric acid and the negatively charged bicarbonate from the baking soda mingle, very quickly undergoing a series of reactions. One of the end products is carbon dioxide (CO2). Because carbon dioxide is a gas, it forms small bubbles in the bath water, creating a delightful fizz.
If there are perfumes or scented oils in the bath bomb, they are released into the air with the carbon dioxide bubbles, Wood-Black said. The sodium from the baking soda and the rest of the citric acid molecule (minus the hydrogen that it lost when it dissolved) simply remain in the water.
The cornstarch in a bath bomb has just one job: It slows down the reaction.
By binding to the baking soda as well as the citric acid, the cornstarch slows down the rate at which both of them dissolve. The effect is that the fizziness may last 3 or 4 minutes, instead of only seconds, Wood-Black said.
Making bath bombs is not difficult, she said. She mixes 1 cup of baking soda, one-half cup of citric acid and one-half cup of cornstarch together in a bowl. All three items can be found at grocery stores. Citric acid is found in soda and candy and can also be used to make cheese, Wood-Black noted. After mixing the three ingredients, she adds about 1 teaspoon of water, which is enough to just barely moisten the ingredient mixture so that the powder sticks together. She then scoops the mixture into a mold (such as a Santa or a star candy mold) to form a shape and lets the shapes dry overnight.
But you can also just mix together the three key ingredients and skip the water. Leave the mixture in a jar, and then scoop it into your bath, she said.
Food coloring can be used to dye bath bombs, she said. But she doesn’t dye the ones she makes. “I opt not [to do that],” she said. “I’m a chemist by profession, but with food coloring, I just get it all over the place.”