The Chemistry Behind Fizzy Bath Bombs

[Inquiring_Mike]

We have recently created "bath bombs" in our chemistry class and I was wondering what it was in these bombs that made them react with(creates a fizz) and then they become soluble in water.
Here is the materials list.
-citric acid
-sodium hydrogen carbonate
-olive oil
-cornstarch
-ester(we created our own)

We mixed the citric acid, cornstarch and sodium hydrogen carbonate first, then mixed in the olive oil and ester. Then we let it sit for 2 days... What is it that makes it react with water? Is it the NaHCO3?

 

[Monique]

Hello Inquiring Mike!

From your description I'd have to guess that all your ingredients are dry right? That would make sense..

NaHCO3 is baking soda, similar to the stuff that goes into pop/soda. This is a base, and it will react with an acid in an aqeous environment -> when you put it into the bathtub CO2 gas forms, creating the bubbles.

The olive oil might just be added since it is good for the skin? Prevent it from drying out, after spending hours in the bathtub experimenting with the bath bomb ;P

The starch too, I'd guess it doesn't really add much to the reaction, besides maybe stabilize the dry form of the product.

The ester is an aromatic substance, nice fragrance!

Did you try it yet?? I wonder if it really works nicely!

 

[Inquiring_Mike]

Yup, it works well...
What would the purpose of the cornstarch and citric acid be?

 

[Monique]

The NaHCO3 is a base and in order for it to decompose it needs an acid, citric acid for instance. You would get water and the CO2 gas as a result.

Cornstarch is not reactive, it serves to keep the dry product in a stable form (so that the citric acid (lemon juice) and the NaHCO3 (baking soda) can't react in dry form). It does this simply by sitting in between the molecules and keeping them apart.

Too bad I don't have a bathtub anymore, I would have tried it myself :P

 

[Chemicalsuperfreak]

Esters smell nice. But they make lousy perfumes. Make sure you rinse well, or you'll be sticking it up all day.