…Aka everything you’d like to know about the geeky chemistry on what is going on when you put them into water.
Okay, so let’s start with the key ingredients to create some magic in the tub (that I use as my basic recipe):
- Sodium bicarbonate more commonly known as baking soda
- Citric acid
- Cream of tartar (known by chemists as potassium bitartrate)
Sodium bicarbonate is normally ingredient you’d have known from baking that is responsible for raising the dough (my favourite type of dough these days is crumpet! What is yours?) with white powder appearance. In bath bombs however, it is taking a crucial role of weak alkaline with pH of approximately 8 (neutral pH is 7) and taking part of in nautralisation reaction together with citric acid. The most popular way to produce baking soda these days is to use the Solvay process, but also could be made from trona ore, which is firstly mined. The source of trona ore is previously evaporated Green River in Wyoming, and apparently it’s enough to meet world’s bicarb soda demands for thousands of years!
And again, citric acid is an ingredient you’d probably find in the kitchen – either in citrus fruits, such as lemon and lime (8% of weight of a citrus is citric acid) or on Pancake Day when you are eating your lemon and sugar crepes. Citric acid is weak acid with pH of around 2.2 and it has white, crystalline structure. More commonly now though it is made in the lab – and rightly so as there would not be enough citric acid in the world to meet the demand! I would like to speak on sustainability of the bath bomb ingredients in future posts, as I think it is very interesting matter that not many people consider. But back to bath bombs…
Without water, baking soda and citric acid would not react – they would happily be sitting mixed with each other as if nothing happened, but once water is introduced to the system, that’s when the magic happens – the neutralisation reaction! It’s called like that because weak acid meets weak base and they neutralise each other. In this case, carbon dioxide gas is produced and hence the fizz we experience when we throw a bath bomb to water. The fizz has other purpose – it distributes other ingredients in the water efficiently and helps the fragrance from essential oils fill the bathroom and make us feel all happy and relaxed. Cool, huh? Below you can see a reaction with scary molecular models that I tried my best to simplify (I do like chemistry).
CREAM OF TARTAR
Last ingredient of my basic recipe, cream of tartar, or potassium tartrate (no one uses that name, so let’s stick with cream of tartar). It has one, simple but important role of binding the bath bomb and making it hard – very important if your bomb could fall, as you don’t want it to break into million pieces (this moment when you’re made some fro your mum and you dropped it on pavement as you were getting into the car… Sad moment of my life). Cream of tartar is a by-product from wine production as “wine crystals”. It is then filtrated and crushed into powder. Also – again baking ingredient – could be used in meringue to make it fluffier!
Other ingredients are water and oil – they are binding agents. I will elaborate much more on oil in other post, but if it comes to water it needs to be used sparingly due to the fizz activating properties – it activates the neutralisation reaction, so we don’t want to start anything prematurely… (wink wink). Your best bet is to spray a bit of water and mix fast, so the mixture won’t start to fizz.
Another very common ingredient in bath bombs is cornstarch. It is used as a “filler” in bath bombs and it also slows down the reaction between baking soda and citric acid. I decided not to include it as I want to offer quality bath bombs packed with nourishing ingredients for body and soul rather than fillers. Yes, fizzes out quicker, but if that’s the sacrifice I have to make I am happy with it!
Other additional ingredients are milk powders, clay and essential oils – more on that in next blog posts!
I hope you found it interesting and not too boring!