Hello and welcome to chemistry in your cupboard. I'm Katherine and I'm the
education coordinator for the Royal Society of Chemistry. Today I'm going to
be making some bath bombs and I'll show you how you can make them at home in
your kitchen. You're going to need a responsible adult to help, and some
ingredients may irritate sensitive skin, so just have a check before you start
experimenting. You may have seen bath bombs before and when you drop them into
water they fizzle out and eventually dissolve. The fizzing happens when an
acid and an alkali in the bath bomb react with each other and make a gas. So
to make bath bombs today I'm going to mix an acid and an alkali together. But
as long as the mixture stays dry there won't be any reaction. To make it
fizz I'll need to drop it into some water. You've probably heard of an acid before,
like lemon juice is an acid. Well, alkalis are the opposite of acids and we often
use them in cleaning. Water is not usually an acid or an alkali. It's
neutral, and if you mix the right acid and alkali together you'll also end up
with something neutral. So for this experiment we're going to
need two bowls to mix everything in, a tablespoon or a big spoon for measuring,
some small containers to shape the bath bombs.
I've got this silicone ice cube tray, you could also use cupcake cases or cookie
cutters. Some bicarbonate of soda or baking soda and this is our alkaline in
dry powder form. For an acid lots of bath bombs use citric acid, which
is found in oranges, but not everyone has citric acid powder at home. Luckily for
us you can also use cream of tartar, which is used in baking and the acid in
this is tartaric acid. Back to our equipment list -
we're going to need a little bit of water and to make them a little bit more
exciting I'm going to add some blue food coloring and three or four drops of
essential oils. First we need to mix the dry ingredients together. Here's two
tablespoons of bicarbonate of soda in a bowl and I'm going to mix it with one
tablespoon of cream of tartar.
In a separate container I'm going to mix together the liquids, so the wet
ingredients. I want a tablespoon water, three or four
drops of essential oil, I'm using jasmine, and three or four drops of food
colouring. Now I'm ready to mix everything together. I'll add the powder to the
liquids and give it a really good mix. Now the ingredients are nicely mixed
together - since I only added a little bit of water there was no reaction and the
mixture is still quite soft, but if I press it down it starts to stick
together. Now we're ready to shape our bath bombs. So, I'm going to separate my
mixture between two sections of my ice cube mold and this mixture will make
about two small bath bombs. Make sure you press it down quite firmly and then I'm
going to leave these to set overnight. So I've left my bath bombs overnight and
they've gotten a bit harder, so I'm just going to ease them out of my mold and
this might be a little easier if you're using cupcake cases at home.
so I've got my two bath bombs. This one has fallen apart a little bit but
that's okay because it would still work just the same. So let's see what happens
when I drop it into a bath of water.
See the fizzing? Some materials change when you mix them together and here
bicarbonate of soda is reacting with tartaric acid to make a gas. This is a
non-reversible reaction we can't get back the bicarbonate of soda or the
tartaric acid even if we evaporated all the water. So now you know how to make a
bath bomb in your kitchen. I wonder whether changing the amount of each
ingredient makes a difference to the reaction in the bath? With a responsible
adult why not investigate? Let us know the best
recipe using the hashtag chemistry in your cupboard. We'll be back for more
experiments soon, in the meantime make sure your grown-up subscribes to the
youtube channel for all the latest chemistry in your cupboard episodes. See
you soon.