Incidental Science Blog #7


“Chemistry is the central science. It deals with the composition, structure and behaviour of the atoms and molecules that make up all forms of matter. Understanding the world at an atomic level is essential to all areas of science.”


It’s also one of the most exciting sciences to teach children of all ages because it implores you to interact with your world to learn about it.


At our Science Snippets (in the library) classes, the most popular topics are the ones where there are surprises involved, kids love to see something unexpected happen. If they’re the ones who created it, the reactions (see what I did there?) are well worth the mess you have to clean up afterwards.


My first tip for creating chemistry experiments at home is to buy a large tarpaulin sheet (or something similar). Then you can scoop everything up once you’re done, take it outside and hose it down.


One of the easiest and cheapest chemistry experiments to do with kids is bath bombs or fizzy potions. Since we only have an hour in our library classes, we stick with the fizzy powders but at home you can leave bath bombs overnight to dry and then use them (perfect for wrangling the kids into their evening baths!).



I’ve created a quick video on how to make a bath bomb at home with household items (many ingredients can be swapped out for others) – mine was an oil based bath bomb which is easier to create. If you choose to add any water based liquids (food colouring, smell essences etc.), I would recommend popping them into a spray bottle. If you add liquids into the mixture too quickly then the chemical reaction caused by the baking soda and citric acid will begin (it will only work once) and your bath bomb will be fizz less.


Before I give you the instructions, I will give you a few science facts to give to your kids before you create your experiments.


  • There are three ‘States of Matter’ in the world; Solid, Liquid and Gas.


  • Each of these states can transform into the other. Can you think of how a liquid could become a solid? (Water becomes ice when frozen.)


  • How does rain get up into the clouds? (Evaporation) It transforms into liquid and rains down on the ground, only to evaporate again or be used by the soil.


  • Gases often can’t be seen but every breath you expel is full of water vapour and carbon dioxide - when it's freezing outside, you can see the water vapour condensing in the air!


  • Liquids will take on the shape of the container that they’re in (show how the same amount of water in one glass, moulds into a different shaped glass when you pour it out. Then show how a solid (a LEGO brick maybe) doesn’t mould into the container it’s in.


  • Baking soda (which is a solid) and a small amount of citric acid (also a solid) mixed together don’t do anything/react. But when you add some liquid to them, it causes a reaction, carbon dioxide gas is formed, along with other products and the solids are changed forever.


  • We leave the bath bombs to dry so that any extra liquid can evaporate and the bath bomb will stay in the shape we’ve moulded it to.


  • Popping the bath bomb in hot water starts many reactions, causing some ingredients to melt, the heat causing the vapour to rise and condense, carbon dioxide is made and disapates into the air and the once solid bath bomb is gone. 




Moisturising Bath Bombs




  • Washing Soda or Soap Crystals (if you have sensitive skin then miss them out or only add a few) - these create the bubbles - 1 cup


  • Baking Soda - 2 tbsp


  • Citric Acid - 2 tbsp


  • Cornflour - 1 cup


  • Epsom Salts or other skin friendly salts - 1 cup


  • Coconut Oil or another skin friendly oil - 1 cup


  • Sprinkles, fine edible glitter, a small amount of food colouring


  • Orange jelly crystals or another smell you enjoy - essential oils are good for this


  • Coco butter (optional) - 1/2 cup


Stir all dry ingredients together and then stir in oils and decorations - be careful adding any liquids (do it in small amounts) as the bath bomb ingredients are inert (don't react) until you drop them in your bath or add liquid. 


Use hands to make sure it’s the right consistency for moulding, add more cornflour or more oil depending on the mixture.


Push firmly into a mould, bath bomb or silicon moulds work well for this.


Leave overnight to dry.


Wrap up for a gift or pop in your own bath :)


Geni McCallum is the Marketing Manager and Community Educator for Science Alive! She lives in Christchurch with her partner, step-daughter and cat. 

The opinions expressed in this article are those of the author, and do not necessarily reflect the views of Science Alive!