Witches potions

So with Halloween (sort of) round the corner I thought I’d do some Halloween themed science stuff, starting with witches potions. These should be one of those ‘easy to do, have all the ingredients in the cupboard’ type of activities but I actually had none of the items needed. So for your information this is the kit:


  • Bicarbonate of soda (essential)
  • Jar/glass/pot/bottle/cauldron/something to make the potion in (essential)
  • lemon juice or clear vinegar (not essential – can just use hot water but when dealing with kids I would opt for the non hot liquid. Lemon juice obviously smells better!)
  • washing up liquid (not essential – turns bubbles foamy so depends what effect you are going for)
  • food colouring (not essential – makes it look pretty though)
  • Container to do it in (not essential but helpful for those who like to keep mess to a minimum – something like a casserole dish will do)


And this is how you do it:

  • Add lemon juice/clear vinegar/hot water to your jar so that it is half full
  • If you are using either of them put in the food colouring (few drops) and washing up liquid (healthy squeeze)
  • Add a heaped teaspoon of the bicarbonate of soda and watch the foaming fun happen!

Version 2



  • The foam flows out of different containers in different ways – try a few to see what happens. We found the small glass jar with the long neck to be the most effective.
  • If using washing up liquid try without and see the different effect (bubbles vs foam)


The science bit

Basically it’s a chemical reaction. The lemon juice and vinegar are acids. They are reacting with the bicarbonate of soda and releasing carbon dioxide (the bubbles!). The washing up liquid makes a foamy effect as it is trapping the bubbles of carbon dioxide gas. The food colouring does nothing, just makes it look good!

Explaining it to children

To my 3 year old I said it was like adding all the different ingredients to a witches cauldron, mixing them together and making something new appear. However in this case not a frog or whatever else witches make but a gas, which we can see as bubbles. My 1 year old was actually napping when we did it but I suspect I would have just said “look, bubbles!” to him if he’d been awake.


Idea based on an experiment in the Usborne Activities: 365 Science Activities book.

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