Fizzy Hidden Coin Pirate Rocks

These are super simple to make and lots of fizzy fun. We used food colouring to make the baking soda look like rocks and added shiny coins for the children to find.

First we cleaned up some pennies to be our shiny pirate coins. To do this we simply placed them in coca cola and vinegar. You can see from the second photo both did a good job. The coin in the middle was in water for the same amount of time.

How to clean coins

How to clean coins

Once we had our shiny coins we set about making the rocks.


Baking soda

Food colouring




Optional – flour


Pour your baking soda into a bowl and add water slowly until it makes a paste.

Add a couple of drops of food colouring and mix well.

Either mould with your hands or use cake moulds to create shapes, press a coin into each.

Leave in the fridge overnight.

If you wanted to pad out the baking soda a little, add some flour when you mix. As long as it’s not more than half and half you should still get a good reaction.

fizzy pirate rocks

We added some coloured rice to make it look a little more appealing and then used a pipette to drop vinegar onto the coins.

fizzy pirate rocks

Why does this happen?

Vinegar (an acid ) and bicarbonate of soda ( an alkali ) react together to neutralise each other. This reaction releases carbon dioxide a gas which is the bubbles you see.

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