You will need:
- A clear container with smooth sides - the taller and skinnier, the better (you could use a plastic bottle or a tall glass, vase) The bigger the container the more vegetable oil you will need.
- Water
- Vegetable oil (just use the cheapest you can find in the supermarket). You can also use baby oil which will be clear rather than pale yellow.
- Fizzing tablets (such as those for cleaning dentures)
- Food colouring
Kids should always be supervised while doing this activity and never let them put the fizzy tablets in their mouth.
- Measure out half a cup of water and colour with a few drops of the food colouring.
- Break a few of the fizzing tablets into 2 or 3 pieces and set them aside in a bowl.
- Pour vegetable oil into your container until it is three quarters full.
- Then add your coloured water until the liquid in the container is about 5 cm from the top. You may have to wait a couple of minutes for the oil and water to separate.
- It would also to be a good idea to do this experiment on a tray – or even outside if the weather is nice - just in case of an overflow!
- Add pieces of the fizzy tablets to the container.
What’s happening?
As water and oil don’t mix, the oil doesn’t change colour – but the fizzy tablets react with the water to make bubbles of carbon dioxide which attach themselves to the blobs of coloured water and float them to the top of the oil. When the bubbles pop the blobs fall back to the bottom of the glass. Once the bits of fizzy tablet are completely dissolved – you can do it all over again!
More fun science activities for kids
Create a Mount Vesuvius volcano!
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