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EXPERIMENT: Make a balloon-inflating machine!

Museum staff demonstrating balloon experiment
Holiday season is a time to celebrate and what better way to do that than with balloons! If you don’t feel like blowing up balloons yourself here’s a trick using another source of CO2.

What you need


About 40 ml of water (a cup is about 250 ml so you don’t need much)

Soft drink bottle

Drinking straw

Lemon or vinegar

1 teaspoon of baking soda


  1. Before you begin, make sure that you stretch out the balloon to make it as easy as possible to inflate.
  2. Pour the 40 ml of water into the soft drink bottle.
  3. Add the teaspoon of baking soda and stir it around with the straw until it has dissolved.
  4. Pour the lemon juice or vinegar in and quickly put the stretched balloon over the mouth of the bottle.

The science!

If all goes well then your balloon should inflate! Adding the lemon juice (or vinegar) to the baking soda creates a chemical reaction. The baking soda is a base, while the lemon juice and vinegar are acids. When the two combine they create carbon dioxide (CO2). The CO2 gas rises up and escapes the soft drink bottle. It doesn’t however escape the balloon, pushing it outwards and blowing it up.

Come and see more experiments like this at Tūhura Otago Museum in our science show on weekends and holidays. For more exciting science visit us at Tūhura Science Centre!

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