Chemical reactions make for some great experiments. Make use of the carbon dioxide given off by a baking soda and lemon juice reaction by funnelling the gas through a soft drink bottle. Blowing up balloons was never so easy!

Materials

Balloon
About 40 ml of water (a cup is about 250 ml so you don't need much)
Soft drink bottle
Drinking straw
Juice from a lemon
1 teaspoon of baking soda

Instructions:

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

What's happening?

If all goes well then your balloon should inflate! Adding the lemon juice to the baking soda creates a chemical reaction. The baking soda is a base, while the lemon juice is an acid, when the two combine they create carbon dioxide (CO2). The gas rises up and escapes through the soft drink bottle, it doesn't however escape the balloon, pushing it outwards and blowing it up. If you don't have any lemons then you can substitute the lemon juice for vinegar.