Use hydrogen peroxide and yeast to make your own elephant's toothpaste
For this experiment you will need some hydrogen peroxide (9% volume is best but no stronger). This can be bought from your local chemist as it is a chemical often used for first aid. You will also need some yeast from your local grocery store and some washing up liquid.
Mix three tablespoons of warm water with four level teaspoons of yeast until it has mixed together as a thick liquid. Put it to one side and get hold of an old (clean) drinks bottle.
You will need to wear safety goggles as a precaution but do not place your face over the bottle as you perform the experiment. Pour half a cup (about 150ml) of the hydrogen peroxide into the drinks bottle and add a good squirt of washing up liquid. Now (using a funnel if you need to) pour the yeast mixture into the drinks bottle and watch as foam starts to build until it pops out the top of the bottle like elephant's toothpaste.
Hydrogen Peroxide contains hydrogen and oxygen and the yeast allows us to extract the oxygen. Since the mixture contains washing up liquid, the soap traps the oxygen gas in loads of tiny little bubbles which squeeze out the top of the bottle. Notice how the bottle feels warm to the touch, the chemical reaction created a little heat too, it is an exothermic reaction. The bubbles and remaining liquid can all be safely washed down the sink.