We made a great fire extinguisher today. Teacher lit a candle and carefully put it into a big glass. This is our fire. Next she put in a few spoonfuls of baking powder. She was very careful not to put the powder on top of the candle.
One of the boys held the funnel while teacher put a little vinegar on top of the powder. The powder and vinegar mixture began to fizz. We heard that when you mix vinegar and baking powder together, a gas called CO2 or Carbon Dioxide (bad air) is made. This gas is heavier than air, so it sits at the bottom of the glass. When enough CO2 is made, it pushes the Oxygen (O2 good air) up higher in the glass. Now that the candle can't reach the O2, the flame goes out. 
We also learned that we breathe in Oxygen and breathe out Carbon Dioxide. Plants and trees do the opposite - they breathe in CO2 and breathe out O2. That is why it is so important to have lots of trees planted around us, and lots of trees in the world.
There is Carbon Dioxide in fizzy drinks too. When we drink it the gas goes into our tummies. If we can't get it out of our tummies, it gives us a tummy ache. When it does escape from our tummies it can go up (burp) or down (fart). Both of these seem very rude, but they are natural. We just have to try and not upset the people around us by being too noisy or smelly, and always say "excuse me" if one slips out. We have often seen mammies put their babies on their shoulder and pat their backs to help them burp. They must have gas in their tummies too!
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