Wednesday 8 August 2018

5 Minute STEM Activity 10: Blowing out a candle with gas

We can't see lots of things, including a lot of gasses, but we can prove that they are there. We can create Carbon Dioxide gas very easily, and because it is heavier than air, we can use it for a trick...

Blowing out a candle by magic...

1 candle - a tealight is perfect
1 bowl with about 1cm water in the bottom
A small jug, mug or beaker.
1 teaspoon bicarbonate of soda
2 big glugs of vinegar (about 1oz)
Cling Film

1. Get your candle ready. Put about 1cm of water into the bottom of the bowl and place a tea light, or candle in a holder in the middle. Whenever you have fire, you should have water nearby - the bigger the fire, the more water. This way, if someone knocks the candle, the worst that happens is it goes out.

2. Light the candle - if you are under 21 get a grown up to do this or supervise you.

3. Put 1 teaspoonful of bicarbonate of soda into your small jug or cup.

4. Get the cling film ready.

5. Add enough vinegar to the jug to make the bicarbonate of soda all wet.

6. Cover quickly with the cling film and make sure it's sealed tightly. Don't shake the jug, it should start fizzing by itself. We are making a gas called Carbon Dioxide and we don't want it to escape or be blown away by a draught.

7. It should look like this... When you mix an acid (vinegar) with bicarbonate of soda, it releases Carbon Dioxide. You can't see the Carbon Dioxide gas, but it is in a layer in your jug, resting on top of the liquid and bubbles.

8. When the fizzing slows down, remove the cling film carefully. Remember your jug is full of Carbon Dioxide gas. Carbon Dioxide is heavier than air, so it won't immediately float away, but it will blow away very quickly!

9. Carefully pour the invisible Carbon Dioxide onto the candle flame. DON'T pour the vinegary liquid, just the gas. I understand this is a bit tricky and seems quite strange the first time.

The flame will go out. If it doesn't work first time, think about why it might not have worked and try again. It can be hard to pour something invisible.

Fire needs Oxygen to burn, and there is Oxygen in air - we need the Oxygen ourselves to survive. By pouring Carbon Dioxide gas over the flame, the Oxygen is pushed away, and the flame can't burn. You have made a gas and then proven that it is there.

I'll take a break again tomorrow, I need to get my thinking hat on, as my Grandma used to say... Until then, if you've missed any, here are the rest of the 5 minute activities to catch up with...

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