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Home School Life Journal ........... painting by Katie Bergenholtz
"Let us strive to make each moment beautiful."
Saint Francis DeSales

What Combustion Needs

Simple Demonstration

For this demonstration, all you need is a small candle, such as a tealight, a match and a glass that will cover the candle.
Light the candle. 
Now put the glass upside down over the candle so that it covers the candle completely.
Watch the candle for a minute or two. Note what happens.
The flame should slowly dim until it goes out.

Why did this happen?

Combustion reaction occurs when a flammable material is burned. The wax in the candle was the flammable material in this demonstration. But combustion also requires oxygen. When the glass was put over the candle, the oxygen in the air surrounding the candle could not be replenished and so when the oxygen was used up, combustion could no longer occur and the flame went out.

More Complex Demonstration

For this demonstration, you will need a few more materials: a bowl that is deep enough so that when the candle is placed at the bottom of the bowl, the sides of the bowl are well above the flame of the candle; a cup-like candleholder; one cup of vinegar and one Tablespoon of baking soda.
Put the cup of vinegar into the bowl.

Place the candle in the candleholder into the bowl. The vinegar should surrounds the candle, but the candle should be taller than the height of the vinegar. The sides of the bowl should also be significantly taller than the level of the candle. Now light the candle.
Slowly sprinkle the baking soda into the vinegar, making sure that it lands in the vinegar and not into the candle. Distribute the baking soda all around the candle so that the bubbles surround the candleholder. Watch what happens to the candle.
When the baking soda and the vinegar mix, a chemical reaction occurs that produces carbon dioxide gas and this gas begins to fill up the bowl, pushing the air that was in the bowl out. Since the air was pushed out by the carbon dioxide, and since combustion needs the oxygen in the air, the flame goes out.
Now, try relighting the candle. When you strike the match outside of the bowl, the match lights, but when you move the match towards the candle, the match goes out. Even though the foaming of the vinegar and baking soda had stopped, the carbon dioxide stayed in the bowl for quite a while and continued to extinguish matches.
It took about five minutes before we were able to relight the candle.

Combustion requires something to burn and oxygen.


sources and resources:
  • Exploring Creation with General Science, Jay Wile

6 comments:

  1. Wonderful demonstration! I'll be doing this one.

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    1. Just got round to doing this and all enjoyed it as I'd expected (once I figured out how not to have the 'volcano' erupt all over the candle. Yes I know you explained clearly but I'm not so good at following instructions ;-)) We'd just been at a science fair where my kids demonstrated elephant toothpaste and rekindling a glowing splint in the oxygen produced, so playing with carbon dioxide in this way followed very nicely. Thank you again!

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    2. Your elephant toothpaste demo sounds interesting, too. I hope you'll share it with us.

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  2. Very cool way to introduce density of gases, too!

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  3. Because I quite needed an excuse to play with fire.

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  4. What a fun activity. One day we will get to this...

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