| For years I taught about density as well as the | | | | rests below the air in the aquarium. Since it is |
| properties of carbon dioxide, though never at the | | | | continually produced, it pushes the air out of the |
| same time. Why it took so long to put the two | | | | aquarium so that it can remain below it. If enough |
| together, I'll never know. Here then, are a few | | | | vinegar / baking soda are added, the aquarium will |
| demonstrations involving the density of carbon | | | | become brim full of carbon dioxide. To prove this just |
| dioxide gas and a flame. These should be done by | | | | light another candle and slowly lower it into the |
| adults or under careful adult supervision as there is a | | | | aquarium. It will extinguish itself once it gets below |
| potential of fire hazard. | | | | the aquarium's opening. In fact, the carbon dioxide will |
| I suggest starting by showing that air and carbon | | | | rest in the aquarium for quite some time, especially if |
| dioxide have different characteristics. Hold a lit candle | | | | the room is still. |
| in a glass for a few moments. It keeps burning. Now | | | | Another demonstration to try is to make a long |
| place a small amount of baking soda in the glass and | | | | trough out of V-shaped aluminum foil and use it as a |
| pour in a bit of vinegar. What do the kids see | | | | guide for pouring carbon dioxide. Place a candle in a |
| happening (bubbles) and what do they think is | | | | candlestick holder and light it. Place some baking soda |
| happening (gas is produced)? Now lower the lit candle | | | | and vinegar in a large bottle and let the bottle fill with |
| into the glass and it will go out instantly (the gas | | | | carbon dioxide. Now, hold the aluminum foil trough so |
| does not support the burning of the candle). | | | | that one end is just above the candle flame. The |
| For the next part of the demonstration you will need | | | | other end is held higher. If water was added to the |
| several candles of different height. You will want as | | | | trough, it would pour down and extinguish the candle. |
| many different heights as possible so some candles | | | | We are going to do this with the carbon dioxide |
| may be broken, some placed on supports such as | | | | instead. "Pour" the carbon dioxide from the bottle |
| candlestick holders, inverted coffee cups, etc. I | | | | into the higher end of the trough. The candle flame |
| always hold these candles in place by lighting one and | | | | will flicker and usually extinguish at the lower end of |
| allowing the hot wax to drip onto the surface where | | | | the trough. Why? (The carbon dioxide, being more |
| I want a candle to be placed. I then place the | | | | dense than air, actually does pour down the trough. |
| bottom end of the candle in the wax and allow the | | | | Once it reaches the other end, it pours out of the |
| wax to harden. The candle will be "glued" in place by | | | | trough and over the candle flame. Since the gas does |
| the cooling wax. I have the candles / supports placed | | | | not support combustion, the flame flickers and goes |
| in the upright aquarium so that one corner remains | | | | out.) This should re-instill the idea that carbon dioxide |
| open. | | | | is more dense than air, as well as the fact that |
| Now, light all of the candles. The effect should be | | | | carbon dioxide does not support combustion. |
| quite pretty, but that is not the purpose. Place one | | | | A final thought... if you have easy access to |
| cup of baking soda in the free corner of the | | | | affordable dry ice, it can be used in place of the |
| aquarium. To this add two cups of vinegar. The | | | | baking soda and vinegar. It really is just carbon |
| familiar bubbling will occur. By watching the candles, | | | | dioxide gas cooled and compressed into solid form. If |
| something intriguing will be seen. They will go out, | | | | you handle it, be sure to use gloves and tongs as it |
| one by one, from the candle closest to the aquarium | | | | can quickly and easily cause frostbite. |
| bottom to the uppermost candle. The reason? The | | | | Until next time... keep having fun with science! |
| carbon dioxide is more dense than air, therefore it | | | | |