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Interactive Primary Bulletin 40 All I need is the air that I breathe.... | |
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Put out that fire - As mentioned earlier, burning can only take place if there is sufficient oxygen available. Some fire extinguishers (Figure 10) are designed to produce carbon dioxide (a gas which does not normally assist burning), which will smother the flames and deprive them of oxygen. Figure 10 - A carbon dioxide fire extinguisher You can demonstrate this by using the vinegar/bicarbonate mixture. Place a tea-light candle in the bottom of a bowl and light it (Figure 11). Pour vinegar to a depth of about 2 cm in a small bottle then sprinkle a teaspoon of bicarbonate onto the vinegar. Bubbles of carbon dioxide will be generated and because this gas is more dense than air, it will collect in the bottom of the bottle. Once the bicarbonate has stopped fizzing carefully tip the bottle over the candle flame (don’t let the liquid drip out) so that the accumulated carbon dioxide gas pours down into the bowl, displacing the air (Figure 12). Because the candle flame will no longer have the oxygen in the air available it will go out. | |
 Figure 11 - Set up tealight in bowl |
 Figure 12 - 'Pouring' the carbon dioxide over the flame |
| Vulcanicity - The same mixture can be used to make a model volcano “erupt”. Place a small bottle half full of bicarbonate in the centre of a tray. Make a volcano round it either from paper maché, or by piling small stones, sand or gravel against it, taking care not to cover the opening to the bottle. Add a small amount of red food colouring to a container of vinegar and pour this into the hole in the top of the volcano. The bubbles of carbon dioxide which form will force out the red vinegar and provide an “eruption”. | |
Bubble
& Fizz (continued)
