WIKI - burn                                                 THERMAL  COMBUSTION

In this lab you will:

EXERCISE 1: ANATOMY AND FUNCTION OF A CANDLE
 
Fire
- fire is the THERMAL combustion of organic compounds in the presence of oxygen

Required components 
  1. Organic matter in gas phase
  2. Oxygen
  3. Ignition (aka a match)

Energy products are:
  1. Light
  2. Heat
  3. Infrared

End matter products of conversion are: CO2 + H2O

Thermal combustion pathway

The overall reaction is: CH4 + O2 => CO2 + H2O

--  thermal combustion follows a specific pathway.

1. The hydrogens are first stripped off the carbons and  dumped on an oxygen to produce H2O. 

CH4 + O2 = H2O 

2.  Then the stripped Carbons are combined with oxygen to make 
      C+ O = CO (carbon monoxide - incomplete combustion)

3. then CO + O --> CO2

Combustion temperature is? 

 
EXERCISE 1: ANATOMY AND FUNCTION OF A CANDLE
MATERIALS: Candle, metal spoon, bowl, glass
METHOD:

Go HERE, read and take notes. Then light your tea candle and with the lights off refer to your own candle as you go thru the lecture and your notes once again. Enter your answers in your wiki. 

1. Questions:
Why do candles form a cup?
What is melting the wax inside the cup? 
What happens to the wick as the candle burns?
Where is the hottest part of the flame?
What color is the flame where it gets the most oxygen?
Where is the coolest part of the flame?
What is the yellow part of the flame?
What does incandescent mean?

 

2. In your wiki answer these questions:
1. How does water put out fires?
2. How does CO2 extinguishers put out fires?
3. Why are people instructed to aim extinguishers at the base of the fire?
4. Given what you know about oxygen and combustion, why do you think opening a door in a burning building causes an explosion of the fire outwards (also known as a back draft)?
5. There are two rooms, one filled with particles of dirt suspended in the air, the other has particles of flour suspended in the air.  A match is lit and the room filled with suspended flour particles explodes, but the room with dirt doesn't.  Why not?
6. Why doesn't a pound of flour sitting on the ground burn when a match is tossed onto it, but a room of suspended flour particles explodes?
7. Why does the alcohol for flambee desserts need to be heated or the alcohol  won't burn?
Take a picture for each of the following experiments to illustrate each experiment. 
 
A.  Re-igniting a Candle

         1. Light a candle and let it burn for about one minute.
         2. Have a lighted match or lighter ready.
         3. Carefully blow out the candle.
         4. Watch the smoke trail coming up from the extinguished candle and quickly place your lighted match into that smoke stream.
         5. The candle should re-ignite.

Describe what happened in scientific terms using what you have learned about the burning of candles and combustion.

B.  Candle Condensation

         1. Place a small amount of crushed ice on a spoon or small square of aluminum foil. 
         2. Pull together the corners to form a sack filled with ice.
         3. Hold this sack about 20 cm over a burning candle. Any lower and all you may see is soot form. 
         4. Water droplets should form on the outside of the aluminum sack or spoon.

Describe what happened in scientific terms using what you have learned about the burning of candles and combustion.

C.  Incomplete combustion

       1. Put a metal spoon or a small square of aluminum foil in the freezer and follow directions 'Certain products...' at the website you were reading.

Describe what happened in scientific terms using what you have learned about the burning of candles and combustion.

D.   Extinguishing a Candle with Carbon Dioxide

         1. In a glass or large beaker put 1/2 teaspoon of dry baking soda in the beaker towards the edge. 
         2. Place a lit candle in the beaker (there are tongs). 
         3. Using a pipette, dribble a little vinegar onto the dry baking soda.
         4. The baking soda will foam. Be careful not to tip the wet vinegar/baking soda mixture into the candle. 
         5. The candle should extinguish.

Describe what happened in scientific terms using what you have learned about the burning of candles and combustion.

E.   Oxygen

         1. Place a candle in a bowl. (there are also tin plates)
         2. Light the candle.
         3. Place an empty jar or glass over the candle.
         4. The candle should extinguish.

Describe what happened in scientific terms using what you have learned about the burning of candles and combustion.

F.    Gases

         1. Pour water into the bowl so that it is partially filled. (there are also tin plates)
         2. Place a lit candle in the bowl.
         3. Place an empty jar or glass over the candle so that the edge is under the water line (a tall narrow glass works best!) Be sure to WAIT after the candle goes out.  That is when something happens. 

Describe what happened in scientific terms using what you have learned about the states of matter in lecture.  Why does what you observed with the water happen? You may need to do a search.

almost entirely from: http://science.pc.athabascau.ca/labinfo.nsf/74fd7b440e095b0f87256b1a000fe7fa/f50eae5405c31c3b87256da5006eea52?OpenDocument