The Chemistry of Fire and Other Oxidation Reactions
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Barbara Pawela Retired
The students will :
1. Gain an understanding of the process of combustion.
2. Realize that fuel and oxygen are necessary in order to have combustion.
3. Discover that air contains about 20% oxygen (actually 21%).
4. Gain knowledge of some types of oxidation reactions.
5. Discover that oxidation is an exothermic reaction.
Activity I Activity II Activity III
wooden matches 2 small glasses steel wool pad
small candle 2 large glasses without soap
lighter 2 glass chimneys 1/4 cup vinegar
paper 6 birthday candles cooking or outdoor
4 saucers 9 corks thermometer
test tube jar with lid (The
dry yeast thermometer must fit
wooden splint inside the jar.)
Activity I: Teacher strikes the match and lights the candle. Ask the students
what they observed. After their comments, discuss the history of man's use of
fire. Strike another match. Hold the yellow part of the flame under the bottom
of one of the saucers. Blow out the match and examine the underside of the
saucer. Follow the same procedure, using candle, lighter, and burning paper.
Discuss what was observed and conclude that whenever the yellow part of a flame
came in contact with a cool dish, a black substance was deposited. Moisture
also was present. Introduce and define vocabulary: fire, flame, combustion,
fuel, and ignition. Explain to the students that anything that will burn can be
called a fuel. Most fuels contain carbon, hydrogen, or both. When carbon burns
incompletely, which is usually the case, it glows with a yellow color. A flame
is made of tiny particles of very hot carbon. When the particles cool quickly,
as they did on striking the cool saucer, they were deposited as black carbon.
When they cool more slowly, as above an open flame, they join with the atoms of
oxygen from the air and become carbon dioxide (CO2), a colorless gas. The
moisture formed on the saucers, because every flame gives of water vapor. This
is because the fuel contains hydrogen, which reacts with oxygen in the air to
form water vapor.
Activity II: On a fireproof tray, arrange the candles so that they are about
6-8 inches apart. Fasten them to the tray by placing the candles on some clay.
Arrange the glassware as follows: a small glass behind each of the first two
candles, a large glass behind each of the next two candles, and a glass chimney
behind each of the last two candles. Put three corks near the second, fourth,
and sixth candles. Light candle No. 1. Cover it with the inverted small glass.
Observe what happens. Light candle No. 2. Arrange the corks in a triangle
around its base and place the glass on the corks. Observe what happens. Repeat
the procedure with the remaining candles and the glassware behind them.
Students observe the behavior of the flames. Several students can be
timekeepers and data recorders. Teacher and students compare observations.
Discuss and conclude that both fuel and air were necessary to maintain the
flame. The teacher pours 6-8ml of hydrogen peroxide into a test tube. Add 1/2
teaspoon dry yeast into the test tube. The yeast will react with the hydrogen
peroxide releasing oxygen. Immediately light a wooden splint. Blow out the
flame gently, so that the splint is still glowing. Stick the splint into the
test tube. It will reignite, and if enough oxygen is present, a popping sound
may occur. Discuss and conclude that although oxygen itself does not burn, it
must be present to have fire, which is an oxidation reaction.
Activity III: Place the thermometer inside a jar and close the lid. Have
student data recorders note the temperature after five minutes. Soak one-half
of the steel wool in vinegar for two minutes. Squeeze excess liquid from steel
wool, and wrap it around the bulb of the thermometer. Place the thermometer
with the steel wool inside the jar and close the lid. Record the temperature
after five minutes. The temperature rises. The vinegar removed the protective
coating from the steel wool, allowing the iron in the steel wool to rust.
Rusting is a slow combination of iron with oxygen, which is an oxidation
reaction. Oxidation is an exothermic reaction, and heat is always released.
Mullin, Virginia L. Chemistry Experiments for Children, Copyright, 1968,
Dover Publications, Inc.