These demonstrations are great attention getters. Kids love watching things blow up, or burn brilliantly.(Caution: Don't let students sit too close. Just in case, have a fire extinguisher nearby)
Combustion of a hydrocarbon:
For this demonstration you will need a five gallon water bottle, ethanol, a 10 ml graduated cylinder, and a match. Using the graduated cylinder, measure out 20 ml of ethanol and pour it into the water bottle. Don't tell students what you are about to do, but you can ask them questions like "what am I pouring in here?", or "what do you think is going to happen?" Roll the bottle around to coat the inside all over with the ethanol. Make it flashy by tossing the bottle in the air a few times. Ask the students, "why am I doing this?" When you are satisfied that the ethanol has coated the inside of the bottle completely, set the bottle on an elevated surface where all students can see it. Light a match, and tell the students to watch closely. Toss it in and stand back! There will be a lot of flame and a whooshing sound as the air is forced out of the bottle. Depending on how much vapor is in the bottle, the flame may flicker a few times before going out. To demonstrate that oxygen is required for combustion, throw in another match. Since all the oxygen was used in the first explosion, you will not get a second one. Walk around the room with the bottle and let students verify for themselves that the bottle is warm.
What's going on?
In general, all combustion reactions require oxygen and a catalyst ( usually heat or electricity). This demonstration involves the combustion of a hydrocarbon. The products of these kinds of reactions are almost always carbon dioxide, water, heat and light. The chemical equation looks like this:
C2H5OH(ethanol) + O2 -> CO2 + H2O + heat and light
If you want a real life application for this experiment, you could tell your students that cherries flambe dessert is made this way in restaurants. The chef pours brandy over the cherries, lights a match, and poof!