A combustion reaction involves a reaction with alcohol and oxygen and gives rise to carbon dioxide and water.
- piece of paper
- dollar bill
- 100 mL beaker
- glass/pie plate
- solution of 50% alcohol, and 50% water. The alcohol is 95% ethanol - may only be obtained in a laboratory.
- Prepare the solution (50 mL of ethyl alcohol and 50 mL of water
- Add the salt to the alcohol/water solution in the beaker (this helps to produce a visible flame)
- Soak the dollar bill in the alcohol/water solution so it is thoroughly wet.
- Use the tongs to pick up the bill from the solution.
- IMPORTANT SAFETY PRECAUTION: Move the 50:50 alcohol solution away from where you are going to light the dollar bill.
- Light the bill on fire over the plate and let it burn until the flame goes out.
- CAUTION - DO NOT DO THIS WITHOUT SUPERVISION.
What do you think would happen if I decided to light a piece of paper on fire? You were right it burned. I think I need more valuable paper. Maybe one of your teachers has a dollar bill they could lend me (before the show give one of the teachers a dollar bill). Have you hear the expression that money burns a hole in your pocket or "you have money to burn"? Maybe your teacher have a lot of money to burn. Let's see what happens (dip the money in the solution and burn it).
When the bill is soaked into the solution, the water molecules soak into the bill while the alcohol remains on the surface. When the match is put to the bill, the alcohol is what actually burns. The temperature at which the alcohol burns is not high enough to evaporate the water and burn the bill. So after the alcohol has burned, the dollar bill is still slightly wet. and the fire goes out.
An application is where you might see a flaming dish or dessert in a fancy restaurant. The combustion reaction is:
C2H5OH + 4 O2 ----> 2 CO2 + 3 H2O + heat energy
Science Demonstrations, January 2001
- Charles Ophardt, Professor Emeritus, Elmhurst College; Virtual Chembook