Dragons Breath!

Concepts:

Flammability, volatility and wide flammable range of alcohols

Safety:

Safety glasses MUST be worn at all times by demonstrator and the audience

Safety shield MUST be placed in front of the audience and the demonstrator

This demonstration requires careful preparation, with strict adherence to the conditions as specified in additional information

To repeat this demo the container shall be cool to the touch.

Used water containers should NOT be used for storing drinking water

Students safe distance away, ~10 feet

Equipment:

• One or more DRY polycarbonate 10 L water bottle (No glass)

• Beaker (250 mL), 1 for each alcohol used

• Wooden splints

• 40 mL methanol (CH3OH)

• Meter measuring stick

Preparation:

No prior preparation is required, however, repeat demonstrations will require additional dry reaction vessels.

Demonstration Instructions

1. Attach a wooden splint to the end of the meter measuring stick using adhesive tape, angling the splint so that when the meter measuring stick is horizontal, the splint is sloping downwards.

2. Pour approximately 40 mL of the selected alcohol into a beaker and then transfer into the water bottle.

3. Swirl the contents in the bottle for about 10 seconds, allowing the alcohol to vaporize to fill the vessel. Do not warm the alcohol.

4. Pour surplus liquid alcohol back into the beaker, draining the vessel as completely as possible, and move the beaker away from any source of the flame.

5. Stand the reaction vessel securely behind a blast shied. Light the wooden splint, and apply the lighted end of the splint to the open neck of the vessel. It is dangerous to ignite by dropping a lighted match into the vessel when using methanol.

Observations:

Wide flammable range 6-36% alcohol vapor ignites and with blue flames coming out the top of the bottle. Vapor pressure is 96mm/Hg and flash point is 52F and with the resulting rapid combustion reaction, often accompanied by a dramatic ‘whoosh’ sound and demonstrates the large amount of energy released in the combustion of alcohols. The flame may bounce back and forth from the igniting vapors then creating a vacuum and pulling air back into the container reigniting. This may continue for a few seconds.

https://www.cdc.gov/niosh/npg/npgd0397.html

Learning Outcomes:

• Empty containers are dangerous. Vapors are what burn.

• Students should understand that simple alcohols are very volatile with wide flammable ranges.

• Vapors are heavier than air and will stay in the container.

• The methanol flames are blue but adding more carbon to a chemical like Propanol will make it have more yellow color.

• You can talk about ethanol fires and mitigation tactics.

Chemical Disposal:

Let the reaction vessel dry for several days before using it again. Pour the left over alcohol back into the original container for reuse.

Chemical Disposal

None

Additional Information:

Select a safe, level place for the demonstration, with at least 6 feet of clearance above the top of the vessel to the ceiling above, and no flammable materials above it. No fire detector or fire sprinklers above it. Set out the bottles containing the alcohols and the beakers at least 10 feet away from the demonstration.