The 'Whoosh' Bottle demonstration
A mixture of alcohol and air in a large polycarbonate bottle is ignited. The resulting rapid combustion reaction, often accompanied by a dramatic ‘whoosh’ sound and flames, demonstrates the large amount of chemical energy released in the combustion of alcohols.
This demonstration requires careful preparation, with strict adherence to the conditions required by the risk assessment provided. Schools are advised not to deviate from the details described in this risk assessment. If any variation is necessary, members should contact CLEAPSS for a Special Risk Assessment.
A single demonstration will take 5 – 10 minutes. Repeat demonstrations will require either the drying out of the reaction vessel used for the first demonstration or spare dry reaction vessels.
One or more of the following alcohols, 40 cm3 of each one used:
Methanol (HIGHLY FLAMMABLE, TOXIC)
Ethanol (IDA, or Industrial Denatured Alcohol) (HIGHLY FLAMMABLE, HARMFUL)
Propan-1-ol (HIGHLY FLAMMABLE, IRRITANT)
Propan-2-ol (HIGHLY FLAMMABLE, IRRITANT)
Refer to Health & Safety and Technical notes section below for additional information.
Reaction vessel, 1 or more (Note 1)
Rubber stopper or plastic cap (to fit the reaction vessel)
Beaker (250 cm3), 1 for each alcohol used
Wooden splints, as needed (Note 2)
Both demonstrator and class should be wearing eye protection. Select a safe, level place for the demonstration, with at least 2.5 m clearance above the top of the vessel to the ceiling above, and no flammable materials above it. If the laboratory bench does not allow for this, four stable laboratory stools supporting a large wooden tray may give sufficient clearance and stability. Set out the bottles containing the alcohols and the beakers at least 1 m away from the demonstration. No flames within 1 m. Students at least 4 m away.
Methanol, CH3OH(l), (HIGHLY FLAMMABLE, TOXIC) - see CLEAPSS Hazcard.
Ethanol (IDA, Industrial Denatured Alcohol), CH3CH2OH(l), (HIGHLY FLAMMABLE, HARMFUL) - see CLEAPSS Hazcard.
Propan-1-ol, CH3CH2CH2OH(l), (HIGHLY FLAMMABLE, IRRITANT) - see CLEAPSS Hazcard.
Propan-2-ol, CH3CHOHCH3(l), (HIGHLY FLAMMABLE, IRRITANT) - see CLEAPSS Hazcard.
1 The reaction vessel consists of a large polycarbonate bottle, as used in workplace water dispensers. These have a volume of 16 - 20 dm3. A clean, dry bottle is required for each demonstration. It takes time to clean and dry once it has been used for a demonstration. For this reason, up to 4 bottles may be required. The bottle must be made of polycarbonate (marked PC) and of no other material.
If using empty but wet water cooler containers, stand them inverted to allow any remaining water to drain and then leave upright for several days until completely dry.
2 Attach a wooden splint to the end of the metre rule or stick using adhesive tape, angling the splint so that when the metre rule is horizontal, the splint is sloping downwards. Provide a lighter or matches well away from the alcohol bottles.
a Pour about 40 cm3 of the selected alcohol into a beaker and then transfer into the reaction vessel.
b Insert the rubber stopper and roll the reaction vessel on its side for 10 seconds, to and fro, allowing the alcohol to vaporise and the vapour to fill the vessel. Do not warm the alcohol.
c Pour surplus liquid alcohol back into the beaker, draining the vessel as completely as possible, and move the beaker back to the rest of the alcohol stock, away from any risk of catching fire. Surplus liquid left in the vessel may ignite and set fire to the vessel as well.
d Stand the reaction vessel securely inside the safety screens and remove the stopper. Light the wooden splint, and apply the lighted end of the splint to the open neck of the vessel. Do not lean over the screens to apply the ignition. It is dangerous to ignite by dropping a lighted match into the vessel when using ethanol or methanol. For both propanols, this method may be used providing the neck of the bottle is above head height
e The alcohol vapour should ignite with a loud ‘whoosh’, with flames shooting out of the top of the vessel.
This demonstration is the subject of a Supplementary Risk Assessment by CLEAPSS, SRA06, which members of CLEAPSS are able to consult on the Science Publications CD-ROM, updated and re-issued annually to all members. Others will, of course, have to consult their own employer's Risk Assessment.
The experiment demonstrates dramatically just how much chemical energy is released from such a small quantity of fuel.
The flame colour varies with the proportion of carbon in the alcohol molecule. With methanol and ethanol there is a very quick ‘whoosh’ sound and a blue flame shoots out of the bottle. With propan-1-ol and propan-2-ol, the sound is similar but the reaction is slightly slower, easier to observe, and blue and yellow flames may be observed ‘dancing’ in the bottle. The presence of water reduces the likelihood of dancing flames.
Health & Safety checked June 2008
Wikipedia - a wide-ranging and up-to-date review of the production and use of alcohols for vehicle fuels, with links to a variety of related sites.
Page last updated on 14 December 2011